JP2018159896A - Wavelength conversion method, wavelength conversion device and laser light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength conversion device that can deal with temperature fluctuations of a nonlinear optical element caused by the power of light to be subjected to wavelength conversion and can achieve stable wavelength conversion with high power.SOLUTION: The wavelength conversion device includes: a nonlinear optical element 70 that converts laser light having a specific wavelength incident to an action area R into laser light at a desired wavelength by a harmonic wave generation method or a light mixing method; and a first temperature adjusting mechanism 73 that adjusts the temperature of the nonlinear optical element 70 by a temperature adjusting element 72. The wavelength conversion device also includes: a second temperature adjusting mechanism 75 that irradiates the action region R with laser light in a wavelength range not contributing to the wavelength conversion, output from a first auxiliary light source 74; and a temperature control unit 78 that controls the temperature of the nonlinear optical element 70 to a target temperature based on the heat amount supplied from the first temperature adjusting mechanism 73 and the heat amount supplied from the second temperature adjusting mechanism 75.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a wavelength conversion method, a wavelength conversion device, and a laser light source device.

  In recent years, laser light has been used for various processes. Laser light having a wavelength in the vicinity of 532 nm to 1064 nm has high energy intensity, and is suitably used for various processing such as cutting or welding of metal or glass. In addition, laser light in the deep ultraviolet region with a wavelength of 200 nm to 350 nm is used for processing electronic materials and composite materials.

  A laser light source device that outputs laser light having a shorter wavelength than the near infrared region includes a seed light source that outputs laser light having a wavelength in the near infrared region, an optical amplifier that amplifies the laser light output from the seed light source, A nonlinear optical element that converts the wavelength of the laser light amplified by the optical amplifier into a target wavelength using a second harmonic generation method or a sum frequency generation method is provided.

As such a nonlinear optical element, for example, an LBO crystal (LiB ₃ O ₅ ) that converts a laser pulse light having a wavelength of 1064 nm output from a seed light source to a wavelength of 532 nm, or a pulse light having a wavelength of 532 nm is converted to a wavelength of 266 nm. A CLBO crystal (CsLiB ₆ O ₁₀ ) or the like is used.

  Patent Documents 1 and 2 disclose an optical wavelength conversion system that can realize an all-solid-state ultraviolet laser oscillator that stably achieves high conversion efficiency and can withstand practical use by using a nonlinear optical crystal.

  The optical wavelength conversion system includes a laser oscillator that oscillates coherent light having a specific wavelength λ, a nonlinear optical crystal that emits light having a wavelength of 1 / 2λ using light from the laser oscillator as incident light, and the nonlinear optical Heating means for heating and holding the crystal at 200 to 600 ° C. By heating and holding at 200 ° C. or higher, the influence of two-photon absorption is reduced, the decrease in conversion efficiency is eliminated, and a power of about 1 to 2 W can be stably obtained.

  In Patent Document 3, the refractive index changes due to heat generation caused by two-photon absorption generated in a lithium tetraborate single crystal, and phase matching is lost. As a result, output loss or destabilization occurs or beam quality is reduced. There has been disclosed a wavelength converter for solving the problem of deterioration and obtaining an ultraviolet laser suitable for precision processing.

  The wavelength conversion device includes a heating block that covers an outer surface excluding an incident end face and an emission end face of the wavelength conversion element and heats the wavelength conversion element from the outside with a heater, a temperature sensor that detects a temperature of the heating block, and the temperature Based on the temperature detected by the sensor, it has a temperature control unit that controls the heating block to a constant temperature. When the length of the wavelength conversion element is L, the vertical and horizontal widths of the wavelength conversion element are L / 4 or less. In addition, the heating block is protruded by L / 3 or more in the length direction from the incident end face and the outgoing end face of the wavelength conversion element.

  Patent Document 4 discloses a wavelength conversion device having a configuration capable of stably performing wavelength conversion by a wavelength conversion optical element having deliquescence for a long period of time with a high conversion efficiency with a simple configuration.

  The wavelength conversion device includes: a heater that heats the wavelength conversion optical element; a temperature detection unit that detects a temperature of the wavelength conversion optical element; and a heater that controls driving of the heater based on the temperature detected by the temperature detection unit. A temperature control unit that adjusts the temperature of the element to be maintained within a predetermined temperature range, and a shift mechanism that shifts the light receiving position of the wavelength conversion optical element by a predetermined amount, the light receiving position of the wavelength conversion optical element is shifted Sometimes, the temperature control unit is configured to control the driving of the heater so that the temperature of the wavelength conversion optical element becomes the optimum temperature at which the output intensity of the laser light whose wavelength is converted within a predetermined temperature range is the maximum. ing.

  In any of the wavelength conversion devices described above, a heater, a Peltier element, or the like is used to adjust the temperature of the wavelength conversion optical element.

JP 2003-50412 A JP 2008-181151 A JP 2004-191963 A JP 2011-59324 A

  However, in order to obtain ultraviolet light having a power of, for example, about 200 W to 400 W, which is sufficiently larger than the power of conventional ultraviolet light obtained by using a nonlinear optical element, when the power of incident light to the nonlinear optical element is increased, The temperature of the nonlinear optical element deviates from the temperature range where the wavelength conversion efficiency is maximized due to the heat generation of the nonlinear optical element caused by two-photon absorption that occurs in the wavelength conversion process. The problem that conversion efficiency falls arises.

  Therefore, it is conceivable to suppress temperature fluctuations with heaters and Peltier elements used to adjust the temperature of nonlinear optical elements. However, since nonlinear optical elements generally require time for heat transfer, the wavelength conversion process is necessary. It was difficult to suppress the generated temperature fluctuation with a heater or a Peltier element.

  In view of the above-described problems, the object of the present invention is to cope with the temperature fluctuation of the nonlinear optical element caused by the power of the wavelength-converted light, and to stably obtain a large power wavelength change, A wavelength converter and a laser light source device are provided.

  In order to achieve the above-mentioned object, the first characteristic configuration of the wavelength conversion method according to the present invention is the first feature of adjusting the temperature of the nonlinear optical element using the temperature control element as described in claim 1 of the claims. A wavelength that is converted into laser light having a desired wavelength by a harmonic generation method or an optical mixing method by entering laser light having a specific wavelength into the action region of the nonlinear optical element that has been adjusted to a predetermined temperature. A second wavelength conversion method configured to irradiate the working region with auxiliary light in a wavelength region that does not contribute to wavelength conversion from the first auxiliary light source to heat the nonlinear optical element. Based on the temperature adjustment step, the amount of heat supplied to the nonlinear optical element in the first temperature adjustment step, and the amount of heat supplied to the nonlinear optical element in the second temperature adjustment step, the temperature of the nonlinear optical element is set to a target temperature. Adjust the temperature to In that it includes a temperature control step.

  In order to adjust the temperature of the nonlinear optical element to the target temperature, the amount of heat supplied by the first temperature adjustment step using the temperature adjustment element and the first auxiliary light source that outputs auxiliary light in a wavelength region that does not contribute to wavelength conversion are used. The amount of heat supplied by the two temperature adjustment steps is adjusted. In the first temperature control step, heat is supplied from the temperature control element that is a heat generation source to the nonlinear optical element having a large thermal time constant by heat conduction, whereas in the second temperature control step, the light is output from the first auxiliary light source. Heat is supplied by the transition of the state of atoms and electrons constituting the nonlinear optical element to a higher energy level by the auxiliary light. Accordingly, the temperature of the nonlinear optical element is statically adjusted in the first temperature adjustment step, and the temperature of the nonlinear optical element is dynamically adjusted in the second temperature adjustment step. In addition, sudden temperature fluctuations can be effectively suppressed.

  According to the second characteristic configuration described in claim 2, in addition to the first characteristic configuration described above, the temperature control step includes the nonlinear optical element generated in a wavelength conversion process with respect to the laser beam having the specific wavelength. The amount of heat supplied from the first auxiliary light source in the second temperature adjustment step is controlled so as to suppress the temperature fluctuation.

  In the process of wavelength conversion of laser light having a specific wavelength incident on the nonlinear optical element, that is, wavelength-converted light, by the harmonic generation method or the light mixing method, the temperature of the nonlinear optical element rises due to two-photon absorption or the like. Even when the conversion efficiency decreases, the energy of the auxiliary light emitted from the first auxiliary light source to the working region is adjusted to suppress the temperature increase of the nonlinear optical element, thereby suppressing the wavelength conversion efficiency from decreasing. Will be able to.

  In the third feature configuration, as described in claim 3, in addition to the first or second feature configuration described above, the second temperature adjustment step uses the wavelength of the auxiliary light from the first auxiliary light source. The nonlinear optical element is irradiated from the output side of the converted light.

  Of the working region from the incident end face to the exit end face of the nonlinear optical element, the heat generation distribution generated in the wavelength conversion process tends to be higher on the exit end face side. By irradiating the nonlinear optical element with the auxiliary light from the first auxiliary light source from the output side of the wavelength converted light, a temperature distribution matched to the heat generation distribution generated in the wavelength conversion process can be realized before the wavelength conversion. If the energy of the auxiliary light from the first auxiliary light source is adjusted so as to maintain the temperature distribution corresponding to the heat generation distribution generated in the wavelength conversion process, wavelength conversion with always good wavelength conversion efficiency can be realized.

  In the fourth feature configuration, as described in the fourth aspect, in addition to the third feature configuration described above, the second temperature control step may assist the wavelength region from the second auxiliary light source that does not contribute to wavelength conversion. The method includes a step of irradiating the nonlinear optical element with light from the input side of the laser beam having the specific wavelength.

  By irradiating the auxiliary light from the second auxiliary light source from the input side of the nonlinear optical element, the temperature of the working region that does not rise so much in the wavelength conversion process is adjusted to a temperature with good wavelength conversion efficiency, so that the wavelength conversion as a whole Efficiency can be improved.

  The first characteristic configuration of the wavelength converter according to the present invention is that, as described in claim 5, a laser beam having a desired wavelength is generated from a laser beam having a specific wavelength incident on the working region by a harmonic generation method or an optical mixing method. A wavelength conversion device configured to include a nonlinear optical element that converts the wavelength into a wavelength and a first temperature control mechanism that adjusts the temperature of the nonlinear optical element using a temperature control element, the wavelength conversion being output from the first auxiliary light source Based on a second temperature control mechanism that irradiates the working region with auxiliary light in a wavelength region that does not contribute to the non-linearity, a heat supply amount from the first temperature control mechanism, and a heat supply amount from the second temperature control mechanism, the nonlinearity And a temperature controller that adjusts the temperature of the optical element to a target temperature.

  According to the second characteristic configuration described in the sixth aspect, in addition to the first characteristic configuration described above, the temperature control unit includes the nonlinear optical element generated in a wavelength conversion process with respect to the laser beam having the specific wavelength. The amount of heat supplied from the second temperature control mechanism is controlled so as to suppress the temperature fluctuation.

  In the third feature configuration, as described in claim 7, in addition to the first or second feature configuration described above, the second temperature control mechanism is configured such that the auxiliary light from the first auxiliary light source has a wavelength. The nonlinear optical element is irradiated from the output side of the converted light.

  In the fourth feature configuration, as described in claim 8, in addition to the third feature configuration described above, the second temperature control mechanism may be configured such that the nonlinear optical element is provided from the laser light input side of the specific wavelength. Is provided with a second auxiliary light source for irradiating auxiliary light.

  In the fifth feature configuration, in addition to any one of the first to fourth feature configurations described above, the auxiliary feature output from the auxiliary light source provided in the second temperature control mechanism is provided. The wavelength of the light is in the range of 1 to 11 μm.

  The characteristic configuration of the laser light source device according to the present invention includes a seed light source that outputs pulsed light by a gain switching method, a fiber amplifier that amplifies pulsed light output from the seed light source, and A solid-state amplifier for amplifying pulsed light output from a fiber amplifier, and a wavelength converter having any one of the first to fifth characteristic configurations described above for wavelength-converting and outputting pulsed light output from the solid-state amplifier It is in the point equipped with.

  As described above, according to the present invention, the wavelength conversion method and the wavelength conversion capable of stably changing the wavelength of the large power in response to the temperature variation of the nonlinear optical element due to the power of the wavelength-converted light. An apparatus and a laser light source device can be provided.

Block configuration diagram of a laser light source device incorporating a wavelength conversion device according to the present invention (A) is explanatory drawing of the temperature change of the nonlinear optical element after wavelength conversion processing is started in the state maintained at the optimal temperature, (b) is wavelength conversion processing in the state maintained at the temperature lower than optimal temperature. Explanatory diagram of temperature change of nonlinear optical element after it has been started Illustration of wavelength converter Characteristic diagram of light transmittance of nonlinear optical element CLBO In (a), pulsed light of frequencies ω1 and ω2 is incident on the nonlinear optical element, pulsed light of frequency ω3 is emitted by the sum frequency, and heating laser light of frequency ω4 is incident from the emission side of the wavelength converted light. (B) is an explanatory diagram of a state in which wavelength-converted light having a constant power is output after t = t1, and (c) is a state in which the temperature is adjusted to T0 by a temperature control element. Explanatory drawing of the temperature fluctuation | variation of the nonlinear optical element after the laser beam for heating is irradiated at t0, (d) is explanatory drawing of the change state of the intensity | strength of the laser beam for heating. In (a), pulsed light of frequencies ω1 and ω2 is incident on a nonlinear optical element having a length Lc in the direction (z) along the optical axis, pulsed light of frequency ω3 is emitted by the sum frequency, and frequency ω4 (B) is an explanatory view of the wavelength conversion power distribution in the direction (z) along the optical axis of the nonlinear optical element, (c) ) Is an explanatory view of the temperature distribution in the direction (z) along the optical axis of the nonlinear optical element when the laser beam for heating is irradiated without wavelength conversion, and (d) is the wavelength without irradiating the laser beam for heating. Explanatory drawing of temperature distribution of the direction (z) along the optical axis of the nonlinear optical element at the time of conversion In (a), pulsed light of frequencies ω1 and ω2 is incident on a nonlinear optical element having a length Lc in the direction (z) along the optical axis, pulsed light of frequency ω3 is emitted by the sum frequency, and frequency ω4 (B) is an illustration of a state in which the laser beam for heating is incident from the output side of the wavelength-converted light and the laser beam for heating of frequency ω5 is input from the incident side of the pulsed light. An explanatory view of the distribution of wavelength conversion power in the direction (z) along the axis, (c) is the direction (z) along the optical axis of the nonlinear optical element when both heating laser beams are irradiated without wavelength conversion. FIG. 4D is an explanatory diagram of the temperature distribution in the direction (z) along the optical axis of the nonlinear optical element when wavelength conversion is performed without irradiating the heating laser beam on the emission side. (A) is explanatory drawing of the incident path | route of the auxiliary light to a nonlinear optical element, (b) is explanatory drawing of the incident path | route of the auxiliary light to the nonlinear optical element of another aspect.

  Hereinafter, embodiments of a wavelength conversion method, a wavelength conversion device, and a laser light source device according to the present invention will be described. FIG. 1 shows an exemplary configuration of the laser light source device 1. In the laser light source device 1, a light source unit 1A, a fiber amplification unit 1B, a solid amplification unit 1C, and a wavelength conversion unit 1D are arranged along the optical axis L, and further control the light source unit 1A, the wavelength conversion unit 1D, and the like. The control unit 100 is configured to be configured.

  The light source unit 1A includes a seed light source 10, a seed light source driver D1, an optical isolator ISL1, and the like. The fiber amplifying unit 1B includes two-stage fiber amplifiers 20 and 30 each having excitation light sources 21 and 31 and multiplexers 22 and 32 each composed of a laser diode, optical isolators ISL2 and ISL3, and an optical switch element. 40 etc. Further, a band pass filter BPF1 is provided in the subsequent stage of the fiber amplifier 20.

  The solid-state amplifier 1C includes a solid-state amplifier 50, reflection mirrors M1, M2, and M3, a lens L1, a collimator CL2, and the like. The wavelength conversion unit 1D includes a first wavelength conversion unit 1E and a second wavelength conversion unit 1F. The wavelength conversion unit 1D includes nonlinear optical elements 60 and 70, respectively, and can be converted to a desired wavelength by a harmonic generation method. . The second wavelength conversion unit 1F is a wavelength conversion device according to the present invention.

  The light source unit 1A, the fiber amplification unit 1B, and the solid amplification unit 1C are accommodated in one metal case made of aluminum, the wavelength conversion unit 1D is accommodated in another metal case, and the metal case of the wavelength conversion unit 1D. In addition, the second wavelength conversion unit 1F is accommodated in another metal case. The division of the functional blocks 1A to 1D accommodated in each case is not particularly limited, but the second wavelength conversion unit 1F is a metal that can be purged with a purge gas depending on the characteristics of the nonlinear optical element accommodated therein. Housed in a case.

  Laser pulse light with a wavelength of 1064 nm output from the seed light source 10 (hereinafter also simply referred to as “pulse light”) is amplified by the two-stage fiber amplifiers 20 and 30 and further amplified to a desired level by the one-stage solid-state amplifier 50. Is done. The pulsed light amplified by the solid-state amplifier 50 is wavelength-converted to a wavelength of 532 nm by the nonlinear optical element 60 and further wavelength-converted to a wavelength of 266 nm by the nonlinear optical element 70 and output.

  A distributed feedback laser diode (hereinafter referred to as “DFB laser”) that outputs a single longitudinal mode laser beam is used as the seed light source 10, and is controlled by a control signal output from the control unit 100 to which the gain switching method is applied. From the DFB laser, pulse light having a desired pulse width of several hundred picoseconds or less is output at a desired frequency of one shot or several megahertz or less.

  Pulse light having a pulse energy of several picojoules to several hundred picojoules output from the seed light source 10 is finally pulsed by the fiber amplifiers 20 and 30 and the solid-state amplifier 50 with a pulse energy of several tens of microjoules to several tens of millijoules. After being amplified to light, it is converted into deep ultraviolet rays having a wavelength of 266 nm by being input to the two-stage nonlinear optical elements 60 and 70.

  The pulsed light output from the seed light source 10 is amplified by the first-stage fiber amplifier 20 via the optical isolator ISL1. As the fiber amplifiers 20 and 30, rare earth-doped optical fibers such as ytterbium (Yb) -doped fiber amplifiers pumped by a pumping light source 21 having a predetermined wavelength (for example, 975 nm) are used. Since the lifetime of the inversion distribution of the fiber amplifier 20 is in the order of milliseconds, the energy excited by the excitation light source 21 is efficiently transferred to pulsed light having a frequency of 1 kilohertz or more.

  The pulse light amplified by about 30 dB by the first-stage fiber amplifier 20 is input to the subsequent-stage fiber amplifier 30 via the optical isolator ISL2 and amplified by about 25 dB. The pulsed light amplified by the subsequent fiber amplifier 30 is beam-shaped by the collimator CL1, passes through the optical isolators ISL3 and ISL4, and is then guided to the solid-state amplifier 50 to be amplified by about 25 decibels.

  Between the collimator CL1 and the solid-state amplifier 50, an acousto-optic modulator AOM (Acousto-Optic Modulator) that incorporates an acousto-optic element and functions as the optical switch element 40, and a pair of reflecting mirrors M1 and M2 are disposed. An optical isolator ISL4 that guides the pulsed light amplified by the solid-state amplifier 50 to the nonlinear optical element 60 is disposed between M1 and M2.

  The optical isolators ISL1 to ISL4 described above are polarization-dependent optical isolators that block the return light by rotating the polarization plane in the reverse direction and the reverse direction using the magneto-optic effect, Each optical element disposed on the upstream side along the optical axis is provided for avoiding thermal destruction by high-intensity return light.

  As the solid-state amplifier 50, a solid-state laser medium such as Nd: YVO4 crystal or Nd: YAG crystal is preferably used. The solid-state laser medium is configured to be excited by the excitation light output from the excitation light source 51 including a laser diode having an emission wavelength of 808 nm or 888 nm and beam-formed by the collimator CL2.

  The pulsed light that has passed through the optical switch element 40 is incident on the solid-state amplifier 50 through the reflection mirrors M1 and M2 and amplified, and then reflected by the reflection mirror M3 and re-enters the solid-state amplifier 50 to be amplified again. Is done. That is, it is configured to be amplified on the forward path and the return path of the solid-state amplifier 50. The lens L1 is for beam shaping.

  The pulse light amplified by the solid-state amplifier 50 is reflected by the reflection mirror M2 and the optical isolator ISL4, enters the nonlinear optical elements 60 and 70 of the wavelength conversion unit 1D, and is converted into a desired wavelength by a harmonic generation method, and then output. Is done.

The first wavelength conversion unit 1E incorporates an LBO crystal (LiB ₃ O ₅ ) that is a nonlinear optical element 60, and the second wavelength conversion unit 1F incorporates a CLBO crystal (CsLiB ₆ O ₁₀ ) that is a nonlinear optical element 70. It is. The pulse light having a wavelength of 1064 nm output from the seed light source 10 is wavelength-converted to a wavelength of 532 nm by the nonlinear optical element 60, and further wavelength-converted to a wavelength of 266 nm by the nonlinear optical element 70.

  The reflection mirrors M4 and M8 function as a filter for separating pulsed light with a wavelength of 1064 nm output from the nonlinear optical element 60, and the reflection mirror M6 is for separating pulsed light with a wavelength of 532 nm output from the nonlinear optical element 70. Each of the separated pulse lights is attenuated by an optical damper.

The second wavelength conversion unit 1F is provided with a stage 71 that is a scanning mechanism that moves a CLBO crystal (CsLiB ₆ O ₁₀ ) in a plane orthogonal to the optical axis. When UV rays are irradiated to the same place for a long time, optical damage occurs in the CLBO crystal (CsLiB ₆ O ₁₀ ), resulting in deterioration of intensity distribution and decrease in wavelength conversion output. Therefore, the CLBO crystal (CsLiB ₆ O ₁₀ ) is used at a predetermined time. This is to shift the irradiation position of the pulsed light on the.

  The stage 71 is provided with a temperature adjustment element for adjusting the temperature of the nonlinear optical element 70, and a first temperature adjustment mechanism that controls the temperature adjustment element so that the temperature of the nonlinear optical element 70 is maintained at a predetermined temperature is the control unit 100. Built in. As the temperature control element, a heater or a Peltier element is preferably used.

  The control unit 100 includes a circuit block including an FPGA (Field Programmable Gate Array), peripheral circuits, and the like, and drives a plurality of logic elements based on a program stored in advance in a storage unit in the FPGA. Each block constituting 1 is controlled sequentially, for example. The control unit 100 is connected to a storage unit necessary for executing a phase matching method described later.

  In addition to the FPGA, the control unit 100 may include a microcomputer, a storage unit, a peripheral circuit such as an IO, or a programmable logic controller (PLC). .

  Specifically, the control unit 100 outputs a trigger signal having a predetermined pulse width to the driver D1 of the DFB laser that is the seed light source 10 in order to cause the seed light source 10 to emit light using the gain switching method. When a pulse current corresponding to the trigger signal is applied from the drive circuit to the DFB laser, relaxation oscillation occurs, and only the first wave having the highest emission intensity immediately after the start of light emission due to relaxation oscillation consists of the second and subsequent sub-pulses. A pulsed laser beam not included is output. The gain switching method refers to a method of generating pulsed light having a short pulse width and high peak power using such relaxation oscillation.

  Further, the control unit 100 outputs a gate signal to the RF driver D2 that drives the acousto-optic modulator AOM that is the optical switch element 40. A diffraction grating is generated in a crystal constituting the acoustooptic device by a transducer (piezoelectric conversion device) to which a high frequency signal is applied from the RF driver D2, and diffracted light of pulsed light incident on the acoustooptic device is incident on the reflection mirror M1. When the RF driver D2 is stopped, the pulsed light incident on the acoustooptic device passes through without being diffracted and does not enter the reflection mirror M1. The light that has passed through the acoustooptic device when the RF driver D2 is stopped is attenuated by an optical damper.

  When the optical switch element 40 is turned on by the gate signal, the diffracted light propagates from the fiber amplifier 30 to the solid-state amplifier 50. When the optical switch element 40 is turned off by the gate signal, light propagation is blocked from the fiber amplifier 30 to the solid-state amplifier 50. The

Further, the control unit 100 controls the stage 71 to move stepwise in order to shift the irradiation position of the pulsed light to the CLBO crystal (CsLiB ₆ O ₁₀ ) at a predetermined time. For example, the control unit 100 monitors the intensity of the wavelength-converted ultraviolet rays, and when the monitored intensity history matches a predetermined pattern, the control unit 100 moves the stage 71 to irradiate the CLBO crystal (CsLiB ₆ O ₁₀ ) with pulsed light. Shift position.

  The stage 71 is controlled by the control unit 100 via the motor driver D3 and / or the Y-direction moving motor so that the stage 71 can move on the XY plane perpendicular to the optical axis of the pulsed light. It is connected to the drive.

  In the process in which narrowband pulsed light having a center wavelength of 1064 nm outputted from the seed light source 10 is guided to the fiber amplifier 20 and amplified, the spectrum width is unnecessarily widened by self-phase modulation, Raman scattering, etc., and further, spontaneous emission light noise (Hereinafter referred to as “ASE noise (amplified spontaneous emission noise)”), the S / N ratio of the light pulse decreases. In the process in which such pulsed light is guided to the subsequent fiber amplifier 30 and amplified, the bandwidth is further increased, and the ASE noise level is increased.

  An optical switch element 40 is provided to efficiently amplify pulsed light in a wavelength range that can be converted by the wavelength converting unit 1D to obtain deep ultraviolet pulsed light having a desired intensity. The control unit 100 allows the optical switch element 40 to allow light propagation during the output period of the pulsed light from the seed light source 10 and to prevent light propagation during a period different from the output period of the pulsed light from the seed light source 10. Configured to control.

  When the optical switching element 40 is turned off by the control unit 100 during a period different from the output period of the pulsed light from the seed light source 10, the propagation of ASE noise to the subsequent solid-state amplifier 50 is prevented during that period. It is avoided that the energy in the active region of the solid-state amplifier 50 is wasted.

  As the optical switch element 40, an electro-optical element that turns on and off light by an electric field using intensity modulation of EO modulation may be used. A micro peristaltic mirror (MEMS (Micro Electro Mechanical Systems)) manufactured by a micromachining technology may be used. It may be configured to switch whether or not the output of the fiber amplifier 30 is propagated to the solid-state amplifier 50 by using a slight swing angle of the swing mirror. Alternatively, a polarization device capable of dynamically switching the polarization state and controlling transmission and blocking of light may be used. That is, the optical switch element only needs to be composed of a dynamic optical element.

  The pulsed light amplified by the solid-state amplifier 50 enters the LBO crystal, which is the nonlinear optical element 60 of the first wavelength conversion unit 1E, from the escape port on the input side of the optical isolator ISL4 and is wavelength-converted into pulsed light having a wavelength of 532 nm. .

  Further, the pulsed light is expanded into a beam diameter of 0.2 to 0.3 mm to about 2 to 3 mm by the lenses L2 and L3, and then enters the CLBO crystal which is the nonlinear optical element 70 of the second wavelength conversion unit 1F. The wavelength of the light is converted into pulsed light having a wavelength of 266 nm, and is output after being shaped into a perfect circle through a plurality of optical lenses. Note that the pulsed light expanded by the lenses L2 and L3 is reduced in diameter by an optical system disposed at the subsequent stage of the laser light source device 1, and is irradiated on the irradiation target after increasing the power per unit area.

  After wavelength conversion by the nonlinear optical element 70, pulsed light having a wavelength of 266 nm is reflected by the reflecting mirror M6, further reflected by the reflecting mirror M5, and output from the exit window. The pulsed light having a wavelength of 532 nm output from the nonlinear optical element 70 passes through the reflection mirror M6 and is attenuated by the optical damper.

  A reflection mirror M10 serving as a sampler is disposed between the reflection mirror M5 and the exit window, and is configured to reflect a small part (about 0.5%) of pulsed light having a wavelength of 266 nm. The reflected light from the reflection mirror M10 is further reflected by the reflection mirror M9 and enters the light receiving element PS1. The power is detected by the light receiving element PS1. The power detected by the light receiving element PS1 is input to the control unit 100, and the phase matching condition and the like of the nonlinear optical element 70 are adjusted based on the value.

  In the upper part of FIG. 2A, pulse light having a wavelength of 532 nm is incident at time t0 and the wavelength conversion process is started in a state where the target temperature To is maintained at the optimum temperature Topt by the first temperature control mechanism described above. The state is shown. The optimum temperature Topt is the temperature in the temperature range where the wavelength conversion efficiency is the highest.

  2A, the cylindrical region around the optical axis of the pulsed light incident on the action region of the nonlinear optical element 70, that is, the region subjected to the wavelength conversion action from the input end to the output end of the nonlinear optical element 70, It is shown that when pulsed light having a wavelength of 532 nm and high energy intensity is incident, the temperature of the working region gradually rises and causes a temperature increase of ΔT from the optimum temperature Topt.

  The middle stage of FIG. 2A shows a state in which the wavelength conversion efficiency decreases as the temperature of the working region of the nonlinear optical element 70 increases. As a result, the power of deep ultraviolet light having a wavelength of 266 nm gradually decreases and becomes stable.

  In the upper part of FIG. 2B, pulse light having a wavelength of 532 nm is incident at time t0 while the target temperature To is maintained at a temperature lower than the optimum temperature Topt by the first temperature control mechanism described above, and wavelength conversion processing is performed. The started state is shown.

  In the lower part of FIG. 2B, when pulse light having a high energy intensity with a wavelength of 532 nm is incident on the working region of the nonlinear optical element 70, the temperature of the working region gradually rises to increase the temperature from the optimum temperature To by ΔT. It is shown that the temperature is stabilized at the invited optimum temperature Topt.

  In the middle part of FIG. 2 (b), it is shown that the wavelength conversion efficiency gradually increases as the temperature of the working region of the nonlinear optical element 70 increases, and the wavelength conversion efficiency becomes maximum at the optimum temperature Topt.

  In the case of FIG. 2A, there is a problem that the wavelength conversion efficiency gradually decreases from the state where the wavelength is converted with the maximum wavelength conversion efficiency. In the case of FIG. 2B, the wavelength conversion is performed with the maximum wavelength conversion efficiency. There is a problem that it takes time to complete. In such a case, if the temperature of the nonlinear optical element 70 having a large thermal time constant is controlled by the temperature control element that is a heat generation source, it takes a very long time to adjust the temperature to the optimum temperature Topt, and the temperature is adjusted to the optimum temperature Topt early. Difficult to warm. Therefore, the present invention includes a second temperature control mechanism that irradiates the working region with auxiliary light in a wavelength region that does not contribute to wavelength conversion output from the first auxiliary light source.

  As shown in FIG. 3, the second wavelength conversion unit 1F has a desired wavelength (this embodiment) from a laser beam having a specific wavelength (532 nm in this embodiment) incident on the action region R by a harmonic generation method or an optical mixing method. For the wavelength conversion output from the first auxiliary light source 74, the nonlinear optical element 70 that converts the wavelength to 266 nm) laser light, the first temperature control mechanism 73 that controls the temperature of the nonlinear optical element 70 using the temperature control element 72, and the like. Based on the second temperature control mechanism 75 that irradiates the action region R with auxiliary light in a wavelength region that does not contribute, the amount of heat supplied from the first temperature control mechanism 73, and the amount of heat supplied from the second temperature control mechanism 75, nonlinear optics A temperature control unit 78 for adjusting the temperature of the element 70 to the target temperature is provided. The temperature control unit 78 is incorporated in the control unit 100. Reference numeral 77 denotes a temperature sensor. The first temperature control mechanism 73 is configured by, for example, a heater control circuit, and the second temperature control mechanism 75 is configured by a semiconductor laser drive circuit.

  The temperature control unit 78 is configured to control the amount of heat supplied from the second temperature adjustment mechanism 75 to the nonlinear optical element 70 so as to suppress temperature fluctuations of the nonlinear optical element 70 that occur in the wavelength conversion process with respect to laser light of a specific wavelength. Has been.

  It is preferable that the second temperature control mechanism 75 is configured to irradiate the action region R of the nonlinear optical element 70 with the auxiliary light from the first auxiliary light source 74 from the output end side of the wavelength converted light. In the action region R from the incident end face to the exit end face of the nonlinear optical element 70, the heat generation distribution generated in the wavelength conversion process tends to be higher on the exit end face side.

  By irradiating the nonlinear optical element with the auxiliary light from the first auxiliary light source 74 from the output side of the wavelength converted light, a temperature distribution matched to the heat generation distribution generated in the wavelength conversion process can be realized before the wavelength conversion, As a result, if the energy of the auxiliary light from the first auxiliary light source 74 is adjusted so as to maintain the temperature distribution corresponding to the heat generation distribution generated in the wavelength conversion process, wavelength conversion with always good wavelength conversion efficiency can be realized.

  Further, it is more preferable that the second temperature control mechanism 75 includes a second auxiliary light source 76 that irradiates the operation region R of the nonlinear optical element 70 from the input end face side of the laser beam having the specific wavelength. By irradiating the auxiliary light from the second auxiliary light source 76 from the input end face side of the nonlinear optical element 70, the temperature of the working region that does not rise so much in the wavelength conversion process is adjusted to a temperature with good wavelength conversion efficiency. As a result, the wavelength conversion efficiency can be improved.

  As the first auxiliary light source 74 and the second auxiliary light source 76, a light source capable of outputting auxiliary light in the wavelength range of 1 μm to 11 μm, preferably in the range of wavelength 1 μm to 3 μm, from near infrared to far infrared is preferably used. A laser light source such as a semiconductor laser that outputs coherent light is preferably used, and a light source that outputs incoherent light such as an LED or a lamp can also be used.

  The auxiliary light having the wavelength output from the first auxiliary light source 74 and the second auxiliary light source 76 does not contribute to wavelength conversion and is used to heat the nonlinear optical element 70. By irradiating the action area R with the auxiliary light from the first auxiliary light source 74, the action area R can be efficiently heated, and by stopping the irradiation, the temperature can be lowered efficiently.

FIG. 4 shows the light transmission characteristics of a CLBO crystal (CsLiB ₆ O ₁₀ ) used as the nonlinear optical element 70. By irradiating the CLBO crystal subjected to wavelength conversion with an electromagnetic wave having appropriate absorption, the inside or the surface is directly heated. Based on FIG. 4, light in the wavelength range of 1 μm to 11 μm can be effectively used as auxiliary light, and in particular, light in the wavelength range of 1 μm to 3 μm is also effective as auxiliary light for temperature adjustment inside the crystal. It can be seen that it works. In this embodiment, since semiconductor lasers are used as the first auxiliary light source 74 and the second auxiliary light source 76, the “auxiliary light” may be expressed as “laser light” below.

  FIG. 5A shows an example of wavelength conversion to a laser beam having a desired wavelength by a light mixing method. In this example, pulsed light having a wavelength ω1 and a wavelength ω2 is incident on the nonlinear optical element 70 by a sum frequency generation method, which is an example of an optical mixing method, to obtain a wavelength ω3. The wavelength ω3 of the obtained wavelength converted light is ω3 = 1 / {(1 / ω1) + (1 / ω2)}. Further, the first auxiliary light source 74 emits laser light having a wavelength ω4 from the output end face side of the nonlinear optical element 70.

  As shown in FIG. 5C, the first auxiliary light source 74 is heated from time t0 in the state where the temperature of the nonlinear optical element 70 is initially adjusted to To by the amount of heat supplied from the first temperature adjustment mechanism 73. The laser is driven (see FIG. 5D), and the temperature of the nonlinear optical element 70 is controlled to the temperature Topt at which the maximum wavelength conversion efficiency is obtained by the energy.

  As shown in FIG. 5B, when the pulsed light of wavelength ω1 and wavelength ω2 is input for wavelength conversion at time t1 and the pulsed light of wavelength ω3 is output by the sum frequency generation method, In the conversion process, a temperature rise occurs in the action region of the nonlinear optical element 70.

  As shown in FIG. 5D, after the time t1, by reducing the intensity of the laser light having the wavelength ω4 emitted from the first auxiliary light source 74, the temperature rise generated in the wavelength conversion process is canceled out and nonlinear The temperature of the working region of the optical element 70 is maintained at a temperature Topt at which the maximum wavelength conversion efficiency is obtained.

  In FIG. 6A, pulsed light with wavelengths ω1 and ω2 is incident from the right end face of the nonlinear optical element 70 having a length Lc, pulsed light with wavelength ω3 is output from the left end face, and first light is output from the left end face. An example of a wavelength converter configured to irradiate laser light having a wavelength ω4 from an auxiliary light source 74 is shown. 6B, 6C, and 6D show the wavelength conversion power distribution or temperature distribution along the longitudinal direction of the nonlinear optical element 70 along the optical axis of the pulsed light having the wavelengths ω1 and ω2. Yes.

  FIG. 6B shows the wavelength conversion power distribution along the longitudinal direction of the nonlinear optical element 70 generated in the wavelength conversion process. The wavelength conversion power that causes heat generation gradually increases from the central portion to the output end side in the action region along the longitudinal direction. FIG. 6C shows a temperature distribution along the longitudinal direction of the nonlinear optical element 70 that is generated when the first auxiliary light source 74 is irradiated with laser light having a wavelength ω4 without performing wavelength conversion. FIG. 6D shows a temperature distribution that occurs along the longitudinal direction of the nonlinear optical element 70 when wavelength conversion is performed with the first auxiliary light source 74 turned off.

  Output from the first auxiliary light source 74 so that FIG. 6D showing the heat generation distribution generated in the wavelength conversion process and FIG. 6C showing the heat generation distribution generated by light irradiation from the first auxiliary light source 74 coincide. By selecting the wavelength ω4 of the emitted light in the range of 1 μm in the near infrared to 3 μm in the mid-infrared, the wavelength conversion process can be efficiently performed from the beginning.

  In FIG. 7A, pulsed light with wavelengths ω1 and ω2 is incident from the right end face of the nonlinear optical element 70 having a length Lc, pulse light with wavelength ω3 is output from the left end face, and first light is output from the left end face. An example of a wavelength conversion device configured such that the auxiliary light source 74 emits laser light having a wavelength ω4 and the second auxiliary light source 76 emits laser light having a wavelength ω5 from the right end surface is shown. 7B, 7C, and 7D show the wavelength conversion power distribution or temperature distribution along the longitudinal direction of the nonlinear optical element 70 along the optical axis of the pulsed light having the wavelengths ω1 and ω2. Yes.

  FIG. 7B shows the wavelength conversion power distribution along the longitudinal direction of the nonlinear optical element 70 generated in the wavelength conversion process. The wavelength conversion power that causes heat generation gradually increases from the central portion to the output end side in the action region along the longitudinal direction. FIG. 7C shows a nonlinear optical element that is generated when the first auxiliary light source 74 is irradiated with the laser light having the wavelength ω4 and the second auxiliary light source 76 is irradiated with the laser light having the wavelength ω5 without performing wavelength conversion. A temperature distribution along the longitudinal direction of 70 is shown. FIG. 7D shows a temperature distribution generated along the longitudinal direction of the nonlinear optical element 70 when wavelength conversion is performed with the first auxiliary light source 74 turned off and the second auxiliary light source 76 turned on.

  The region extending from the incident end face of the nonlinear optical element 70 to the center in the longitudinal direction can be adjusted to the optimum temperature Topt with high wavelength conversion efficiency by the second auxiliary light source 76, and the wavelength conversion efficiency can be improved.

  For example, when a semiconductor laser that outputs laser light with a wavelength of 1 μm to 3 μm with a low absorptance of the nonlinear optical element 70 is used as the auxiliary light source 74, wavelength conversion is performed so that the inside of the nonlinear optical element 70 can be adjusted appropriately. It is preferable to irradiate laser light along the optical axis of light.

  Such a configuration is shown in FIG. In FIG. 8A, the optical axis of the wavelength-converted light output from the nonlinear optical element 70 is deflected downward by the semi-transmissive mirror 79, and the laser light from the auxiliary light source 74 is semi-transmissive along the optical axis. It is configured to pass through the mirror 79 and enter the nonlinear optical element 70. An optical system that shapes the output light from the auxiliary light source 74 into parallel light or condenses it toward the incident surface of the nonlinear optical element 70 may be provided.

When a CO ₂ gas laser that outputs laser light having a wavelength of 10.6 μm, for example, is used as the auxiliary light source 74, the nonlinear optical element 70 has a very high absorptance and is absorbed almost only on the surface. By irradiating the emitting end face of the optical element 70, a desired temperature gradient can be obtained more rapidly than at least when the first temperature control mechanism 73 is used.

  Such a configuration is shown in FIG. In FIG. 8B, the laser light from the auxiliary light source 74 is transmitted at an arbitrary angle of the nonlinear optical element 70 regardless of the semi-transmissive mirror 79 that deflects the optical axis of the wavelength-converted light output from the nonlinear optical element 70. Irradiation can be performed toward the emission end face.

  As described above, the temperature control unit 78 specifies the first temperature adjustment step for adjusting the temperature of the nonlinear optical element 70 using the temperature adjustment element 72 and the operation region of the nonlinear optical element 70 adjusted to a predetermined temperature. A wavelength conversion method configured to include a wavelength conversion step of inputting laser light of a wavelength and converting the wavelength of the laser light to a desired wavelength by a harmonic generation method or an optical mixing method is executed.

  More specifically, in the wavelength conversion method, the second temperature control step of irradiating the working region R with laser light in a wavelength region that does not contribute to wavelength conversion from the first auxiliary light source 74 and supplying heat to the nonlinear optical element 70; There is a temperature control step for adjusting the temperature of the nonlinear optical element 70 to a target temperature based on the amount of heat supplied to the nonlinear optical element 70 in one temperature adjustment step and the amount of heat supplied to the nonlinear optical element 70 in the second temperature adjustment step. Executed.

  In the temperature control step, the amount of heat supplied from the first auxiliary light source 74 in the second temperature control step is controlled so as to suppress temperature fluctuations of the nonlinear optical element 70 that occur in the wavelength conversion process with respect to laser light of a specific wavelength. It is configured.

  Then, the second temperature adjustment step changes the laser light from the first auxiliary light source 74 from the output side of the wavelength converted light so as to coincide with the heat generation distribution of the nonlinear optical element 70 generated in the wavelength conversion process for the laser light of the specific wavelength. The nonlinear optical element 70 is configured to irradiate.

  Further, the second temperature adjustment step includes a step of irradiating the nonlinear optical element 70 from the input side of the laser beam having a specific wavelength with a laser beam in a wavelength region that does not contribute to wavelength conversion from the second auxiliary light source 76. By irradiating the laser beam from the second auxiliary light source 76 from the input side of the nonlinear optical element 70, the temperature of the working region that does not rise so much in the wavelength conversion process is adjusted to a temperature with good wavelength conversion efficiency. The wavelength conversion efficiency can be improved.

  The laser light source device in which the wavelength conversion device according to the present invention is incorporated is not limited to a seed light source with an oscillation wavelength of 1064 nm. It is possible. Furthermore, it is possible to generate harmonics, sum frequencies, and difference frequencies having these wavelengths as fundamental waves through a nonlinear optical element. Nonlinear optical elements other than those described above can be used as the nonlinear optical element. For example, a BBO crystal, a KBBF crystal, an SBBO crystal, a KABO crystal, a BABO crystal, or the like can be used instead of the CLBO crystal.

  The plurality of embodiments described above are all descriptions of one embodiment of the present invention, and the scope of the present invention is not limited by the description. Needless to say, the specific circuit configuration of each part and the optical elements used in the circuit can be appropriately selected or modified as long as the effects of the present invention can be achieved.

1: Laser light source device 1F: Wavelength converter 10: Seed light source 20, 30: Fiber amplifier 40: Optical switch element 50: Solid state amplifier 60: Nonlinear optical element (LBO crystal)
70: Nonlinear optical element (CLBO crystal)
71: Stage 72: Temperature control element 73: First temperature control mechanism 74: First auxiliary light source 75: Second temperature control mechanism 76: Second auxiliary light source 77: Temperature sensor 78: Temperature control unit R: Action region

Claims (10)

A first temperature adjustment step of adjusting the temperature of the nonlinear optical element using the temperature adjustment element;
A wavelength conversion step of allowing laser light of a specific wavelength to enter the working region of the nonlinear optical element adjusted to a predetermined temperature and converting the wavelength of the laser light to a desired wavelength by a harmonic generation method or an optical mixing method. A wavelength conversion method comprising:
A second temperature control step of irradiating the working region with auxiliary light in a wavelength region that does not contribute to wavelength conversion from the first auxiliary light source and supplying heat to the nonlinear optical element;
A temperature at which the temperature of the nonlinear optical element is adjusted to a target temperature based on the amount of heat supplied to the nonlinear optical element in the first temperature adjustment step and the amount of heat supplied to the nonlinear optical element in the second temperature adjustment step Control steps;
A wavelength conversion method comprising:   The temperature control step controls the amount of heat supplied from the first auxiliary light source in the second temperature control step so as to suppress temperature fluctuation of the nonlinear optical element that occurs in a wavelength conversion process with respect to the laser light of the specific wavelength. Item 2. The wavelength conversion method according to Item 1. 3. The wavelength conversion method according to claim 1, wherein the second temperature adjusting step is configured to irradiate the nonlinear optical element with auxiliary light from the first auxiliary light source from an output side of the wavelength converted light.
(This coincides with the heat generation distribution of the nonlinear optical element generated in the wavelength conversion process for the laser light of the specific wavelength)   4. The wavelength according to claim 3, wherein the second temperature adjusting step includes a step of irradiating the nonlinear optical element from the input side of the laser beam having the specific wavelength with an auxiliary light in a wavelength region that does not contribute to wavelength conversion from the second auxiliary light source. Conversion method. A non-linear optical element that converts the wavelength of laser light incident on the active region into laser light of a desired wavelength by a harmonic generation method or a light mixing method, and a first temperature adjusting the non-linear optical element by a temperature adjusting element A wavelength conversion device configured to include a temperature control mechanism,
A second temperature control mechanism that irradiates the working region with auxiliary light in a wavelength region that does not contribute to wavelength conversion output from the first auxiliary light source;
A temperature control unit that regulates the temperature of the nonlinear optical element to a target temperature based on a heat supply amount from the first temperature control mechanism and a heat supply amount from the second temperature control mechanism;
A wavelength conversion device comprising:   The wavelength conversion according to claim 5, wherein the temperature control unit controls the amount of heat supplied from the second temperature control mechanism so as to suppress temperature fluctuation of the nonlinear optical element that occurs in a wavelength conversion process with respect to the laser light having the specific wavelength. apparatus. The wavelength conversion device according to claim 5 or 6, wherein the second temperature control mechanism is configured to irradiate the nonlinear optical element with auxiliary light from the first auxiliary light source from an output side of wavelength converted light.
(This coincides with the heat generation distribution of the nonlinear optical element generated in the wavelength conversion process for the laser light of the specific wavelength)   The wavelength conversion device according to claim 7, wherein the second temperature control mechanism includes a second auxiliary light source that irradiates the nonlinear optical element with auxiliary light from a laser light input side of the specific wavelength.   The wavelength converter according to any one of claims 5 to 8, wherein a wavelength of auxiliary light output from an auxiliary light source provided in the second temperature control mechanism is in a range of 1 to 11 µm.   A seed light source that outputs pulsed light by a gain switching method, a fiber amplifier that amplifies pulsed light output from the seed light source, a solid-state amplifier that amplifies pulsed light output from the fiber amplifier, and an output from the solid-state amplifier 10. A laser light source device comprising: the wavelength conversion device according to claim 5 that outputs a wavelength-converted pulsed light.

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