Laser device and laser processing device

Abstract

A laser device (100) is provided with: a seed light source (10) that outputs pulsed light and can control the repetition frequency of the pulsed light; an aberration generation 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 the intensity distribution of the pulsed light; a solid-state amplifier (40) that amplifies the pulsed light and emits laser light; and an arrangement adjustment unit (21, 31) that can operate at least one of the aberration generation unit (20) and the beam shaping optical system (30) in accordance with the repetition frequency of the pulsed light.

Description

Laser device and laser processing device

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

[0002] In recent years, laser devices that output short pulsed light with high peak power have been widely used as laser light sources for micromachining. These laser devices often employ a Master Oscillator Power Amplifier (MOPA) system, in which short pulsed light output from a seed light source is amplified by a solid-state amplifier. The advantages of the MOPA system include easy control of the repetition rate and the ability to increase output power by increasing the number of stages in the solid-state amplifier.

[0003] When performing micromachining using a MOPA-type laser device, productivity can sometimes be improved by changing the laser repetition rate according to the machining shape. However, with a typical seed light source, the peak power of the pulsed light output changes depending on the repetition rate. A change in peak power changes the influence of nonlinear optical effects that occur when the pulsed light passes through optical elements and solid-state active media. In particular, due to the optical Kerr effect, in which the refractive index of a medium changes depending on the intensity of the pulsed light, the beam propagation characteristics of the pulsed light after passing through the solid-state active medium change depending on the repetition rate. Changes in the beam quality of the pulsed light change the minimum focal diameter and intensity distribution at the machining point, making it difficult to maintain consistent machining quality after changing the repetition rate.

[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.

[0005] International Publication No. 2015 / 122375

[0006] However, the configuration of the above-mentioned conventional laser light source device does not take into consideration changes 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 rate is changed. In other words, the configuration of the above-mentioned conventional laser light source device has a problem in that when the repetition rate of the pulsed light output from the seed light source is changed, the peak power of the pulsed light changes, making it difficult to suppress changes in the beam propagation characteristics of the amplified pulsed light.

[0007] The present disclosure has been made in view of the above, and aims to provide a laser device that can suppress changes in the propagation characteristics of the amplified beam due to changes in the repetition frequency of the seed light source.

[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 placement 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.

[0009] The laser device according to the present disclosure has the 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.

[0010] FIG. 1 is a block diagram schematically showing an example of the configuration of a laser processing apparatus including a laser apparatus according to embodiment 1; FIG. 2 is a diagram showing an example of the hardware configuration of a control unit of a laser apparatus according to embodiment 1; FIG. 3 is a diagram showing another example of the configuration of an aberration generation unit in a laser apparatus according to embodiment 1; FIG. 4 is a diagram showing an example of a simulation result of beam quality after pulsed light in a general solid-state amplifier has passed through a solid active medium; FIG. 5 is a diagram showing another example of the configuration of an aberration generation unit in a laser apparatus according to embodiment 1;

[0011] Hereinafter, a laser apparatus and a laser processing apparatus according to embodiments 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 the configuration of a laser processing apparatus including a laser apparatus according to embodiment 1. The laser processing apparatus 1 includes a laser apparatus 100 that outputs laser light and a processing optical system 60 that focuses the laser light output from the laser apparatus 100 onto an object to be processed 70 and irradiates the object to be processed 70. The laser apparatus 100 is an apparatus that stimulates emission of laser light using a solid active medium 41. The laser apparatus 100 can also be configured to output laser light of a desired wavelength using a wavelength conversion crystal 50. The laser processing apparatus 1 is an apparatus that processes an object to be processed 70 using laser light output from the laser apparatus 100 that uses 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 placement adjusting unit 21 , a beam shaping optical system 30 , a placement 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 laser light with a pulse width of several tens of picoseconds or less. The short pulse light output from the seed light source 10 is laser light amplified by a solid-state active medium 41. Hereinafter, the short pulse light output from the seed light source 10 will be referred to as pulse light. As an example, the seed light source 10 may be 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 configured with 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 the hardware configuration of the control unit 11. Fig. 2 is a diagram showing an example of the 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. Examples of the processor 401 include 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). Examples of the memory 402 include 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. It can also be said that this control program causes 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 by the control unit 11 has a modular configuration in which the processing for emitting pulsed light from the seed light source 10 is modularized, and these programs are loaded onto the main storage device and generated on the main storage device.

[0019] The memory 402 stores data to be set in the seed light source 10 when performing the pulsed light emission process. 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 stored in a computer-readable storage medium as an installable or executable file. Alternatively, the control program executed by the processor 401 may be provided to the control unit 11 of the laser device 100 via a network such as the Internet.

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

[0022] Returning to FIG. 1 , the aberration generation unit 20 transmits the pulsed light output from the seed light source 10, which is subjected to phase modulation due to the optical Kerr effect. As a result, the aberration generation unit 20 adds aberration due to the optical Kerr effect to the pulsed light. That is, the aberration generation unit 20 is composed of an optical Kerr medium, which is a material that exhibits the optical Kerr effect. The optical Kerr effect is a phenomenon in which the refractive index of a medium that transmits laser light changes according to the intensity distribution of the transmitted high-intensity laser light. An optical Kerr medium is a medium whose refractive index changes according to the intensity distribution of the transmitted laser light. Since laser light generally has a Gaussian intensity distribution, the refractive index distribution is Gaussian. The Gaussian refractive index distribution in the medium acts as a lens, focusing the laser. This is called a Kerr lens. Because the refractive index distribution of a Kerr lens is Gaussian, aberration occurs. This disrupts the wavefront of the transmitted laser, causing degradation of beam quality.

[0023] The aberration generation unit 20 is configured to suppress reflection of the incident pulsed light and the outgoing pulsed light. In one example, the aberration generation unit 20 has anti-reflection coatings for the wavelength of the pulsed light on the incident and exit surfaces of the pulsed light. In another example, the incident and reflective surfaces of the aberration generation unit 20 may not be provided with anti-reflection coatings for the wavelength of the pulsed light. FIG. 3 is a diagram schematically showing another example of the configuration of the aberration generation unit in the laser device according to the first embodiment. As schematically shown in FIG. 3 , the aberration generation unit 20 may be configured such that the incident surface 201 and exit surface 202 of the aberration generation unit 20 for the pulsed light LP are uncoated, and the pulsed light LP is incident on the aberration generation unit 20 at a Brewster angle θBi and the pulsed light LP is exited at a Brewster angle θBo. In this case, the pulsed light LP enters and exits the aberration generation unit 20 at Brewster angles θBi and θBo, so that even without an anti-reflection coating, it is possible to reduce the reflectance at the entrance surface 201 and the exit surface 202. Furthermore, since no anti-reflection coating is provided on the aberration generation unit 20, there is an advantage in that damage to the anti-reflection coating can be avoided.

[0024] Returning to Fig. 1 , the placement adjustment unit 21 is a component 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 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 selected from the group consisting of a spherical lens and a curved mirror. The pulsed light that has passed through the beam shaping optical system 30 is amplified by the solid-state amplifier 40.

[0026] The placement adjustment unit 31 is a component that adjusts the placement of the beam shaping optical system 30. The placement adjustment unit 31 is operated by a user of the laser processing apparatus 1 or the laser apparatus 100 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 placement adjustment unit 31 corresponds to a first placement adjustment unit that moves components that are optical elements that make up the beam shaping optical system 30. Details of the placement adjustment unit 31 will be described later. The placement adjustment units 21 and 31 correspond to placement adjustment units in a broad sense that can operate at least one of the aberration generation unit 20 and the beam shaping optical system 30 in accordance with 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 defined as a material that has the property of amplifying laser light, i.e., gain, by exciting a solid-state active medium 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 will be referred to as pulsed amplified light.

[0028] A medium whose gain band includes the wavelength of the pulsed light emitted from the seed light source 10 is selected for the solid-state active medium 41. 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 in which pumping light from the pumping light source 42 is incident on the solid-state active medium 41 in a direction coaxial with the optical axis of the laser light emitted from the solid-state active medium 41 to pump the solid-state active medium 41. The incident direction of the pumping light from the pumping light source 42 with respect to the solid-state active medium 41 is appropriately selected depending on 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 to excite the solid-state active medium 41. A semiconductor laser is preferably used as the excitation light source 42. In the case of end-face pumping, 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. For 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 with 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 that accompanies 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 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 pulsed amplified light. 10 (Cesium Lithium Borate: CLBO) or β-BaB2O4 (Barium Metaborate: BBO) crystal is used, and wavelength conversion to the second harmonic, third harmonic, or fourth harmonic is performed by harmonic generation. Note that a wavelength conversion crystal 50 is provided as needed.

[0032] As a result of the above, the laser device 100 emits pulsed laser light having a wavelength determined by the wavelength conversion crystal 50 .

[0033] The processing optical system 60 forms an optical path to guide 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 by including at least one of the arrangement adjustment unit 21 and the arrangement adjustment unit 31, which are arrangement adjustment units that can operate at least one of the aberration generation unit 20 and the beam shaping optical system 30 in accordance with the repetition frequency set in the seed light source 10. 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 the user in accordance with the repetition frequency of the changed pulsed light. Specifically, at least one of the arrangement adjustment unit 21 and the arrangement adjustment unit 31 is operated by the 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 generation 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 generation 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 position of 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 through a user 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 beam quality. The effects and methods of the above operations are described in detail below.

[0036] When short pulsed 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 equation (1): where r represents the radial position of the pulsed light, which is laser light, no 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 pulsed light at the radial position r of the pulsed light.

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

[0038] Equation (1) indicates that the refractive index at the 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. Furthermore, the phase change φ(r) at the radial position r of the pulsed light that occurs when the pulsed light passes through the solid active medium 41 with a 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 active medium 41 increases as the medium length L increases, the nonlinear refractive index n2 of the solid 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 varies depending on the repetition frequency of the pulsed light, and therefore, the phase change due to the optical Kerr effect varies depending on the repetition frequency of the pulsed light. For example, if 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 produces a focusing effect similar to that of a convex lens, and is therefore called a Kerr lens. Because the refractive index distribution of a Kerr lens differs from that of an ideal lens, the pulsed light is subject 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 shows an example of the simulation results of the beam quality of pulsed light after it passes through a solid-state active medium in a typical solid-state amplifier. In this figure, the horizontal axis represents the repetition frequency of the pulsed light, and the vertical axis represents M2 (M Square), which indicates the quality of the pulsed light that has passed through the solid-state active medium 41. Since we focus on changes in beam quality due to the optical Kerr effect, we do not consider changes in the intensity of the pulsed light due to amplification within the solid-state active medium 41 or the thermal lens effect associated with excitation. Furthermore, the average output of the pulsed light is fixed at 50 W regardless of the repetition frequency. The pulsed light has a pulse width of 10 ps, ​​a wavelength of 1064 nm, and a beam diameter of 1 mm. The solid-state active medium 41 is assumed to be a 30 mm long Nd:YVO4 crystal. 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 change, making it difficult to maintain constant processing quality.

[0043] To address this issue, in the first embodiment, the aberration generation unit 20, which is 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 generation 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 out changes in the beam propagation characteristics after passing through the solid active medium 41 due to changes in the repetition frequency. This makes it possible to suppress changes 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 constant processing quality even when the repetition frequency of the pulsed light is changed.

[0044] As shown in equation (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, the amount of aberration due to the optical Kerr effect can be adjusted by adjusting the beam diameter of the pulsed light incident on the aberration generation unit 20 according to the repetition frequency. Here, an example of adjusting the beam diameter of the pulsed light is shown. FIG. 5 is a diagram schematically illustrating an example of the configuration of the aberration generation unit of the laser device according to embodiment 1. As described above, the laser device 100 includes one aberration generation unit 20 and a placement adjustment unit 21 that moves the one aberration generation unit 20. In the example shown in FIG. 5, the placement adjustment unit 21 is configured by a movement mechanism 211 that can move the aberration generation unit 20 relative to 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 generation unit 20 relative to the direction of the optical axis OA of the pulsed light LP by operating the movement mechanism 211 according to the repetition frequency. In this case, by disposing the aberration generation unit 20 at a position where the pulsed light LP propagates divergently or convergently, the beam diameter can be adjusted with a small amount of movement, which makes it possible to miniaturize the device. In other words, the aberration generation unit 20 can be disposed at a position on the optical path where the beam propagation of the pulsed light LP converges or diverges, and the movement mechanism 211 can be operated to dispose the aberration generation unit 20 at the position where the beam propagation converges or diverges.

[0045] As shown in equation (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 generation unit 20 according to the repetition frequency. Here, an example of adjusting the medium length L is shown. FIG. 6 is a diagram schematically illustrating another example of the configuration of the aberration generation unit of the laser device according to embodiment 1. In the example illustrated in FIG. 6, the laser device 100 has two aberration generation units 20 and a rotation mechanism 212 provided for each of the two aberration generation units 20. The two rotation mechanisms 212 are an example of the placement adjustment unit 21 that adjusts the placement of the aberration generation units 20. The rotation mechanism 212 rotates the aberration generation 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 generation unit 20 can be changed. The length of the pulsed light LP passing through the aberration generation unit 20 is the interaction length between the pulsed light LP and the aberration generation unit 20. The interaction length between the pulsed light LP and the aberration generation unit 20 corresponds to the medium length L of the pulsed light LP passing through the aberration generation unit 20. In one example, the rotation mechanism 212 is capable of rotating the aberration generation unit 20 around an axis perpendicular to the plane of the paper in FIG. 6 . By providing the rotation mechanism 212 to the aberration generation unit 20 and rotating the aberration generation unit 20, the interaction length between the pulsed light LP and the aberration generation unit 20 can be adjusted, and the amount of aberration due to the optical Kerr effect can be adjusted. In this case, as shown in FIG. 6 , two aberration generation units 20 are arranged facing each other and rotated in opposite directions by the same angle, which has the effect of canceling out the optical axis shift caused by the rotation of the aberration generation unit 20. 6, the laser device 100 includes two aberration generators 20 and two rotation mechanisms 212, but may include one aberration generator 20 and one rotation mechanism 212. The placement adjustment unit 21 may include the movement mechanism 211 shown in FIG. 5 and the rotation mechanism 212 shown in FIG.

[0046] As described above, the amount of aberration can be adjusted by adjusting the position of the aberration generation unit 20 with respect to 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 that the phase change around the optical axis of the pulsed light LP in the aberration generation unit 20 is π / 10 or more. By setting the phase change around the optical axis of the pulsed light LP to π / 10 or more, it becomes possible to generate significant aberrations by the Kerr lens.

[0047] The beam shaping optical system 30 utilizes the aberration of the pulsed light generated by the aberration generation 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 generation 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 applies 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 equations (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). Therefore, 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] For example, if the intensity distribution of the pulsed light near the optical axis center 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 will be large. On the other hand, if the intensity distribution of the pulsed light near the optical axis center is thicker 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 will be small.

[0050] Furthermore, if the intensity distribution of the pulsed light near the center of the optical axis 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 remains unchanged.

[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 occurring 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 focal length when the beam shaping optical system 30 is considered as a single 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 that changes at least one of the principal point position and focal length when the beam shaping optical system 30 is considered as a single 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 that changes at least one element of the ABCD matrix of the composite lens.

[0054] FIG. 7 is a diagram schematically illustrating 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 examples of optical elements that constitute the beam shaping optical system 30. A movement mechanism 311 is provided for each of the two plano-convex lenses 301 and one plano-concave lens 302. The movement mechanism 311 has a function of moving the components of the beam shaping optical system 30 in the optical axis direction of the pulsed light, or a function of moving the components of the beam shaping optical system 30 in a direction that removes them from the optical axis of the pulsed light. In other words, the movement mechanism 311 has a function of adjusting the positions of the lenses 301 and 302 with respect to the optical axis direction of the pulsed light and removing the lenses 301 and 302 from the optical path. The movement 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 shows an example of the results of a simulation of the intensity distribution at the incident surface of the solid active medium 41 when a beam shaping optical system is applied to pulsed light that has passed through the aberration generation unit. In this figure, the horizontal axis represents the position of the pulsed light that has passed through the incident surface of the solid active medium 41, and the vertical axis represents the intensity of the pulsed light. The dotted line graph in FIG. 8 shows the results of a simulation of the intensity distribution at the incident surface of the solid active medium 41 when a beam shaping optical system 30 is applied to pulsed light that has passed through the aberration generation 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 as a solid line graph in FIG. 8. The results in FIG. 8 show 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 and 302 that constitute the beam shaping optical system 30 or by removing the lenses 301 and 302 from the optical path.

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

[0057] It is desirable that the beam shaping optical system 30 be operated 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 is capable of controlling the repetition frequency of the pulsed light, an aberration generation 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, and at least one of a placement adjustment unit 21 and a placement adjustment unit 31 that are placement adjustment units that are capable of operating at least one of the aberration generation unit 20 and the beam shaping optical system 30 in accordance with the repetition frequency of the pulsed light. Specifically, the ratio of the on-axis intensity of the pulsed light to the on-axis intensity of an ideal Gaussian beam having the same output and beam diameter as the pulsed light is changed in accordance with 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-state active medium 41 from before the repetition frequency was changed, or changes in the beam propagation characteristics of the amplified pulsed light output from the solid-state active medium 41, even when the repetition frequency of the pulsed light is changed.

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

[0060] Second Embodiment Fig. 9 is a diagram schematically showing an example of the configuration of a laser processing apparatus equipped with a laser device according to a 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 was used in the aberration generation unit 20. In the second embodiment, the aberration generation 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 generation unit 20a. However, the solid active medium used in the aberration generation unit 20a also functions as an optical Kerr medium. The solid active medium constituting such an aberration generation unit 20a is preferably a material having a nonlinear refractive index n2 of 1 x 10, such as Nd:YVO4. -19 m 2 With this configuration, the aberration generating portion 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 made 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 that excites the aberration generation unit 20a. A semiconductor laser is preferably used for the excitation light source 22. In the case of end-face pumping, 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 generation unit 20a. As an 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 with 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 that accompanies 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 incident on the same axis 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 configured with a two-stage solid-state amplifier. The optical Kerr effect generated in the aberration generation unit 20a, which is the first-stage solid-state active medium, is utilized to suppress changes in the beam propagation characteristics of the pulsed amplified light after it is emitted from the second-stage solid-state active medium 41. Furthermore, by using the same solid-state active medium for the aberration generation unit 20a and the solid-state active medium 41, it is possible to reduce the number of component types and lower costs.

[0065] In the second embodiment, the aberration generating unit 20a is configured such that the nonlinear refractive index n is 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. Furthermore, 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 component types and lowering costs.

[0066] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0067] 1, 1a laser processing apparatus, 10 seed light source, 11 control unit, 20, 20a aberration generation unit, 21, 31 placement adjustment unit, 22, 42 excitation light source, 23, 43 dichroic mirror, 30 beam shaping optical system, 40 solid-state amplifier, 41 solid-state 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 rotation mechanism, 301 plano-convex lens, 302 plano-concave lens, LP pulsed light, OA optical axis, θBi, θBo Brewster angle.

Claims

1. A laser device comprising: 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.

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

3. A laser device as described in claim 1 or 2, characterized in that 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. A laser device as described in any one of claims 1 to 3, characterized in that the positioning adjustment unit has a first positioning adjustment unit that moves a component which is an optical element that constitutes the beam shaping optical system, and the first positioning adjustment unit has a function of moving the component in the optical axis direction of the pulsed light, or a function of moving the component in a direction that removes it from the optical axis of the pulsed light.

5. A laser device according to any one of claims 1 to 4, wherein the placement adjustment section has a second placement adjustment section that adjusts the placement of the aberration generating section.

6. The laser device according to claim 5, wherein the second position adjustment section has a movement mechanism capable of moving the aberration generating section in the optical axis direction of the pulsed light.

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

8. A laser device as described in any one of claims 5 to 7, characterized in that the second positioning adjustment unit has a rotation mechanism that rotates the aberration generating unit around an axis in a direction different from the optical axis direction of the pulsed light.

9. A laser device as described in any one of claims 1 to 8, characterized in that the aberration generating unit is arranged so that the pulsed light is incident on the entrance surface of the aberration generating unit at a Brewster angle, and so that the pulsed light is exited at the exit surface of the aberration generating unit at a Brewster angle.

10. The aberration generating unit is 1×10 -19 m 2 10. The laser device according to claim 1, wherein the solid active medium has a nonlinear refractive index of at least 1.0 W.

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

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