Wavelength conversion device and method for wavelength conversion

Abstract

To provide a wavelength conversion mechanism capable of outputting a plurality of systems of ultraviolet laser beams having high output power (pulse energy) without causing deterioration of an optical element for branching.SOLUTION: There is provided the wavelength conversion mechanism for wavelength-converting wavelength-conversion target light, which is pulsed laser light having a predetermined repetition frequency, into laser light in an ultraviolet region, the wavelength conversion mechanism including: a branching optical system for spatially branching the wavelength-conversion target light; and a plurality of ultraviolet wavelength conversion elements for wavelength-converting each wavelength-conversion target light branched by the branching optical system into laser light in an ultraviolet region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wavelength conversion mechanism and a wavelength conversion method for obtaining ultraviolet laser light used in various laser processing and laser measurement. [Background technology]

[0002] In recent years, laser light has been used for various processing such as inspection, marking, cutting, drilling, welding, and hardening of objects. Laser light with a wavelength of around 532 nm to 1064 nm has high energy intensity and is suitable for various processing such as cutting or welding of metals, glass, etc. Laser light in the deep ultraviolet region with a wavelength of around 200 nm to 350 nm is also used for microprocessing and inspection of electronic materials such as semiconductors and composite materials.

[0003] A solid-state laser light source device that outputs laser light with a wavelength shorter than the near-infrared region is configured to include a seed light source that outputs laser light with a wavelength in the near-infrared region, an optical amplifier that amplifies the laser light output from the seed light source, and a nonlinear optical element that functions as a wavelength conversion element that converts the wavelength of the laser light amplified by the optical amplifier to a target wavelength.

[0004] In order to improve processing efficiency and processing accuracy, there is a demand for a laser light source device that can generate ultraviolet laser pulse light with a pulse width of several nanoseconds or less, preferably several tens of picoseconds or less, a repetition frequency of several hundred megahertz or less, and a high peak power.

[0005] For example, Patent Document 1 proposes 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; a nonlinear optical element that wavelength-converts the pulsed light output from the solid-state amplifier and outputs the converted pulsed light; a semiconductor optical amplifier that is disposed between the seed light source and the solid-state amplifier and amplifies the pulsed light output from the seed light source; and a control unit.

[0006] The control unit is configured to execute a gain switching control process for driving the seed light source at a desired repetition rate, and a semiconductor optical amplifier control process for controlling an injection current of the semiconductor optical amplifier in accordance with the repetition rate of the seed light source. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] WO2018 / 203483 publication Summary of the Invention [Problem to be solved by the invention]

[0008] The above-described laser light source device can produce ultraviolet laser light with a large output power of several watts to several tens of watts. If the pulsed light output from such a laser light source device can be branched into multiple systems of pulsed light using a branching optical system, it becomes possible to process multiple objects simultaneously, dramatically improving processing efficiency.

[0009] However, ultraviolet laser light with a high output power causes a photochemical reaction between oxygen and impurities in the air, such as sulfurous acid, and the reaction products adhere to the surface of the branching optical element, causing it to become cloudy, or cause a photochemical reaction with the components of the branching optical element, causing the optical element to become cloudy. Not only does this cause deterioration of the optical element, but it also poses the problem of causing a decrease in the output power of the ultraviolet laser light at the processing point.

[0010] An object of the present invention is to provide a wavelength conversion mechanism and a wavelength conversion method that can output multiple systems of ultraviolet laser light with high output power (pulse energy) without causing deterioration of the branching optical elements. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, a first characteristic configuration of the wavelength conversion mechanism according to the present invention is that it is a wavelength conversion mechanism that converts the wavelength of wavelength-converted light, which is pulsed laser light with a predetermined repetition frequency, into ultraviolet laser light, and is equipped with a branching optical system that spatially branches the wavelength-converted light, and a plurality of ultraviolet wavelength conversion elements that wavelength-convert each wavelength-converted light branched by the branching optical system into ultraviolet laser light.

[0012] When wavelength-converted light, i.e., long-wavelength laser light before being wavelength-converted to ultraviolet laser light by an ultraviolet wavelength conversion element, enters the branching optical system, the wavelength-converted light is spatially branched by the branching optical system, and each of the branched light beams is wavelength-converted to ultraviolet laser light by an ultraviolet wavelength conversion element. The wavelength of the wavelength-converted light may be any wavelength longer than the ultraviolet range, and may be the wavelength of the seed light. Therefore, the branching optical system is not deteriorated by ultraviolet laser light, and it is possible to stably obtain multiple systems of ultraviolet laser light from a single system of wavelength-converted light.

[0013] The second characteristic configuration is that, in addition to the first characteristic configuration described above, the branching optical system includes a polarizing optical element that adjusts the polarization state of the wavelength-converted light, and a polarizing beam splitter that branches the wavelength-converted light that has passed through the polarizing optical element.

[0014] Such a splitting optical system can be composed of a polarizing optical element and a polarizing beam splitter. When linearly polarized wavelength-converted light enters the polarizing beam splitter, it is split into two laser beams with orthogonal polarization directions. By adjusting the polarization state of the wavelength-converted light entering the polarizing beam splitter in advance using the polarizing optical element, it becomes possible to adjust the power ratio of the two pulsed beams split by the polarizing beam splitter.

[0015] The third characteristic configuration is that, in addition to the second characteristic configuration described above, the polarization optical element is composed of a wave plate or a Pockels cell that can be adjusted so that the distribution ratio of the P polarization component and the S polarization component of the wavelength-converted light becomes a predetermined ratio.

[0016] A wave plate or a Pockels cell can be suitably used to adjust the polarization state of the wavelength-converted light. For example, when a half-wave plate is used as the polarization optical element, the distribution ratio of the P-polarized component and the S-polarized component can be adjusted by rotating the half-wave plate around the optical axis. Furthermore, when a Pockels cell, which is an electro-optic modulator (EOM) used to switch the polarization direction of the laser light passing through, is used as the polarization optical element, the distribution ratio of the P-polarized component and the S-polarized component of the wavelength-converted light in the linearly polarized state can be adjusted to a predetermined ratio by adjusting the voltage applied to the EOM.

[0017] The fourth characteristic feature of the present invention is that, in addition to the first characteristic feature described above, the branching optical system is provided in a plurality of stages.

[0018] By providing multiple stages of branching optical systems, multiple systems of wavelength-converted light can be obtained by dividing the pulse energy from a single system of wavelength-converted light with high pulse energy, thereby further extending the life of the ultraviolet wavelength conversion element and enabling multiple systems of ultraviolet wavelength-converted light to be obtained stably over a long period of time.

[0019] The fifth characteristic feature of the present invention is that, in addition to any one of the first to fourth characteristic features described above, the ultraviolet wavelength conversion element is made of CLBO or BBO.

[0020] CLBO or BBO can be suitably used as the ultraviolet wavelength conversion element.

[0021] The wavelength conversion method according to the present invention is characterized in that it is a wavelength conversion method for converting wavelength-converted light, which is pulsed laser light having a predetermined repetition frequency, into ultraviolet laser light, and includes a branching step for spatially branching the wavelength-converted light using a branching optical system, and an ultraviolet wavelength conversion step for wavelength-converting each wavelength-converted light branched in the branching step into multiple lines of ultraviolet laser light using multiple ultraviolet wavelength conversion elements. [Effects of the Invention]

[0022] As described above, according to the present invention, it is possible to provide a wavelength conversion mechanism and a wavelength conversion method that can output multiple systems of ultraviolet laser light with high output power (pulse energy) without causing deterioration of the branching optical elements. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a block diagram of a laser light source device equipped with a wavelength conversion mechanism according to the present invention; [Figure 2] 1A is an explanatory diagram of a four-system branching optical system having two stages of branching optical systems, and FIG. 1B is an explanatory diagram of a branching optical system showing another embodiment. [Figure 3] FIG. 10 is a block diagram of a laser light source device equipped with a wavelength conversion mechanism according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser light source device including a wavelength conversion mechanism and a wavelength conversion method according to embodiments of the present invention will be described below. As shown in FIG. 1, the laser light source device 1 includes a seed light source 10 that outputs linearly polarized pulsed laser light at a predetermined repetition rate, an optical amplifier 20 that amplifies the laser light output from the seed light source 10, a wavelength conversion unit 40 that converts the wavelength of the laser light amplified by the optical amplifier 20, and a control unit 100.

[0025] A distributed feedback laser diode (hereinafter referred to as "DFB laser") that outputs laser light in a single longitudinal mode is used as the seed light source 10. The seed light source 10 is driven by a control unit 100 using a gain switching method, and the DFB laser outputs laser light S1 with a wavelength of 1064 nm, a single pulse, or a predetermined repetition rate arbitrarily selected within a range of several megahertz or less, and a desired pulse width of several nanoseconds or less, preferably several hundred picoseconds or less.

[0026] The gain switching method is a method for generating pulsed laser light with a short pulse width and high peak power by utilizing relaxation oscillation, a resonance phenomenon that appears in the frequency and time domains when an injection current is applied to a semiconductor laser.

[0027] A fiber amplifier or a solid-state amplifier can be used as the optical amplifier 20. An optical switch element 30 composed of an acousto-optic modulator (AOM) is provided downstream of the optical amplifier 20. When a gate signal is output from the control unit 100 to an RF driver that drives the acousto-optic modulator AOM, a diffraction grating is generated in the crystal that constitutes the acousto-optic element by a transducer (piezoelectric conversion element) to which a high-frequency signal is applied from the RF driver, and diffracted light of the laser light S3 incident on the acousto-optic element proceeds to the downstream stage via a reflecting mirror M1. When the RF driver is stopped, the pulsed light incident on the acousto-optic element passes through as is without being diffracted and is attenuated by an optical damper D.

[0028] That is, when the optical switch element 30 is turned on by a gate signal, the diffracted laser light S4 propagates from the optical amplifier 20 to a first wavelength conversion element 42 described below, and when the optical switch element 30 is turned off by a gate signal, the propagation of the laser light from the optical amplifier 20 to the first wavelength conversion element 42 is blocked. The optical switch element 30 makes it possible to selectively stop the output of laser light from the laser light source device 1. The optical switch element 30 is switched by a switching signal input to the control unit 100 from a laser processing apparatus that uses the laser light source device 1, or the like.

[0029] The wavelength conversion unit 40 includes a first wavelength conversion element 42 and a second wavelength conversion element 44. The laser light S4 having a wavelength of 1064 nm amplified by the optical amplifier 20 is incident on an LBO crystal (LiB3O5), which is a nonlinear optical element functioning as the first wavelength conversion element 42, and is wavelength-converted into laser light S5 having a wavelength of 532 nm. The reflecting mirrors M2 and M3 function as filters for separating the pulsed light having a wavelength of 1064 nm that has passed through the first wavelength conversion element 42, and the separated laser light is attenuated by an optical damper D.

[0030] The laser beam S5 wavelength-converted by the first wavelength conversion element 42 is split into two laser beams S6 and S7 via a splitting optical system 50, and then split into two laser beams S6 and S7. These laser beams are then split into two laser beams S6 and S7 via a splitting optical system 50. The splitting optical system 50 splits the laser beam S5 wavelength-converted by the first wavelength conversion element 42 into two laser beams S6 and S7. The splitting optical system 50 splits the laser beam S6 and S7 ... 10 ) and is wavelength-converted into deep ultraviolet light S8 and S9 with a wavelength of 266 nm. Reflecting mirrors M4 and M5 function as filters for separating the laser light with a wavelength of 532 nm generated by the first wavelength conversion element 42, and the separated laser light is attenuated by an optical damper D.

[0031] The branching optical system 50 spatially branches the wavelength-converted light, i.e., in this embodiment, the laser light before being wavelength-converted to ultraviolet laser light by the ultraviolet wavelength conversion element 44 (laser light S5 wavelength-converted by the first wavelength conversion element 42), and guides it to the second wavelength conversion element 44.

[0032] That is, the wavelength conversion mechanism 80 of the present invention is configured by the branching optical system 50 and the second wavelength conversion element 44, and the second wavelength conversion element 44 functions as the ultraviolet wavelength conversion element of the present invention. Hereinafter, the second wavelength conversion element 44 will be referred to as the ultraviolet wavelength conversion element 44. Note that the ultraviolet wavelength conversion element 44 is made of a CLBO crystal (CsLiBO 10 It is also possible to use a nonlinear optical element other than the above, such as a BBO crystal (β-BaB2O4).

[0033] The splitting optical system 50 includes a polarizing optical element 52 that adjusts the polarization state of the wavelength-converted light, a polarizing beam splitter 54 that splits the wavelength-converted light that has passed through the polarizing optical element 52, a reflecting mirror 55 that reflects one of the laser beams split by the polarizing beam splitter 54, and a second wave plate 56 onto which the reflected laser beam is incident.

[0034] When the wavelength-converted light output from the seed light source 10 and in a linearly polarized state enters the polarizing beam splitter 54, it is split into two systems of laser light whose polarization directions are orthogonal to each other. By adjusting the polarization state of the wavelength-converted light entering the polarizing beam splitter 54 in advance using the polarizing optical element 52, the intensity of the P-polarized component of the laser light that passes through the polarizing beam splitter 54 and the intensity of the S-polarized component of the laser light that is reflected by the polarizing beam splitter 54 are adjusted. Note that the polarizing beam splitter 54 may have the property of reflecting the P-polarized component and transmitting the S-polarized component.

[0035] In this embodiment, an adjustable wave plate is used as the polarization optical element 52 so that the distribution ratio between the P-polarized component and the S-polarized component of the wavelength-converted light becomes a predetermined ratio. A half-wave plate is used as the polarization optical element 52, and the distribution ratio between the P-polarized component and the S-polarized component can be adjusted by rotating the half-wave plate around the optical axis using an actuator such as an electromagnetic motor.

[0036] If the output of the 532 nm laser light is P1, the P-polarized light transmittance of polarizing beam splitter 54 is t1 (t1: 0 to 1), the S-polarized light reflectance of polarizing beam splitter 54 is r1 (r1: 0 to 1), and the distribution ratio of polarizing beam splitter 54 is OA1, then the output P2t of the laser light that passes through polarizing beam splitter 54 is P2t = t1 · OA1, and the output P2r of the laser light that is reflected by polarizing beam splitter 54 is P2r = r1 · (1 - OA1).

[0037] The control unit 100 adjusts the polarization transmission characteristics of the wave plate, which is the polarizing optical element 52, i.e., the component ratio between the P component and the S component, so that the output ratio P2t / P2r of the laser light split by the polarizing beam splitter 54 can be adjusted to a target value. The wave plate 56 is provided to match the polarization state of the laser light S6 passing through the polarizing beam splitter 54 and the polarization state of the laser light S7 reflected by the polarizing beam splitter 54 to P polarization, thereby adjusting the phase matching state with the ultraviolet wavelength conversion element 44 at the subsequent stage.

[0038] 1 illustrates waveform diagrams of the laser beam S5 incident on the branching optical system 50 and the laser beams S8 and S9 wavelength-converted by the ultraviolet wavelength conversion elements 44. The laser beams S8 and S9 wavelength-converted by the ultraviolet wavelength conversion elements 44 are adjusted so that their output timing is synchronized with that of the laser beam S5 incident on the branching optical system 50 and their output powers are half that of the laser beam S5. For example, two 10 W laser beams S8 and S9 can be obtained from the 20 W laser beam S5.

[0039] By providing the branching optical system 50 in a stage preceding the ultraviolet wavelength conversion element 44, there is no need for a branching optical system that branches the ultraviolet laser light, which would cause deterioration of optical elements after wavelength conversion by the ultraviolet wavelength conversion element 44. Furthermore, the polarizing optical element 52 provided in a stage preceding the polarizing beam splitter 54 can appropriately adjust the output power of the ultraviolet laser light wavelength-converted by each ultraviolet wavelength conversion element 44. Even in the laser light source device 1 that outputs such high-power deep ultraviolet laser light, deterioration of the branching optical system 50 does not occur.

[0040] The reflecting mirrors M4 and M5 function as filters for separating the pulsed light of 532 nm wavelength that passes through the ultraviolet wavelength conversion element 44, and the separated laser light is attenuated by the optical damper D.

[0041] Although not shown, a portion of the laser beams S8, S9 wavelength-converted by each ultraviolet wavelength conversion element 44 is guided to a photosensor by a respective reflecting mirror, and the output intensities of the two laser beams detected by the photosensor are input to the control unit 100. Based on the values ​​of the respective photosensors, the control unit 100 adjusts the polarization transmission characteristics of the polarizing optical element 52 so that the laser beams S8, S9 wavelength-converted by each ultraviolet wavelength conversion element 44 have predetermined target intensities.

[0042] A power density adjusting unit 60 composed of a beam expander is provided between the polarizing optical element 52 and the polarizing beam splitter 54. The power density adjusting unit 60 adjusts the power density of the laser light incident on the ultraviolet wavelength conversion element 44 to maintain the pulse energy required for wavelength conversion of the wavelength-converted light to deep ultraviolet. The power density adjusting unit 60 can adjust the wavelength conversion efficiency to deep ultraviolet by the ultraviolet wavelength conversion element 44 to a good value.

[0043] 2(a) shows a branching optical system 50 in which the above-mentioned branching optical systems are cascaded in two stages. For example, a first-stage branching optical system 501 includes a polarization optical element 521 made of a wavelength plate that adjusts the linear polarization state of laser light in the infrared region with a wavelength of 1064 nm or laser light in the visible light region with a wavelength of 532 nm (green light in this example), a polarization beam splitter 541 that branches the laser light that has passed through the polarization optical element 521, and a reflection mirror 551 that reflects one of the laser lights branched by the polarization beam splitter 541, and a second-stage branching optical system 502 having a similar configuration is provided for each of the first-stage branching optical systems 501, thereby enabling branching into four systems.

[0044] By adjusting the polarization transmission characteristics of the polarization optical elements 521 and 522, the intensity of the P-polarized component of the laser light that passes through the polarization beam splitters 541 and 542 and the intensity of the S-polarized component of the laser light that is reflected by the polarization beam splitters 541 and 542 are adjusted.

[0045] The wave plate 562 is provided to match the polarization state of the laser light passing through the polarizing beam splitter 542 with the polarization state of the laser light reflected by the polarizing beam splitter 542 to P polarization, thereby adjusting the phase matching state for the downstream ultraviolet wavelength conversion element 44.

[0046] In this example, the output timing is synchronized with the laser beam S5 entering the branching optical system 50, and adjustments are made to obtain ultraviolet laser beams with output powers that are 1 / 4 of the original. For example, four systems of 5 W laser beams can be obtained from the 20 W laser beam S5.

[0047] As described above, by providing multiple branching optical systems, it becomes possible to output multiple laser beams. For example, if a branching optical system is provided for each of two branches of laser beam, the laser beam can be branched into four branches of laser beam, and if a branching optical system is provided for each of the four branches of laser beam, the laser beam can be branched into eight branches of laser beam.

[0048] The branching optical system 50 using a wave plate as the polarizing optical element 52 is not limited to the configuration shown in Figures 1 and 2(a), but may include a polarizing optical element that adjusts the polarization state of the wavelength-converted light, and a polarizing beam splitter that branches the wavelength-converted light that has passed through the polarizing optical element.

[0049] 2(b), the branching optical system 50 may include a polarizing beam splitter 54 that branches the laser beam S5 having a wavelength of 532 nm, a wave plate 52A that adjusts the linear polarization state of the laser beam that has passed through the polarizing beam splitter 54, a reflection mirror 55 that reflects the laser beam reflected by the polarizing beam splitter 54, and a wave plate 52B that adjusts the linear polarization state of the laser beam reflected by the reflection mirror 55. The wave plates 52A and 52B are each composed of a half-wave plate, and each is equipped with a motor that serves as an actuator for rotating the incident surface orthogonally to the optical axis of the incident laser beam. Reference numeral 56 denotes a wave plate 56 that is located upstream of the polarizing beam splitter 54 and whose transmittance for the P-polarized component and the S-polarized component can be manually adjusted.

[0050] It is also possible to use a Pockels cell, which is an electro-optic modulator (EOM) used to switch the polarization direction of the laser light passing through, as the polarization optical element 52. By adjusting the voltage applied to the electro-optic modulator, it is possible to adjust the distribution ratio of the P-polarized component and the S-polarized component of the linearly polarized wavelength-converted light to a predetermined ratio.

[0051] 3 shows a branching optical system 50 that uses a Pockels cell as a polarization optical element 52. The configuration other than the branching optical system 50 is the same as that shown in FIG. The distribution ratio between the P-polarized component and the S-polarized component of the wavelength-converted light in a linearly polarized state is adjusted to a predetermined ratio by the Pockels cell. The wavelength-converted light, whose distribution ratio between the P-polarized component and the S-polarized component has been adjusted to a predetermined ratio by the Pockels cell, is then incident on the polarizing beam splitter 54, where the P-polarized component and the S-polarized component are separated and extracted. The predetermined ratio is not limited to a specific value, but is preferably set to a value such that the beam intensities of the P-polarized component and the S-polarized component are equal, for example.

[0052] In the embodiment described above, a configuration has been described in which a laser beam having a wavelength of 1064 nm is output from the seed light source 10, is wavelength-converted by the first wavelength conversion element 42 to a laser beam having a wavelength of 532 nm, and is then wavelength-converted to a laser beam having a wavelength of 266 nm by the ultraviolet wavelength conversion element 44. However, the wavelength of the seed light, the converted wavelength by the first wavelength conversion element 42, and the converted wavelength by the ultraviolet wavelength conversion element 44 are not limited to the values ​​described above, and it is possible to select a seed light source having an appropriate wavelength depending on the application, such as 1030 nm, 1550 nm, or 976 nm as the wavelength of the seed light.

[0053] Furthermore, it is possible to generate harmonics, sum frequencies, and difference frequencies with these wavelengths as fundamental waves through nonlinear optical elements. Nonlinear optical elements other than those mentioned above can also be used as nonlinear optical elements. For example, instead of the CLBO crystal, which is an ultraviolet wavelength conversion element, BBO crystal, KBBF crystal, SBBO crystal, KABO crystal, BABO crystal, etc. can be used.

[0054] That is, the wavelength conversion mechanism 80 according to the present invention may be provided with a branching optical system that causes laser light to be incident on each of the ultraviolet wavelength conversion elements, which are second wavelength conversion elements. In other words, it may be provided with a branching optical system in front of the wavelength conversion elements that convert the wavelength into ultraviolet laser light.

[0055] The seed light source 10 is not limited to a DFB laser, and a general Fabry-Perot type semiconductor laser other than a DFB laser can also be used. Also, the seed light source 10 is not limited to a pulsed laser light driven by a gain switching method.

[0056] As described above, the wavelength conversion method according to the present invention is a wavelength conversion method for converting wavelength-converted light, which is pulsed laser light having a predetermined repetition frequency, into ultraviolet laser light, and includes a branching step for spatially branching the wavelength-converted light using a branching optical system, and an ultraviolet wavelength conversion step for wavelength-converting each wavelength-converted light branched in the branching step into multiple lines of ultraviolet laser light using multiple ultraviolet wavelength conversion elements.

[0057] The branching optical system preferably includes a polarizing optical element that adjusts the polarization state of the wavelength-converted light, and a polarizing beam splitter that branches the wavelength-converted light that has passed through the polarizing optical element. The polarizing optical element is preferably configured as a wave plate or a Pockels cell that can be adjusted so that the distribution ratio between the P-polarized component and the S-polarized component of the wavelength-converted light is a predetermined ratio.

[0058] The above-described embodiment is merely an example of the present invention, and the scope of the present invention is not limited by the description. Furthermore, it goes without saying that the specific circuit configuration of each part and the optical elements used in the circuit can be appropriately selected or modified within the scope of the effects of the present invention. [Explanation of symbols]

[0059] 1: Laser light source device 10: Seed light source 20: Optical amplifier 30: Optical switch element 40: Wavelength conversion unit 42: First wavelength conversion element 44: Ultraviolet wavelength conversion element (second wavelength conversion element) 50: Branching optical system 52: Deflecting optical elements (wave plate, Pockels cell) 54: Polarizing beam splitter 60: Power density adjustment section 80: Wavelength conversion mechanism 100: Control unit

Claims

1. A wavelength conversion mechanism that converts wavelength-converted light, which is pulsed laser light having a predetermined repetition frequency, into ultraviolet laser light, a branching optical system that spatially branches the wavelength-converted light; a plurality of ultraviolet wavelength conversion elements for converting the wavelength of each wavelength-converted light beam split by the splitting optical system into ultraviolet laser light; A wavelength conversion mechanism comprising:

2. 2. The wavelength conversion mechanism according to claim 1, wherein the branching optical system comprises a polarizing optical element that adjusts the polarization state of the wavelength-converted light, and a polarizing beam splitter that branches the wavelength-converted light that has passed through the polarizing optical element.

3. 3. The wavelength conversion mechanism according to claim 2, wherein the polarization optical element is composed of a wave plate or a Pockels cell that can be adjusted so that the distribution ratio of the P-polarized component and the S-polarized component of the wavelength-converted light becomes a predetermined ratio.

4. 2. The wavelength conversion mechanism according to claim 1, wherein the branching optical system is provided in a plurality of stages.

5. 5. The wavelength conversion mechanism according to claim 1, wherein the ultraviolet wavelength conversion element is made of CLBO or BBO.

6. A wavelength conversion method for converting wavelength-converted light, which is pulsed laser light having a predetermined repetition frequency, into ultraviolet laser light, comprising: a branching step of spatially branching the wavelength-converted light using a branching optical system; The wavelength conversion method further comprises an ultraviolet wavelength conversion step of converting the wavelength-converted light beams branched in the branching step into a plurality of ultraviolet laser beams using a plurality of ultraviolet wavelength conversion elements.

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