WO2019026912A1 - Light source device and laser light irradiation device - Google Patents

Abstract

This light source device is provided with: a fiber laser that emits randomly polarized laser light; a polarization beam splitter that splits the laser light emitted by the fiber laser into first split laser light and second split laser light for each polarization component; a wavelength plate that changes the polarization direction of the second split laser beam so as to be the same as the polarization direction of the first split laser beam; and a half mirror that combines the first split laser beam which was split by the polarization beam splitter and the second split laser beam for which the polarization direction was changed by the wavelength plate, and outputs the result as combined laser light.

Description

Light source device and laser beam irradiation device

One aspect of the present invention relates to a light source device and a laser beam irradiation device provided with the light source device.

Conventionally, as a technique related to a light source device, for example, a linearly polarized light source described in Patent Document 1 is known. The linearly polarized light source described in Patent Document 1 includes a light source having a reflecting mirror, a polarization beam splitter that splits a light flux from the light source into two light fluxes whose polarization directions are orthogonal to each other, and between the light source and the polarization beam splitter And a luminous flux reflecting element for reflecting any one of the two luminous fluxes to make the light incident on a reflecting mirror of a light source. The linearly polarized light source described in Patent Document 1 is intended to efficiently generate linearly polarized light.

Japanese Patent Application Laid-Open No. 2-264904

In the light source device as described above, for example, a fiber laser that emits laser light of randomly polarized light may be used from the viewpoint of low price, high output, and high distribution. In this case, there are the following problems caused by the fiber laser. That is, in the laser light of random polarization, the polarization direction is not constant but changes. Therefore, when laser light is branched for each polarization component using a polarization beam splitter to obtain linearly polarized laser light, the ratio of each laser light after branching is not constant but fluctuates. As a result, the laser output of the linearly polarized laser light obtained may also fluctuate (become unstable).

An object of one aspect of the present invention is to stably obtain linearly polarized laser light in a light source device and a laser light irradiation device using a fiber laser that emits randomly polarized laser light.

A light source device according to one aspect of the present invention branches a fiber laser that emits laser light of random polarization, and a laser light emitted by the fiber laser into a first branch laser light and a second branch laser light for each polarization component. Polarization beam splitter, a wavelength plate for changing the polarization direction of the second branch laser beam to be the same as the polarization direction of the first branch laser beam, and a first branch laser beam and a wavelength plate branched by the polarization beam splitter And a half mirror that multiplexes the second branched laser beam whose polarization direction has been changed and outputs it as a multiplexed laser beam.

In this light source device, laser light of random polarization emitted from the fiber laser is branched for each polarization component by the polarization beam splitter. The polarization direction of the second branch laser beam is changed by the wave plate so as to be the same as the polarization direction of the first branch laser beam. Then, the first and second split laser beams having the same polarization direction are multiplexed and output by the half mirror. Therefore, even when using a fiber laser that emits laser light of randomly polarized light, it is possible to stably obtain linearly polarized laser light regardless of the polarization characteristics of the fiber laser.

In the light source device according to one aspect of the present invention, the fiber laser has a main body that amplifies seed light, and a laser head that is connected to the main body via a light guide fiber and emits laser light. May be In this configuration, the fiber laser constitutes a so-called head separation type fiber laser. In this case, the polarization of the laser light emitted from the fiber laser is likely to be affected by the bending of the light guide fiber or the like. Therefore, the above-mentioned effect of stably obtaining linearly polarized laser light regardless of the polarization characteristics of the fiber laser used is particularly effective.

In the light source device according to one aspect of the present invention, the optical path difference between the optical path of the first branched laser beam and the optical path of the second branched laser beam may be longer than the coherence length of the fiber laser. According to this configuration, it is possible to suppress interference of the first and second branched laser beams combined by the half mirror.

In the light source device according to one aspect of the present invention, the combined laser beam includes the first combined laser beam coaxial with the first branched laser beam and the second combined laser beam coaxial with the second branched laser beam. It may be. According to this configuration, two linearly polarized laser beams can be obtained, which facilitates application to various specifications and the like.

A laser beam irradiation apparatus according to one aspect of the present invention is a laser beam irradiation apparatus including the above light source device, wherein a first polarization element to which a first combined laser beam is incident and a second combined laser beam are An optical system having a second polarizing element to be incident is provided.

Since this laser beam irradiation apparatus includes the above-described light source device, the above-described effect of stably obtaining linearly polarized laser light when using a fiber laser that emits randomly polarized laser light is exhibited. Moreover, in this laser beam irradiation apparatus, it becomes possible to perform laser beam irradiation using both of the two linearly polarized laser beams obtained by multiplexing by the half mirror.

The laser beam irradiation apparatus according to one aspect of the present invention is a laser beam irradiation apparatus including the above light source device, and is a polarizing element to which any one of the first combined laser beam and the second combined laser beam is incident. And an optical system having a beam damper for blocking either the first combined laser beam or the second combined laser beam.

Since this laser beam irradiation apparatus includes the above-described light source device, the above-described effect of stably obtaining linearly polarized laser light when using a fiber laser that emits randomly polarized laser light is exhibited. Moreover, in this laser beam irradiation apparatus, it becomes possible to perform laser beam irradiation using only one of two linearly polarized laser beams obtained by multiplexing by the half mirror.

According to one aspect of the present invention, it is possible to stably obtain linearly polarized laser light in a light source device and a laser light irradiation device using a fiber laser that emits randomly polarized laser light.

FIG. 1 is a schematic configuration view showing a laser beam irradiation apparatus according to the first embodiment. FIG. 2 is a graph for explaining the laser light emitted from the fiber laser of FIG. FIG. 3 is a graph for explaining the combined laser light output from the light source device of FIG. FIG. 4 is a schematic configuration view showing a laser beam irradiation apparatus according to the second embodiment.

Hereinafter, embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and redundant description will be omitted.

First Embodiment
FIG. 1 is a schematic configuration view showing a laser beam irradiation apparatus 100 according to the first embodiment. The laser beam irradiation apparatus 100 is an apparatus for irradiating the laser light L of linearly polarized light to the object T, and includes the light source device 1 and the optical system 30. Linear polarization means a polarization state in which the vibration direction of the electric field (and the magnetic field) is constant.

The light source device 1 includes a fiber laser 10 and a polarization adjustment unit 20. The fiber laser 10 emits laser light L0 of randomly polarized light. Random polarization means linearly polarized light, but a polarization state in which the polarization direction is not constant but changes with time. The fiber laser 10 has a main body 11 for amplifying seed light, and a laser head 13 connected to the main body 11 via a light guide fiber 12. The fiber laser 10 is a solid-state laser using an optical fiber as an amplification medium. The fiber laser 10 here is a so-called head separation type fiber laser. The main body 11 includes a laser diode 14 that oscillates seed light, and an amplification unit 15 that amplifies and outputs the seed light. The laser head unit 13 emits laser light L0 of random polarization.

The polarization adjustment unit 20 includes a polarization beam splitter 21, a mirror 22, a half wave plate (wave plate) 23, a mirror 24, and a half mirror 25. The polarization beam splitter 21 splits the laser beam L0 emitted by the fiber laser 10 into a first split laser beam L1 and a second split laser beam L2 for each polarization component. In other words, the polarization beam splitter 21 divides the optical path P0 of the laser beam L0 into a first optical path P1 which is an optical path of the first branched laser light L1 and a second optical path P2 which is an optical path of the second branched laser light L2. Branch.

The polarization directions of the first branched laser light L1 and the second branched laser light L2 are orthogonal to each other. The first branched laser beam L1 is a P-polarized laser beam, and has, for example, the vertical direction in the drawing as the polarization direction. The second branched laser beam L2 is an S-polarized laser beam, and has, for example, a direction perpendicular to the paper surface as a polarization direction. P-polarization is linear polarization in which an electric field vibrates in the incident plane. The s-polarized light is linearly polarized light in which the electric field oscillates perpendicularly to the incident plane.

The mirror 22 is disposed in the second optical path P2. The mirror 22 reflects the second branched laser light L2 toward the half-wave plate 23. The half-wave plate 23 is disposed downstream of the mirror 22 in the second optical path P2. The half-wave plate 23 rotates the polarization component of the second branched laser beam L2 to change the polarization direction of the second branched laser beam L2 to be the same as the polarization direction of the first branched laser beam L1.

The mirror 24 is disposed downstream of the half wave plate 23 in the second optical path P2. The mirror 24 reflects the second branched laser beam L2 toward the half mirror 25. The half mirror 25 is disposed at the junction of the downstream side of the first optical path P1 and the downstream side of the second optical path P2. The half mirror 25 combines the first split laser beam L1 split by the polarization beam splitter 21 and the second split laser beam L2 whose polarization direction is changed by the half wave plate 23, and combines the combined laser beam L3. Output as The half mirror 25 is a cube-shaped non-polarization half mirror. The half mirror 25 has a transmittance of 50% and a reflectance of 50%.

The combined laser beam L3 is a linearly polarized laser beam, and here. P-polarized laser light. The combined laser beam L3 includes a first combined laser beam L31 coaxial with the first branched laser beam L1, and a second combined laser beam L32 coaxial with the second branched laser beam L2. The first combined laser beam L31 is a laser beam formed by combining a part of the first branched laser beam L1 transmitted through the half mirror 25 and a part of the second branched laser beam L2 reflected by the half mirror 25. is there. The second combined laser beam L32 is a laser beam formed by combining a part of the first branched laser beam L1 reflected by the half mirror 25 and a part of the second branched laser beam L2 transmitted through the half mirror 25. is there.

The second optical path P2 includes a third optical path P21 from the polarization beam splitter 21 to the mirror 22, a fourth optical path P22 from the mirror 24 to the half mirror 25, and a fifth optical path P23 from the mirror 22 to the mirror 24. The fifth optical path P23 has the same optical path length as the first optical path P1. The optical path difference between the first optical path P1 and the second optical path P2 (that is, the optical path lengths of the third optical path P21 and the fourth optical path P22) is longer than the coherence length of the fiber laser 10. The coherence length is the upper limit of the distance in which the light interference phenomenon appears when the first branched laser light L1 and the second branched laser light L2 are combined.

The optical system 30 includes a spatial light modulator (first polarizing element) 31 and 4 f optical system 32, a condensing lens 33, a spatial light modulator (second polarizing element) 35 and 4 f optical system 36, and a condensing lens 37. Have. The spatial light modulators 31 and 35 are, for example, spatial light modulators (SLM: Spatial Light Modulator) of a reflective liquid crystal (LCOS: Liquid Crystal on Silicon). The spatial light modulator 31 is a polarizing element on which the first combined laser beam L31 is incident. The spatial light modulator 31 modulates and reflects the incident first combined laser beam L31. The spatial light modulator 35 is a polarizing element on which the second combined laser beam L32 is incident. The spatial light modulator 35 modulates and reflects the incident second combined laser beam L32.

The spatial light modulators 31 and 35 have a display unit capable of displaying a modulation pattern. The spatial light modulator 31 adjusts the wavefront of the first combined laser beam L31 according to the modulation pattern by causing the first combined laser beam L31 to be incident on the modulation pattern. The spatial light modulator 35 adjusts the wavefront of the second combined laser beam L32 according to the modulation pattern by causing the second combined laser beam L32 to be incident on the modulation pattern. In each of the spatial light modulators 31 and 35, modulation of each of the first and second combined laser beams L31 and L32 (for example, intensity, amplitude, phase, polarization, etc.) by appropriately setting each modulation pattern to be displayed Modulation) is possible.

The 4f optical system 32 is an adjustment optical system that adjusts the wavefront shape (wavefront adjustment) of the first combined laser light L31 modulated by the spatial light modulator 31. The 4f optical system 32 is disposed on the optical path between the spatial light modulator 31 and the condensing lens 33. The 4f optical system 36 is an adjustment optical system that adjusts the wavefront shape of the second combined laser light L32 modulated by the spatial light modulator 35. The 4f optical system 36 is disposed on the optical path between the spatial light modulator 35 and the condenser lens 37.

The condensing lens 33 condenses the first combined laser beam L31 on the object T. The condensing lens 37 condenses the second combined laser beam L32 on the object T. Each of the condenser lenses 33 and 37 may be configured to include a plurality of lenses.

In the laser beam irradiation apparatus 100 described above, the laser beam L0 of random polarization emitted from the fiber laser 10 in the light source device 1 is branched by the polarization beam splitter 21 for each polarization component. The half-wave plate 23 rotates the polarization component of the second split laser beam L2 so that the polarization direction of the second split laser beam L2 becomes the same (parallel) as the polarization direction of the first split laser beam L1. be changed. Then, the first and second branched laser beams L1 and L2 having the same polarization direction are multiplexed by the half mirror 25, and finally output as a multiplexed laser beam L3 aligned with a single linearly polarized light. Ru.

The first combined laser beam L31 in the combined laser beam L3 is incident on the spatial light modulator 31 in the optical system 30, and is modulated according to the modulation pattern displayed on the display unit of the spatial light modulator 31. Thereafter, the wavefront is adjusted by the 4f optical system 32. The first combined laser beam L31 whose wavefront is adjusted by the 4f optical system 32 is condensed by the condenser lens 33 and is irradiated as the laser beam L on the object T. In the optical system 30, the second combined laser beam L32 of the combined laser beam L3 is incident on the spatial light modulator 35, and is modulated according to the modulation pattern displayed on the display unit of the spatial light modulator 35. Then, the wavefront is adjusted by the 4f optical system 36. The second combined laser beam L32 whose wavefront is adjusted by the 4f optical system 36 is condensed by the condenser lens 37 and is emitted as the laser beam L to the object T.

FIG. 2 is a graph for explaining the laser beam L0 emitted from the fiber laser 10. As shown in FIG. The vertical axis is the normalized laser output obtained by dividing the laser output by the reference output value. The horizontal axis is time (hour). The data label value of “P polarization” indicates the normalized laser output of the polarization component of P polarization formed by separating the laser light L 0 emitted by the fiber laser 10 with a polarizer or the like. The data label value of “S polarization” indicates the normalized laser output of the polarization component of S polarization formed by separating the laser light L 0 emitted by the fiber laser 10 with a polarizer or the like. The "total" data label value indicates the sum of the polarization component of the P polarization and the polarization component of the S polarization.

As shown in FIG. 2, the total laser output is stable after a predetermined time, while the P-polarized and S-polarized laser outputs have larger fluctuations than the total. This is because the laser light L0 emitted from the fiber laser 10 has randomly polarized light, and the ratio of the p-polarized light component to the s-polarized light component fluctuates. Accordingly, the laser output of P-polarization and S-polarization is affected by the polarization characteristic of the fiber laser 10 and becomes unstable. For example, in the fiber laser 10, when a fiber such as the light guide fiber 12 is bent or crushed, the polarization of the emitted laser light L0 may be affected. While moving the light guiding fiber 12, the polarization may fluctuate while moving. Therefore, in general, it is difficult to use a polarization element (spatial light modulator etc.) for the linearly polarized laser light obtained by using the fiber laser 10 that emits the laser light L0 of random polarization in the light source device. I understand that there is.

On the other hand, according to the light source device 1 according to the present embodiment, as described above, the randomly polarized laser beam L0 emitted from the fiber laser 10 is split into the first and second split laser beams L1 and L2. The polarization direction of the second split laser beam L2 is changed by the half-wave plate 23 to be the same as the polarization direction of the first split laser beam L1, and the first and second split laser beams L1 and L2 are half mirrors The light is combined at 25 and output as combined laser light L3. Therefore, even when using the fiber laser 10 for emitting the laser light L0 of random polarization, the laser light L (multiplexing laser light L3) of linear polarization can be stably obtained regardless of the polarization characteristic of the fiber laser 10 It becomes possible. It is possible to obtain a high-power light source device 1 that is cheaper than the existing light source device.

FIG. 3 is a graph for explaining the combined laser light L3 output from the light source device 1. The vertical axis is the normalized laser output obtained by dividing the laser output by the reference output value. The horizontal axis is time (min). The data label value of “original output” indicates the normalized laser output of the laser light L0 of random polarization emitted by the fiber laser 10.

The data label value of the “first branched laser beam” indicates the normalized laser output of the first branched laser beam L1 which is obtained by just branching the randomly polarized laser beam L0 by the polarization beam splitter 21. The data label value of the “first branched laser light” here is the polarization adjustment (that is, the second branched laser light whose polarization direction is changed by the first branched laser light L1 and the half wavelength plate 23 by the half mirror 25). It is a normalized laser output of the 1st branch laser beam L1 of P polarization in front of combining with L2. The data label value of “combined laser light” indicates the normalized laser output of the combined laser light L3. The data label value of “multiplexed laser light” here is a normalized laser output of the first multiplexed laser light L31 of P-polarization after the polarization adjustment. According to the results shown in FIG. 3, it can be confirmed that the laser output of the combined laser light L3 after the polarization adjustment has an output fluctuation equal to that of the stable laser output of the original output.

In the light source device 1, the fiber laser 10 constitutes a so-called head separation type fiber laser having a main body portion 11 and a laser head portion 13. In this case, the polarization of the laser beam L0 emitted from the fiber laser 10 is likely to be affected by the bending or the like of the light guide fiber 12. Therefore, the above-mentioned effect of stably obtaining linearly polarized laser light L regardless of the polarization characteristic of the fiber laser 10 used is particularly effective.

In the light source device 1, the optical path difference between the first optical path P1 of the first branched laser light L1 and the second optical path P2 of the second branched laser light L2 is longer than the coherence length of the fiber laser 10. According to this configuration, it is possible to suppress interference of the first and second split laser beams L1 and L2 combined by the half mirror 25. The combined laser light L3 having the same beam profile as the laser light L0 emitted from the fiber laser 10 can be output.

In the light source device 1, the combined laser beam L3 includes a first combined laser beam L31 coaxial with the first split laser beam L1, and a second combined laser beam L32 coaxial with the second split laser beam L2. According to this configuration, since the two linearly polarized first and second combined laser beams L31 and L32 can be obtained, application to various specifications and the like can be facilitated.

Also in the laser beam irradiation apparatus 100, when the fiber laser 10 emitting the laser beam L0 of random polarization is used by the light source device 1, the above-described effect of stably obtaining the linearly polarized laser beam L is exerted. Further, in the laser beam irradiation apparatus 100, laser beam irradiation can be performed using both of the two first and second combined laser beams L31 and L32 obtained by multiplexing by the half mirror 25. It is possible to obtain a laser beam irradiation apparatus 100 having a specification having two ports of laser output (using two beams).

Second Embodiment
Next, a laser beam irradiation apparatus according to a second embodiment will be described. In the description of the present embodiment, points different from the first embodiment will be described.

FIG. 4 is a schematic configuration view showing a laser beam irradiation apparatus 200 according to the second embodiment. As shown in FIG. 4, the laser beam irradiation apparatus 200 differs from the first embodiment in that an optical system 40 is provided instead of the optical system 30 (see FIG. 1). The optical system 40 includes a spatial light modulator (polarization element) 31, a 4 f optical system 32, a condenser lens 33, and a beam damper 44. The beam damper 44 blocks the second combined laser beam L32.

In the laser beam irradiation apparatus 200, the first combined laser beam L31 of the combined laser beam L3 is incident on the spatial light modulator 31 in the optical system 30, and displayed on the display unit of the spatial light modulator 31. After being modulated according to the modulation pattern, the wavefront is adjusted by the 4f optical system 32. The first combined laser beam L31 whose wavefront is adjusted by the 4f optical system 32 is condensed by the condenser lens 33 and is irradiated as the laser beam L on the object T. On the other hand, the second combined laser beam L32 of the combined laser beam L3 is blocked by the beam damper 44 and terminated.

As described above, also in the laser beam irradiation apparatus 200, when the fiber laser 10 emitting the randomly polarized laser beam L0 is used by the light source device 1, the above-described effect of stably obtaining the linearly polarized laser beam L is exhibited. Further, in the laser beam irradiation apparatus 200, laser beam irradiation can be performed using only one of the two first and second combined laser beams L31 and L32 obtained by multiplexing by the half mirror 25. It is possible to obtain a laser light irradiation apparatus 200 having a specification having one port of laser output (using one beam).

The embodiment has been described above, but one aspect of the present invention is not limited to the above-described embodiment, and may be modified or applied to other things without departing from the scope of the invention described in each claim.

Although the said embodiment is equipped with the spatial light modulators 31 and 35 as a polarizing element, the polarizing element applied to the laser beam irradiation apparatuses 100 and 200 is not specifically limited, It replaces with the spatial light modulators 31 and 35. Alternatively or additionally, other polarization elements may be provided.

In the second embodiment, the first combined laser beam L31 is made incident on the spatial light modulator 31, and the second combined laser beam L32 is made incident on the beam damper 44. Conversely, the second combined laser beam L32 is made second The wave laser light L32 may be made incident on the spatial light modulator 31, and the first combined laser light L31 may be made incident on the beam damper 44. In this case, the first combined laser beam L31 is shielded and terminated by the beam damper 44, while the second combined laser beam L32 is modulated according to the modulation pattern displayed on the display unit of the spatial light modulator 31. Then, the wavefront is adjusted by the 4f optical system 32, and the light is condensed by the condensing lens 33 and irradiated as the laser light L on the object T.

DESCRIPTION OF SYMBOLS 1 ... Light source device, 10 ... Fiber laser, 11 ... Main-body part, 12 ... Light guide fiber, 13 ... Laser head part, 21 ... Polarization beam splitter, 23 ... 1/2 wavelength plate (wave plate), 25 ... Half mirror, Reference Signs List 30 optical system 31 spatial light modulator (polarization element, first polarization element) 35 spatial light modulator (second polarization element) 40 optical system 44 beam damper 100, 200 laser light Irradiation device, P1 ... first light path (light path of first branched laser light), P2 ... second light path (light path of second branched laser light).

Claims (6)

A fiber laser that emits randomly polarized laser light;
A polarization beam splitter that branches the laser beam emitted by the fiber laser into a first branch laser beam and a second branch laser beam for each polarization component;
A wavelength plate that changes the polarization direction of the second branched laser beam to be the same as the polarization direction of the first branched laser beam;
And a half mirror that multiplexes the first split laser beam split by the polarization beam splitter and the second split laser beam whose polarization direction is changed by the wavelength plate, and outputs the combined laser beam as a combined laser beam. Light source device. The fiber laser is
A main unit that amplifies seed light;
The light source device according to claim 1, further comprising: a laser head unit connected to the main body via a light guide fiber and configured to emit the laser light. The light source device according to claim 1, wherein an optical path difference between an optical path of the first branched laser light and an optical path of the second branched laser light is longer than a coherent distance of the fiber laser. The combined laser beam according to any one of claims 1 to 3, wherein the combined laser beam includes a first combined laser beam coaxial with the first branched laser beam and a second combined laser beam coaxial with the second branched laser beam. The light source device according to one item. A laser beam irradiation apparatus comprising the light source apparatus according to claim 4, wherein
A laser beam irradiation apparatus comprising: an optical system having a first polarization element to which the first combined laser beam is incident, and a second polarization element to which the second combined laser beam is incident. A laser beam irradiation apparatus comprising the light source apparatus according to claim 4, wherein
A polarization element on which any one of the first combined laser beam and the second combined laser beam is incident, and the other one of the first combined laser beam and the second combined laser beam is blocked. Laser light irradiation apparatus provided with the optical system which has a beam damper.

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