Wavelength conversion mechanism and wavelength conversion method

Abstract

This wavelength conversion mechanism comprises: a branch optical system including a Pockels cell that adjusts and outputs a beam to be wavelength-converted, which is a pulsed laser beam of a predetermined repetition frequency, such that the distribution ratio between a P polarization component and an S polarization component becomes a predetermined ratio on a pulse-by-pulse basis in a time domain, and a polarization beam splitter that branches, on the basis of the predetermined ratio, the beam to be wavelength-converted adjusted to the predetermined ratio; and multiple ultraviolet-region wavelength conversion elements that wavelength-convert each beam to be wavelength-converted branched by the branch optical system into a laser beam in an ultraviolet region, each ultraviolet-region wavelength conversion element being caused to function as a filter for preventing wavelength conversion, into the laser beam in the ultraviolet region, of a pulsive noise light component included between pulses having a high distribution ratio of the P polarization component and a pulsive noise light component included between pulses having a high distribution ratio of the S polarization component.

Description

Wavelength conversion mechanism and wavelength conversion method

[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.

[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.

[0007] WO2018 / 203483 publication

[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.

[0011] In order to achieve the above-mentioned object, a first characteristic configuration of a wavelength conversion mechanism according to the present invention is a wavelength conversion mechanism that wavelength-converts wavelength-converted light, which is pulsed laser light having a predetermined repetition frequency, into ultraviolet laser light, and is equipped with a branching optical system including a Pockels cell that adjusts the wavelength-converted light on a pulse-by-pulse basis in the time domain so that the distribution ratio of P-polarized components to S-polarized components is a predetermined ratio and outputs the adjusted wavelength-converted light, and a polarizing beam splitter that branches the wavelength-converted light adjusted to the predetermined ratio by the Pockels cell based on the predetermined ratio, and a plurality of ultraviolet wavelength conversion elements that wavelength-convert each of the wavelength-converted light branches off by the branching optical system into ultraviolet laser light, and is characterized in that each ultraviolet wavelength conversion element functions as a filter that prevents wavelength conversion of pulsative noise light components contained between pulses having a high distribution ratio of the P-polarized component and pulsative noise light components contained between pulses having a high distribution ratio of the S-polarized component, into ultraviolet laser light.

[0012] A Pockels cell is an electro-optic modulator (EOM) used to switch the polarization direction of laser light. By adjusting the voltage applied to the electro-optic modulator, for example, in synchronization with the repetition rate of the wavelength-converted light, the ratio of the P-polarized and S-polarized components of the wavelength-converted light can be adjusted to a predetermined ratio. When the wavelength-converted light, whose ratio of the P-polarized and S-polarized components has been adjusted to a predetermined ratio by a Pockels cell utilizing this principle, is incident on a polarizing beam splitter, the P-polarized and S-polarized components are separated and alternately extracted, for example, in synchronization with the pulse repetition rate of the wavelength-converted light. In other words, the wavelength-converted light is split into multiple beams in the time domain without attenuation of the pulse energy.

[0013] Due to the characteristics of the Pockels cell, the wavelength-converted light separated into an S-polarized component contains a P-direction component of very low intensity, and the wavelength-converted light separated into a P-polarized component contains an S-direction component of very low intensity. Therefore, pulsed noise light containing a P-direction component of very low intensity, which is contained in the wavelength-converted light separated into an S-polarized component, is superimposed between pulses of the P-polarized component reflected by or transmitted through the polarizing beam splitter, and pulsed noise light containing an S-direction component of very low intensity, which is contained in the wavelength-converted light separated into a P-polarized component, is superimposed between pulses of the S-polarized component reflected by or transmitted through the polarizing beam splitter.

[0014] However, since the ultraviolet wavelength conversion element functions as a filter that prevents the wavelength conversion of the pulsating noise light components contained between pulses with a high distribution ratio of P-polarized components and the pulsating noise light components contained between pulses with a high distribution ratio of S-polarized components into ultraviolet laser light, the wavelength conversion of these pulsating noise light components with small intensity is prevented.

[0015] As a result, only the P-polarized component and the S-polarized component having a high distribution ratio adjusted to a predetermined ratio by the Pockels cell are wavelength-converted into ultraviolet laser light by the ultraviolet wavelength conversion element.

[0016] Therefore, the repetition frequency of the wavelength-converted light incident on each ultraviolet wavelength conversion element is lower than the repetition frequency of the wavelength-converted light before branching, which extends the life of the ultraviolet wavelength conversion element and maintains the pulse intensity of the wavelength-converted light to obtain wavelength-converted light in the ultraviolet range. By using such wavelength-converted light in laser processing, high-precision processing can be achieved over a long period of time. For example, in drilling, a high-power deep ultraviolet laser pulse can be used with a small number of pulses, i.e., in a short time, to achieve a uniform shape.

[0017] The second characteristic feature of the present invention is that, in addition to the first characteristic feature described above, the ultraviolet wavelength conversion element is made of CLBO or BBO.

[0018] As the ultraviolet wavelength conversion element, CLBO or BBO can be suitably used.

[0019] A wavelength conversion method according to the present invention is a wavelength conversion method for wavelength-converting wavelength-converted light, which is pulsed laser light having a predetermined repetition frequency, into laser light in the ultraviolet region, comprising: a polarization adjustment step of adjusting the wavelength-converted light by a Pockels cell in a time domain on a pulse-by-pulse basis so that a distribution ratio of P-polarized components to S-polarized components is a predetermined ratio, and outputting the adjusted wavelength-converted light; a branching step of branching the wavelength-converted light, adjusted to the predetermined ratio in the polarization adjustment step, based on the predetermined ratio by a polarized beam splitter; and a pulse having a high distribution ratio of the P-polarized component among the wavelength-converted light beams branched in the branching step. and a filtering step, which is executed in parallel with the ultraviolet wavelength conversion step, of using each ultraviolet wavelength conversion element to prevent the wavelength conversion, into ultraviolet laser light, of pulsed noise light components contained between pulses of pulses with a high distribution ratio of the P-polarized component and pulsed noise light components contained between pulses of pulses with a high distribution ratio of the S-polarized component, among the wavelength-converted light components branched in the branching step, by each ultraviolet wavelength conversion element.

[0020] 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.

[0021] Fig. 1 is a block diagram of a laser light source device using a wavelength conversion mechanism according to the present invention. Fig. 2A is an explanatory diagram of a wavelength conversion mechanism equipped with a branching optical system and an ultraviolet wavelength conversion element. Fig. 2B is an explanatory diagram of waveforms of the main parts of the wavelength conversion mechanism. Fig. 2C is an explanatory diagram of a wavelength conversion mechanism equipped with a power density adjustment unit. Fig. 2B is an explanatory diagram of a wavelength conversion mechanism equipped with branching optical systems arranged in multiple stages.

[0022] Hereinafter, an embodiment of a laser light source device equipped with a wavelength conversion mechanism and a wavelength conversion method according to the present invention will be described. 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.

[0023] 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 having 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 converted into a nonlinear optical element, such as an LBO crystal (LiB ３ O ５ The pulsed light having a wavelength of 1064 nm that has passed through the first wavelength conversion element 42 is then incident on the first wavelength conversion element 42 and 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 the optical damper D.

[0028] The laser beam S5 wavelength-converted by the first wavelength conversion element 42 is branched into two laser beams S6 and S7 via a branching optical system 50, and is then converted into a laser beam S7 by a CLBO crystal (CsLiB ６ O １０The reflected light is incident on the first wavelength conversion element 42 and converted into deep ultraviolet light S8 and S9 having a wavelength of 266 nm. The reflecting mirrors M4 and M5 function as filters for separating the laser light having a wavelength of 532 nm generated by the first wavelength conversion element 42, and the separated laser light is attenuated by the optical damper D.

[0029] The branching optical system 50 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), into pulse units in the time domain and guides the light to each ultraviolet wavelength conversion element.

[0030] 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 a CLBO crystal (CsLiB ６ O １０ ), nonlinear optical elements other than BBO crystal (β-BaB ２ O ４ ) can also be used.

[0031] The splitting optical system 50 includes a Pockels cell 52 that adjusts the wavelength-converted light so that the distribution ratio of the P-polarized component and the S-polarized component becomes a predetermined ratio in the time domain and outputs the adjusted light, and a polarizing beam splitter 54 that splits, based on the predetermined ratio, the wavelength-converted light adjusted to the predetermined ratio by the Pockels cell 52. By adjusting the distribution ratio of the P-polarized component and the S-polarized component, it is possible to adjust the pulse energy of each deep-ultraviolet light wavelength-converted by each ultraviolet wavelength conversion element 44.

[0032] As also shown in FIG. 2A , in this embodiment, the wavelength-converted light S5 is switched in the time domain by the Pockels cell 52 to either a P-polarized component or an S-polarized component and output, and the wavelength-converted light switched into the P-polarized component and the S-polarized component by the Pockels cell 52 is separated into the P-polarized component and the S-polarized component by the polarizing beam splitter 54.

[0033] The S-polarized component S7 transmitted through the polarizing beam splitter 54 is incident along the optical axis on one of the ultraviolet wavelength conversion elements 44, and deep-ultraviolet laser light S9 is output. The P-polarized component S6 reflected by the polarizing beam splitter 54 is reflected by the reflecting mirror 56, and after its polarization direction is rotated by 90° by the half-wave plate 58, it is incident on the other ultraviolet wavelength conversion element 44, and deep-ultraviolet laser light S8 is output. The half-wave plate 58 is intended to adjust the polarization direction of the incident light so that a phase matching condition for the downstream ultraviolet wavelength conversion element 44 is established, and the half-wave plate 58 may be installed on the side of the S-polarized component S7 transmitted through the polarizing beam splitter 54.

[0034] The Pockels cell 52 is an electro-optic modulator (EOM) used to switch the polarization direction through which laser light passes. By adjusting the voltage applied to the electro-optic modulator, for example, in synchronization with the repetition frequency of the wavelength-converted light, the distribution ratio between the P-polarized component and the S-polarized component of the wavelength-converted light output from the seed light source 10 and in a linearly polarized state is adjusted to a predetermined ratio. The wavelength-converted light, the distribution ratio between the P-polarized component and the S-polarized component of which has been adjusted to a predetermined ratio by the Pockels cell, is incident on the polarizing beam splitter, whereby the P-polarized component and the S-polarized component are separated and extracted. The predetermined ratio may be any value that allows the polarizing beam splitter 54 to separate and extract the P-polarized component and the S-polarized component, and is not limited to a specific value.

[0035] When wavelength-converted light S5 with a predetermined repetition rate f is incident on Pockels cell 52, whose polarization direction is switched by control unit 100 at a period of 1 / f, the light is separated in the time domain into an S-polarized component with a repetition rate of f / 2 and a P-polarized component with a repetition rate of f / 2. As shown in Figure 2A, when the laser light output from Pockels cell 52 is incident on polarizing beam splitter 54, the light is split into an S-polarized component S7 with a repetition rate of f / 2 and a P-polarized component S6 with a repetition rate of f / 2. The S-polarized component S7 and the P-polarized component S6 are out of phase with each other by half a period (1 / f).

[0036] As shown in FIG. 2B, due to the characteristics of the Pockels cell 52, there is a small intensity of S-polarized component S between the pulses of the wavelength-converted light S7 that has been separated into S-directional components. Ｌ The wavelength-converted light S6 split into P-directional components contains pulsed noise light components including a small elliptically polarized component, and a small intensity P-polarized component P Ｌ The noise light component includes pulsed noise components including small elliptically polarized components.

[0037] Therefore, as shown in FIG. 2B, a pulsed noise light component of slight intensity shifted by half a period (1 / f) is superimposed on the P-polarized light component S6 of repetition frequency f / 2 reflected by the polarized beam splitter 54, and a pulsed noise light component of slight intensity shifted by half a period (1 / f) is superimposed on the S-polarized light component of repetition frequency f / 2 that has passed through the polarized beam splitter 54.

[0038] However, the pulsating noise light component with a low intensity is not wavelength converted because its incident intensity is not sufficient to allow wavelength conversion by the ultraviolet wavelength conversion element 44, and ultimately wavelength-converted light S8 corresponding to a P-polarized component with a repetition frequency of f / 2 and a phase shift of half a period (½f) and wavelength-converted light S9 corresponding to an S-polarized component with a repetition frequency of f / 2 and a phase shift of half a period (½f) from that of the wavelength-converted light S8 are output from the ultraviolet wavelength conversion element 44.

[0039] In other words, the ultraviolet wavelength conversion element 44 functions as a filter that removes, without wavelength conversion, the P-direction component of slight intensity that is shifted by half a period and superimposed on the P-polarized component of repetition frequency f / 2 that is branched in pulse units in the time domain by the branching optical system 50, and the S-direction component of slight intensity that is shifted by half a period and superimposed on the S-polarized component of repetition frequency f / 2.

[0040] By providing the branching optical system 50 in the 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 the optical elements after wavelength conversion by the ultraviolet wavelength conversion element 44. Even in a laser light source device 1 that outputs such high-power deep ultraviolet laser light, deterioration of the branching optical system 50 does not occur. Furthermore, the wavelength-converted light incident on each ultraviolet wavelength conversion element 44 has its repetition frequency reduced to f / 2 while substantially maintaining the intensity (pulse energy) of the wavelength-converted light having the repetition frequency f, thereby extending the life of the ultraviolet wavelength conversion elements 44.

[0041] 1, the laser light source device 1 includes a power density adjusting unit 60 that adjusts the power density of the laser light incident on the ultraviolet wavelength conversion element 44 to maintain the pulse energy of the wavelength-converted deep ultraviolet laser light at a target value. The power density adjusting unit 60 can be configured with a beam expander provided between the Pockels cell 52 and the polarizing beam splitter 54. The power density adjusting unit 60 makes it possible to most efficiently convert the wavelength of the wavelength-converted light to deep ultraviolet, and also to extend the life of the ultraviolet wavelength conversion element 44.

[0042] 1, the beam expander constituting the power density adjusting unit 60 is disposed inside the branching optical system 50, specifically between the Pockels cell 52 and the polarizing beam splitter 54, but it may be disposed in a stage upstream of the ultraviolet wavelength conversion element 44. For example, as shown in FIG. 2C, in addition to being disposed between the Pockels cell 52 and the polarizing beam splitter 54, the beam expander may be disposed in a stage upstream of the Pockels cell 52, immediately before the ultraviolet wavelength conversion element 44, or the like.

[0043] In the embodiment described above, an example has been described in which the laser light having a wavelength of 532 nm, which has been wavelength-converted by the first wavelength conversion element 42, is branched into multiple paths by the branching optical system 50. However, the branching optical system 50 may be arranged in the optical path upstream of the first wavelength conversion element 42. That is, the branching optical system 50 may be configured to branch the laser light having a wavelength of 1064 nm output from the seed light source 10. In this case, it is preferable to arrange the branching optical system 50 in a stage subsequent to the optical amplifier 20. This is because if the branching optical system 50 is arranged in a stage prior to the optical amplifier 20, an optical amplifier 20 is required for each branched light, which increases costs.

[0044] In other words, the wavelength conversion mechanism 80 according to the present invention only needs to include a branching optical system 50 that branches the wavelength-converted light, and a plurality of ultraviolet wavelength conversion elements 44 that respectively convert the wavelength of the wavelength-converted light branched by the branching optical system 50, and it is permissible to place other optical elements between the branching optical system 50 and the ultraviolet wavelength conversion elements 44.

[0045] 3 shows branching optical systems 50A and 50B in which the branching optical systems 50 of the first embodiment are cascaded in two stages. The branching optical system 50A in the first stage includes a first Pockels cell 52A that switches the incident wavelength-converted light into either a P-polarized component or an S-polarized component in the time domain and outputs the converted light, a polarizing beam splitter 54A that splits the wavelength-converted light separated into the P-polarized component and the S-polarized component by the first Pockels cell 52A, and a first reflecting mirror 56A.

[0046] The downstream branching optical system 50B includes a second Pockels cell 52B that switches the incident wavelength-converted light into either a P-polarized component or an S-polarized component in the time domain and outputs the converted light, a polarizing beam splitter 54B that branches the wavelength-converted light separated into the P-polarized component and the S-polarized component by the second Pockels cell 52B, and a second reflecting mirror 56B.

[0047] For example, 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 and a repetition rate of f is split by the first-stage splitting optical system 50A into a P-polarized component with a repetition rate of f / 2 and an S-polarized component with a repetition rate of f / 2 that is shifted in phase from the P-polarized component by half a period (1 / f).

[0048] Furthermore, the P-polarized light component with a repetition rate of f / 2 and the S-polarized light component with a repetition rate of f / 2 are each branched by the second-stage branching optical system 50B into a P-polarized light component with a repetition rate of f / 4 and an S-polarized light component with a repetition rate of f / 4 that is shifted in phase from the P-polarized light component by a half period (½f). The wavelength-converted light is branched into four systems by the second-stage branching optical system 50B. Furthermore, either the P-polarized light component or the S-polarized light component of the wavelength-converted light branched into four systems is polarized by 90° by the wave plate 58 and is incident on the four ultraviolet wavelength conversion elements 44 provided downstream.

[0049] As described above, by providing multiple stages of branching optical systems 50, 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, and if a branching optical system is provided for each of four branches of laser beam, the laser beam can be branched into eight branches. Although the repetition frequency decreases with each branching, deep ultraviolet light with high output intensity can be obtained over a long period of time without causing a decrease in output power (pulse energy) while suppressing deterioration of the ultraviolet wavelength conversion element 44.

[0050] 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.

[0051] Furthermore, it is possible to generate harmonics, sum frequencies, and difference frequencies with these wavelengths as fundamental waves through a nonlinear optical element. Nonlinear optical elements other than those described above can also be used as the nonlinear optical element. For example, instead of a CLBO crystal, a BBO crystal, a KBBF crystal, an SBBO crystal, a KABO crystal, a BABO crystal, etc. can be used.

[0052] That is, the wavelength conversion mechanism 80 according to the present invention may include a plurality of ultraviolet wavelength conversion elements 44 and a branching optical system 50 that causes laser light to be incident on each of the ultraviolet wavelength conversion elements 44. In other words, it may include a branching optical system in front of the wavelength conversion elements that convert the wavelength into ultraviolet laser light.

[0053] The seed light source 10 is not limited to a DFB laser, and may be a general Fabry-Perot type semiconductor laser other than a DFB laser. The seed light source 10 is also not limited to a pulsed laser light driven by a gain switching method.

[0054] As described above, the wavelength conversion method according to the present invention is a wavelength conversion method for wavelength-converting wavelength-converted light, which is pulsed laser light with a predetermined repetition frequency, into ultraviolet laser light, and includes a polarization adjustment step of adjusting the wavelength-converted light by a Pockels cell in a time domain on a pulse-by-pulse basis so that the distribution ratio of P-polarized components to S-polarized components is a predetermined ratio, and outputting the adjusted wavelength-converted light; a branching step of branching the wavelength-converted light, which has been adjusted to the predetermined ratio in the polarization adjustment step, based on the predetermined ratio by a polarized beam splitter; and a step of branching the wavelength-converted light, which has been branched in the branching step, into pulses with a high distribution ratio of P-polarized components. and an ultraviolet wavelength conversion step in which pulses having a high distribution ratio of S-polarized components are wavelength converted into ultraviolet laser light by each ultraviolet wavelength conversion element to obtain multiple systems of ultraviolet laser light; and a filtering step which is executed in parallel with the ultraviolet wavelength conversion step and uses each ultraviolet wavelength conversion element to prevent wavelength conversion into ultraviolet laser light of pulsating noise light components contained between pulses having a high distribution ratio of P-polarized components and pulsating noise light components contained between pulses having a high distribution ratio of S-polarized components, among the wavelength-converted lights branched in the branching step, by each ultraviolet wavelength conversion element.

[0055] 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.

[0056] 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: Pockels cell 54: Polarizing beam splitter 56: Reflecting mirror 60: Power density adjustment unit (beam expander) 80: Wavelength conversion mechanism 100: Control unit

Claims

1. 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, comprising: a branching optical system including a Pockels cell that adjusts the wavelength-converted light so that the distribution ratio of P-polarized and S-polarized components is a predetermined ratio on a pulse-by-pulse basis in the time domain and outputs the adjusted light; and a polarizing beam splitter that branches the wavelength-converted light, which has been adjusted to the predetermined ratio by the Pockels cell, based on the predetermined ratio; and a plurality of ultraviolet wavelength conversion elements that wavelength-convert each of the wavelength-converted light branches off by the branching optical system into ultraviolet laser light, wherein each ultraviolet wavelength conversion element functions as a filter that prevents the wavelength conversion of pulsating noise light components contained between pulses with a high distribution ratio of P-polarized components and pulsating noise light components contained between pulses with a high distribution ratio of S-polarized components, into ultraviolet laser light.

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

3. A wavelength conversion method for wavelength-converting wavelength-converted light, which is pulsed laser light with a predetermined repetition frequency, into ultraviolet laser light, comprising: a polarization adjustment step in which a Pockels cell is used to adjust the wavelength-converted light in the time domain on a pulse-by-pulse basis so that the distribution ratio of P-polarized components to S-polarized components is a predetermined ratio, and output the adjusted light; a branching step in which a polarized beam splitter is used to branch the wavelength-converted light, which has been adjusted to the predetermined ratio in the polarization adjustment step, based on the predetermined ratio; and an ultraviolet wavelength conversion step in which, of the wavelength-converted light beams branched in the branching step, pulses with a high distribution ratio of P-polarized components and pulses with a high distribution ratio of S-polarized components are wavelength-converted into ultraviolet laser light by ultraviolet wavelength conversion elements, thereby obtaining multiple lines of ultraviolet laser light. a filtering step, which is performed in parallel with the ultraviolet wavelength conversion step, for preventing, by each ultraviolet wavelength conversion element, the wavelength conversion of pulsed noise light components contained between pulses having a high distribution ratio of the P-polarized component and pulsed noise light components contained between pulses having a high distribution ratio of the S-polarized component, among each wavelength-converted light branched in the branching step, into ultraviolet laser light.

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