WO2025195633A1

WO2025195633A1 - Laser system for operating in two modes

Info

Publication number: WO2025195633A1
Application number: PCT/EP2025/050183
Authority: WO
Inventors: Albert Seifert
Original assignee: NKT Photonics AS
Current assignee: NKT Photonics AS
Priority date: 2024-03-21
Filing date: 2025-01-06
Publication date: 2025-09-25
Anticipated expiration: 2026-09-21

Abstract

The present disclosure relates to a laser system for operating in two different modes, the laser system comprising: a seed laser configured for providing a laser beam comprising one or more laser pulses; a process shutter configured for controlling the emission of the laser pulses and/or for setting an output pulse repetition rate of the laser pulses; and a hollow-core fiber for transporting the laser pulses, said hollow-core fiber comprising a hollow core; wherein the laser system is configured for operating in two different modes: an optimization mode, wherein the laser system is configured for actively aligning the laser beam to the hollow core and coupling said laser beam into the hollow core, wherein the process shutter is non-operable by an end-user in the optimization mode; and an operational mode, wherein the laser system is configured for transporting the laser pulses in the hollow-core fiber for delivering said laser pulses to a target. The present disclosure further relates to a method of operating such a laser system.

Description

LASER SYSTEM FOR OPERATING IN TWO MODES

Technical field

The present disclosure relates to a laser system. In particular, the present disclosure relates to a laser system for operating in two different modes. The disclosure further relates to a chirped pulse amplification (CPA) laser system for operating in two different modes. The disclosure further relates to an alignment system for a laser system.

Background

High-power pulsed laser systems, such as chirped pulse amplification (CPA) laser systems, have found widespread applications across various fields, ranging from scientific research and industrial processes to medical and defense applications. As the demand for higher peak powers and shorter pulse durations continues to grow, so does the need for innovative solutions to address the challenges posed by efficiently coupling these intense laser beams into delivery fibers.

One of the most promising avenues in the field of high-power pulsed lasers lies in the utilization of advanced laser architectures, such as CPA systems. These systems offer unparalleled performance, delivering ultrashort pulses with extremely high peak powers. The applications of such high-power pulsed lasers are diverse. Some examples include scientific research, materials processing and micromachining, medical imaging and surgery, and defense and security.

However, the integration of high-power pulsed lasers into delivery systems, particularly fiber-optic systems, presents some challenges. The increased power and energy densities associated with these lasers pose a risk of damaging the delivery fiber, especially when coupling into intricate structures such as hollow-core fibers. This issue necessitates the development of innovative solutions to optimize the coupling efficiency and mitigate the risk of damage to the delivery fiber, ensuring the seamless integration of high-power pulsed laser systems across diverse applications.

Thus, there is a need for a novel laser system for addressing the challenges associated with coupling high-power pulsed lasers into a delivery fiber. In particular, there is a desire to enhance the reliability, efficiency, and safety of high-power laser delivery systems across a broad spectrum of applications. Summary

As will be described in greater detail below, the present disclosure describes various laser systems and methods. The systems and methods disclosed herein may be used to couple and/or align a laser beam from a laser to a delivery fiber. In addition, the systems and methods described herein may improve alignment and monitoring of pulsed laser beams.

The above-mentioned challenges are solved by providing a laser system for operating in two different modes, the laser system comprising:

- a seed laser or short-pulse oscillator configured for providing a laser beam comprising one or more laser pulses, each laser pulse having a given pulse energy;

- a process shutter configured for controlling the emission of the laser pulses, such as by actively blocking or allowing the passage of the laser beam, and/or configured for setting an output pulse repetition rate of the laser pulses; and

- a delivery fiber for transporting the laser pulses, said delivery fiber comprising a hollow core surrounded by a cladding structure; wherein the laser system is configured for operating in two different modes:

- an optimization mode, wherein the laser system is configured for actively aligning the laser beam to the hollow core and coupling said laser beam into the hollow core, wherein the process shutter is non-operable by an end-user in the optimization mode; and

- an operational mode, wherein the laser system is configured for transporting the laser pulses in the delivery fiber for delivering said laser pulses to a target, such as the eye of a patient, wherein the process shutter is operable by the end-user in the operational mode.

Typically, high-power pulsed laser systems comprise a process shutter enabling a user of the laser system to modulate or control the emission of the laser pulses. Preferably, the process shutter is configured to control the emission of the laser pulses by actively blocking or allowing passage of the laser beam. This is in contrast to polarization devices, such as halfwave plates, that are used for polarization control by altering the polarization state of the laser beam. Such devices are generally not able to control emission by blocking or interrupting the laser beam. In some cases, the process shutter forms part of the laser system. For example, it can be arranged inside the laser system, e.g., before a delivery fiber for delivering the laser pulses to a target, such as the eye of a patient. A problem hereof is if the user opens the process shutter at a point where the high-power pulsed laser beam is misaligned with the delivery fiber, this can cause damage to the delivery fiber. For example, in case the delivery fiber is a hollow-core fiber, this can cause damage to the cladding structure, e.g., the capillaries in the cladding, whereby the input end of said fiber can be damaged or destroyed. To solve this problem, the presently disclosed laser system is configured for operating in at least two modes, wherein the process shutter is non-operable by the user in at least one mode, such as the optimization mode, of the laser system.

The optimization mode has the purpose of actively aligning the laser beam to the delivery fiber, such as to the core of a hollow-core fiber, while setting one or more parameters of the laser emission such that any potential damage is minimized or avoided. Thus, preferably, the optimization mode provides a safe mode for aligning and coupling the pulsed laser beam with the core of the delivery fiber. The detailed description provides many examples of how to achieve this.

The operational mode has the purpose of delivering high-power laser pulses from the laser system to a target via the delivery fiber. In case of eye surgery, the target may be the eye(s) of a patient. In case of material processing, the target may be a material to be processed, e.g. a workpiece, such as a metal for being cut or similar. Thus, the laser system is preferably configured to start up in the optimization mode and safely align the pulsed laser beam to the core of the delivery fiber before the operational mode is available to the user. In the operational mode, the user can preferably operate the process shutter in order to control the emission of the laser pulses. Thus, the process shutter may be configured for actively blocking or allowing passage of the laser beam depending on a state set by the user.

The present disclosure further relates to a method of operating a laser system, the system comprising a process shutter operable by a user in at least one operational mode of the laser system, the method comprising the steps of:

- providing a pulsed laser beam comprising one or more laser pulses;

- actively aligning the laser beam to a core of a hollow-core fiber in an optimization mode of the laser system, wherein the process shutter is non-operable by the user in the optimization mode; and

- delivering laser pulses to a target, such as the eye of a patient, or a workpiece to be processed, wherein the laser pulses are transported by the hollow-core fiber in an operational mode of the laser system, wherein the process shutter is operable by the user in said operational mode, whereby the user can control or modulate the emission of the laser pulses.

The presently disclosed laser system may be configured for carrying out the method disclosed herein. The present disclosure further relates to an active alignment system comprising two or more detectors for detecting one or more, such as two or more, beam parameters of the laser beam, and two or more actuatable mirrors or lenses configured for adjusting a beam spot of the laser beam, e.g. by adjusting the position and/or angle of the laser beam, such that it aligns with the delivery fiber. The active alignment system may form part of the laser system disclosed herein. In some embodiments, the active alignment system is a separate unit that can be attached to an existing laser system. Thus, the alignment system may constitute a modular unit for easy integration with a laser system.

The present disclosure further relates to a laser system for ophthalmology applications, comprising: a seed laser or short-pulse oscillator configured for providing a laser beam comprising one or more seed laser pulses, each seed laser pulse having a given pulse energy and pulse duration; a pulse stretcher for temporally stretching the seed laser pulses to increase the pulse duration of the seed laser pulses; an electronically controlled process shutter configured for controlling the emission of the laser beam to provide output laser pulses, wherein the process shutter is configured to actively block or allow the passage of the laser beam through mechanical blocking, electro-optic modulation, or acousto-optic modulation; and a hollow-core fiber for transporting the output laser pulses, said hollow-core fiber comprising a hollow core surrounded by a cladding structure; wherein the laser system is configured for operating in two different modes: an optimization mode, wherein the laser system is configured for actively aligning the laser beam to the hollow core and coupling said laser beam into the hollow core, wherein the process shutter is non-operable by an end-user in the optimization mode; and an operational mode, wherein the laser system is configured for transporting the output laser pulses in the hollow-core fiber for delivering said output laser pulses to a target, wherein the process shutter is operable by the end-user in the operational mode.

The present disclosure further relates to a chirped pulse amplification (CPA) laser system for ophthalmology applications, the laser system comprising: a seed laser or shortpulse oscillator configured for providing a laser beam comprising one or more seed laser pulses, each seed laser pulse having a given pulse energy; a pulse stretcher for temporally stretching the seed laser pulses to provide stretched laser pulses; optionally one or more optical amplifiers for amplifying the stretched laser pulses to provide amplified laser pulses; an electronically controlled process shutter configured for controlling the emission of the stretched laser pulses, or the amplified laser pulses, by actively blocking or allowing the passage of the laser beam; a pulse compressor for temporally compressing the amplified pulses to provide compressed pulses; and a hollow-core fiber for transporting the compressed laser pulses, said hollow-core fiber comprising a hollow core surrounded by a cladding structure; wherein the laser system is configured for operating in two different modes: an optimization mode, wherein the laser system is configured for actively aligning the laser beam to the hollow core and coupling said laser beam into the hollow core, wherein the process shutter is non-operable by an end-user in the optimization mode; and an operational mode, wherein the laser system is configured for transporting the compressed laser pulses in the hollow-core fiber for delivering said laser pulses to a target, wherein the process shutter is operable by the end-user in the operational mode.

The present disclosure further relates to an active alignment system for aligning, coupling, and monitoring a pulsed laser beam from a laser system, the active alignment system comprising: two or more detectors configured for detecting one or more beam parameters of the laser beam, said laser beam comprising one or more laser pulses, the detectors comprising at least: a first detector configured for determining a position of the laser beam, e.g., with respect to a center of a hollow-core fiber; and a second detector configured for determining an angle of the laser beam, e.g., with respect to an axis of the hollow-core fiber; wherein the two or more detectors are configured for providing a feedback signal used for active alignment of the laser beam to the hollow-core fiber, the active alignment system further comprising: two or more actuatable mirrors or lenses for adjusting the position and/or angle of the laser beam, such as wherein the actuatable mirrors or lenses are mounted on motorized mirror mounts for translating and/or rotating said mirrors or lenses; a control unit configured for receiving the feedback signal from the detectors and providing a control signal for actuating the one or more actuatable mirrors or lenses, such that the laser beam is actively aligned to the hollow-core fiber; wherein the active alignment system is enclosed in a housing such that it constitutes a modular unit for removably attaching to the laser system; and wherein the active alignment system is configured for continuously monitoring the beam parameters to realign the laser beam during operation of the laser system.

The present disclosure further relates to a fiber delivery system comprising: a hollowcore fiber for guiding a pulsed laser beam to a target, said hollow-core fiber comprising a hollow core surrounded by a cladding structure; an active alignment system comprising: a first detector configured for determining a position of the laser beam with respect to a center of the hollow-core fiber; and a second detector configured for determining an angle of the laser beam with respect to a longitudinal axis of the hollow-core fiber; two or more actuatable mirrors or lenses for adjusting the position and/or angle of the laser beam, such as wherein the actuatable mirrors or lenses are mounted on motorized mirror mounts for translating and/or rotating said mirrors or lenses; wherein the first and second detectors are configured for providing a feedback signal used for active alignment of the laser beam to the hollow-core fiber by actuating the two or more actuatable mirrors or lenses; wherein the active alignment system is enclosed in a housing such that it constitutes a modular unit for removably attaching to a laser system; and wherein the active alignment system is configured for continuously monitoring the position and angle to realign the laser beam during operation of the laser system. Accordingly, the presently disclosed laser system, alignment system and corresponding method provide several advantages over the prior art. At least one advantage is an improved safety due to the different modes, wherein the process shutter is only accessible to the enduser in some of these modes. Another advantage is a fast and accurate active alignment of the laser beam to the delivery fiber while keeping the intensity of the laser beam below a given threshold, such that the delivery fiber is not damaged during the alignment. Yet another advantage is that the alignment system constitutes a modular, separate unit, that can be easily integrated into existing laser systems as an add-on device. Thus, the presently disclosed active alignment system is configured for aligning, coupling, and monitoring the laser beam during operation of the laser system when the process shutter is open.

The invention is further described in the following detailed description and accompanying drawings.

Brief description of the drawings

Fig. 1 shows an embodiment of a laser system according to the present disclosure.

Fig. 2 shows another embodiment of a laser system according to the present disclosure.

Fig. 3 shows yet another embodiment of a laser system according to the present disclosure.

Fig. 4 shows an embodiment of an alignment system according to the present disclosure.

Detailed description

A better understanding of the features and advantages of the present disclosure will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of embodiments of the present disclosure are utilized, and the accompanying drawings. Although the detailed description contains many specifics, these should not be construed as limiting the scope of the disclosure but merely as illustrating different examples and aspects of the present disclosure.

The laser system may comprise a seed laser configured for providing a laser beam comprising one or more laser pulses, each laser pulse having a given pulse energy. Thus, the seed laser may provide a train of laser pulses at a given initial pulse repetition rate. In some embodiments, the initial pulse repetition rate is between 1 MHz and 80 MHz. The seed laser may comprise or constitute a short-pulse oscillator. In some embodiments, the seed laser is a mode-locked laser for generating ultrashort laser pulses. As an example, the ultrashort laser pulses may have a pulse duration in the femtosecond or picosecond range. In some embodiments, the pulse duration is selected in a range from 10 fs and 10 ps, such as between 50 fs and 5 ps, such as between 100 fs and 3 ps. In some embodiments, the seed laser is a mode-locked laser, such as a mode-locked fiber laser. Alternatively, the ultrashort pulses may be generated by Q-switching. The seed laser may form part of a chirped pulse amplification (CPA) laser system as disclosed herein.

The laser system may further comprise a pulse stretcher for temporally stretching the laser pulses from the seed laser. The pulse stretcher may comprise one or more elements selected from the group of: dispersive prism pairs, dispersive mirrors, diffraction gratings, grating prisms, chirped Bragg gratings, chirped volume Bragg gratings, and/or combinations thereof. The pulse stretcher may be arranged in optical communication with the seed laser and/or in optical communication with one or more optical amplifiers forming part of the system. In some embodiments, the pulse stretcher is arranged to receive the laser pulses from the seed laser and temporally stretch said laser pulses, whereby the pulse duration of the laser pulses is increased. The pulse stretcher may be a dispersive pulse stretcher for applying chromatic dispersion to the seed laser pulses.

In some embodiments, the pulse stretcher is tunable, such that it is configured for controlling or adjusting the dispersion applied to the seed laser pulses. In some embodiments, the pulse stretcher comprises a chirped fiber Bragg-grating (cFBG) and a temperature control for controlling the temperature of the FBG. Thus, by changing the temperature, the FBG may be stretched and/or compressed whereby the dispersion properties of the pulse stretcher changes. This can be used to tune the dispersion profile of the stretcher to oppose the dispersion profile of the pulse compressor when the laser operates in the operational mode. Correspondingly, when the laser operates in the optimization mode, the laser system may be configured to detune the pulse stretcher, e.g. by changing the temperature settings, whereby the dispersion profile of the pulse compressor no longer opposes the profile of the stretcher. As a result, the peak power of the laser pulses is reduced.

The laser system may further comprise one or more optical amplifiers for amplifying the laser pulses. The optical amplifiers may be configured to provide a predefined gain to the stretched pulses received from the pulse stretcher and/or to the laser pulses received from the seed laser. The one or more optical amplifiers may comprise a gain medium doped with rare earth ions such as erbium, ytterbium, thulium, neodymium, or praseodymium. As an example, the one or more optical amplifiers may be selected from the group of: Erbium-Doped Fiber Amplifier (EDFA), or Ytterbium-Doped Fiber Amplifiers (YDFA), bulk-crystal amplifiers, or Semiconductor Optical Amplifiers (SOA). In some embodiments, the optical amplifiers are fiber-based amplifiers. The optical amplifiers may be optically pumped, e.g., by a laser diode. The laser system may comprise two or more optical amplifiers arranged in an amplifier chain, such as a fiber-based amplifier chain. As an example, the optical amplifiers may comprise one or more pre-amplifiers and power amplifiers. In some embodiments, one or more of the optical amplifiers are Yb-doped fiber amplifiers. In some cases, the pulse stretcher is spliced into the amplifier chain. In other embodiments, the one or more optical amplifiers comprises or constitutes a regenerative amplifier. In accordance with some embodiments, the one or more optical amplifiers are configured to provide a predefined gain to the stretched pulses, wherein the laser system is configured to reduce the gain of at least one of said optical amplifiers when operating in the optimization mode.

The laser system may further comprise a pulse picker configured for down picking and/or adjusting the initial pulse repetition rate set by the seed laser. Thus, the pulse picker may be configured for changing the initial pulse repetition rate of the laser pulses. The pulse picker may be arranged in optical communication with the pulse stretcher and/or one or more of the optical amplifiers. As an example, the pulse picker may be arranged between two of the optical amplifiers, such as between two pre-amplifiers, or between a pre-amplifier and a power amplifier. The pulse picker may be embodied as an optical modulator, such as an acoustooptic modulator (AOM) or an electro-optic modulator (EOM). In some embodiments, the pulse picker comprises or constitutes a fiber-coupled AOM. The fiber-coupled AOM may be spliced into the fiber-based amplifier chain. The pulse picker may be configured to adjust the initial pulse repetition rate upon receiving a control signal from a pulse rate controller.

In some embodiments, the seed laser, pulse stretcher, optical amplifiers, and pulse picker are fiber-based components arranged in a fiber chain. In other embodiments, all components of the laser system are arranged in free space. In some embodiments, the seed laser is a fiber laser, such as a mode-locked fiber laser. In some embodiments, the seed laser and the process shutter are components of an external laser for integration with the presently disclosed alignment system and delivery fiber.

The laser system may further comprise a process shutter configured for controlling the emission of the laser pulses, such as by actively blocking or allowing the passage of the laser beam, and/or configured for setting an output pulse repetition rate of the laser pulses. Thus, the process shutter is able to fully interrupt the laser beam and release it again in the open state, such as through mechanical blocking, electro-optic modulation, or acousto-optic modulation. The process shutter may be electronically controlled. The process shutter may be embodied as an optical modulator, such as an acousto-optic modulator (AOM) or an electrooptic modulator (EOM). In case of an AOM, the AOM may comprise a crystal, such as a tellurium dioxide (TeO₂) or a quartz crystal, which exhibits acousto-optic properties. The AOM may further comprise a piezoelectric transducer attached to one end of the crystal. The AOM may be operatively connected to a radio-frequency (RF) signal generator, which may be configured for applying an RF signal to the transducer, whereby a travelling acoustic wave is generated within the crystal. The acoustic wave may cause a periodic modulation in the refractive index of the crystal. Due to the periodic modulation of the refractive index, an incident laser beam may undergo diffraction, whereby diffracted orders around the original laser beam may be generated. The intensity of the diffracted orders may be directly related to the amplitude of the acoustic wave. By controlling the frequency and/or amplitude of the RF signal applied to the transducer, the direction and/or characteristics of the diffracted laser beams may be controlled. In some embodiments, the laser system is configured for reducing the intensity or power of the RF signal in the optimization mode, whereby the average power of the laser pulses is reduced. As an alternative, the process shutter may be an electro-optic modulator (EOM) configured for controlling the emission of the laser pulses and/or for setting an output pulse repetition rate of the laser pulses. The EOM may comprise a Pockels Cell.

In general, the process shutter may be configured to operate through mechanical blocking, electro-optic modulation, or acousto-optic modulation. AOMs and EOMs are preferred as process shutter due to their ultra-fast response. The process shutter may be configured to control the transmission of light by, e.g., blocking or allowing the passage of light through the process shutter, whereby it can be used to control whether light is received by the alignment system and/or the delivery fiber. Thus, the process shutter may be arranged upstream of the alignment system, and/or upstream of the delivery fiber. Furthermore, it may be arranged downstream of the seed laser or oscillator. In some embodiments, the process shutter is arranged downstream of the pulse stretcher or downstream of the optical amplifiers.

In some embodiments, the process shutter is operable by a user only in the operational mode. The user may then be able to modulate the emission of the laser pulses via the process shutter. The process shutter may be configured to modulate the amplitude of the laser pulses. The user may be able to open or close, such as fully open, partially open, or fully close, the process shutter when the laser system operates in the operational mode. The process shutter may be arranged in free space. In some embodiments, the process shutter is arranged to receive amplified laser pulses from the one or more optical amplifiers, such as from a power amplifier. As an example, the process shutter may be arranged between one of the optical amplifiers and the pulse compressor. As another example, the process shutter may be arranged between the pulse picker and the delivery fiber, e.g. the hollow-core fiber. Thus, the process shutter may be arranged before the delivery fiber. This arrangement may also be referred to as upstream of the delivery fiber. The process shutter may be further configured for high-speed operation, such that it may be capable of rapidly switching, or diverting, the beam in order to provide high-frequency pulsed operations. The process shutter may further act as a safeguard to prevent unintended laser exposure.

In some cases, it can cause a problem if the user has closed the process shutter for too long time in the operational mode. To close the process shutter may be understood as to interrupt the laser beam, e.g. via mechanical blocking, electro-optic modulation, or acoustooptic modulation. As an example, the laser beam may drift out of alignment with the delivery fiber, whereby there is a risk of damaging the structure, such as the cladding structure, of said fiber. Therefore, in some embodiments, the laser system is configured for automatically switching from the operational mode to the optimization mode. This may for instance occur in case of no signal on the detectors for a predetermined amount of time. Additionally, or alternatively, the laser system may be configured for providing a warning to the user in case of no signal on the detectors for a predetermined amount of time. As an example, the predetermined amount of time may be between 10 seconds and 5 minutes, such as between 30 seconds and 3 minutes, such as between 1 minute and 3 minutes. The active alignment system may be configured to compensate for a beam drift of the laser beam.

The laser system may further comprise a pulse compressor for temporally compressing the laser pulses. In some embodiments, the pulse compressor is configured for temporally compressing amplified pulses received from the one or more optical amplifiers. In some embodiments, the pulse compressor is configured for temporally compressing the amplified pulses to a duration similar to the initial pulse duration of the pulses generated by the seed laser or short-pulse oscillator.

The pulse compressor may be a dispersive compressor. Thus, the pulse compressor may be configured to apply a given chromatic dispersion to the laser pulses, whereby the pulses are temporally compressed. The pulse compressor may form part of the chirped pulse amplification (CPA) laser system disclosed herein. The pulse stretcher and the pulse compressor may be configured or adapted to have opposite dispersion profiles when the laser system operates in the operational mode. In other words, the pulse compressor may have a phase profile exactly compensating the phase profile of the pulse stretcher when the system operates in the operational mode. In some embodiments, the pulse stretcher or pulse compressor is tunable such that the dispersion profile can be adjusted. This may be used in the optimization mode to detune either the stretcher or the compressor, such that their dispersion profiles no longer balance. Accordingly, in some embodiments, the pulse stretcher or compressor is detuned to adjust the dispersion such that the dispersion profile of the two components no longer balance or compensates each other, when the laser system operates in the optimization mode. This will cause a non-optimal compression of the pulses, whereby the pulses are no longer compressed to the initial pulse duration. Consequently, the pulse peak power is reduced in the optimization mode. However, this can be achieved in other ways as well, as mentioned herein.

The pulse compressor may be arranged in free space. Thus, the pulse compressor may comprise one or more optical components arranged in free space. In some embodiments, the pulse compressor is selected from the group of: a diffraction grating, a pair of diffraction gratings, a prism, a prism pair, a chirped mirror, a Bragg grating, a chirped fiber Bragg grating, or a chirped volume Bragg grating. The pulse compressor may comprise one or more diffraction grating arranged in free-space. The pulse compressor may further comprise a translation stage configured to be translated in at least one dimension, such that the pulse compressor constitutes a tunable compressor.

The pulse compressor may be arranged between the process shutter and the delivery fiber, such as the hollow-core fiber. In some embodiments, the pulse compressor is arranged to receive laser pulses from the modulator or process shutter and compress said pulses, whereby compressed pulses are obtained. In some embodiments, the laser system is configured to adjust the dispersion profile of the pulse compressor, such that the peak power of the laser pulses is reduced in the optimization mode compared to the operational mode.

The laser system may further comprise one or more detectors, such as two or more detectors, configured for detecting one or more, such as two or more, beam parameters of the laser beam. The beam parameters may comprise at least a position and/or an incident angle of the laser beam. In some embodiments, the laser system comprises a first detector configured for determining the position of the laser beam and a second detector configured for determining the angle of the laser beam. The position of the laser beam may refer to the beam spot position of the laser beam with respect to the core of the delivery fiber. This position may be determined at another plane by the first detector. The angle of the laser beam may refer to the incident angle at the input end of the delivery fiber. Similarly, this angle may be determined at another plane by the second detector. The detectors may be selected from the group of: position sensitive detectors (PSD), quad photodiodes, quadrant photodiode arrays, image sensors, phototransistors, and/or combinations thereof. However, other types of detectors can be envisaged, as long as the detector(s) are suitable for determining the position and/or incident angle of the laser beam. In particular, the detector(s) should be suitable for use in an active alignment system of a laser system.

In some embodiments, the detectors are used in an active alignment system forming part of the laser system. Thus, the detectors may be configured for providing a feedback signal used for active alignment of the laser beam to the hollow core when operating in the optimization mode. The active alignment system may further comprise one or more actuatable mirrors or lenses. The actuatable mirrors or lenses may be configured for adjusting a beam spot of the laser beam, e.g. for adjusting the position and/or angle of the laser beam, such that it aligns with the hollow core of the delivery fiber. The actuatable mirrors or lenses may be operatively connected to the detectors, such that they form part of the same active alignment system. As an example, the actuatable mirrors or lenses may be actuated in response to the feedback signal from the detectors. The actuatable mirrors or lenses may be mounted on motorized mirror mounts for translating and/or rotating said mirrors or lenses. The active alignment system may comprise a driver for actuating the mirrors or lenses. In some embodiments, the active alignment system is only activated in the optimization mode. In some embodiments, the active alignment system is active in both modes provided the process shutter is open. Thus, the laser system may be configured for aligning the laser beam to the hollow core and coupling said laser beam into the hollow core in the optimization mode. The detectors may be arranged in free space. The detectors and/or actuatable mirrors/lenses may be arranged inside a housing. In some embodiments, the entirety of the alignment system is housed inside the housing, such that the alignment system constitutes a modular unit. Accordingly, the two or more detectors of the alignment system may be enclosed in a housing such that the alignment system constitutes a modular unit for attachment, and coupling, to a laser, such as an external laser. Thus, the alignment system may be configured for an easy and fast attachment to a laser system, such as an ultrafast pulsed laser system. The alignment system may thus comprise an input for receiving a free-space optical beam and an output for coupling said optical beam into a delivery fiber, such as a hollow-core fiber. In some embodiments, the seed laser or short-pulse oscillator, and the process shutter, are components of a pulsed laser that constitutes an external laser to the alignment system. The modular unit may be configured for attaching to the external laser, wherein the alignment system is fully enclosed inside the modular unit, said modular unit being further configured for receiving a laser beam from the external laser when attached. The modular unit may further comprise a fiber-coupling to attach and couple a delivery fiber, such as a hollow-core fiber.

In some embodiments, the process shutter is arranged before the hollow-core fiber, e.g. between the one or more amplification stages and the hollow-core fiber. In some cases, the process shutter is arranged before the alignment system comprising the aforementioned detectors for determining the position and/or incident angle of the laser beam. The process shutter may in some cases be operated by a user only in the operational mode of the laser system. Thus, the process shutter may be configured to control delivery of the laser beam to the delivery fiber. The process shutter may be further configured to modulate the amplitude of the laser pulses. This allows the user to control and/or modulate the emission of the laser beam via the process shutter. In other words, in some cases the user can open or close the process shutter in the operational mode. Thus, the process shutter may be operated in an open or closed state, wherein the laser beam is allowed through or interrupted, respectively. A drawback hereof is that a closed process shutter can cause some issues when operating with high-power laser pulses in the operational mode once the process shutter is opened again. As an example, over time the laser beam may drift, causing it to go out of alignment with the hollow-core delivery fiber. If the user then opens the process shutter in a case where the beam is not perfectly aligned with the hollow-core fiber, there is a risk of incurring damage to said fiber. This is in particular a problem in case the process shutter is arranged before, i.e. upstream of, the detectors, since if the shutter is closed in the operational mode, the laser beam is not incident on said detectors, which means the detectors can not provide the feedback signal for active alignment. To mitigate this, the laser system may be configured for automatically switching from the operational mode to the optimization mode in case of no signal on the detectors for a predetermined amount of time. Furthermore, the laser system may be configured for providing a warning to a user in case of no signal on the detectors for a predetermined amount of time when the system operates in the operational mode. The active alignment system may be configured to compensate for the beam drift of the laser beam upon detecting a beam drift or a misalignment of the beam.

The laser system may further comprise a third detector, such as a power sensor, configured for determining the power of the laser beam at the output of the delivery fiber. The third detector may be configured for monitoring the output power from the laser system, preferably when the system operates in the optimization mode. Thus, the active alignment system may comprise the third detector configured for determining the power of the laser beam at the output of the delivery fiber. In some embodiments, the third detector is a power sensor configured to provide a safety feature of the laser system. In such case, the power sensor may continuously monitor the power of the output beam at the output of the delivery fiber. In case there is a mismatch of the input power and the output power, the laser system may be configured to trigger an interlock and shut down the laser system for safety. The third detector may additionally, or alternatively, be configured for calibration purposes, i.e., such that it is configured for providing a calibration of the laser system. This may be achieved by measuring the power of the output beam and comparing the output power with the input power. The laser system may be configured to provide a single optical output, i.e., a mono-mode output. Therefore, the system may be configured to adjust, or calibrate, such that maximum power at the output is achieved. The maximum power may correspond to the best coupling scenario, i.e., an optimized coupling of light into the delivery fiber. The laser system may be configured to set one or more parameters to a safe configuration, e.g., below a damagethreshold of the delivery fiber, and subsequently monitor the output power.

The laser system may further comprise a delivery fiber, such as a hollow-core fiber for guiding and/or transporting the laser pulses. In some embodiments, the delivery fiber is a hollow-core fiber (HCF) comprising a hollow core surrounded by a cladding structure. As an example, the delivery fiber may be a hollow-core photonic crystal fiber (HC-PCF). The hollowcore fiber may be configured for transporting the laser pulses within the hollow core when the laser system operates in the operational mode. Thus, the laser pulses may be delivered to a target upon exiting the hollow-core fiber. In some applications of the laser system, the target corresponds to the eye(s) of a patient or a workpiece to be processed, such as a metal to be cut. In some embodiments, the delivery fiber, such as the hollow-core fiber, has a length of between 1 m and 10 m, such as between 2 m and 5 m, such as between 2.5 m and 3.5 m. In some embodiments, the delivery fiber has a length of less than 10 m, such as less than 5 m. Delivery fibers in these lengths are preferred in order to keep the loss at a minimum. The delivery fiber may be arranged downstream of the alignment system.

The laser beam may be primarily guided in the hollow core; thus, having only a minor spatial overlap with the cladding structure. The hollow-core fiber may be configured for guiding laser pulses having a high peak-power without damaging the hollow-core fiber. The hollowcore fiber may be a hollow-core photonic bandgap fiber. Thus, the laser pulses may be guided based on a photonic bandgap effect. Alternatively, the delivery fiber may be a revolver-type hollow-core fiber comprising a pattern of silica rings around the hollow core. Such a fiber is sometimes referred to as an antiresonant hollow-core fiber (AR-HCF). The delivery fiber may be suitable for delivering ultrashort pulses with little to no non-linear effects or material damage. Accordingly, the nonlinearity of the hollow-core fiber may be negligible such that the laser pulses transported by the fiber approximately maintain their pulse shape. Thus, the hollow-core fiber may have a low non-linearity. This is beneficial for the present purpose of delivering ultrashort pulses ideally maintaining their pulse shape throughout the delivery fiber.

In some embodiments, the hollow-core fiber is an anti-resonant hollow-core fiber (AR- HCF). The hollow core of the fiber may comprise a gas, such as air, or it may comprise a vacuum, such as a low or medium vacuum. The gas pressure in the hollow core may be low, such as less than 100 mbar, such as less than 50 mbar, such as less than 10 mbar, or even less than 1 mbar. This may aid to reduce, or ideally avoid, any non-linear effects within the fiber. In other cases, the core of the fiber may be largely free from gas, such that it only accommodates a vacuum. Accordingly, the ultra-short laser pulses may be guided in vacuum within the core of the hollow-core fiber. Thus, a vacuum may be present inside the hollow-core fiber. In practice, it does not need to be a perfect vacuum, but may instead be a very low pressure vacuum. The hollow-core fiber is preferably evacuated from gas. The hollow-core fiber may be arranged inside a cable. The cable may further comprise a protective window arranged inside a ferrule or connector. The laser system may further comprise a collimator for collimating the laser beam, wherein the collimator is attached to the distal end (output end) of the hollow-core fiber. The collimator may be arranged inside the ferrule or connector. The collimator may comprise a sensor arranged inside the collimator, said sensor being configured for measuring stray light, or reflected light, from a lens of the collimator. The sensor may be a power sensor, or other suitable sensors. In some embodiments, the laser system further comprises a mechanical shutter arranged between the output of the hollow-core fiber and the target. This shutter may be used for blocking the emission of the laser beam.

Any of the components described herein may form part of a chirped pulse amplification (CPA) laser system. Thus, said CPA laser system may comprise any one or more of the following components: the seed laser, the pulse stretcher, the optical amplifier(s), the pulse picker, the process shutter, the pulse compressor, the active alignment system, the delivery fiber, and/or combinations thereof. The laser system, such as the CPA laser system, may be configured for operating in at least two different modes: an optimization mode and an operational mode. The laser system may be configured for operating in one or more additional modes not described herein.

The laser system may be configured for operating in an optimization mode, wherein the laser system is configured for actively aligning the laser beam to the hollow core and coupling said laser beam into the hollow core of the delivery fiber. The active alignment may be performed by the active alignment system of the laser system. In particular, the laser system may be configured to actively align the laser beam to the core of the delivery fiber by utilizing the one or more detectors and actuatable mirrors forming part of the alignment system disclosed herein. Preferably, the laser system is configured to start up in the optimization mode upon powering up the system. In some cases, the operational mode is only available to the end-user after the system has run in the optimization mode and aligned the laser beam to the core of the delivery fiber.

In the optimization mode, the laser system may be configured to set one or more parameters of the laser emission, such that the output from the laser is safe for coupling the laser emission into the delivery fiber. Accordingly, the purpose of the optimization mode may be to provide a safe alignment and/or coupling of the laser beam to the core of the delivery fiber, such as to the core of the hollow-core fiber. This may be achieved by adjusting one or more parameters of the laser pulses such that any potential damage of the fiber facet is reduced or entirely avoided. As an example, the parameters may be selected from the group of: pulse peak power, pulse energy, average power, pulse repetition rate, and/or combinations thereof. A safe alignment and/or a safe coupling may be understood as providing a laser emission that minimizes or lowers the risk of damaging the delivery fiber, such as the risk of damaging the cladding structure of the hollow-core fiber. This may be achieved in several ways that are described herein below.

In some embodiments, the laser system is configured for reducing the average power of the laser pulses in the optimization mode via the process shutter. As an example, the process shutter may be embodied as an acousto-optic modulator (AOM) driven by a radiofrequency (RF) signal generator. Thus, the average power may be controlled by controlling the power or intensity of the RF signal provided by the RF signal generator. The average power of the laser pulses output by the laser system may sometimes be referred to as the output power. Said output power or average power may be defined as the product of the pulse energy and the pulse repetition rate. Thus, a reduction of the average power via the process shutter may affect the output power of the laser emission as well as the pulse energy and/or the peak power of the laser pulses. A reduction of the pulse energy and/or peak power may cause a reduction of the average power density or the intensity of the laser beam at the input end, i.e. the input facet, of the delivery fiber, whereby a safe alignment/coupling regime is provided.

In some embodiments, the laser system is configured for reducing the average power of the laser pulses in the optimization mode by reducing the gain of one or more of the optical amplifiers. A reduction of the gain may similarly cause a reduction of the average power, the pulse energy and/or the peak power of the laser pulses. In some embodiments, this is achieved by adjusting the gain of the main amplifier, e.g. the power amplifier, when the system operates in the optimization mode. In some embodiments, the average power output from the laser system is between 1 W and 10 W, such as between 2 W and 6 W. The average output power may be less than 10 W.

In some embodiments, the laser system is configured for reducing the average power of the laser pulses in the optimization mode by reducing the output repetition rate via the process shutter. This may be equivalent to a pulse down picking, where only some of the laser pulses are let through the process shutter, whereby the repetition rate is digitally modulated. In some embodiments, the output repetition rate is between 1 kHz and 10 MHz, such as between 2 kHz and 5 MHz.

In some embodiments, the laser system comprises a pulse stretcher for temporally stretching the laser pulses from the seed laser. The laser system may be configured for increasing the pulse duration of the laser pulses in the optimization mode, whereby the peak power of the laser pulses is reduced. Alternatively, the laser system may comprise a pulse compressor for temporally compressing the laser pulses. In the optimization mode, said pulse compressor may be configured to not fully compress the laser pulses to their initial pulse duration, whereby the peak power of the laser pulses is reduced compared to the operational mode. In some embodiments, the pulse duration is selected between 10 fs and 10 ps, such as between 50 fs and 5 ps, such as between 100 fs and 3 ps.

In some embodiments, the laser system is configured for increasing the initial repetition rate of the system to reduce the pulse energy and/or the peak power of the laser pulses, assuming a constant average power output by the system. Reducing the peak power and/or the pulse energy may consequently lead to a reduction of the power density and/or a reduction of the pulse energy density at the input end of the delivery fiber, e.g. at the fiber facet of the hollow-core fiber. Preferably, the process shutter is non-operable by the end-user when the laser system is operating in the optimization mode.

The laser system may be configured for operating in an operational mode, wherein the laser system is configured for transporting the laser pulses in the hollow-core fiber for delivering said laser pulses to a target. Preferably, the process shutter is operable by the enduser, when the laser system is operating in the operational mode. In some cases, the process shutter is only operable by the end-user in said operational mode. This may ensure that high- power laser pulses are only coupled into, and transported within, the delivery fiber during the operational mode. The process shutter may be either fully open, fully closed, or partially closed. The process shutter may be configured to control the emission of the laser pulses by actively blocking or allowing passage of the laser beam. Thus, the end-user may be able to control and/or modulate the laser emission via the process shutter. As an example, the process shutter may be configured to modulate the amplitude of the laser beam.

Detailed description of the drawings

Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings.

Fig. 1 shows an embodiment of a laser system (100) according to the present disclosure. The laser system comprises a seed laser (102) configured for providing a laser beam (104) comprising one or more laser pulses. Each laser pulse may have a predefined pulse energy and/or pulse duration. The seed laser (102) may be a mode-locked seed laser for generating ultrashort laser pulses. The laser pulses (104) from the seed laser (102) are directed to a pulse stretcher (106), optionally via an optical circulator (not shown). The pulse stretcher (106) may be embodied as a chirped fiber Bragg grating (cFBG), optionally with temperature control (108), such that the pulse stretcher (106) may be a tunable pulse stretcher. The pulse stretcher (106) may be a fiber-based component, such as a cFBG, spliced into an optical fiber chain. The pulse stretcher is configured for temporally stretching the laser pulses (104) from the seed laser (102), whereby stretched laser pulses (110) are obtained and input into one or more amplification stages (112, 120). Thus, the laser system may further comprise one or more optical amplifiers, such as one or more pre-amplifiers (112) and a main amplifier, such as a power amplifier (120). Each of the optical amplifiers may be optically pumped by a pump source (114, 122), such as a laser diode. The optical amplifiers may be fiber-based amplifiers, such as Erbium-doped fiber amplifiers (EDFAs) or Ytterbium-doped fiber amplifiers (YDFAs). Alternatively, the amplifiers (112, 120) may be embodied as bulk-crystal amplifiers, or semiconductor optical amplifiers (SOAs). In some embodiments, more than two optical amplifiers form part of the laser system. As an example, the system may comprise an additional pre-amplifier (not shown) located between the pulse picker (116) and the power amplifier (120). Alternatively, or additionally, the system may comprise a pre-amplifier located between the seed laser (102) and the pulse stretcher (106).

In the embodiment of fig. 1 , the laser system further comprises a pulse picker (116), such as a fiber-coupled AOM. The pulse picker may be configured for modulating the laser pulses (110), such as for modulating or adjusting the pulse repetition rate of the pulses (110). The pulse picker (116) may be configured for adjusting the pulse repetition rate in response to a control signal provided by a pulse rate controller (118). The stretched pulses (110) are amplified by the one or more optical amplifiers (112, 120) to provide amplified laser pulses (124), which are input to a process shutter (126). The process shutter (126) may be embodied as an optical modulator, such as an acousto-optic modulator (AOM) driven by a radiofrequency (RF) signal generator (128). The process shutter (126) may be operable by an enduser in the operational mode of the laser system, and it may be configured for controlling the emission of the laser pulses (124) and/or for setting an output pulse repetition rate of the laser pulses (124) in said operational mode. In some cases, the output pulse repetition rate is selected between 1 kHz and 10 MHz, such as between 1 kHz and 5 MHz. The process shutter (126) be either fully open, fully closed, or partially closed. In some cases, the output power of the laser pulses is reduced by reducing the power of the RF signal to the process shutter (126) in the optimization mode. Thus, the average power of the output laser pulses may be adjusted or reduced at an analog level by controlling the power of the process shutter (126). The output pulses from the modulator or process shutter (126) may be provided as the input to a pulse compressor (130). The pulse compressor (130) may be embodied as a diffraction grating, a pair of diffraction gratings, a prism, a prism pair, a chirped mirror, a Bragg grating, a chirped fiber Bragg grating, or a chirped volume Bragg grating. In some embodiments, the pulse compressor comprises a single diffraction grating where the laser beam is folded over the grating, such that a single grating operates similar to a pair of diffraction gratings. The pulse compressor (130) may be a free-space arrangement of components. In this embodiment, the pulse compressor is configured for temporally compressing the laser pulses, e.g. to a pulse duration similar to that of the initial pulse duration of the laser pulses (104) from the seed laser (102). The compressed pulses (132) are input to an alignment system (134).

The alignment system (134) in the embodiment of fig. 3 may comprise one or more detectors (not shown) configured for determining one or more beam parameters of the laser beam, such as for determining the position and/or incident angle of the laser beam. The alignment system (134) may further comprise one or more actuatable mirrors, such as mirrors on motorized mirror mounts (not shown). The alignment system may further comprise a control unit (not shown) configured for receiving a sensor signal from the detectors and/or configured for providing an actuator signal for actuating the one or more actuatable mirrors (not shown). Thus, the laser system may be configured for translating and/or actuating the motorized mirror mounts in response to the sensor signal, whereby the laser beam can be actively aligned to a delivery fiber (138), such as a hollow-core fiber. Thus, the output of the alignment system is an aligned laser beam (136) with respect to the core of the delivery fiber (138). Accordingly, the alignment system (134) may be an active alignment system. The laser system (100) may be a chirped pulse amplification (CPA) laser system for generating ultrashort laser pulses, such as laser pulses having a pulse duration in the femtosecond- or picosecond range. The laser system may be configured for delivery of high power femtosecond pulses.

Fig. 2 shows another embodiment of a laser system (200) according to the present disclosure. In this embodiment, the seed laser is embodied as a short-pulse oscillator (202) for generating ultrashort laser pulses (204), such as laser pulses having a pulse duration in the femtosecond- or picosecond range. The ultrashort laser pulses may be high power pulses for ophthalmology applications or materials processing applications. The laser system further comprises a pulse stretcher (206). In this embodiment, the pulse stretcher (202) may be fixed pulse stretcher, such as a diffraction grating. The laser beam (204) may be folded over the diffraction grating (not shown), such that the grating provides a similar function as a pair of diffraction gratings. The stretched laser pulses from the pulse stretcher (206) are input into a regenerative amplifier (208, 212). Thus, the pulse picker (208) and the regenerative amplifier (212) may be embodied as a single arrangement, i.e. as a free-space regenerative amplifier comprising a Pockels cell. The regenerative amplifier may further comprise one or more additional optical components, such as one or more thin-film polarizers, half-wave plates, quarter-wave plates, Faraday rotator, amplifier crystal, laser diode, pump optics, mirrors, lenses, and/or combinations thereof. The pulse repetition rate may be set via a pulse rate controller (210). The regenerative amplifier (212) may be optically pumped via a pump source (214), such as a laser diode. The amplified laser pulses output from the regenerative amplifier (212) may be input to a process shutter (216). This may be embodied as a free-space acoustooptic modulator (AOM) driven by an RF-signal generator (218). The modulated laser pulses from the process shutter may be input to a pulse compressor (220) for compressing the laser pulses. Thus, the pulse compressor may be configured for reversing the dispersion of the pulse stretcher and recompressing the pulses to a pulse duration similar to that of the ultrashort pulses (204) output from the short-pulse oscillator (202). The compressed pulses (222) are then input to an alignment system (224) for aligning the laser beam comprising said pulses (222) to a delivery fiber (228), such as a hollow-core fiber. The alignment system (224) is described in relation to figure 1. The embodiment shown in figure 2 may be composed entirely of free-space optical components with the exception of the delivery fiber (228). In other words, the laser beam (204, 222, 226) may propagate in free-space within the laser system from the short-pulse oscillator (202) to the input of the delivery fiber (228). The output laser pulses from the laser system (200) may be soliton pulses or soliton-shaped pulses.

Fig. 3 shows another embodiment of a laser system (300) according to the present disclosure. This embodiment is largely similar to the embodiment shown in figure 1 , however with a few changes. In this embodiment, the pulse stretcher (306) is a chirped fiber Bragg grating (cFBG). The laser pulses (304) from the seed laser may be directed to the CFBG via an optical circulator (308). In this example, the process shutter (320) is embodied as an acousto-optic modulator (AOM) driven by a radio-frequency (RF) signal generator (322). Furthermore, the delivery fiber is embodied as a hollow-core fiber (332). The laser system (300) may be a chirped pulse amplification (CPA) laser system for generating ultrashort laser pulses, such as laser pulses having a pulse duration in the femtosecond- or picosecond range. As an example, the pulse duration may be between 10 fs and 10 ps. The laser pulses output by the laser system (300) may be high-energy laser pulses having a high peak power, e.g. suitable for medical applications, ophthalmology, surgery, materials processing and/or micromachining.

Fig. 4 shows an embodiment of an alignment system (400) according to the present disclosure. The alignment system (400) may form part of the laser system disclosed herein. The figure shows a laser beam (401), e.g. a pulsed laser beam, which is input to the alignment system. The laser beam (401) may be provided by the laser system described herein, e.g. provided by a CPA laser system. As an example, a pulse compressor (not shown) may be provided upstream of the alignment system, such that the output from the pulse compressor is input to the alignment system. This is shown in figures 1-3. The laser beam may be incident on a first mirror (402) for redirecting the laser beam (401) onto one or more actuatable mirrors (403, 404). The actuatable mirrors may be embodied as mirrors mounted on motorized mirror mounts for moving said mirrors. Thereby, the laser beam (401) can be steered, i.e. adjusted, such as adjusted in one or more dimensions. As an example, the alignment system may be configured for adjusting the position of the laser beam in at least two dimensions via the actuatable mirrors (403, 404). Downstream of the actuatable mirrors (403, 404), one or more partially reflecting mirrors (405, 406) may be positioned within the alignment system (400). The partially reflecting mirrors may be configured for partially reflecting the laser beam, such that the laser beam is incident on one or more detectors (407, 408). The detectors may comprise a first detector configured for determining the position of the laser beam and a second detector configured for determining the angle of the laser beam. The detectors (407, 408) may be embodied as position sensitive detectors (PSDs). Downstream of the partially reflecting mirrors (405, 406), a lens (409) may be positioned. The lens (409) may be configured for focusing the laser beam (401) into the core of the delivery fiber (410). The active alignment system (400) may be enclosed in a housing such that it constitutes a modular unit for removably attaching to a laser system, such as the laser system disclosed herein. Additionally, the active alignment system (400) may be configured for continuously monitoring the beam parameters to realign the laser beam during operation of the laser system. Accordingly, the alignment system (400) may be used for both alignment of the laser beam to the delivery fiber, coupling light into said fiber, and monitoring beam parameters of the laser beam during operation of the laser system when the process shutter is open.

Further details of the disclosure

1 . A laser system for operating in two different modes, the laser system comprising:

- a process shutter configured for controlling the emission of the laser pulses such as by actively blocking or allowing the passage of the laser beam and/or configured for setting an output pulse repetition rate of the laser pulses; and

- a hollow-core fiber for transporting the laser pulses, said hollow-core fiber comprising a hollow core surrounded by a cladding structure; wherein the laser system is configured for operating in two different modes:

- an optimization mode, wherein the laser system is configured for actively aligning the laser beam to the hollow core and coupling said laser beam into the hollow core, wherein the process shutter is non-operable by an end-user in the optimization mode; and - an operational mode, wherein the laser system is configured for transporting the laser pulses in the hollow-core fiber for delivering said laser pulses to a target, wherein the process shutter is operable by the end-user in the operational mode.

2. The laser system according to item 1 , wherein the process shutter is operable by the end-user only in the operational mode.

3. The laser system according to any of the preceding items, wherein the laser system further comprises two or more detectors configured for detecting one or more, such as two or more, beam parameters of the laser beam.

4. The laser system according to item 3, wherein the beam parameters include at least a position and/or an incident angle of the laser beam.

5. The laser system according to any of the items 3-4, wherein the two or more detectors comprise a first detector configured for determining the position of the laser beam and a second detector configured for determining the angle of the laser beam.

6. The laser system according to any of the items 3-5, wherein the detectors are configured for providing a feedback signal used for active alignment of the laser beam to the hollow core when operating in the optimization mode.

7. The laser system according to any of the items 3-6, wherein the detectors are selected from the group of: position sensitive detectors (PSD), quad photodiodes, quadrant photodiode arrays, image sensors, phototransistors, and/or combinations thereof.

8. The laser system according to any of the items 3-7, wherein the laser system is configured for automatically switching from the operational mode to the optimization mode in case of no signal on the detectors for a predetermined amount of time.

9. The laser system according to any of the items 3-8, wherein, when operating in the operational mode, the laser system is configured for providing a warning to a user in case of no signal on the detectors for a predetermined amount of time. 10. The laser system according to any of the preceding items, wherein the laser system further comprises a third detector configured for determining power of the laser beam at the output of the hollow-core fiber.

11. The laser system according to item 10, wherein the third detector is configured for monitoring the output power from the laser system, when the system operates in the optimization mode.

12. The laser system according to any of the items 10-11 , wherein the laser system, when operating in the optimization mode, is configured for maximizing the output power by an active alignment of the laser beam.

13. The laser system according to any of the items 10-12, wherein the laser system is configured to stop emission of the laser beam in case of the output power being below a certain threshold in the operational mode.

14. The laser system according to any of the items 10-13, wherein the laser system is configured to stop emission of the laser beam in case the output power differs from the input power by a certain predefined amount, said input power measured at the input end of the hollow-core fiber.

15. The laser system according to any of the items 3-14, wherein the laser system comprises an active alignment system comprising the two or more detectors, and optionally the third detector.

16. The laser system according to item 15, wherein the active alignment system further comprises one or more, such as two or more, actuatable mirrors or lenses for adjusting the position and/or angle of the laser beam.

17. The laser system according to any of the items 15-16, wherein the active alignment system further comprises a control unit configured for receiving the feedback signal from the detectors and/or configured for providing a control signal for actuating the one or more actuatable mirrors or lenses.

18. The laser system according to any of the items 15-17, wherein the active alignment system further comprises the third detector configured for determining power of the laser beam at the output of the hollow-core fiber. 19. The laser system according to any of the items 15-18, wherein the signal from the third detector is used for calibration of the active alignment system in the optimization mode.

20. The laser system according to any of the items 15-19, wherein the alignment system is configured for continuously monitoring the one or more beam parameters of the laser beam in the optimization mode and/or in the operational mode, provided the process shutter is open.

21. The laser system according to any of the items 15-20, wherein, when the process shutter is open such that the laser beam is transmitted through the alignment system, said alignment system is configured for continuously monitoring the one or more beam parameters.

22. The laser system according to any of the items 15-21 , wherein, when the process shutter is open, the alignment system is configured for continuously realigning the laser beam by actuating the one or more actuatable mirrors or lenses based on the feedback signal from the detectors.

23. The laser system according to item 22, wherein the system is configured for performing the realignment in the operational mode provided the process shutter is open.

24. The laser system according to any of the items 22-23, wherein the realignment of the laser beam includes adjusting the position and/or the incident angle of the laser beam such that a coupling loss to the hollow-core fiber is lowered and/or such that the output power of the laser beam from the hollow-core fiber is increased.

25. The laser system according to any of the items 15-24, wherein, provided the process shutter has been closed for a predetermined period of time when the laser system operates in the operational mode, the laser system is configured to force the laser system back in the optimization mode.

26. The laser system according to any of the items 15-25, wherein the two or more detectors of the alignment system are enclosed in a housing such that the alignment system constitutes a modular unit for attachment to a laser. 27. The laser system according to any of the items 15-26, wherein the seed laser, or short-pulse oscillator, and the process shutter, are components of a pulsed laser that constitutes an external laser.

28. The laser system according to any of the items 15-27, wherein the modular unit is configured for attaching to the external laser, wherein the alignment system is fully enclosed inside the modular unit, and further configured for receiving a laser beam from the external laser when attached.

29. The laser system according to any of the items 15-28, wherein the modular unit further comprises a fiber-coupling to attach the hollow-core fiber for delivery of laser pulses to a target.

30. The laser system according to any of the preceding items, wherein the laser system is configured for switching between the two modes.

31. The laser system according to any of the preceding items, wherein the laser system is configured to switch between the two modes in less than 5 seconds, such as in less than 1 second.

32. The laser system according to any of the preceding items, wherein the optimization mode provides a safe alignment and/or coupling of the laser beam by adjusting one or more parameters of the laser pulses.

33. The laser system according to item 32, wherein the parameters are selected from the group of: pulse peak power, pulse energy, average power, pulse repetition rate, and/or combinations thereof.

34. The laser system according to any of the preceding items, wherein the laser system is configured for reducing the average power of the laser pulses in the optimization mode via the process shutter.

35. The laser system according to any of the preceding items, wherein the laser system further comprises a radio-frequency (RF) signal generator for providing an RF signal to the process shutter. 36. The laser system according to item 35, wherein the laser system is configured for reducing the intensity or power of the RF signal in the optimization mode, whereby the average power of the laser pulses is reduced.

37. The laser system according to any of the preceding items, wherein the laser system is configured for reducing the output repetition rate via the process shutter in the optimization mode.

38. The laser system according to any of the preceding items, wherein the laser system is configured for increasing an initial repetition rate of the laser pulses from the seed laser or short-pulse oscillator in the optimization mode.

39. The laser system according to any of the preceding items, wherein the average power output by the laser system is the same in the two modes.

40. The laser system according to any of the preceding items, wherein the laser system is configured for reducing the pulse energy of the laser pulses by increasing an initial repetition rate of the laser pulses in the optimization mode.

41. The laser system according to any of the preceding items, wherein the laser system is configured for reducing the peak power of the laser pulses by increasing the pulse duration of said laser pulses in the optimization mode.

42. The laser system according to any of the preceding items, wherein the laser system further comprises one or more optical amplifiers for amplifying the laser pulses.

43. The laser system according to any of the preceding items, wherein the laser system is configured for reducing the gain of one or more of the optical amplifiers in the optimization mode.

44. The laser system according to any of the preceding items, wherein the laser system is configured to output laser pulses having a first peak power in the optimization mode, and further configured to output laser pulses having a second peak power in the operational mode, wherein the first peak power is lower than the second peak power. 45. The laser system according to item 44, wherein the first peak power is half the second peak power or lower.

46. The laser system according to any of the preceding items, wherein the laser system is a chirped pulse amplification (CPA) laser system.

47. The laser system according to any of the preceding items, wherein the laser system comprises a pulse stretcher for temporally stretching the laser pulses from the seed laser to provide stretched laser pulses.

48. The laser system according to any of the preceding items, wherein the laser system comprises a pulse compressor for temporally compressing the laser pulses to provide compressed laser pulses.

49. The laser system according to item 48, wherein the pulse compressor is arranged downstream of the process shutter.

50. The laser system according to any of the preceding items, wherein the compressed pulses have a pulse duration between 10 fs and 10 ps, such as between 50 fs and 5 ps, such as between 100 fs and 3 ps.

51. The laser system according to any of the preceding items, wherein the compressed pulses have a pulse energy of between 1 J and 200 pJ, such as between 1 pJ and 100 pJ, such as between 5 pJ and 50 pJ.

52. The laser system according to any of the preceding items, wherein the laser system is configured for outputting the compressed pulses, wherein the average power output from the laser system is between 0.1 W and 10 W, such as between 1 W and 6 W.

53. The laser system according to any of the preceding items, wherein the laser system is configured for increasing the pulse duration of the laser pulses in the optimization mode, whereby the peak power of the laser pulses is reduced.

54. The laser system according to any of the preceding items, wherein the laser system comprises a pulse stretcher comprising a chirped fiber Bragg-grating (cFBG) and a temperature control for controlling the temperature of the cFBG. 55. The laser system according to any of the preceding items, wherein the laser system is configured for adjusting the dispersion profile of the pulse stretcher in the optimization mode, whereby the pulse duration of the laser pulses is increased.

56. The laser system according to any of the items 47-55, wherein the pulse stretcher is arranged upstream of the process shutter.

57. The laser system according to any of the preceding items, wherein the laser system further comprises a mechanical shutter arranged after the hollow-core fiber.

58. The laser system according to any of the preceding items, wherein the process shutter comprises or constitutes an acousto-optic modulator (AOM).

59. The laser system according to any of the preceding items, wherein the hollow-core fiber is an anti-resonant hollow-core fiber (AR-HCF).

60. The laser system according to any of the preceding items, wherein the hollow-core fiber is hollow-core photonic bandgap fiber (PBG-HC fiber).

61. The laser system according to any of the preceding items, wherein the hollow core comprises a gas, such as air, and wherein the gas pressure in the hollow core is less than 100 mbar, such as less than 10 mbar, such as less than 1 mbar.

62. The laser system according to any of the preceding items, wherein the hollow core comprises a vacuum and/or is evacuated from air or other gases.

63. The laser system according to any of the preceding items, wherein the hollow-core fiber encloses a vacuum or a gas having a gas pressure of less than 100 mbar.

64. The laser system according to any of the preceding items, wherein the nonlinearity of the hollow-core fiber is negligible such that the laser pulses transported by the fiber approximately maintain their pulse shape.

65. The laser system according to any of the preceding items, wherein the hollow-core fiber has a length of between 1 m and 5 m, such as between 2.5 m and 3.5 m. 66. The laser system according to any of the preceding items, wherein the laser system further comprises a collimator for collimating the laser beam, said collimator attached to the distal end of the hollow-core fiber.

67. The laser system according to any of the preceding items, wherein the hollow-core fiber is arranged inside a cable, preferably a flexible cable.

68. The laser system according to item 67, wherein the cable further comprises a protective window arranged inside a ferrule or connector.

69. The laser system according to any of the preceding items, wherein the process shutter comprises or constitutes an electro-optic modulator (EOM).

70. The laser system according to any of the preceding items, wherein the process shutter is configured to operate through mechanical blocking, electro-optic modulation, or acousto-optic modulation.

71. The laser system according to any of the preceding items, wherein the process shutter is electronically-controlled.

72. The laser system according to any of the items 47-71 , wherein the compressed pulses have a pulse duration in the femtosecond range.

73. The laser system according to any of the preceding items, wherein the compressed pulses have a pulse duration of between 10 fs and 10 ps, such as between 50 fs and 5 ps, such as between 100 fs and 3 ps.

74. The laser system according to any of the preceding items, wherein the compressed pulses have a pulse energy of between 1 J and 20 pJ, such as between 5 pJ and 10 pJ.

75. The laser system according to any of the preceding items, wherein the laser system is configured for outputting the compressed pulses, wherein the average power of the compressed pulses is between 1 W and 6 W. 76. The laser system according to any of the preceding items, wherein the target is the eye(s) of a patient, or wherein the target is a workpiece to be processed by laser pulses output from the laser system.

77. The laser system according to any of the preceding items, wherein the laser system is suitable for ophthalmology applications.

78. The laser system according to any of the preceding items, wherein the laser system is suitable for applications within materials processing.

79. A method of operating a laser system comprising a process shutter operable by a user in at least some operational modes of the laser system, the method comprising the steps of:

- providing a pulsed laser beam comprising one or more laser pulses;

- actively aligning the laser beam to a core of a hollow-core fiber in an optimization mode of the laser system, wherein the process shutter is non- operable by the user in the optimization mode; and

- delivering laser pulses to a target, wherein the laser pulses are transported by the hollow-core fiber in an operational mode of the laser system, wherein the process shutter is operable by the user in said operational mode, whereby the user can control or modulate the emission of the laser pulses.

80. The method according to item 79, wherein the laser beam is actively aligned using two or more detectors for determining a position and/or angle of the laser beam, and two or more actuatable mirrors for adjusting said position and/or angle.

Although some embodiments have been described and shown in detail, the disclosure is not restricted to such details, but may also be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it is to be understood that other embodiments may be utilized, and structural and functional modifications may be made without departing from the scope of the present disclosure. Furthermore, the skilled person would find it apparent that unless an embodiment is specifically presented only as an alternative, different disclosed embodiments may be combined to achieve a specific implementation and such specific implementation is within the scope of the disclosure.

Claims

1. A laser system for operating in two different modes, the laser system comprising:

- a process shutter configured for controlling the emission of the laser pulses by actively blocking or allowing the passage of the laser beam; and

- an operational mode, wherein the laser system is configured for transporting the laser pulses in the hollow-core fiber for delivering said laser pulses to a target, wherein the process shutter is operable by the end-user in the operational mode.

2. The laser system according to claim 1 , wherein the laser system further comprises an alignment system comprising two or more detectors configured for detecting one or more beam parameters of the laser beam, said beam parameters comprising at least a position and/or an incident angle of the laser beam.

3. The laser system according to claim 2, wherein the two or more detectors comprise a first detector configured for determining the position of the laser beam and a second detector configured for determining the angle of the laser beam.

4. The laser system according to any of the claims 2-3, wherein the detectors are configured for providing a feedback signal used for active alignment of the laser beam to the hollow core when operating in the optimization mode and/or in the operational mode.

5. The laser system according to any of the claims 2-4, wherein the laser system is configured for automatically switching from the operational mode to the optimization mode in case of no signal on the detectors for a predetermined amount of time.

6. The laser system according to any of the claims 2-5, wherein, when operating in the operational mode, the laser system is configured for providing a warning to a user in case of no signal on the detectors for a predetermined amount of time.

7. The laser system according to any of the claims 2-6, wherein the active alignment system further comprises one or more, such as two or more, actuatable mirrors or lenses for adjusting the position and/or angle of the laser beam.

8. The laser system according to any of the claims 2-7, wherein the active alignment system further comprises a control unit configured for receiving the feedback signal from the detectors and/or configured for providing a control signal for actuating the one or more actuatable mirrors or lenses.

9. The laser system according to any of the claims 2-8, wherein the alignment system is configured for continuously monitoring the one or more beam parameters of the laser beam in the optimization mode and/or in the operational mode, provided the process shutter is open.

10. The laser system according to any of the claims 2-9, wherein, when the process shutter is open such that the laser beam is transmitted through the alignment system, said alignment system is configured for continuously monitoring the one or more beam parameters.

11. The laser system according to any of the claims 2-10, wherein, when the process shutter is open, the alignment system is configured for continuously realigning the laser beam by actuating the one or more actuatable mirrors or lenses based on the feedback signal from the detectors.

12. The laser system according to claim 11 , wherein the system is configured for performing the realignment in the operational mode provided the process shutter is open.

13. The laser system according to any of the claims 11-12, wherein the realignment of the laser beam includes adjusting the position and/or the incident angle of the laser beam such that a coupling loss to the hollow-core fiber is lowered and/or such that the output power of the laser beam from the hollow-core fiber is increased.

14. The laser system according to any of the claims 2-13, wherein, provided the process shutter has been closed for a predetermined period of time when the laser system operates in the operational mode, the laser system is configured to force the laser system back in the optimization mode.

15. The laser system according to any of the claims 2-14, wherein the seed laser or short-pulse oscillator, and the process shutter, are components of a pulsed laser that constitutes an external laser.

16. The laser system according to any of the claims 2-15, wherein the two or more detectors of the alignment system are enclosed in a housing such that the alignment system constitutes a modular unit for attachment to a laser.

17. The laser system according to claim 16, wherein the modular unit is configured for attaching to an external laser, wherein the alignment system is fully enclosed inside the modular unit, and further configured for receiving a laser beam from the external laser when attached.

18. The laser system according to any of the claims 16-17, wherein the modular unit further comprises a fiber-coupling to attach the hollow-core fiber for delivery of laser pulses to a target.

19. The laser system according to any of the preceding claims, wherein the laser system is configured for reducing the average power of the laser pulses in the optimization mode via the process shutter.

20. The laser system according to any of the preceding claims, wherein the process shutter is further configured for setting an output pulse repetition rate of the laser pulses.

21. The laser system according to any of the preceding claims, wherein the output repetition rate is between 1 kHz and 5 MHz.

22. The laser system according to any of the preceding claims, wherein the laser system is configured for reducing the output repetition rate via the process shutter in the optimization mode.

23. The laser system according to any of the preceding claims, wherein the laser system is configured for reducing the peak power of the laser pulses by increasing the pulse duration of said laser pulses in the optimization mode.

24. The laser system according to any of the claims 1-18, wherein the average power output by the laser system is the same in the two modes.

25. The laser system according to any of the preceding claims, wherein the laser system further comprises one or more optical amplifiers for amplifying the laser pulses, wherein the laser system is configured for reducing the gain of one or more of the optical amplifiers in the optimization mode.

26. The laser system according to any of the preceding claims, wherein the laser system is configured to output laser pulses having a first peak power in the optimization mode, and further configured to output laser pulses having a second peak power in the operational mode, wherein the first peak power is lower than the second peak power.

27. The laser system according to any of the preceding claims, wherein the hollow-core fiber is an anti-resonant hollow-core fiber (AR-HCF), wherein the hollow core comprises a gas, such as air, and wherein the gas pressure in the hollow core is less than 50 mbar.

28. The laser system according to any of the preceding claims, wherein the hollow-core fiber encloses a vacuum and/or is evacuated from air or other gases.

29. The laser system according to any of the preceding claims, wherein the length of the hollow-core fiber is between 1 m and 5 m.

30. The laser system according to any of the preceding claims, wherein the process shutter is configured to operate through mechanical blocking, electro-optic modulation, or acousto-optic modulation.

31. The laser system according to any of the preceding claims, wherein the process shutter is an acousto-optic modulator (AOM) or an electro-optic modulator (EOM).

32. The laser system according to any of the preceding claims, wherein the laser system is a chirped pulse amplification (CPA) laser system.

33. The laser system according to any of the preceding claims, wherein the laser system comprises a pulse stretcher for temporally stretching the laser pulses from the seed laser or short-pulse oscillator.

34. The laser system according to any of the preceding claims, wherein the laser system is configured for increasing the pulse duration of the laser pulses in the optimization mode, whereby the peak power of the laser pulses is reduced.

35. The laser system according to any of the preceding claims, wherein the laser system comprises a pulse compressor for temporally compressing the laser pulses to provide compressed laser pulses.

36. The laser system according to any of the preceding claims, wherein the laser system is suitable for ophthalmology applications.

37. A method of operating the laser system according to any of the preceding claims, the method comprising the steps of:

- providing a pulsed laser beam comprising one or more laser pulses;

- actively aligning the laser beam to the core of the hollow-core fiber when operating in the optimization mode, wherein the process shutter is non- operable by the user in the optimization mode; and

- delivering laser pulses to a target, wherein the laser pulses are transported by the hollow-core fiber in the operational mode, wherein the process shutter is operable by the user in said operational mode, whereby the user can control and/or modulate the emission of the laser pulses.