Laser device and laser processing device

Abstract

The laser device (100) includes a seed light source (10) that outputs pulsed light and is capable of controlling the repetition frequency of the pulsed light, an aberration generating unit (20) that adds aberration due to the optical Kerr effect to the pulsed light, a beam shaping optical system (30) that adjusts at least one of the beam diameter and intensity distribution of the pulsed light, a solid-state amplifier (40) that amplifies the pulsed light and emits laser light, and a placement adjustment unit (21, 31) that is capable of operating at least one of the aberration generating unit (20) and the beam shaping optical system (30) in accordance with the repetition frequency of the pulsed light.

Description

[Technical field]

[0001] The present disclosure relates to a laser device that emits laser light used in laser processing, and a laser processing device. [Background technology]

[0002] In recent years, laser devices that output short pulse light with high peak power are widely used as laser light sources for micromachining. Such laser devices often adopt the MOPA (Master Oscillator Power Amplifier) ​​method, in which the short pulse light output from a seed light source is amplified by a solid-state amplifier and output. Advantages of the MOPA method include the ease of controlling the repetition frequency and the ability to increase output by increasing the number of stages in the solid-state amplifier.

[0003] When performing micromachining with a MOPA type laser device, productivity can be improved by changing the repetition frequency of the laser depending on the machining shape. However, in a typical seed light source, the peak power of the pulsed light output changes depending on the repetition frequency. When the peak power changes, the influence of the nonlinear optical effect that occurs when the pulsed light passes through an optical element and a solid active medium changes. In particular, there was a problem that the beam propagation characteristics of the pulsed light after passing through a solid active medium change depending on the repetition frequency due to the optical Kerr effect, in which the refractive index of the medium changes depending on the intensity of the pulsed light. When the beam quality of the pulsed light changes, the minimum focusing diameter and intensity distribution at the machining point change, making it difficult to maintain a constant machining quality after changing the repetition frequency.

[0004] Patent Document 1 discloses a laser light source device including a seed light source that outputs pulsed light by a gain switching method, a fiber amplifier that amplifies the pulsed light output from the seed light source, a solid-state amplifier that amplifies the pulsed light output from the fiber amplifier, and a nonlinear optical element that converts the wavelength of the pulsed light output from the solid-state amplifier. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2015 / 122375 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the configuration of the conventional laser light source device, the change in the beam propagation characteristics of the pulsed light after passing through the solid active medium due to the optical Kerr effect when the repetition frequency is changed is not taken into consideration. In other words, in the configuration of the conventional laser light source device, when the repetition frequency of the pulsed light output from the seed light source is changed, the peak power of the pulsed light changes, and it is difficult to suppress the change in the beam propagation characteristics of the amplified pulsed light.

[0007] The present disclosure has been made in consideration of the above, and aims to provide a laser device that can suppress changes in beam propagation characteristics after amplification due to changes in the repetition frequency of a seed light source. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the laser device of the present disclosure includes a seed light source that outputs pulsed light and is capable of controlling the repetition frequency of the pulsed light, an aberration generation unit that adds aberration due to the optical Kerr effect to the pulsed light, a beam shaping optical system that adjusts at least one of the beam diameter and intensity distribution of the pulsed light, a solid-state amplifier that amplifies the pulsed light and emits laser light, and a configuration adjustment unit that is capable of operating at least one of the aberration generation unit and the beam shaping optical system in accordance with the repetition frequency of the pulsed light. Effect of the Invention

[0009] The laser device according to the present disclosure has an advantage of being able to suppress changes in the propagation characteristics of the amplified beam caused by changes in the repetition frequency of the seed light source. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram showing a schematic example of a configuration of a laser processing device including a laser device according to a first embodiment; [Diagram 2] FIG. 1 is a diagram showing an example of a hardware configuration of a control unit of a laser device according to a first embodiment. [Diagram 3] FIG. 13 is a diagram illustrating another example of the configuration of the aberration generating unit in the laser device according to the first embodiment; [Figure 4] FIG. 1 shows an example of a simulation result of beam quality after a pulsed light passes through a solid-state active medium in a typical solid-state amplifier. [Diagram 5] FIG. 2 is a diagram illustrating an example of the configuration of an aberration generating unit of the laser device according to the first embodiment; [Figure 6] FIG. 13 is a diagram illustrating another example of the configuration of the aberration generating unit of the laser device according to the first embodiment; [Figure 7] FIG. 2 is a diagram illustrating an example of the configuration of a beam shaping optical system of the laser device according to the first embodiment; [Figure 8] FIG. 13 shows an example of the results of simulating the intensity distribution on the incident surface of a solid active medium by applying a beam shaping optical system to pulsed light that has passed through an aberration generating unit. [Figure 9] FIG. 13 is a schematic diagram showing an example of the configuration of a laser processing apparatus including a laser apparatus according to a second embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a laser device and a laser processing device according to an embodiment of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below are merely examples, and the scope of the present disclosure is not limited to the embodiments described below.

[0012] Embodiment 1 FIG. 1 is a block diagram showing a schematic example of a configuration of a laser processing apparatus including a laser device according to the first embodiment. The laser processing apparatus 1 includes a laser device 100 that outputs laser light, and a processing optical system 60 that focuses and irradiates the laser light output from the laser device 100 on an object 70. The laser device 100 is an apparatus that induces emission of laser light by a solid active medium 41. The laser device 100 can also output laser light of a desired wavelength by a wavelength conversion crystal 50. The laser processing apparatus 1 is an apparatus that processes an object 70 by using laser light output from the laser device 100 using the solid active medium 41.

[0013] The laser device 100 includes a seed light source 10 , a control unit 11 , an aberration generating unit 20 , a position adjusting unit 21 , a beam shaping optical system 30 , a position adjusting unit 31 , a solid-state amplifier 40 , and a wavelength conversion crystal 50 .

[0014] The seed light source 10 outputs short pulse light, which is a laser light having a pulse width of several tens of picoseconds or less. The short pulse light output from the seed light source 10 is a laser light amplified by a solid active medium 41. Hereinafter, the short pulse light output from the seed light source 10 is referred to as pulse light. As an example, the seed light source 10 is a gain switch-driven semiconductor laser, a mode-locked fiber laser oscillator, or a solid-state laser oscillator. The seed light source 10 may be a MOPA light source composed of a seed pulse light source that outputs pulse light and an amplifier that amplifies the pulse light. An example of the wavelength of the pulse light is 1064 nm.

[0015] The control unit 11 controls various parameters such as the wavelength, average output, repetition frequency, and pulse width of the pulsed light output from the seed light source 10. The repetition frequency is the number of pulses generated per second at a constant period.

[0016] Here, a description will be given of a hardware configuration of the control unit 11. Fig. 2 is a diagram showing an example of a hardware configuration of the control unit of the laser device according to the first embodiment.

[0017] The control unit 11 can be realized by a control circuit 400 shown in Fig. 2, that is, a processor 401 and a memory 402. An example of the processor 401 is a CPU (also called a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor)) or a system LSI (Large Scale Integration). An example of the memory 402 is a RAM (Random Access Memory) or a ROM (Read Only Memory).

[0018] The processor 401 reads out and executes a control program stored in the memory 402, which is a program for executing processing in the control unit 11, thereby realizing the functions of the control unit 11. This control program can also be said to cause a computer to execute a method for emitting pulsed light from the seed light source 10 in the control unit 11. The control program executed in the control unit 11 has a modular configuration in which the process for emitting pulsed light from the seed light source 10 is modularized, and these are loaded onto the main storage device and generated on the main storage device.

[0019] The memory 402 stores data and the like to be set in the seed light source 10 when performing the process of emitting pulsed light. The memory 402 is also used as a temporary memory when the processor 401 executes various processes.

[0020] The control program executed by the processor 401 may be provided as a computer program product by being stored in a computer-readable storage medium in the form of an installable or executable file. The control program executed by the processor 401 may also be provided to the control unit 11 of the laser device 100 via a network such as the Internet.

[0021] Moreover, the control unit 11 may be realized by dedicated hardware. Moreover, the functions of the control unit 11 may be partially realized by dedicated hardware and partially realized by software or firmware.

[0022] Returning to FIG. 1, the aberration generating unit 20 transmits the pulsed light output from the seed light source 10, and at this time, the pulsed light is phase-modulated by the optical Kerr effect. As a result, the aberration generating unit 20 adds aberration due to the optical Kerr effect to the pulsed light. That is, the aberration generating unit 20 is composed of an optical Kerr medium, which is a material having the optical Kerr effect. The optical Kerr effect is a phenomenon in which the refractive index of a medium, which is a material that transmits laser light, changes according to the intensity distribution of the high-intensity laser light that is transmitted. In addition, the optical Kerr medium is a medium whose refractive index changes according to the intensity distribution of the laser light that is transmitted. In general, laser light has a Gaussian intensity distribution, so the refractive index distribution is Gaussian. The Gaussian refractive index distribution in the medium acts as a lens, and the laser is focused. This is called a Kerr lens. Since the refractive index distribution of the Kerr lens is Gaussian, aberration occurs. This causes the wavefront of the transmitted laser to become distorted, causing deterioration of the beam quality.

[0023] The aberration generating unit 20 is configured to suppress reflection of the incident pulsed light and the outgoing pulsed light. In one example, the aberration generating unit 20 has an anti-reflection coating for the wavelength of the pulsed light on the incident surface and the outgoing surface of the pulsed light. In another example, the incident surface and the reflective surface of the aberration generating unit 20 may not be provided with an anti-reflection coating for the wavelength of the pulsed light. FIG. 3 is a diagram showing a schematic diagram of another example of the configuration of the aberration generating unit in the laser device according to the first embodiment. As shown in FIG. 3, the aberration generating unit 20 may be configured such that the incident surface 201 and the outgoing surface 202 of the pulsed light LP in the aberration generating unit 20 are non-coated, and the pulsed light LP is incident on the aberration generating unit 20 at a Brewster angle θBi and the pulsed light LP is outgoing from the aberration generating unit 20 at a Brewster angle θBi and θBo. In this case, since the pulsed light LP is incident on and outgoes from the aberration generating unit 20 at the Brewster angles θBi and θBo, the reflectance at the incident surface 201 and the outgoing surface 202 can be reduced even without an anti-reflection coating. Furthermore, since the aberration generating section 20 does not have an anti-reflection film, there is an advantage in that damage to the anti-reflection film can be avoided.

[0024] Returning to Fig. 1, the placement adjustment unit 21 is a member that adjusts the placement of the aberration generation unit 20. When the repetition frequency of the pulsed light is changed, the placement adjustment unit 21 is operated by a user of the laser processing apparatus 1 or the laser apparatus 100 in order to adjust the pulsed light so as not to significantly degrade the beam quality of the laser light output from the solid-state amplifier 40. The placement adjustment unit 21 corresponds to a second placement adjustment unit. Details of the placement adjustment unit 21 will be described later.

[0025] The beam shaping optical system 30 adjusts at least one of the beam diameter and intensity distribution of the pulsed light that has been phase-modulated by the aberration generating unit 20. The beam shaping optical system 30 has at least one optical element of a spherical lens and a curved mirror as a component. The pulsed light that has passed through the beam shaping optical system 30 is amplified by the solid-state amplifier 40.

[0026] The arrangement adjustment unit 31 is a member that adjusts the arrangement of the beam shaping optical system 30. The arrangement adjustment unit 31 is operated by a user of the laser processing device 1 or the laser device 100 in order to adjust the pulsed light so as not to significantly degrade the beam quality of the laser light output from the solid-state amplifier 40 when the repetition frequency of the pulsed light is changed. The arrangement adjustment unit 31 corresponds to a first arrangement adjustment unit that moves components that are optical elements that configure the beam shaping optical system 30. Details of the arrangement adjustment unit 31 will be described later. The arrangement adjustment unit 21 and the arrangement adjustment unit 31 correspond to a broader arrangement adjustment unit that can operate at least one of the aberration generation unit 20 and the beam shaping optical system 30 according to the repetition frequency of the pulsed light.

[0027] The solid-state amplifier 40 amplifies the pulsed light output from the beam shaping optical system 30 and emits laser light. The solid-state amplifier 40 includes a solid-state active medium 41, an excitation light source 42, and a dichroic mirror 43. In the present disclosure, a solid-state active medium is a medium having a property of amplifying laser light by exciting it at a determined wavelength, that is, a gain, and is formed by doping a solid base material such as YAG (Yttrium Aluminum Garnet) or YVO4 with laser active ions such as Nd, Yb, or Tm. Hereinafter, the pulsed light amplified by the solid-state amplifier 40 is referred to as a pulsed amplified light.

[0028] For the solid-state active medium 41, a medium is selected whose gain band includes the wavelength of the pulsed light emitted from the seed light source 10. For example, when the wavelength of the pulsed light emitted from the seed light source 10 is 1064 nm, Nd:YVO4, Nd:YAG, or the like is suitably used for the solid-state active medium 41. When the wavelength of the pulsed light emitted from the seed light source 10 is 1030 nm, Yb:YAG, or the like is used for the solid-state active medium 41. The solid-state active medium 41 is end-pumped by the pumping light source 42. End-pumping is a method of pumping the solid-state active medium 41 by making the pumping light from the pumping light source 42 enter the solid-state active medium 41 in the same axial direction as the optical axis of the laser light emitted from the solid-state active medium 41. The incident direction of the pumping light from the pumping light source 42 to the solid-state active medium 41 is appropriately selected according to the shape of the solid-state active medium 41 or the beam propagation characteristics of the pumping light source 42 used. The pulsed light incident on the solid active medium 41 is amplified and emitted as a laser beam, which is a pulsed amplified light.

[0029] The excitation light source 42 is a light source that outputs laser light for exciting the solid-state active medium 41. A semiconductor laser is preferably used for the excitation light source 42. In the case of end face excitation, the excitation light source 42 is often a fiber-coupled semiconductor laser. The wavelength of the laser light output from the excitation light source 42 is selected according to the absorption spectrum of the solid-state active medium 41. In one example, when the solid-state active medium 41 is Nd:YVO4, laser light with wavelengths of 808 nm, 879 nm, 888 nm, and 914 nm is used. In particular, excitation by laser light with wavelengths of 879 nm, 888 nm, and 914 nm, which is direct excitation, has the advantage of generating less heat due to quantum defects and reducing the temperature rise of the solid-state active medium 41 associated with excitation.

[0030] The dichroic mirror 43 is provided to make the pulsed light from the seed light source 10 and the excitation light from the excitation light source 42 coaxially incident on the solid active medium 41. The excitation light output from the excitation light source 42 is transmitted through or reflected by the dichroic mirror 43 and is incident on the solid active medium 41 coaxially with the pulsed light. In the example of Fig. 1, the dichroic mirror 43 is configured to transmit the pulsed light from the seed light source 10 and reflect the excitation light from the excitation light source 42.

[0031] The wavelength conversion crystal 50 converts the wavelength of the amplified pulse light. 10 (Cesium Lithium Borate: CLBO), β-BaB2O4 (Barium Metaborate: BBO) crystal is used, and the wavelength is converted to the second harmonic, the third harmonic, or the fourth harmonic by harmonic generation. Note that the wavelength conversion crystal 50 is provided as necessary.

[0032] In this manner, the laser device 100 emits pulsed laser light having a wavelength determined by the wavelength conversion crystal 50.

[0033] The processing optical system 60 has an optical path that guides the pulsed amplified light emitted from the laser device 100 to the work-piece 70, and has optical elements that focus the pulsed amplified light at a desired position on the work-piece 70. The processing optical system 60 includes one or more lenses that adjust the beam diameter of the pulsed amplified light, a transmission mirror that transmits the pulsed amplified light, a galvanometer scanner that scans the pulsed amplified light, an fθ lens that focuses the pulsed amplified light, etc. The wavelength-converted pulsed amplified light is transmitted to the work-piece 70 by the processing optical system 60.

[0034] The first embodiment is characterized in that at least one of the arrangement adjustment unit 21 and the arrangement adjustment unit 31, which are arrangement adjustment units capable of operating at least one of the aberration generation unit 20 and the beam shaping optical system 30 according to the repetition frequency set in the seed light source 10, is provided. In other words, when the repetition frequency of the pulsed light output from the seed light source 10 is changed, at least one of the aberration generation unit 20 and the beam shaping optical system 30 is operated by a user according to the changed repetition frequency of the pulsed light. Specifically, at least one of the arrangement adjustment unit 21 and the arrangement adjustment unit 31 is operated by a user so as to adjust at least one of the arrangement of the aberration generation unit 20 and the arrangement of the beam shaping optical system 30.

[0035] The aberration generating unit 20 applies a phase change to the pulsed light by the optical Kerr effect, generating aberration. The beam shaping optical system 30 utilizes the aberration generated in the aberration generating unit 20 to adjust at least one of the beam diameter and intensity distribution of the pulsed light in the solid active medium 41. By adjusting the arrangement of at least one of the aberration generating unit 20 and the beam shaping optical system 30 according to the repetition frequency of the pulsed light by the user's operation, it becomes possible to suppress changes in the beam propagation characteristics of the pulsed light after passing through the solid active medium 41, particularly changes in the beam quality. The effects and methods of the above operations are described in detail below.

[0036] When a short pulse light having a high peak power passes through the solid active medium 41, the influence of the optical Kerr effect occurring in the solid active medium 41 cannot be ignored. The refractive index change n(r) due to the optical Kerr effect is expressed by the following formula (1). Here, r represents the radial position of the pulse light which is a laser beam, n0 is the linear refractive index of the solid active medium 41, n2 is the nonlinear refractive index of the solid active medium 41, and I(r) is the peak intensity of the pulse light at the radial position r of the pulse light.

[0037] n(r) = n0 + n2I(r) (1)

[0038] Equation (1) indicates that the refractive index at radial position r of the pulsed light in the solid active medium 41 varies depending on the nonlinear refractive index n2 and the peak intensity I(r) of the pulsed light. In addition, the phase change φ(r) at radial position r of the pulsed light that occurs when the pulsed light passes through the solid active medium 41 with length L is given by the following equation (2), where k is the wave number of the pulsed light.

[0039] φ(r) = kLn2I(r) (2)

[0040] From equation (2), the phase change experienced by the pulsed light passing through the solid-state active medium 41 increases as the medium length L increases, the nonlinear refractive index n2 of the solid-state active medium 41 increases, and the peak intensity I(r) of the pulsed light increases.

[0041] Generally, the peak power of the pulsed light output from the seed light source 10 changes according to the repetition frequency of the pulsed light, so the phase change due to the optical Kerr effect changes according to the repetition frequency of the pulsed light. For example, when the intensity distribution of the pulsed light is a Gaussian distribution, the phase of the pulsed light is modulated to a Gaussian shape by the optical Kerr effect. This phase change brings about a focusing effect like a convex lens, so it is called a Kerr lens. Because the refractive index distribution of the Kerr lens is different from that of an ideal lens, the pulsed light is subjected to the aberration of the Kerr lens when passing through the solid active medium 41, and the beam quality of the pulsed light changes.

[0042] FIG. 4 is a diagram showing an example of a simulation result of the beam quality after the pulsed light passes through the solid-state active medium in a general solid-state amplifier. In this diagram, the horizontal axis indicates the repetition frequency of the pulsed light, and the vertical axis indicates M2 (M Square), which indicates the quality of the pulsed light that passes through the solid-state active medium 41. Since we focus on the change in beam quality due to the optical Kerr effect, we do not consider the change in intensity of the pulsed light due to amplification in the solid-state active medium 41 and the thermal lens effect associated with excitation. In addition, the average output of the pulsed light is fixed at 50 W regardless of the repetition frequency. The pulse width of the pulsed light is 10 ps, ​​the wavelength is 1064 nm, and the beam diameter is 1 mm. The solid-state active medium 41 is assumed to be a Nd:YVO4 crystal with a length of 30 mm. The nonlinear refractive index n2 of Nd:YVO4 is 1.5×10 -19 m 2 / W. As shown in Figure 4, it can be seen that the beam quality M2 after passing through Nd:YVO4 changes depending on the repetition rate. If the beam quality changes due to a change in the repetition rate, the minimum focused diameter and intensity distribution of the pulsed light at the processing point will also change, making it difficult to maintain a constant processing quality.

[0043] To address such a problem, in the first embodiment, the aberration generating unit 20 made of an optical Kerr medium and the beam shaping optical system 30 are applied to the pulsed light output from the seed light source 10. That is, the arrangement of at least one of the aberration generating unit 20 and the beam shaping optical system 30 is manipulated to adjust the pulsed light incident on the solid active medium 41 so as to cancel the change in the beam propagation characteristics after passing through the solid active medium 41 due to the change in the repetition frequency. This makes it possible to suppress the change in the beam propagation characteristics after passing through the solid active medium 41 when the repetition frequency of the pulsed light is changed. As a result, it becomes possible to maintain a constant processing quality even if the repetition frequency of the pulsed light is changed.

[0044] As shown in formula (1), the optical Kerr effect depends on the peak intensity I(r) of the pulsed light, and the peak intensity I(r) depends on the beam diameter. Therefore, by adjusting the beam diameter of the pulsed light incident on the aberration generating unit 20 according to the repetition frequency, the amount of aberration due to the optical Kerr effect can be adjusted. Here, an example of adjusting the beam diameter of the pulsed light is shown. FIG. 5 is a diagram showing a schematic example of a configuration of the aberration generating unit of the laser device according to the first embodiment. As described above, the laser device 100 has one aberration generating unit 20 and a position adjustment unit 21 that moves the one aberration generating unit 20. In the example shown in FIG. 5, the position adjustment unit 21 is configured by a moving mechanism 211 that can move the aberration generating unit 20 in the direction of the optical axis OA of the pulsed light LP. The beam diameter of the pulsed light LP can be adjusted by adjusting the position of the aberration generating unit 20 in the direction of the optical axis OA of the pulsed light LP by operating the moving mechanism 211 according to the repetition frequency. At this time, by disposing the aberration generating unit 20 at a position where the pulsed light LP propagates divergently or convergently, the effect of adjusting the beam diameter can be achieved with a small amount of movement, and therefore the device can be made smaller. That is, the aberration generating unit 20 may be disposed at a position on the optical path where the beam propagation of the pulsed light LP converges and diverges, and the movement mechanism 211 may be operated to dispose the aberration generating unit 20 at the position where the beam propagation converges or diverges.

[0045] As shown in formula (2), the optical Kerr effect also depends on the medium length L. Therefore, the amount of aberration due to the optical Kerr effect can be adjusted by adjusting the medium length L of the pulsed light passing through the aberration generating unit 20 according to the repetition frequency. Here, an example of adjusting the medium length L is shown. FIG. 6 is a diagram showing a schematic diagram of another example of the configuration of the aberration generating unit of the laser device according to the first embodiment. In the example shown in FIG. 6, the laser device 100 has two aberration generating units 20 and a rotation mechanism 212 provided in each of the two aberration generating units 20. The two rotation mechanisms 212 are an example of the arrangement adjustment unit 21 that adjusts the arrangement of the aberration generating unit 20. The rotation mechanism 212 rotates the aberration generating unit 20 around an axis in a direction different from the direction of the optical axis OA of the pulsed light LP, i.e., an axis that is not parallel to the optical axis OA of the pulsed light LP, so that the length of the pulsed light LP passing through the aberration generating unit 20 can be changed. The length of the pulsed light LP passing through the aberration generating unit 20 is the interaction length between the pulsed light LP and the aberration generating unit 20. The interaction length between the pulsed light LP and the aberration generating unit 20 corresponds to the medium length L of the pulsed light LP passing through the aberration generating unit 20. In one example, the rotation mechanism 212 can rotate the aberration generating unit 20 around an axis perpendicular to the paper surface of FIG. 6. By providing the rotation mechanism 212 to the aberration generating unit 20 and rotating the aberration generating unit 20, it is possible to adjust the interaction length between the pulsed light LP and the aberration generating unit 20 and adjust the amount of aberration due to the optical Kerr effect. At this time, as shown in FIG. 6, two aberration generating units 20 are arranged facing each other and rotated by the same angle in opposite directions, which has the effect of canceling out the optical axis shift caused by the rotation of the aberration generating unit 20. 6, the laser device 100 has two aberration generating units 20 and two rotation mechanisms 212, but may have one aberration generating unit 20 and one rotation mechanism 212. The placement adjustment unit 21 may have the moving mechanism 211 shown in FIG. 5 and the rotation mechanism 212 shown in FIG. 6.

[0046] As described above, the amount of aberration can be adjusted by adjusting the position of the aberration generation unit 20 in the direction of the optical axis OA, or by adjusting the rotation angle of the aberration generation unit 20 about an axis that is not parallel to the optical axis OA of the pulsed light LP. Note that it is desirable for the phase change around the optical axis of the pulsed light LP in the aberration generation unit 20 to be π / 10 or more. By making the phase change around the optical axis of the pulsed light LP π / 10 or more, it becomes possible to generate a significant aberration by the Kerr lens.

[0047] The beam shaping optical system 30 utilizes the aberration of the pulsed light generated by the aberration generating unit 20 to adjust at least one of the beam diameter and intensity distribution of the pulsed light in the solid active medium 41. However, if the beam diameter and intensity distribution in the solid active medium 41 of the pulsed light in which the aberration has been generated by the aberration generating unit 20 when the repetition frequency of the pulsed light is changed does not change the beam quality of the pulsed light after passing through the solid active medium 41, the beam shaping optical system 30 does not need to adjust the beam diameter and intensity distribution of the pulsed light in the solid active medium 41.

[0048] When the aberration generating unit 20 gives aberration to the pulsed light, the intensity distribution of the pulsed light on the optical axis at the incident surface of the solid active medium 41 deviates from an ideal Gaussian distribution. As shown in formulas (1) and (2), the refractive index distribution and phase modulation due to the optical Kerr effect depend on the distribution of the peak intensity I(r), so even if the beam diameter is the same, if the distribution of the peak intensity I(r) is different, the beam quality after passing through the solid active medium 41 may change. Note that the beam diameter in this disclosure refers to the second moment diameter.

[0049] As an example, when the intensity distribution near the optical axis center of the pulsed light is narrower than an ideal Gaussian distribution having the same beam diameter as the pulsed light, the change in the beam quality of the pulsed light after passing through the solid active medium 41 becomes large. On the other hand, when the intensity distribution near the optical axis center of the pulsed light is broader than an ideal Gaussian distribution having the same beam diameter as the pulsed light, the change in the beam quality of the pulsed light after passing through the solid active medium 41 becomes small.

[0050] Furthermore, if the intensity distribution near the center of the optical axis of the pulsed light can be approximated by a quadratic curve, the refractive index distribution due to the optical Kerr effect can be regarded as an ideal lens with no aberration, and the beam quality after transmission does not change.

[0051] Furthermore, when the intensity distribution of the pulsed light is top-hat or high-order super-Gaussian, no refractive index distribution is formed due to the optical Kerr effect, and the beam quality after transmission does not change.

[0052] In this way, by adjusting the intensity distribution of the pulsed light incident on the solid active medium 41 by the beam shaping optical system 30, it is possible to increase or reduce the change in beam quality caused by the optical Kerr effect in the solid active medium 41. By appropriately performing this operation, it is possible to suppress the change in beam quality of the pulsed light after passing through the solid active medium 41 caused by changing the repetition frequency of the seed light source 10.

[0053] In order to adjust at least one of the beam diameter and intensity distribution of the pulsed light, the beam shaping optical system 30 is operated so that at least one of the principal point position and the focal length when the beam shaping optical system 30 is regarded as one composite lens is changed. That is, the arrangement of the components that are optical elements constituting the beam shaping optical system 30 is operated by the arrangement adjustment unit 31. This operation is an operation of changing at least one of the principal point position and the focal length when the beam shaping optical system 30 is regarded as one composite lens. Alternatively, when the beam shaping optical system 30 is considered as an ABCD ray matrix, this operation can also be considered as an operation of changing at least one of the elements of the ABCD matrix of the composite lens.

[0054] FIG. 7 is a diagram showing a schematic diagram of an example of the configuration of the beam shaping optical system of the laser device according to the first embodiment. In the example of FIG. 7, the beam shaping optical system 30 has two plano-convex lenses 301 and one plano-concave lens 302. The two plano-convex lenses 301 and one plano-concave lens 302 are an example of optical elements constituting the beam shaping optical system 30. A moving mechanism 311 is provided for each of the two plano-convex lenses 301 and one plano-concave lens 302. The moving mechanism 311 has a function of moving components of the beam shaping optical system 30 in the optical axis direction of the pulsed light, or a function of moving components of the beam shaping optical system 30 in a direction to remove them from the optical axis of the pulsed light. That is, the moving mechanism 311 has a function of adjusting the position of each lens 301, 302 with respect to the optical axis direction of the pulsed light and removing each lens 301, 302 from the optical path. The moving mechanism 311 is an example of the arrangement adjustment unit 31. The number and types of the lenses 301 and 302 are not limited to those shown in FIG.

[0055] FIG. 8 is a diagram showing an example of the results of simulating the intensity distribution at the incident surface of the solid active medium by applying a beam shaping optical system to the pulsed light transmitted through the aberration generating unit. In this diagram, the horizontal axis indicates the position of the pulsed light incident on the incident surface of the solid active medium 41, and the vertical axis indicates the intensity of the pulsed light. The dotted line graph in FIG. 8 shows the results of simulating the intensity distribution at the incident surface of the solid active medium 41 by applying a beam shaping optical system 30 to the pulsed light transmitted through the aberration generating unit 20. Of these, the four dotted line graphs correspond to four different operations of the beam shaping optical system 30. These four dotted line graphs have different intensity distributions, but all have the same beam diameter. For comparison, an ideal Gaussian distribution having the same beam diameter as each dotted line is shown in FIG. 8 as a solid line graph. From the results shown in Figure 8, it can be seen that at least one of the beam diameter and intensity distribution of the pulsed light in the solid active medium 41 can be adjusted by manipulating the beam shaping optical system 30, i.e., by configuring the positions of the lenses 301, 302 that constitute the beam shaping optical system 30 or by removing the lenses 301, 302 from the optical path.

[0056] As described above, the position of the aberration generating unit 20 is changed by the arrangement adjustment unit 21, or at least one of the principal point position and the focal length when the beam shaping optical system 30 is regarded as one composite lens is changed by the arrangement adjustment unit 31, depending on the repetition frequency of the pulsed light. In other words, the arrangement adjustment unit in a broad sense changes the position of the aberration generating unit, or at least one of the principal point position and the focal length when the beam shaping optical system is regarded as one composite lens, depending on the repetition frequency of the pulsed light.

[0057] It is desirable to operate the beam shaping optical system 30 so that the central optical axis intensity of the pulsed light at the incident surface of the solid active medium 41 becomes lower as the repetition frequency of the seed light source 10 becomes lower, i.e., as the peak power of the seed light source 10 becomes higher.

[0058] The laser device 100 of the first embodiment includes a seed light source 10 that outputs pulsed light and can control the repetition frequency of the pulsed light, an aberration generating unit 20 that adds an aberration due to the optical Kerr effect to the pulsed light, a beam shaping optical system 30 that adjusts at least one of the beam diameter and intensity distribution of the pulsed light, and at least one of the arrangement adjusting units 21 and 31 that are arrangement adjusting units that can operate at least one of the aberration generating unit 20 and the beam shaping optical system 30 according to the repetition frequency of the pulsed light. Specifically, the ratio of the axial intensity of the pulsed light to the axial intensity of an ideal Gaussian beam with the same output and beam diameter as the pulsed light is changed according to the repetition frequency of the pulsed light. This has the effect of suppressing changes in the beam quality of the pulsed light incident on the solid active medium 41 from before the repetition frequency was changed, or changes in the beam propagation characteristics of the pulsed amplified light output from the solid active medium 41, even when the repetition frequency of the pulsed light is changed.

[0059] In the above description, a case has been shown in which the user operates at least one of the arrangement adjustment unit 21 that adjusts the arrangement of the aberration generation unit 20 and the arrangement adjustment unit 31 that adjusts the arrangement of the beam shaping optical system 30 when the repetition frequency of the pulsed light is changed. However, the control unit 11 may control at least one of the arrangement adjustment unit 21 that adjusts the arrangement of the aberration generation unit 20 and the arrangement adjustment unit 31 that adjusts the arrangement of the beam shaping optical system 30 so that a change in the beam quality of the pulsed light incident on the solid active medium 41 is suppressed when the repetition frequency of the pulsed light is changed.

[0060] Embodiment 2 FIG. 9 is a diagram showing a schematic example of the configuration of a laser processing apparatus including a laser device according to the second embodiment. The same components as those in FIG. 1 are given the same reference numerals, and their description will be omitted. In the first embodiment, an optical Kerr medium is used in the aberration generating unit 20. In the second embodiment, the aberration generating unit 20a is different from that in the first embodiment. That is, in the laser device 100a in the laser processing apparatus 1a according to the second embodiment, a solid active medium is used in the aberration generating unit 20a. However, the solid active medium used in the aberration generating unit 20a also functions as an optical Kerr medium. The solid active medium constituting such an aberration generating unit 20a has a nonlinear refractive index n2 of 1×10, such as Nd:YVO4. -19 m 2 / W or more of a solid-state active medium is used. With this configuration, the aberration generating section 20a, which is an optical Kerr medium, can function as a solid-state amplifier.

[0061] In this way, when the aberration generation unit 20a is caused to function as a solid-state amplifier, the laser device 100a further includes an excitation light source 22 and a dichroic mirror 23 in addition to the configuration of the first embodiment.

[0062] The excitation light source 22 is a light source that outputs laser light for exciting the aberration generating unit 20a. A semiconductor laser is preferably used for the excitation light source 22. In the case of end face excitation, the excitation light source 22 is often a fiber-coupled semiconductor laser. The wavelength of the laser light output from the excitation light source 22 is selected according to the absorption spectrum of the aberration generating unit 20a. In one example, when the solid active medium 41 is Nd:YVO4, laser light with wavelengths of 808 nm, 879 nm, 888 nm, and 914 nm is used. In particular, excitation by laser light with wavelengths of 879 nm, 888 nm, and 914 nm, which is direct excitation, has the advantage of generating less heat due to quantum defects and reducing the temperature rise of the solid active medium 41 associated with excitation.

[0063] The dichroic mirror 23 is provided to make the pulsed light from the seed light source 10 and the excitation light from the excitation light source 22 coaxially incident on the aberration generation unit 20a. The excitation light output from the excitation light source 22 is transmitted through or reflected by the dichroic mirror 23 and incident on the solid active medium 41 coaxially with the pulsed light. In the example of Fig. 9, the dichroic mirror 23 is configured to transmit the pulsed light from the seed light source 10 and reflect the excitation light from the excitation light source 22.

[0064] As an example, the technology of the second embodiment can be applied to a laser device composed of a two-stage solid-state amplifier. By utilizing the optical Kerr effect occurring in the aberration generating part 20a, which is the first-stage solid-state active medium, changes in the beam propagation characteristics of the pulsed amplified light after it is emitted from the second-stage solid-state active medium 41 are suppressed. In addition, by using the same solid-state active medium for the aberration generating part 20a and the solid-state active medium 41, it is possible to reduce the number of parts and lower costs.

[0065] In the second embodiment, the aberration generating unit 20a has a nonlinear refractive index n2 of 1×10 -19 m 2 / W or more. This has the effect of making the aberration generation unit 20a function as a solid-state amplifier. In addition, by using the same solid-state active medium for the aberration generation unit 20a and the solid-state active medium 41, it has the effect of reducing the number of parts and lowering costs.

[0066] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or the embodiments may be combined with each other. Also, parts of the configurations may be omitted or modified without departing from the spirit of the invention. [Explanation of symbols]

[0067] 1,1a laser processing device, 10 seed light source, 11 control unit, 20,20a aberration generating unit, 21,31 arrangement adjustment unit, 22,42 excitation light source, 23,43 dichroic mirror, 30 beam shaping optical system, 40 solid amplifier, 41 solid active medium, 50 wavelength conversion crystal, 60 processing optical system, 70 processing object, 100,100a laser device, 201 incident surface, 202 exit surface, 211,311 moving mechanism, 212 rotating mechanism, 301 plano-convex lens, 302 plano-concave lens, LP pulsed light, OA optical axis, θBi,θBo Brewster angle.

Claims

1. a seed light source that outputs pulsed light and is capable of controlling the repetition frequency of the pulsed light; an aberration generating unit that adds aberration due to the optical Kerr effect to the pulsed light; a beam shaping optical system for adjusting at least one of the beam diameter and the intensity distribution of the pulsed light; a solid-state amplifier that amplifies the pulsed light and emits laser light; a placement adjustment unit that can operate at least one of the aberration generation unit and the beam shaping optical system in accordance with a repetition frequency of the pulsed light; A laser device comprising:

2. 2. The laser device according to claim 1, wherein the beam shaping optical system has at least one optical element selected from the group consisting of a spherical lens and a curved mirror.

3. 2. The laser device according to claim 1, wherein the placement adjustment unit changes at least one of the position of the aberration generating unit, or the principal point position and focal length when the beam shaping optical system is considered as a single composite lens.

4. the placement adjustment unit includes a first placement adjustment unit that moves components that are optical elements that configure the beam shaping optical system, 2. The laser device according to claim 1, wherein the first placement adjustment unit has a function of moving the component in a direction of an optical axis of the pulsed light, or a function of moving the component in a direction to remove it from the optical axis of the pulsed light.

5. 2. The laser device according to claim 1, wherein the placement adjustment unit includes a second placement adjustment unit that adjusts the placement of the aberration generating unit.

6. 6. The laser device according to claim 5, wherein the second placement adjustment unit has a movement mechanism that can move the aberration generation unit in the optical axis direction of the pulsed light.

7. 7. The laser device according to claim 6, wherein the movement mechanism disposes the aberration generating unit at a position where beam propagation of the pulsed light converges or diverges.

8. 6. The laser device according to claim 5, wherein the second placement adjustment unit has a rotation mechanism that rotates the aberration generation unit around an axis that is in a direction different from the optical axis direction of the pulsed light.

9. 2. The laser device according to claim 1, wherein the aberration generating unit is arranged so that the pulsed light is incident on an incident surface of the aberration generating unit at a Brewster angle, and the pulsed light is emitted from an exit surface of the aberration generating unit at a Brewster angle.

10. The aberration generating unit is 1×10 -19 m 2 2. The laser device according to claim 1, wherein the solid active medium has a nonlinear refractive index of at least 1 / W.

11. A laser device according to any one of claims 1 to 10; a processing optical system that irradiates the laser light emitted from the laser device onto an object to be processed; A laser processing device comprising:

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