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WO2022163245A1 - Résonateur optique et dispositif de traitement au laser - Google Patents

Résonateur optique et dispositif de traitement au laser Download PDF

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Publication number
WO2022163245A1
WO2022163245A1 PCT/JP2021/047969 JP2021047969W WO2022163245A1 WO 2022163245 A1 WO2022163245 A1 WO 2022163245A1 JP 2021047969 W JP2021047969 W JP 2021047969W WO 2022163245 A1 WO2022163245 A1 WO 2022163245A1
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optical
optical system
light source
light
light beam
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English (en)
Japanese (ja)
Inventor
宏基 市橋
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Panasonic Holdings Corp
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Panasonic Holdings Corp
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/022—Mountings; Housings
    • H01S5/0225—Out-coupling of light
    • H01S5/02255—Out-coupling of light using beam deflecting elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/14—External cavity lasers

Definitions

  • the present disclosure relates to an optical resonator that resonates a plurality of light beams, and a laser processing apparatus that includes the optical resonator.
  • Patent Document 1 discloses a wavelength combining laser system that superimposes individual light beams to form a combined beam. Patent Document 1 discloses condensing light beams from a plurality of diode bars onto an optical fiber from the viewpoint of increasing light output. Also, for the purpose of downsizing the laser system, an optical system is separately included for removing the arrangement of the coupling lens in wavelength synthesis from the focal length, or the beam rotator is rotated.
  • the present disclosure provides an optical resonator and a laser processing apparatus capable of improving the efficiency of resonating light beams having multiple wavelengths.
  • the optical resonator resonates multiple light beams having different wavelengths.
  • An optical resonator comprises a light source, a diffraction grating, an output coupler, and an optical system.
  • the light source includes a plurality of light source elements each emitting a plurality of light beams.
  • the diffraction grating diffracts each light beam at an angle corresponding to the wavelength of the light beam from each light source element.
  • the output coupler reflects a portion of the light beam diffracted at the grating back to the light source and outputs the remainder of the light beam.
  • the optical system includes one or more lenses disposed between the light source and the diffraction grating to collimate each light beam incident from the light source and output to the diffraction grating.
  • the optical system has a diffractive surface that diffracts each light beam so as to adjust chromatic aberration across the wavelengths of the multiple light beams.
  • a laser processing apparatus includes the optical resonator described above and a processing head that irradiates an object to be processed with a light beam output from an output coupler of the optical resonator.
  • optical resonator and laser processing apparatus of the present disclosure it is possible to improve the efficiency of resonating light beams having multiple wavelengths.
  • FIG. 2 is a plan view illustrating the configuration of the optical resonator according to Embodiment 1;
  • FIG. 2 is a side view illustrating the configuration of the optical resonator according to Embodiment 1;
  • FIG. 4 illustrates the configuration of an LD array in an optical resonator;
  • FIG. 2 is a side view illustrating the configuration of an optical unit in an optical resonator;
  • FIG. 4 is a perspective view illustrating the configuration of a beam twister in an optical unit; Plan view of beam twister unit in optical unit A diagram illustrating the configuration of a collimator optical system in an optical resonator Diagram explaining how light beams are combined in the diffraction grating of the optical resonator A diagram for explaining the problem of coupling efficiency of return light in an optical resonator. Diagram for explaining correction of chromatic aberration in an optical cavity The figure which shows the numerical example of the diffraction surface of a collimator optical system. A diagram showing a numerical example of the diffractive surface following FIG. A diagram showing a numerical example of the diffractive surface following FIG. Graph showing measurement results of diffraction efficiency on the diffraction surface of the collimator optical system Graph illustrating axial chromatic aberration in the collimator optical system of the modified example
  • Embodiment 1 In Embodiment 1, a wavelength-combining optical resonator and a laser processing apparatus including the same will be described.
  • FIG. 1 is a diagram showing the configuration of a laser processing apparatus 1 according to this embodiment.
  • the laser processing apparatus 1 includes, for example, an optical resonator 2, a transmission optical system 10, a processing head 11, and a controller 12, as shown in FIG.
  • the laser processing apparatus 1 is an apparatus for performing various laser processing by irradiating various processing objects 15 with laser light.
  • Various laser processes include, for example, laser welding, laser cutting, and laser drilling.
  • the optical resonator 2 generates laser light that is output from the laser processing apparatus 1, for example.
  • the optical resonator 2 is a wavelength combining type external resonator that resonates and synthesizes a plurality of light beams at each wavelength. According to the wavelength combining type optical resonator 2, it is easy to obtain good beam quality and narrow the beam diameter.
  • the optical resonator 2 includes a laser light source 13 including a plurality of laser elements 31 to 33, an output coupler 14 for emitting output light L1, and an optical system arranged between 14 .
  • the optical system includes, for example, the diffraction grating 20 and a collimator optical system 25 for collimating each light beam incident on the diffraction grating 20 .
  • the optical resonator 2 of this embodiment resonates each light beam of a specific wavelength band on the optical path that goes back and forth between the laser light source 13 and the output coupler 14 via such an optical system.
  • the wavelength-combining optical resonator 2 by securing a wide wavelength band in which light beams resonate, that is, a resonant wavelength band, for example, a large number of laser elements 31 to 33 can be used, and the optical output can be increased.
  • a resonant wavelength band for example, a large number of laser elements 31 to 33 can be used, and the optical output can be increased.
  • FIG. 1 three laser elements 31, 32, and 33 in the laser light source 13 are illustrated.
  • the number of laser elements 31 to 33 included in the laser light source 13 is, for example, several tens to several hundred.
  • the configuration of the collimator optical system 25 in the optical resonator 2 of this embodiment can solve the problem of oscillation efficiency that may occur when using a wide resonant wavelength band (details will be described later).
  • the transmission optical system 10 is an optical system that transmits the laser light from the optical resonator 2 to the processing head 11, and includes, for example, an optical fiber.
  • the processing head 11 is, for example, a device that is arranged to face an object 15 to be processed and that irradiates the object 15 with laser light transmitted from the optical resonator 2 .
  • the controller 12 is a control device that controls the overall operation of the laser processing device 1.
  • the controller 12 has a CPU or MPU that cooperates with software to realize a predetermined function, for example.
  • the controller 12 may include an internal memory that stores various programs and data, and various interfaces that allow the user to input oscillation conditions and the like.
  • the controller 12 may include hardware circuits such as ASICs and FPGAs that implement various functions. Also, the controller 12 may be configured integrally with the driving circuit of the light source.
  • FIG. 2 is a plan view illustrating the configuration of the optical resonator 2 in this embodiment.
  • FIG. 3 shows a side view of the optical resonator 2 of FIG.
  • the optical axis direction of the light beam output from the output coupler 14 of the optical resonator 2 is defined as the Z direction
  • the two directions orthogonal to the Z direction and mutually orthogonal are defined as the X and Y directions.
  • 2 illustrates the optical resonator 2 viewed from the +Y side
  • FIG. 3 illustrates the optical resonator 2 viewed from the -X side.
  • the optical resonator 2 of this embodiment includes a plurality of LD (laser diode) arrays 3-1 to 3-3 constituting a laser light source 13, and each LD array 3-1 to 3- A plurality of optical units 4-1 to 4-3 provided corresponding to 3 are provided. Furthermore, the optical resonator 2 includes a plurality of mirrors 21 to 23, a collimator optical system 25, a half-wave plate 24, a diffraction grating 20, a telescope optical system 26, and an output coupler 14.
  • LD laser diode
  • the optical resonator 2 of this configuration example for example, as shown in FIG. It has a two-stage configuration with a stage on the +Y side arranged on the plane. With such a two-stage configuration, the optical resonator 2 can be miniaturized.
  • FIG. 2 and 3 illustrate three LD arrays 3-1, 3-2, and 3-3 corresponding to three laser elements 31, 32, and 33.
  • FIG. The number of LD arrays 3-1 to 3-3 included in the laser light source 13 is, for example, eleven.
  • the LD arrays 3-1 to 3-3 are collectively referred to as "LD array 3”
  • the optical units 4-1 to 4-3 are collectively referred to as "optical unit 4”.
  • the laser elements 31 to 33 may be collectively referred to as "laser element 30" (see FIG. 4).
  • FIG. 4 illustrates the configuration of the LD array 3 in the optical resonator 2.
  • FIG. The LD array 3 is, for example, an array in which a plurality of laser elements 30 are arranged one-dimensionally.
  • the direction in which the laser elements 30 are arranged in the LD array 3 will be referred to as the "Xi direction”
  • the direction of the optical axis of the light beam emitted from the LD array 3 will be referred to as the "Zi direction”.
  • Each LD array 3 is arranged, for example, so that the Xi and Zi directions are orthogonal to the Y direction.
  • the LD array 3 is composed of direct diode lasers, for example.
  • a rear (that is, ⁇ Zi side) facet of the LD array 3 is coated with a high reflectance coating having a reflectance of 99.9% or more, for example.
  • An anti-reflection coating with a transmittance of 99.9% or more is applied to the front (that is, +Zi side) facet of the LD array 3, for example.
  • FIG. 4 illustrates apertures (also referred to as "LD apertures") through which the five laser elements 30 emit light beams in the LD array 3 .
  • the number of laser elements 30 included in one LD array 3 is, for example, several tens to several hundred.
  • a plurality of laser elements 30 in the LD array 3 have a common spontaneous emission spectrum according to, for example, the material of the LD emission layer.
  • the spectrum corresponds, for example, to the resonance wavelength band and includes, for example, wavelengths of 405 nm to 445 nm.
  • the LD array 3 emits a light beam having a fast axis with a relatively large divergence angle and a slow axis with a relatively small divergence angle from each laser element 30 (see FIG. 5).
  • the fast axis of the light beam expands the beam diameter more rapidly than the slow axis and tends to achieve good beam quality.
  • Each laser element 30 is an example of a light source element forming an emitter of the LD array 3, and emits a light beam to the +Zi side.
  • the optical unit 4 is an optical system that adjusts and guides a plurality of light beams from each laser element 30 of the LD array 3 .
  • the optical unit 4 includes a BTU (beam twister unit) 40, a SAC (slow axis collimator) 45, and a mirror 46 in order toward the +Zi side.
  • the optical unit 4 is arranged on the +Zi side of the LD array 3 .
  • each light beam from the LD array 3 is collimated about the fast axis and the slow axis, and the slow axis is oriented in the Y direction. Details of such an optical unit 4 will be described later.
  • the mirror 46 of each optical unit 4 reflects the light beam from the corresponding LD array 3 to the -Z side and emits it toward the mirror 21 .
  • the mirror 46 of the optical unit 4 is arranged parallel to the Y direction and at a predetermined angle to the Xi direction.
  • the angle of the mirror 46 is set for each optical unit 4 so that the light beams from each LD array 3 are focused on the diffraction grating 20 with the fast axis directed in the X direction, for example 44 degrees or more. 72 degrees or less.
  • the mirrors 21 and 22 are arranged opposite to each other on the -Z side and the +Z side, for example, and are oriented parallel to each other.
  • the orientation of each mirror 21, 22 is, for example, parallel to the X direction and has a predetermined tilt angle with respect to the Y direction.
  • the tilt angles of the mirrors 21 and 22 are set in consideration of the optical path in the two-stage structure of the optical resonator 2, and are, for example, 4 degrees.
  • the mirror 21 reflects light between the mirror 46 of each optical unit 4 and the mirror 22 .
  • the mirror 21 reflects each light beam incident from the mirror 46 of each optical unit 4 toward the +Y side by the tilt angle, and emits it toward the mirror 22 (FIG. 3).
  • the mirror 22 reflects each light beam incident from the mirror 21 to the -Z side, and emits the light beam so as to converge on the XZ plane.
  • Mirror 22 has a smaller size than mirror 21, for example.
  • a collimator optical system 25 On the -Z side of the mirror 22, a collimator optical system 25, a half-wave plate 24 and a diffraction grating 20 are arranged in order along the Z direction. For example, as shown in FIG. 2, a plurality of light beams enter the collimator optical system 25 while being aligned with each other in the X direction.
  • the collimator optical system 25 includes one or more lenses, collimates each light beam incident from each LD array 3 via the mirror 22 or the like again in the fast axis, that is, in the X direction, and emits it toward the diffraction grating 20. do.
  • Each optical path length between the collimator optical system 25 and the BTU 40 of each optical unit 4 is set to substantially match the focal length (denoted as "f") of the collimator optical system 25, for example.
  • the optical path length between the collimator optical system 25 and the diffraction grating 20 can be set to the focal length f of the collimator optical system 25 or less.
  • the collimator optical system 25 is configured to suppress chromatic aberration in the wavelength band in which the light beam resonates, that is, in the resonance wavelength band. Details of the collimator optical system 25 will be described later.
  • the half-wave plate 24 rotates the polarization of the incident light beam by 90 degrees. For example, if the light beam is linearly polarized light parallel to the X direction, it is converted into linearly polarized light parallel to the Y direction.
  • the half-wave plate 24 can appropriately control the polarization of the light beam from the viewpoint of the diffraction efficiency of the diffraction grating 20 .
  • the half-wave plate 24 may be arranged not only between the collimator optical system 25 and the diffraction grating 20 but also on the +Z side of the collimator optical system 25, for example.
  • the diffraction grating 20 is composed of, for example, a transmissive dispersive element, and diffracts incident light at a diffraction angle corresponding to its wavelength.
  • the diffraction grating 20 has, for example, a periodic structure with a predetermined pitch in the XZ cross section.
  • the periodic structure of the diffraction grating 20 may have, for example, a rectangular wave shape, a triangular wave shape, or a sawtooth shape in cross section.
  • the diffraction grating 20 is not limited to a transmissive type, and may be of a reflective type.
  • the mirror 23 reflects light between the diffraction grating 20 and the telescope optical system 26.
  • the mirror 23 is arranged so that the reflected light of the light beams combined at the diffraction grating 20 travels in the Z direction and enters the telescope optical system 26 .
  • the telescope optical system 26 includes, for example, cylindrical lenses 26a and 26b having positive optical power in the X direction and a cylindrical lens 26c having negative optical power in the X direction.
  • the telescope optical system 26 reduces, for example, the beam diameter in the X direction of the light beam from the mirror 23 and emits it to the output coupler 14 .
  • the telescopic optics 26 can reduce the angular error sensitivity of the output coupler 14 about the fast axis of the light beam.
  • the output coupler 14 is composed of, for example, a partially reflective mirror having predetermined transmittance and reflectance, and is arranged parallel to the XY plane.
  • the reflectance of the output coupler 14 is set to, for example, about 2% to 6%.
  • a transmission component corresponding to the transmittance is emitted to the transmission optical system 10 (FIG. 1), for example, as laser light output from the optical resonator 2.
  • FIG. 1 the reflected component corresponding to the reflectance is returned so as to travel backward through the telescope optical system 26 and the like due to optical resonance.
  • the output coupler 14 may be provided with a mechanism capable of adjusting such reflectance and transmittance.
  • the light beams from the laser elements 30 of the large number of LD arrays 3 can be resonated together to increase the light output. Further, by using various mirrors 46, 21 to 23 to fold the optical paths of the respective light beams, the optical resonator 2 can be made compact.
  • the optical resonator 2 is not limited to the above configuration example.
  • the optical resonator 2 may further include an optical element such as a prism, or various optical elements such as the mirrors 46, 21 to 23 may be omitted as appropriate.
  • FIG. 5 shows a side view of the optical unit 4 viewed from the -Xi side.
  • FIG. 5 exemplifies the optical path of the light beam from one laser element 30, omitting illustration of the mirror 46 and the like.
  • a BTU 40 in the optical unit 4 includes a FAC (fast axis collimator) 41 and a BT (beam twister) 42 .
  • the FAC 41, BT 42 and SAC 45 are arranged in order from the vicinity of the laser element 30 to the +Zi side.
  • the fast axis Af of the light beam is oriented in the Y direction and the slow axis As is oriented in the Xi direction.
  • the FAC 41 is provided for collimating the light beam on the fast axis Af, and is composed of, for example, a cylindrical lens with positive optical power.
  • the FAC 41 is arranged at a focal distance from the +Zi side end face of the LD array 3 with its longitudinal direction directed in the Xi direction.
  • the light beam from the laser element 30 is collimated in the Y direction (that is, the fast axis Af) by the FAC 41 and enters the BT 42 .
  • Fig. 6 shows a configuration example of BT42.
  • the BT 42 is an optical element that rotates a plurality of light beams, for example, and includes a plurality of oblique lens portions 43 .
  • the oblique lens portion 43 is a portion that forms a lens for each laser element 30 in the BT 42, and forms, for example, a cylindrical lens. Note that the BT 42 and the FAC 41 may be provided separately.
  • the BT 42 is formed, for example, by arranging a plurality of oblique lens portions 43 at a predetermined pitch in the Xi direction.
  • the oblique lens portion 43 is tilted by 45 degrees with respect to both the arrangement direction (that is, the Xi direction) and the thickness direction of the BT 42 (that is, the Y direction). 30 rotates by a predetermined minute angle around the optical axis.
  • the minute angle is, for example, 0.01 degrees or less. Note that the BT 42 does not have to have such a small angle.
  • the BT 42 rotates the light beam incident from the laser element 30 via the FAC 41 by a rotation angle of 90 degrees on the XiY plane.
  • the slow axis As of the light beam emitted from the BT 42 is oriented in the Y direction
  • the fast axis Af is oriented in the Xi direction.
  • the light beam emitted from the BT 42 becomes divergent light in the Y direction and parallel light in the Xi direction.
  • FIG. 7 shows a plan view of the BTU 40 viewed from the +Y side.
  • FIG. 7 illustrates optical paths of respective light beams from the central laser element 30 and the -Xi side laser element 30 in the LD array 3 .
  • the minute angle of the BT 42 described above as shown in FIG. 7, the more the position of the laser element 30 in the LD array 3 is on the outside, the more the light beam can be directed inward (see Patent Document 1).
  • the SAC 45 is provided for collimating the light beam on the slow axis As, and is composed of, for example, a cylindrical lens with positive optical power.
  • the SAC 45 is arranged at a focal distance from the +Zi side surface of the BTU 40 with its longitudinal direction directed in the Xi direction.
  • the light beam from BT 42 is collimated in the Y direction (ie slow axis As) by SAC 45 and exits optical unit 4 .
  • the light beam emitted from each laser element 30 of the LD array 3 is basically collimated on the fast axis Af and the slow axis As.
  • the beam diameter may widen due to the influence of waves from the +Zi side surface of the BT 42 or the like.
  • collimation of each light beam by the collimator optical system 25 makes it possible to suppress the above effects.
  • FIG. 8 is a diagram illustrating the configuration of the collimator optical system 25 in the optical resonator 2 of this embodiment.
  • the collimator optical system 25 of this embodiment includes, for example, a diffractive lens 50 and a refractive lens 55, as shown in FIG.
  • the collimator optical system 25 has, for example, a positive optical power in the X direction in the optical resonator 2 and no particular optical power in the Y direction.
  • the diffractive lens 50 and the refractive lens 55 are arranged in order from the +Z side to the -Z side with a predetermined distance d (eg, 1 mm), for example.
  • the diffractive lens 50 is configured by providing a diffractive surface 51 on a lens material having translucency in the resonant wavelength band of the optical resonator 2, for example.
  • Diffractive surface 51 is configured to provide optical power by diffraction of incident light.
  • the diffractive surface 51 is provided on the opposite side of the refracting lens 55 , for example.
  • the surface opposite to the diffraction surface 51 and facing the refractive lens 55 is, for example, a flat surface.
  • the diffractive lens 50 Based on the diffractive surface 51, the diffractive lens 50 has positive optical power in the X direction and no particular optical power in the Y direction. The optical power of the diffraction lens 50 in the X direction is smaller than that of the collimator optics 25 .
  • the diffractive lens 50 has a focal length fa corresponding to such optical power and a dispersion va due to the diffractive surface 51 .
  • the surface opposite to the diffractive lens 50 is a convex refracting surface, and the surface facing the diffractive lens 50 is a flat surface.
  • the refracting lens 55 is made of a lens material having translucency in the resonant wavelength band.
  • the refractive lens 55 has a refractive index n due to the lens material and a dispersion vb according to the wavelength dependence of the refractive index n.
  • the lens material of the diffractive lens 50 and the lens material of the refractive lens 55 may be the same.
  • the wavelength dependence of the dispersion va by the diffractive surface 51 generally has an opposite tendency to the dispersion vb of the refractive lens 55 .
  • the optical resonator 2 of this embodiment by providing the diffraction surface 51 in the collimator optical system 25, at least part of the chromatic aberration of the refractive lens 55 can be offset or corrected, and chromatic aberration at the resonant wavelength can be suppressed.
  • the two-lens structure of the diffraction lens 50 and the refraction lens 55 as described above facilitates the manufacture of the collimator optical system 25 .
  • the diffractive surface 51 of the diffractive lens 50 is configured with a periodic structure in which, for example, stepped unevenness is repeated in the X direction.
  • the periodic structure of the diffractive surface 51 includes, for example, a plurality of unit structures 52 forming unevenness for one period.
  • FIG. 8 shows displacement in the Z direction, ie, sag amount, and position x in the X direction, with the center of the diffraction surface 51 as the origin.
  • the unit structure 52 has, for example, a predetermined number of steps (eg, 4 to 16 steps) of steps xn.
  • the periodic structure of the diffractive surface 51 is defined, for example, by the sag amount of each step xn of the unit structure 52 and is symmetrically formed on the ⁇ X side from the central optical axis of the diffractive lens 50 .
  • the width (that is, period) of the unit structures 52 in the X direction becomes shorter toward the outer unit structures 52 in the diffractive lens 50 .
  • the amount of sag is set to be lower on the outer side than on the inner side.
  • the periodic structure of the diffractive surface 51 is not limited to a staircase shape, and may be, for example, a sawtooth shape or various wave shapes. Numerical examples of the optical resonator 2 for the collimator optical system 25 as described above will be described later.
  • the laser processing apparatus 1 (FIG. 1) of the present embodiment drives the laser light source 13 of the optical resonator 2 based on, for example, oscillation conditions set by the controller 12 to cause the optical resonator 2 to generate laser light.
  • the laser processing apparatus 1 irradiates a laser beam generated in the optical resonator 2 from the processing head 11 to the processing object 15 under the control of the controller 12, for example, to perform various laser processing.
  • the laser light source 13 of the optical resonator 2 optically emits light beams from the laser elements 31 to 33 in the LD arrays 3-1 to 3-3 as illustrated in FIG. Output to units 4-1 to 4-3.
  • a plurality of light beams from each LD array 3 travel through optical paths via the optical unit 4 and various mirrors 21 and 22 and enter the collimator optical system 25 .
  • the beam diameter of the fast axis Af of each light beam can gradually widen from the middle of the optical unit 4, for example, while the light path travels. Therefore, the collimator optical system 25 collimates each light beam from each LD array 3 of the laser light source 13 in the X direction and emits it toward the diffraction grating 20 . Further, the optical paths are set for each light beam so that, for example, the more the light beams travel, the closer they are to each other in the X direction and the light beams are condensed at the diffraction grating 20 (see FIG. 2).
  • the diffraction grating 20 diffracts light so that light having a wavelength ⁇ is incident at an incident angle ⁇ and emitted at a diffraction angle ⁇ according to a diffraction condition such as the following equation (2).
  • a diffraction condition such as the following equation (2).
  • d is the pitch of the diffraction grating 20
  • m is the diffraction order.
  • 9A and 9B are diagrams illustrating a method of coupling light beams in the diffraction grating 20 of the optical resonator 2.
  • ⁇ 2 and ⁇ 3 are set.
  • the light beams from the plurality of LD arrays 3 are emitted from the diffraction grating 20 in the same direction after being diffracted along the optical paths illustrated in FIG.
  • the combined light beams enter the output coupler 14 via telescopic optics 26, for example.
  • the output coupler 14 reflects a portion of the light beams combined at the diffraction grating 20 and returns them to each laser element 30 by reversing the telescope optical system 26 and the like.
  • Each of the separated light beams further travels backward through the collimator optical system 25 and the like, and is returned to the laser elements 31, 32, and 33 from which they are incident.
  • the optical resonator 2 of this embodiment can resonate the light beams of the multiple laser elements 31 to 33 together in a wide resonant wavelength band ⁇ 1 to ⁇ 3 to obtain a high optical output.
  • the resonance wavelength ⁇ is set separately for each laser element 30 of each LD array 3, for example.
  • the difference in resonance wavelength ⁇ between the laser elements 30 in one LD array 3 is, for example, about several nm.
  • FIG. 10 is a diagram for explaining the problem of return light coupling efficiency in an optical resonator.
  • a graph G1 shows the coupling efficiency of return light in a typical optical resonator provided with a conventional collimator optical system in the same resonance wavelength band as the optical resonator 2 of this embodiment.
  • Conventional collimator optics typically consist only of refractive lenses.
  • FIG. 10 illustrates the relationship between the spots S1 and S2 of the returned light corresponding to the wavelengths ⁇ 1 and ⁇ 2 in the graph G1 and the LD aperture 30a.
  • This example shows the case where the optical resonator is set so that the spot S2 of the return light converges at the LD aperture 30a at the reference wavelength ⁇ 2 (for example, 425 nm) such as the center of the resonance wavelength bands ⁇ 1 to ⁇ 3.
  • the return light coupling efficiency at the reference wavelength ⁇ 2 is relatively high.
  • the coupling efficiency of the returned light decreases as the distance from the reference wavelength ⁇ 2 increases.
  • the spot S1 of the return light at the wavelength ⁇ 1 at the edge protrudes significantly from the LD aperture 30a in the direction of the fast axis.
  • the conventional optical resonator has a problem that the coupling efficiency of the return light decreases depending on the resonance wavelength, so that it is difficult to increase the oscillation efficiency in the entire resonance wavelength band ⁇ 1 to ⁇ 3. .
  • the inventors of the present application conducted extensive research on this problem, and found that the cause was the chromatic aberration of the collimator optical system, and came up with the optical resonator 2 of the present embodiment.
  • FIG. 11 is a diagram for explaining correction of chromatic aberration in the optical resonator 2 of this embodiment.
  • FIG. 11A illustrates graphs G11 and G12 of chromatic aberration in the collimator optical system.
  • FIG. 11B shows a graph G2 of the return light coupling efficiency in the optical resonator 2 of this embodiment.
  • FIG. 11A shows a chromatic aberration graph G11 of a conventional collimator optical system and a chromatic aberration graph G12 of the collimator optical system 25 of this embodiment.
  • the horizontal axis indicates the wavelength in nm, and the vertical axis indicates the longitudinal chromatic aberration in mm.
  • the collimator optical system 25 in the optical resonator 2 of the present embodiment suppresses axial chromatic aberration in the resonance wavelength band ⁇ 1 to ⁇ 3 more than the conventional one, and corrects it with high precision.
  • a collimator optical system 25 can converge the return lights of various wavelengths over the resonance wavelength bands ⁇ 1 to ⁇ 3 at the same focal length f in the optical resonator 2 and converge the respective spots at the respective LD apertures.
  • sufficiently high coupling efficiency of the returned light can be ensured over various resonance wavelengths ⁇ in the resonance wavelength bands ⁇ 1 to ⁇ 3.
  • the oscillation efficiency of the optical resonator 2 can be increased.
  • the optical resonator 2 of the present embodiment is set, for example, so that the collimator optical system 25 satisfies the achromatic condition in the resonant wavelength band ⁇ 1 to ⁇ 3 including the reference wavelength ⁇ 2.
  • the dispersion vb of the refractive lens 55 is expressed by the following equation (12) using refractive indices n1, n2 and n3 of the refractive lens 55 at respective wavelengths ⁇ 1, ⁇ 2 and ⁇ 3.
  • vb n2/(n1-n3) (12)
  • chromatic aberration can be corrected with high accuracy by canceling out axial chromatic aberration between the diffractive lens 50 and the refractive lens 55 .
  • the variation in the focal length fa of the diffractive lens 50 and the variation in the focal length fb of the refracting lens 55 cancel each other out over the resonant wavelength band ⁇ 1 to ⁇ 3, and the collimator optical system 25 Fluctuations in the overall focal length f can be suppressed.
  • the collimator optical system 25 of the present embodiment may appropriately satisfy the above formula (10) within the allowable error range.
  • the optical working distance from the output surface of the BT 42 to the diffraction surface 51 of the collimator optical system 25 was 997.2 mm, and the optical path length between each BT 42 and the collimator optical system 25 was 1000.5 mm.
  • Quartz was used as the lens material for the refractive lens 55 in the collimator optical system 25 .
  • the refractive lens 55 had an outer shape of 30 ⁇ 30 mm and a central thickness of 2 mm.
  • the curvature radius of the convex surface of the refractive lens 55 was 506.33497 mm.
  • the diffractive lens 50 quartz was used as the lens material in the same manner as the refractive lens 55 described above.
  • the diffractive lens 50 in this case has a refractive index similar to the refractive index n of the refractive lens 55 described above.
  • the diffractive lens 50 had an outer shape of 30 ⁇ 30 mm and a central thickness of 1 mm.
  • FIGS. 12 to 14 Numerical examples of the diffraction surface 51 in the diffraction lens 50 are illustrated in FIGS. 12 to 14.
  • FIG. a stepped periodic structure is adopted for the diffractive surface 51, and the number of steps of the unit structure is set to 16 steps.
  • the total number of steps on the diffraction surface 51 is 324 steps.
  • 12 to 14 show the positions and sag amounts of the steps x1 to x324 in the X direction. With such a diffraction surface 51 and the like, a collimator optical system 25 in which axial chromatic aberration is suppressed as shown in FIG. 11A is obtained.
  • FIG. 15 is a graph showing measurement results of the diffraction efficiency on the diffraction surface 51. As shown in FIG.
  • the horizontal axis of FIG. 15 is the wavelength, and the vertical axis is the diffraction efficiency.
  • a graph E16 shows the diffraction efficiency of the diffraction surface 51 when the unit structure 52 has 16 stages.
  • graphs E8, E4, and E2 show diffraction efficiencies when the number of unit structures 52 is 8, 4, or 2, respectively. Note that the diffraction order is the first order.
  • the diffraction efficiency was about 40% as shown in graph E2 but in the case of 4 steps, a diffraction efficiency of 80% or more was obtained as shown in graph E4, and in the case of 8 steps, the diffraction efficiency was about 40%. obtained a diffraction efficiency of about 95%.
  • the optical resonator 2 in this embodiment resonates a plurality of light beams having different wavelengths.
  • the optical resonator 2 includes a laser light source 13 as an example of a light source, a diffraction grating 20, an output coupler 14, and a collimator optical system 25 as an example of a first optical system.
  • the laser light source 13 includes a plurality of laser elements 30, which are examples of a plurality of light source elements that respectively emit a plurality of light beams.
  • the diffraction grating 20 diffracts each light beam at angles of incidence ⁇ 1 to ⁇ 3 corresponding to the wavelengths of the light beams from the laser elements 31 to 33, respectively.
  • Output coupler 14 reflects a portion of the light beam diffracted at diffraction grating 20 back to laser source 13 and outputs the rest of the light beam.
  • the collimator optical system 25 is arranged between the laser light source 13 and the diffraction grating 20 , collimates each light beam incident from the laser light source 13 , and emits the collimated light beam to the diffraction grating 20 .
  • the collimator optical system 25 has a diffraction surface 51 that diffracts each light beam so as to adjust the chromatic aberration over the wavelengths ⁇ 1 to ⁇ 3 of the multiple light beams.
  • the oscillation efficiency of the wavelength combining optical resonator 2 can be improved by resonating light beams having a plurality of wavelengths. efficiency can be improved.
  • Another method of using a diffractive lens to correct chromatic aberration is a method of using a plurality of refractive lenses made of lens materials having different dispersion characteristics.
  • the lens materials that can be used for the laser processing apparatus 1 having a relatively high output as in this embodiment are limited, and it is difficult to solve the problems in the laser processing apparatus 1 by the above method.
  • correction of chromatic aberration using a diffractive lens as in the optical resonator 2 of the present embodiment can suitably solve the problem of chromatic aberration in, for example, the high-power laser processing apparatus 1 .
  • the collimator optical system 25 includes one or more lenses. Diffractive surface 51 diffracts each light beam so as to correct for chromatic aberration in the one or more lenses. In this way, it is possible to improve the efficiency of resonating the plurality of light beams by adjusting the chromatic aberration over the wavelengths ⁇ 1 to ⁇ 3 of the plurality of light beams.
  • the collimator optical system 25 has positive optical power in the X direction as an example of the predetermined direction.
  • the predetermined direction is the direction in which a plurality of light beams are arranged when entering the collimator optical system 25 (see FIG. 2).
  • the diffractive surface 51 corresponds to a positive optical power below the optical power of the collimator optics 25 in the X direction. With such a diffraction surface 51, at least a part of the chromatic aberration of the lens in the collimator optical system 25 when collimating the light beam on the fast axis Ax can be canceled to correct the chromatic aberration.
  • the collimator optical system 25 includes a refracting lens 55 that refracts each light beam in the X direction, and a diffractive lens 50 that is provided with a diffractive surface 51 and corrects chromatic aberration in the refracting lens. With such a configuration, the collimator optical system 25 can be configured easily.
  • the diffractive surface 51 has a periodic structure in which a plurality of unevennesses are repeated in the X direction (see FIG. 8).
  • the optical resonator 2 further includes a BTU 40, which is an example of a second optical system.
  • the BTU 40 is arranged between the laser light source 13 and the collimator optical system 25, and collimates and emits the light beams incident from the plurality of laser elements 30 in the direction of the fast axis Af corresponding to the X direction.
  • the collimator optical system 25 collimates each light beam emitted from the BTU 40 in the X direction and corrects chromatic aberration with the diffraction surface 51 . This makes it possible to correct the chromatic aberration when reducing the influence of wave-like expansion of the light beam once collimated by the BTU 40 , and improve the oscillation efficiency in the optical resonator 2 .
  • the laser light source 13 includes an LD array 3, which is an example of a plurality of light source arrays each provided with a plurality of laser elements 30.
  • the optical resonator 2, for example, as shown in FIG. It is provided so as to be stacked with the arranged +Y side stage (second stage).
  • a plurality of LD arrays 3 are arranged on the same plane (FIG. 3).
  • the collimator optical system 25 , the diffraction grating 20 and the output coupler 14 are arranged on the same plane as each other and on a different plane from the plurality of LD arrays 3 . With such a two-stage configuration, the optical resonator 2 can be made compact.
  • the optical resonator 2 further includes mirrors 46, 21, and 22 as an example of a reflecting optical system.
  • the mirrors 46 , 21 , 22 are arranged between the laser light source 13 and the collimator optical system 25 to reflect each light beam from the laser light source 13 and guide it to the collimator optical system 25 .
  • the optical resonator 2 can be made compact while suppressing the occurrence of chromatic aberration, for example.
  • the laser light source 13 emits light beams from the plurality of laser elements 30 in a wavelength band including wavelengths of 405 nm to 445 nm.
  • the diffraction surface 51 corrects chromatic aberration in the wavelength band in the collimator optical system 25 .
  • the oscillation efficiency of the optical resonator 2 can be improved in the resonant wavelength band of such a blue region.
  • the laser processing device 1 includes an optical resonator 2 and a processing head 11.
  • a processing object 15 is irradiated with a light beam output from an output coupler 14 of the processing head 11 optical resonator 2 .
  • the laser processing apparatus 1 can improve the oscillation efficiency in a wide resonant wavelength band.
  • Embodiment 1 has been described as an example of the technology disclosed in the present application.
  • the technology in the present disclosure is not limited to this, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate.
  • the diffraction lens 50 is designed to suppress axial chromatic aberration, but the optical resonator 2 of this embodiment is not limited to this.
  • the diffraction lens 50 of the collimator optical system 25 allows each optical path Axial chromatic aberration can also be generated so that the focal length changes according to the lens length.
  • a numerical example for such a case is shown below.
  • Optical path length between BTU 40 of optical unit 4-1 and collimator optical system 25 1008.0 mm
  • Optical path length between BTU 40 of optical unit 4-2 and collimator optical system 25 998.1 mm
  • Optical path length between BTU 40 of optical unit 4-3 and collimator optical system 25 988.0 mm
  • the deviations in the optical path lengths of the optical units 4-1, 4-2, 4-3 as described above correspond to the deviations in the optical path lengths of the respective laser elements 31, 32, 33 (see FIG. 2).
  • FIG. 16 shows longitudinal chromatic aberration generated in the collimator optical system 25 with respect to such optical path length deviation.
  • the return lights of various wavelengths over the resonance wavelength bands ⁇ 1 to ⁇ 3 of the laser elements 31 to 33 are condensed at respective focal lengths. Similarly, each spot can be converged at each LD aperture. Therefore, in the optical resonator 2 of this embodiment as well, the same effect as in the first embodiment can be obtained.
  • the plurality of laser elements 31 to 33 may be arranged with the optical path length from each laser element 30 to the collimator optical system 25 shifted from each other.
  • the diffractive surface 51 of the diffractive lens 50 diffracts each light beam so as to cause chromatic aberration in the collimator optical system 25 in accordance with the deviation of the optical path length.
  • the configuration of the optical resonator 2 is not limited to this.
  • the laser light source 13 may be composed of one LD array 3 . Even in this case, it is possible to correct the chromatic aberration in the resonance wavelength band of the plurality of laser elements 30 included in the LD array 3, and improve the efficiency of resonating light beams having a plurality of wavelengths.
  • the light source of the optical resonator 2 may be a light source array other than the LD array 3, or may be configured using a laser light source such as various non-arrayed semiconductor lasers or a light source element.
  • the collimator optical system 25 of the optical resonator 2 is composed of two lenses, the diffractive lens 50 and the refractive lens 55, is described, but the collimator optical system 25 is not limited to this.
  • the collimator optical system 25 may be composed of three or more lenses, or may be composed of one lens.
  • the collimator optical system 25 may be composed of a single lens having one surface as the diffractive surface 51 and the other surface as a refractive surface such as a convex surface. Also in this case, the collimator optical system 25 corrects chromatic aberration using the diffraction surface 51, and the same effect as in the first embodiment can be obtained.
  • the resonant wavelength band of the optical resonator 2 is not limited to the above, and may be, for example, a red region, or may be, for example, a wavelength of 900 nm or more and 950 nm or less.
  • the present disclosure can be applied to various uses in which a plurality of light beams are resonated, and can be applied to various laser processing techniques, for example.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Electromagnetism (AREA)
  • Semiconductor Lasers (AREA)
  • Diffracting Gratings Or Hologram Optical Elements (AREA)

Abstract

Le résonateur optique (2) selon l'invention, qui fait résonner une pluralité de faisceaux lumineux ayant des longueurs d'onde mutuellement différentes comprend une source de lumière (13), un réseau de diffraction (20), un coupleur de sortie (14) et un système optique (25). La source de lumière (13) comprend une pluralité d'éléments de source de lumière (31, 32, 33) qui émettent respectivement une pluralité de faisceaux lumineux. Le réseau de diffraction (20) diffracte chaque faisceau lumineux selon un angle correspondant à la longueur d'onde du faisceau lumineux provenant de chaque élément de source de lumière (31, 32, 33). Le coupleur de sortie (14) réfléchit une partie du faisceau lumineux diffracté dans le réseau de diffraction (20) et renvoie la partie à la source de lumière (13), et délivre la partie restante du faisceau lumineux. Le système optique (25) est disposé entre la source de lumière (13) et le réseau de diffraction (20), collimate chaque faisceau lumineux incident à partir de la source de lumière (13) et émet chaque faisceau lumineux vers le réseau de diffraction (20). Le système optique (25) a une surface de diffraction qui diffracte chaque faisceau lumineux pour ajuster l'aberration chromatique à travers les longueurs d'onde d'une pluralité de faisceaux lumineux.
PCT/JP2021/047969 2021-02-01 2021-12-23 Résonateur optique et dispositif de traitement au laser Ceased WO2022163245A1 (fr)

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Citations (7)

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US6414973B1 (en) * 1999-08-31 2002-07-02 Ruey-Jen Hwu High-power blue and green light laser generation from high powered diode lasers
US20130121360A1 (en) * 2011-05-12 2013-05-16 Natalia Trela Multi-Wavelength Diode Laser Array
JP2016111339A (ja) * 2014-10-17 2016-06-20 ルメンタム オペレーションズ エルエルシーＬｕｍｅｎｔｕｍ Ｏｐｅｒａｔｉｏｎｓ ＬＬＣ 波長合成レーザシステム
WO2018167975A1 (fr) * 2017-03-17 2018-09-20 三菱電機株式会社 Dispositif d'oscillation laser
WO2019163335A1 (fr) * 2018-02-26 2019-08-29 パナソニックＩｐマネジメント株式会社 Résonateur optique et machine de traitement laser
WO2020174752A1 (fr) * 2019-02-28 2020-09-03 パナソニックＩｐマネジメント株式会社 Résonateur optique et dispositif de traitement au laser
WO2020202395A1 (fr) * 2019-03-29 2020-10-08 三菱電機株式会社 Dispositif laser à semi-conducteur

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6414973B1 (en) * 1999-08-31 2002-07-02 Ruey-Jen Hwu High-power blue and green light laser generation from high powered diode lasers
US20130121360A1 (en) * 2011-05-12 2013-05-16 Natalia Trela Multi-Wavelength Diode Laser Array
JP2016111339A (ja) * 2014-10-17 2016-06-20 ルメンタム オペレーションズ エルエルシーＬｕｍｅｎｔｕｍ Ｏｐｅｒａｔｉｏｎｓ ＬＬＣ 波長合成レーザシステム
WO2018167975A1 (fr) * 2017-03-17 2018-09-20 三菱電機株式会社 Dispositif d'oscillation laser
WO2019163335A1 (fr) * 2018-02-26 2019-08-29 パナソニックＩｐマネジメント株式会社 Résonateur optique et machine de traitement laser
WO2020174752A1 (fr) * 2019-02-28 2020-09-03 パナソニックＩｐマネジメント株式会社 Résonateur optique et dispositif de traitement au laser
WO2020202395A1 (fr) * 2019-03-29 2020-10-08 三菱電機株式会社 Dispositif laser à semi-conducteur

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