JP2014149315A - Harmonic laser oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long-life harmonic laser oscillator.SOLUTION: The harmonic laser oscillator includes: an SHG crystal 9 and a THG crystal 10 that convert a wavelength of infrared laser L1 outputted from a YAG rod 5 to output UV laser L3; an SHG temperature controller 17 and a THG temperature controller 18 that adjust temperatures of the SHG crystal 9 and the THG crystal 10; an operation unit 19 that controls the SHG temperature controller 17 and the THG temperature controller 18 on the basis of a UV laser L3 output value. When the THG crystal 10 starts outputting the UV laser L3 after initial temperatures of the SHG crystal 9 and the THG crystal 10 are adjusted, the operation unit 19, in a case that the UV laser L3 output value to the outside falls below a first minimum allowable value, causes the SHG temperature controller 17 and the THG temperature controller 18 to perform temperature control so that the UV laser L3 output value increases greater than a second minimum allowable value.

Description

  The present invention relates to a harmonic laser oscillator that outputs a harmonic laser using a nonlinear crystal.

  When laser light is incident on the nonlinear crystal, laser light having a frequency that is an integral multiple of the incident light frequency is generated. In such wavelength conversion, since birefringence (refractive index) of a nonlinear crystal is used, it is important to achieve phase matching for efficient wavelength conversion. Therefore, when the laser oscillator is started up, the nonlinear crystal is adjusted to a temperature for obtaining the designed refractive index in order to achieve phase matching, and thereafter, the temperature is controlled to be kept constant (for example, Patent Document 1).

  In an oscillator that obtains a UV laser as a harmonic laser, if the UV laser is continuously irradiated in the nonlinear crystal for a long time, optical damage occurs in the nonlinear crystal. As a result, the wavelength conversion efficiency is lowered, and a harmonic laser having a desired intensity cannot be obtained. As a technique for solving this, there is a technique for changing the position where the laser light passes through the nonlinear crystal (see Patent Documents 2 to 6).

JP 2005-327839 A JP 2010-231237 A JP 2003-57696 A JP 2004-22946 A JP-A-10-268367 JP 2010-128119 A

  However, the first prior art has a problem that the wavelength conversion efficiency is lowered when the nonlinear crystal is irradiated with a UV laser for a long time to cause optical damage to the nonlinear crystal. Further, as in the second to sixth prior arts, simply changing the position at which the laser light passes through the nonlinear crystal is insufficient to prevent the wavelength conversion efficiency from being lowered, and the life of the laser oscillator is short. There was a problem.

  The present invention has been made in view of the above, and an object thereof is to obtain a long-lived harmonic laser oscillator.

  In order to solve the above-described problems and achieve the object, the present invention provides a fundamental wave output unit that outputs a fundamental wave laser by exciting a laser medium, and the fundamental wave when irradiated with the fundamental wave laser. Based on the wavelength conversion unit that converts the wavelength of the laser and outputs it as a harmonic laser, the temperature adjustment unit that adjusts the temperature of the wavelength conversion unit, and the output value of the harmonic laser that is output from the wavelength conversion unit A control unit that controls the temperature adjustment unit, and after the initial temperature of the wavelength conversion unit is adjusted, the fundamental wave output unit starts output of the fundamental laser and the wavelength conversion unit is The output of the harmonic laser is started, and after the wavelength converter starts the output of the harmonic laser, the control unit outputs an output value to the outside of the harmonic laser smaller than a first minimum allowable value. When it becomes So that the output value of the serial harmonic laser is larger than the second minimum allowable value, characterized in that to perform temperature adjustment to the temperature adjusting portion.

  According to the present invention, when the output value of the harmonic laser to the outside becomes smaller than the first minimum allowable value, the temperature of the wavelength conversion unit is adjusted, so that the wavelength conversion efficiency is improved over a long period of time. Can be maintained. Therefore, it is possible to obtain a long-lived harmonic laser oscillator.

FIG. 1 is a diagram showing a configuration of a laser oscillator according to Embodiment 1 of the present invention. FIG. 2 is a flowchart showing an operation procedure of the laser oscillator according to the first embodiment. FIG. 3 is a flowchart showing the processing procedure of the current adjustment flow. FIG. 4 is a flowchart showing the temperature adjustment processing procedure of the nonlinear crystal. FIG. 5 is a flowchart showing the temperature adjustment processing procedure of the THG crystal. FIG. 6 is a flowchart showing the temperature adjustment processing procedure of the SHG crystal. FIG. 7 is a diagram for explaining the temperature dependence of the 3ω output in the nonlinear crystal. FIG. 8 is a diagram showing the configuration of the nonlinear crystal and the crystal holder. FIG. 9 is a diagram for explaining a change in 3ω output accompanying temperature adjustment according to the first embodiment. FIG. 10 is a diagram showing the configuration of the laser oscillator according to the second embodiment of the present invention. FIG. 11 is a flowchart showing an operation procedure of the laser oscillator according to the second embodiment. FIG. 12 is a diagram for explaining a change in 3ω output accompanying temperature adjustment according to the second embodiment. FIG. 13 is a flowchart showing an operation procedure of the laser oscillator according to the third embodiment.

  Embodiments of a harmonic laser oscillator according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a laser oscillator according to Embodiment 1 of the present invention. The laser oscillator 101 includes a ω power monitor 1, a TR mirror 2A, an LD 4, a YAG rod 5, a Q switch 6, a PR mirror 2B, an SHG crystal 9, a THG crystal 10, a 3ω transmission mirror 11, An external shutter 12, a 3ω power monitor 13, and a control device 20 are provided.

  The laser oscillator 101 includes a resonator (fundamental laser output unit) that generates an infrared laser L1 that is a fundamental wave laser, a wavelength conversion unit that converts the infrared laser L1 generated by the resonator into a UV laser L3, It is comprised including. The resonator includes a TR mirror 2A, an LD 4, a YAG rod 5, a Q switch 6, and a PR mirror 2B. The wavelength conversion unit includes an SHG crystal 9, a THG crystal 10, and an external shutter 12.

  In the resonator, an LD 4, a YAG rod 5, and a Q switch 6 are arranged between the TR mirror 2A and the PR mirror 2B. In the wavelength conversion unit, an SHG crystal 9 and a THG crystal 10 are disposed between the PR mirror 2B and the external shutter 12.

  In the laser oscillator 101, when the generation side of the infrared laser L1 is the upstream side and the output side of the UV laser L3 is the downstream side, the TR mirror 2A, LD4, YAG rod 5, The Q switch 6, the PR mirror 2B, the SHG crystal 9, the THG crystal 10, and the external shutter 12 are arranged in this order.

  The TR mirror 2A is a mirror that totally reflects the infrared (ω) laser L1, and the PR mirror 2B is a mirror that partially reflects the infrared laser L1. A laser excitation unit that excites a laser medium includes a YAG (Yttrium Aluminum Garnet) rod 5 and an LD (Laser Diode) 4. The YAG rod 5 is an excitation medium (laser medium), and the LD 4 is an excitation light source that excites the YAG rod 5 with LD light (excitation light) 3.

  The Q switch 6 is an acousto-optic element, and is configured by attaching a transducer to a quartz block. The Q switch 6 applies ultrasonic waves to the transducer to advance ultrasonic waves in the quartz block, and thereby causes the Q laser 6 to diffract the infrared laser L1. The resonator outputs an infrared laser L1 as a pulse laser by turning on / off the ultrasonic wave from the transducer at a high frequency.

  The SHG (Second Harmonic Generation) crystal 9 is a nonlinear crystal, and when irradiated with the infrared laser L1, a part of the incident light (infrared laser L1) is converted to a harmonic twice as high as the frequency of the infrared laser L1. Wavelength conversion to a wave (second harmonic) (green laser L2). The green (2ω) laser L2 wavelength-converted by the SHG crystal 9 and the infrared laser L1 not wavelength-converted are both sent to the THG crystal 10.

  The THG (Third Harmonic Generation) crystal 10 is a nonlinear crystal, and uses an infrared laser L1 and a green laser L2 to generate a harmonic (third harmonic) three times the frequency of the infrared laser L1. Wavelength conversion to UV laser L3). The UV (3ω) laser L3 wavelength-converted by the THG crystal 10 is sent to the 3ω transmission mirror 11.

  The 3ω transmission mirror 11 is a mirror that blocks the infrared laser L1 and the green laser L2 and transmits the UV laser L3. The UV laser L3 that has passed through the 3ω transmission mirror 11 is sent to the external shutter 12.

  The external shutter 12 includes a reflection mirror. While the external shutter 12 is open, the laser oscillator 101 outputs the UV laser L3. While the external shutter 12 is closed, the UV laser L 3 is reflected by the reflection mirror and sent to the 3ω power monitor 13. As a result, the UV laser L3 enters the 3ω power monitor 13.

  The ω power monitor 1 measures the infrared laser output (power) of the infrared laser L1 emitted from the TR mirror 2A, and sends the measurement result to the control device 20. The 3ω power monitor 13 measures the UV laser output of the UV laser L <b> 3 reflected by the external shutter 12 and sends the measurement result to the control device 20.

  The control device 20 includes an LD power source (power source unit) 15, an RF driver 16, an SHG temperature controller 17, a THG temperature controller 18, and a calculation unit 19. The LD power source 15, the RF driver 16, the SHG temperature controller 17, and the THG temperature controller 18 are connected to the calculation unit 19 and operate according to instructions from the calculation unit 19.

  The LD power source 15 is a power source that supplies power to the LD 4. The RF driver 16 is a signal generator that turns on / off the RF power of the Q switch 6. The SHG temperature controller 17 adjusts the temperature of the SHG crystal 9, and the THG temperature controller 18 adjusts the temperature of the THG crystal 10.

  The computing unit 19 is based on the detection result (power of the infrared laser L1) sent from the ω power monitor 1 and the detection result (power of the UV laser L3) sent from the 3ω power monitor 13. The LD power source 15, the RF driver 16, the SHG temperature controller 17, and the THG temperature controller 18 are controlled.

  The infrared laser L1 in the resonator reciprocates between the TR mirror 2A and the PR mirror 2B, and is output from the PR mirror 2B side as a laser pulse when the Q switch 6 is turned off. The outputted infrared laser L1 is partly converted into a green laser L2 by the SHG crystal 9, and sent to the THG crystal 10. The infrared laser L1 and the green laser L2 output from the SHG crystal 9 are wavelength-converted to the UV laser L3 by the THG crystal 10, and the infrared laser L1, the green laser L2, and the UV laser L3 are output from the THG crystal 10. The The infrared laser L1 and the green laser L2 are blocked by the 3ω transmission mirror 11, and the UV laser L3 is transmitted through the 3ω transmission mirror 11. The UV laser L3 transmitted through the 3ω transmission mirror 11 is sent to the external shutter 12 and output from the external shutter 12. In other words, in the wavelength conversion unit, the UV laser L3 is generated by passing the infrared laser L1 through the SHG crystal 9 and the THG crystal 10, and the UV laser L3 is output from the external shutter 12.

  For example, when the power of the UV laser L3 becomes lower than a predetermined value, the calculation unit 19 of the present embodiment performs the temperature adjustment of the SHG temperature controller 17 and the THG temperature controller so as to adjust the temperature of the SHG crystal 9 and the THG crystal 10. An instruction is sent to the device 18.

  When the SHG crystal 9 and the THG crystal 10 are used for a long time, fine dust may be baked onto the surface of the nonlinear crystal without causing optical damage. In this case, the SHG crystal 9 or the THG crystal 10 absorbs the harmonic laser and generates heat, and the wavelength conversion efficiency may decrease due to the temperature change of the refractive index at the beam passing point due to the heat generation. . When the wavelength conversion efficiency is lowered, a harmonic laser having a desired intensity cannot be obtained and cannot be used as a laser oscillator. Therefore, the laser oscillator 101 of the present embodiment has a refractive index at the beam passing point even when the refractive index changes in temperature due to heat generation due to deterioration of the nonlinear crystal over time and the UV laser output falls below a desired intensity. Is adjusted so that the temperature of the nonlinear crystal (SHG crystal 9 or THG crystal 10) is adjusted.

  Here, the SHG crystal 9 and the THG crystal 10 are the first nonlinear crystal and the second nonlinear crystal described in the claims, respectively. Further, the SHG temperature controller 17 and the THG temperature controller 18 are a first temperature adjustment unit and a second temperature adjustment unit, respectively.

  FIG. 2 is a flowchart showing an operation procedure of the laser oscillator according to the first embodiment. In the laser oscillator 101, the initial temperatures of the SHG crystal 9 and the THG crystal 10 are adjusted before the output of the UV laser L3 is started. Thereafter, the YAG rod 5 starts the output of the infrared laser L1, and the SHG crystal 9 and the THG crystal 10 start the outputs of the green laser L2 and the UV laser L3, respectively.

  The laser oscillator 101 performs automatic output control when outputting the UV laser L3. The automatic output control here is a process for controlling the LD power source 15, the SHG temperature controller 17, and the THG temperature controller 18 so that the output value of the UV laser L3 falls within a predetermined range.

  When the laser oscillator 101 starts output of the UV laser L3, the external shutter 12 is closed at a predetermined timing. As a result, the UV laser L3 enters the 3ω power monitor 13 and the 3ω power monitor 13 causes the UV laser of the UV laser L3. Output is measured. Then, the UV laser output (3ω output P0) measured by the 3ω power monitor 13 is sent to the calculation unit 19 of the control device 20.

  The computing unit 19 determines the magnitude of the 3ω output P0 measured by the 3ω power monitor 13 (step S100). It is assumed that the allowable range of UV laser output is P1 or more and P2 or less (the minimum allowable value is P1 and the maximum allowable value is P2).

  In this case, if the 3ω output P0 is within the allowable range (step S100, P1 ≦ P0 ≦ P2), the calculation unit 19 determines that automatic output adjustment is unnecessary. In this case, a message such as “automatic output adjustment completion” is displayed on a display device (not shown) or the like (step S110).

  When the 3ω output P0 is larger than the maximum allowable value P2 (step S100, P0> P2), the calculation unit 19 determines that the 3ω output P0 is excessive. In this case, the calculating part 19 performs the below-mentioned electric current adjustment flow (step S120).

  FIG. 3 is a flowchart showing the processing procedure of the current adjustment flow. The current adjustment flow is a flow for adjusting the LD current to the LD 4 and adjusting the temperature of the nonlinear crystals (SHG crystal 9 and THG crystal 10). When performing LD current adjustment, the calculating part 19 adjusts LD current so that it may become P0 = P3 +/- P4, for example (step S400). Specifically, the calculation unit 19 sends an instruction to the LD power source 15 so that P0 = P3 ± P4. Here, P3 is, for example, P3 = (P1 + P2) / 2, and P4 is, for example, P4 = 0.05 × P3. Further, the calculation unit 19 adjusts the temperature of the nonlinear crystal (step S410). The temperature adjustment of the nonlinear crystal here is a temperature adjustment for using the UV laser L3 efficiently.

  FIG. 4 is a flowchart showing the temperature adjustment processing procedure of the nonlinear crystal. The calculation unit 19 sends an instruction to the THG temperature controller 18 so as to adjust the temperature of the THG crystal 10. Thereby, the THG temperature controller 18 starts temperature adjustment (temperature adjustment) of the THG crystal 10 (step S500), and the temperature of the THG crystal 10 is adjusted. Thereafter, the calculation unit 19 sends an instruction to the SHG temperature controller 17 to adjust the temperature of the SHG crystal 9. Thereby, the SHG temperature controller 17 starts temperature adjustment of the SHG crystal 9 (step S510), and the temperature of the SHG crystal 9 is adjusted.

  The temperature adjustment of the THG crystal 10 and the temperature adjustment of the SHG crystal 9 may be repeated a plurality of times in order. As a result, the THG crystal 10 and the SHG crystal 9 can be accurately adjusted to appropriate temperatures.

  In the laser oscillator 101, the processes in steps S100 and S120 are repeated until the 3ω output P0 satisfies P0 ≦ P2. When the 3ω output P0 satisfies P1 ≦ P0 ≦ P2, the process of step S110 is performed.

  When the 3ω output P0 is smaller than the minimum allowable value P1 (step S100, P0 <P1), the calculation unit 19 determines that the 3ω output P0 is insufficient. In this case, the calculation unit 19 sends an instruction to the SHG temperature controller 17 and the THG temperature controller 18 so as to adjust the temperature of the nonlinear crystal. Thereby, the SHG temperature controller 17 and the THG temperature controller 18 adjust the temperature of the SHG crystal 9 and the THG crystal 10, respectively. For example, the temperature adjustment of the nonlinear crystal (SHG crystal 9, THG crystal 10) is performed by the processing procedure described in FIG. 4 (step S130).

  Specifically, in the temperature adjustment, the maximum value of the 3ω output P0 is searched by changing the current crystal temperature by ± several degrees around the center value. Since the amplitude depends on the temperature dependence characteristic of the refractive index of the nonlinear crystal to be used and the optical path design, it is determined according to the design of the laser oscillator 101. In the present embodiment, for example, the temperature of the nonlinear crystal is changed in a range of about ± 3 ° C. to search for a crystal temperature at which the maximum UV output can be obtained. The minimum order of temperature adjustment is performed up to a temperature of 1/10 to 1/100 of the above change range.

  After the temperature of the nonlinear crystal is adjusted, the 3ω power monitor 13 measures the UV laser output of the UV laser L3. Then, the UV laser output (3ω output P0) measured by the 3ω power monitor 13 is sent to the calculation unit 19 of the control device 20.

  The computing unit 19 determines the magnitude of the 3ω output P0 measured by the 3ω power monitor 13 (step S140). Here, it is assumed that the allowable range of the UV laser output is P5 or more and P2 or less (the minimum allowable value is P5 and the maximum allowable value is P2). The minimum allowable value P5 is slightly larger than the minimum allowable value P1. This makes it possible to determine whether or not the 3ω output P0 is within the allowable range under slightly more severe conditions than the first determination of the 3ω output P0.

  If P0 is within this allowable range (P2 to P5) (step S140, P5 ≦ P0 ≦ P2), the arithmetic unit 19 determines that automatic output adjustment is not necessary. In this case, a message such as “automatic output adjustment completed” is displayed on the display device or the like (step S110).

  When the 3ω output P0 is larger than the maximum allowable value P2 (step S140, P0> P2), the calculation unit 19 determines that the 3ω output P0 is excessive in output. And the calculating part 19 performs an electric current adjustment flow (step S150). The current adjustment flow here is a processing flow similar to the processing flow in step S120.

  In the laser oscillator 101, the processes in steps S140 and S150 are repeated until the 3ω output P0 satisfies P0 ≦ P2. When the 3ω output P0 satisfies P5 ≦ P0 ≦ P2, the process of step S110 is performed.

  When the 3ω output P0 is smaller than the minimum allowable value P5 (step S140, P0 <P5), the calculation unit 19 determines that the 3ω output P0 is insufficient. In this case, the calculation unit 19 determines the magnitude of the ω output P based on the infrared laser output measured by the ω power monitor 1 (step S160). Assume that the allowable range of the infrared laser output is P6 or more (the minimum allowable value is P6). The minimum allowable value P6 here is a theoretical minimum output value necessary to obtain P0 ≧ P2.

  In this case, if the ω output P is outside the allowable range (step S160, P <P6), the calculation unit 19 determines that the current adjustment flow is necessary. In this case, the calculation unit 19 performs a current adjustment flow (step S170). The current adjustment flow here is a processing flow similar to the processing flow in step S120.

  After the current adjustment flow is performed, the 3ω power monitor 13 measures the UV laser output of the UV laser L3. Then, the UV laser output (3ω output P0) measured by the 3ω power monitor 13 is sent to the calculation unit 19 of the control device 20.

  The computing unit 19 determines the magnitude of the 3ω output P0 measured by the 3ω power monitor 13 (step S180). Here, it is assumed that the allowable range of the UV laser output is P5 or more and P2 or less.

  If P0 is within this allowable range (step S180, P5 ≦ P0 ≦ P2), the calculation unit 19 determines that automatic output adjustment is unnecessary. In this case, a message such as “automatic output adjustment completed” is displayed on the display device or the like (step S110).

  When the 3ω output P0 is larger than the maximum allowable value P2 (step S180, P0> P2), the calculation unit 19 determines that the 3ω output P0 is excessive in output. In this case, the calculation unit 19 performs a current adjustment flow (step S190). The current adjustment flow here is a processing flow similar to the processing flow in step S120.

  In the laser oscillator 101, the processes in steps S180 and S190 are repeated until the 3ω output P0 satisfies P0 ≦ P2. When the 3ω output P0 satisfies P5 ≦ P0 ≦ P2, the process of step S110 is performed.

  When the 3ω output P0 is smaller than the minimum allowable value P5 (step S180, P0 <P5), the calculation unit 19 determines that the 3ω output P0 is insufficient. In this case, a message such as “oscillator life, replacement” is displayed on the display device or the like (step S200).

  In addition, when the magnitude of the ω output P is determined as the processing of step S160, if the ω output P is within the allowable range (step S160, P ≧ P6), the calculation unit 19 has a lifetime of the nonlinear crystal. Judge. In other words, if there is sufficient ω output P to obtain P0 ≧ P2, but P0 <P5 and the 3ω output P0 is insufficient, it is determined that the nonlinear crystal has reached the end of its life. Is done. In this case, a message such as “oscillator life, replacement” is displayed on the display device or the like (step S200).

  Here, detailed processing procedures for adjusting the temperature of the THG crystal 10 and adjusting the temperature of the SHG crystal 9 will be described. FIG. 5 is a flowchart showing the temperature adjustment processing procedure of the THG crystal. For adjusting the temperature of the THG crystal 10, for example, the THG crystal temperature T2, which is the crystal temperature of the THG crystal 10, is gradually decreased from the highest temperature (T2_max) to the lowest temperature (T2_min) in order, and the 3ω output P0 at each crystal temperature. Among them, the crystal temperature at which the 3ω output P0 is the maximum value is adopted as the THG crystal temperature T2.

  When the temperature of the THG crystal 10 is adjusted, the crystal temperature of the SHG crystal 9 is kept at a constant value. For example, the SHG crystal temperature T1, which is the crystal temperature of the SHG crystal 9, is fixed to the SHG crystal temperature T1 = T1_max. T1_max is the highest temperature among the crystal temperatures of the SHG crystal 9.

  As an initial setting, the calculation unit 19 sends instructions to the SHG temperature controller 17 and the THG temperature controller 18 so that the SHG crystal temperature T1 = T1_max and the THG crystal temperature T2 = T2_max. Then, the calculation unit 19 measures the UV laser output (3ω output P0) when the SHG crystal temperature T1 = T1_max and the THG crystal temperature T2 = T2_max are reached (step S600).

  Thereafter, the calculation unit 19 sends an instruction to the THG temperature controller 18 so that the new THG crystal temperature T2 'becomes T2' = T2- [Delta] T (step S610). As a result, the crystal temperature of the THG crystal 10 becomes the latest THG crystal temperature T2 ', and the latest 3ω output P0' is measured (step S620).

  The computing unit 19 determines whether or not the latest 3ω output P0 ′ is larger than the maximum value of the 3ω output P0 measured so far (step S630). The maximum value of the 3ω output P0 measured so far indicates the maximum value of the 3ω output P0 measured in the temperature adjustment processing (flow in FIG. 5) of the THG crystal 10 this time. Accordingly, the maximum value of the 3ω output P0 here is the 3ω output P0 at the time of initial setting.

  When the latest 3ω output P0 ′ is larger than the maximum value of the 3ω output P0 measured so far (step S630, Yes), the calculation unit 19 updates the maximum value. Thus, at this time, the THG crystal temperature T2 = T2 ′ and the 3ω output P0 = P0 ′ is obtained (step S640).

  On the other hand, when the latest 3ω output P0 ′ is not larger than the maximum value of the 3ω output P0 measured so far (No in step S630), the calculation unit 19 does not update the maximum value, and does not update the current maximum value. Remember.

  Thereafter, when the new THG crystal temperature T2 ′ is set to T2 ′ = T2′−ΔT (step S650), the calculation unit 19 determines whether or not the new THG crystal temperature T2 ′ satisfies T2 ′> T2_min. Is determined (step S660).

  If the new THG crystal temperature T2 'is T2'> T2_min (step S660, Yes), the laser oscillator 101 repeats the processing from step S620 to S660. That is, the calculation unit 19 sends an instruction to the THG temperature controller 18 so that the latest THG crystal temperature T2 'is T2' = T2 '-[Delta] T. As a result, the crystal temperature of the THG crystal 10 becomes the latest THG crystal temperature T2 ', and the latest 3ω output P0' is measured (step S620).

  The computing unit 19 determines whether or not the latest 3ω output P0 ′ is larger than the maximum value of the 3ω output P0 measured so far (step S630). When the latest 3ω output P0 ′ is larger than the maximum value of the 3ω output P0 measured so far (step S630, Yes), the calculation unit 19 updates the maximum value. Thus, at this time, the THG crystal temperature T2 = T2 ′ and the 3ω output P0 = P0 ′ is obtained (step S640). When the latest 3ω output P0 ′ is not larger than the maximum value of the 3ω output P0 measured so far (No in step S630), the calculation unit 19 does not update the maximum value.

  Thereafter, when the new THG crystal temperature T2 ′ is set to T2 ′ = T2′−ΔT (step S650), the calculation unit 19 determines whether or not the new THG crystal temperature T2 ′ satisfies T2 ′> T2_min. Is determined (step S660).

  The laser oscillator 101 repeats the processing from step S620 to S660 until the new THG crystal temperature T2 'becomes T2'≤T2_min. If the new THG crystal temperature T2 'is not T2'> T2_min (step S660, No), the laser oscillator 101 ends the temperature adjustment process of the THG crystal 10. The calculation unit 19 employs the THG crystal temperature T2 'that is the maximum value of the 3ω output P0 at this time as the crystal temperature of the THG crystal 10 (THG crystal temperature T2). Thereafter, the laser oscillator 101 starts the temperature adjustment process for the SHG crystal 9.

  FIG. 6 is a flowchart showing the temperature adjustment processing procedure of the SHG crystal. Note that the description of the same process as the temperature adjustment process of the THG crystal 10 described in FIG. 5 is omitted. For temperature adjustment of the SHG crystal 9, for example, the SHG crystal temperature T1 is gradually decreased from the maximum temperature (T1_max) to the minimum temperature (T1_min) in order, and the ω output P is the maximum among the ω outputs P at each crystal temperature. The value of the crystal temperature is adopted as the SHG crystal temperature T1.

  When the temperature of the SHG crystal 9 is adjusted, the crystal temperature of the THG crystal 10 is kept at a constant value. For example, the THG crystal temperature T2 is fixed to the crystal temperature (THG crystal temperature T2 at which the 3ω output P0 is the maximum value) obtained by the flow of FIG.

  As an initial setting, the calculation unit 19 sets the SHG temperature controller 17 and the THG temperature controller so that the SHG crystal temperature T1 = T1_max and the THG crystal temperature T2 = T2 (THG crystal temperature T2 at which the 3ω output P0 is the maximum). Send instructions to 18. Then, the calculation unit 19 measures the UV laser output (3ω output P0) when the SHG crystal temperature T1 = T1_max and the THG crystal temperature T2 = T2 are reached (step S700).

  Thereafter, the calculation unit 19 sends an instruction to the SHG temperature controller 17 so that the new SHG crystal temperature T1 'becomes T1' = T1-ΔT (step S710). As a result, the crystal temperature of the SHG crystal 9 becomes the latest SHG crystal temperature T1 ', and the latest 3ω output P0' is measured (step S720).

  The calculation unit 19 determines whether or not the latest 3ω output P0 ′ is larger than the maximum value of the 3ω output P0 measured so far (step S730). The maximum value of the 3ω output P0 measured so far indicates the maximum value of the 3ω output P0 measured in the temperature adjustment process (the flow of FIG. 6) of the SHG crystal 9 this time. Accordingly, the maximum value of the 3ω output P0 here is the 3ω output P0 at the time of initial setting.

  When the latest 3ω output P0 ′ is larger than the maximum value of the 3ω output P0 measured so far (step S730, Yes), the calculation unit 19 updates the maximum value. Accordingly, at this time, the SHG crystal temperature T1 = T1 ′ and the 3ω output P0 = P0 ′ is obtained (step S740).

  On the other hand, when the latest 3ω output P0 ′ is not larger than the maximum value of the 3ω output P0 measured so far (No in step S730), the calculation unit 19 does not update the maximum value and does not update the current maximum value. Remember.

  Thereafter, when the new SHG crystal temperature T1 ′ is set to T1 ′ = T1′−ΔT (step S750), the calculation unit 19 determines whether or not the new SHG crystal temperature T1 ′ satisfies T1 ′> T1_min. Is determined (step S760).

  If the new SHG crystal temperature T1 'is T1'> T1_min (step S760, Yes), the laser oscillator 101 repeats the processing from step S720 to S760. That is, the calculation unit 19 sends an instruction to the SHG temperature controller 17 so that the latest SHG crystal temperature T1 ′ is T1 ′ = T1′−ΔT. As a result, the crystal temperature of the SHG crystal 9 becomes the latest SHG crystal temperature T1 ', and the latest 3ω output P0' is measured (step S720).

  The calculation unit 19 determines whether or not the latest 3ω output P0 ′ is larger than the maximum value of the 3ω output P0 measured so far (step S730). When the latest 3ω output P0 ′ is larger than the maximum value of the 3ω output P0 measured so far (step S730, Yes), the calculation unit 19 updates the maximum value. Accordingly, at this time, the SHG crystal temperature T1 = T1 ′ and the 3ω output P0 = P0 ′ is obtained (step S740). When the latest 3ω output P0 ′ is not larger than the maximum value of the 3ω output P0 measured so far (No in step S730), the calculation unit 19 does not update the maximum value.

  Thereafter, when the new SHG crystal temperature T1 ′ is set to T1 ′ = T1′−ΔT (step S750), the calculation unit 19 determines whether or not the new SHG crystal temperature T1 ′ satisfies T1 ′> T1_min. Is determined (step S760).

  The laser oscillator 101 repeats the processing from step S720 to step S760 until the new SHG crystal temperature T1 'becomes T1'≤T1_min. If the new SHG crystal temperature T1 'is not T1'> T1_min (step S760, No), the laser oscillator 101 ends the temperature adjustment process of the SHG crystal 10. The calculation unit 19 employs the SHG crystal temperature T1 'that is the maximum value of the 3ω output P0 at this time as the crystal temperature of the SHG crystal 10 (SHG crystal temperature T1).

  When the temperature adjustment process including the temperature adjustment of the THG crystal 10 and the temperature adjustment of the SHG crystal 9 is repeated a plurality of times, the laser oscillator 101 derives the SHG crystal temperature T1 that is the maximum value of the 3ω output P0. After that, the temperature adjustment process of the THG crystal 10 is performed again. At this time, as an initial setting, the calculation unit 19 sets the SHG temperature controller 17 so that the SHG crystal temperature T1 = T1 (the latest SHG crystal temperature T1 at which the 3ω output P0 is the maximum value) and the THG crystal temperature T2 = T2_max. Then, an instruction is sent to the THG temperature controller 18 (step S600). Thereafter, the latest THG crystal temperature T2 at which the 3ω output P0 has the maximum value is derived by a processing procedure similar to the processing procedure described in FIG.

  Further, the laser oscillator 101 derives the THG crystal temperature T2 that is the maximum value of the 3ω output P0, and then performs the temperature adjustment process for the SHG crystal 9 again. At this time, as an initial setting, the calculation unit 19 sets the SHG temperature controller 17 so that the SHG crystal temperature T1 = T1_max and the THG crystal temperature T2 = T2 (the latest THG crystal temperature T2 at which the 3ω output P0 is the maximum value). Then, an instruction is sent to the THG temperature controller 18 (step S700). Thereafter, the latest SHG crystal temperature T1 at which the 3ω output P0 becomes the maximum value is derived by a processing procedure similar to the processing procedure described in FIG.

  When the temperature adjustment processing of the THG crystal 10 and the SHG crystal 9 is repeated a plurality of times, the maximum value of the 3ω output P0 measured so far is the maximum value for each temperature adjustment processing (each flow in FIGS. 5 and 6). It is. Therefore, when the temperature adjustment processing of the THG crystal 10 is performed 1 to M times (M is a natural number of 2 or more) according to the flow of FIG. 5, the maximum value of the 3ω output P0 obtained previously is reset at the initial setting of each time. The Similarly, when the temperature adjustment process of the SHG crystal 9 is performed 1 to M times in accordance with the flow of FIG. 6, the maximum value of the 3ω output P0 obtained previously is reset at the initial setting of each time.

  When the temperature adjustment process of the THG crystal 10 is repeated a plurality of times, the maximum temperature of the THG crystal temperature T2 may be T2 = T2_max−Tx and the minimum temperature may be T2_min + Tx in the second and subsequent temperature adjustment processes. Thereby, the temperature scan range when searching for the THG crystal temperature T2 at which the 3ω output P0 is the maximum output can be narrowed. Here, Tx is, for example, Tx = (T2_max−T2_min) / 4.

  Similarly, when the temperature adjustment process of the SHG crystal 9 is repeated a plurality of times, the maximum temperature of the SHG crystal temperature T1 may be T1 = T1_max−Ty and the minimum temperature may be T1_min + Ty in the second and subsequent temperature adjustment processes. Thereby, the temperature scan range when searching for the SHG crystal temperature T1 at which the 3ω output P0 is the maximum output can be narrowed. Here, Ty is, for example, Ty = (T1_max−T1_min) / 4.

  As described above, in the present embodiment, when the UV laser output is lower than the specified value, the SHG crystal 9 and the THG crystal are based on the 3ω output P0 so that the UV laser output (3ω output P0) becomes maximum. A crystal temperature of 10 is adjusted.

  FIG. 7 is a diagram for explaining the temperature dependence of the 3ω output in the nonlinear crystal. In FIG. 7, the horizontal axis represents the crystal temperature of the nonlinear crystal (SHG crystal / THG crystal temperature), and the vertical axis represents the 3ω output.

  In the present embodiment, only the crystal temperature of the THG crystal 10 is changed with the crystal temperature of the SHG crystal 9 fixed at a constant value, and the crystal temperature of the THG crystal 10 that maximizes the UV output (3ω output P0) is derived. To do. Thereafter, only the crystal temperature of the SHG crystal 9 is changed in a state where the crystal temperature of the derived THG crystal 10 is fixed to a constant value, and the crystal temperature of the SHG crystal 9 at which the UV output becomes maximum is searched. Thereafter, the process of deriving the crystal temperature at which the 3ω output P0 is maximized is repeated for one nonlinear crystal and the other crystal being fixed at the derived crystal temperature.

  Next, the configuration of the nonlinear crystal and the crystal holder will be described. FIG. 8 is a diagram showing the configuration of the nonlinear crystal and the crystal holder. A nonlinear crystal 63 such as the SHG crystal 9 or the THG crystal 10 is stored in a crystal holder 64 as a casing. The Peltier element 62 is disposed so that the outer wall of the crystal holder 64 and the Peltier element 62 are in contact with each other. Further, the heat sink 61 is disposed so that the Peltier element 62 and the heat sink 61 are in contact with each other.

  In the laser oscillator 101, a crystal holder 64 for the SHG crystal 9, a Peltier element 62, a heat sink 61, and a crystal holder 64 for the THG crystal 10, a Peltier element 62, and a heat sink 61 are arranged. The temperature is controlled separately from the crystal 10.

  For example, when the temperature of the SHG crystal 9 is adjusted, the SHG temperature controller 17 supplies a current to the Peltier element 62 for SHG. The SHG temperature controller 17 reverses the polarity of the current flowing through the Peltier element 62 depending on whether the temperature of the SHG crystal 9 is raised or lowered. Similarly, when the temperature of the THG crystal 10 is adjusted, the THG temperature controller 18 causes a current to flow through the Peltier element 62 for THG. The THG temperature controller 18 reverses the polarity of the current flowing through the Peltier element 62 depending on whether the temperature of the THG crystal 10 is raised or lowered.

  The non-linear crystal 63 is burned in by using it for a long time. As the burn-in progresses, the crystal temperature at the laser beam passing point in the nonlinear crystal 63 rises. In the present embodiment, the temperature of the crystal holder 64 is adjusted so that the crystal temperature at the laser beam passing point is optimized.

  FIG. 9 is a diagram for explaining a change in 3ω output accompanying temperature adjustment according to the first embodiment. In FIG. 9, the horizontal axis represents the oscillation time of the laser beam (UV laser L3), and the vertical axis represents 3ω output. As shown in FIG. 9, the output change characteristic Px of the 3ω output P0 changes with the oscillation time.

  At the start of use of the SHG crystal 9 and the THG crystal 10, which are nonlinear crystals, the 3ω output P0 is within the range of the minimum allowable value P1 to the maximum allowable value P2. The non-linear crystal 63 at this time is in a state 50 where no seizure occurs.

  If the non-linear crystal is continuously used, the 3ω output P0 is lowered. When the 3ω output P0 becomes smaller than the minimum allowable value P1, the temperature of the nonlinear crystal is adjusted, whereby the 3ω output P0 recovers within the range of the minimum allowable value P5 to the maximum allowable value P2 (ST31). The nonlinear crystal 63 at this time is in a state 51 in which a slight burn-in has occurred.

  Thereafter, when the nonlinear crystal is further used, the 3ω output P0 is lowered again. When the 3ω output P0 becomes smaller than the minimum allowable value P1, the temperature of the nonlinear crystal is adjusted, whereby the 3ω output P0 recovers within the range of the minimum allowable value P5 to the maximum allowable value P2 (ST32). The nonlinear crystal 63 at this time is in a state 52 in which the burn-in has further progressed.

  Thereafter, when the nonlinear crystal is further used, the 3ω output P0 is lowered again. When the 3ω output P0 becomes smaller than the minimum allowable value P1, the temperature of the nonlinear crystal is adjusted, whereby the 3ω output P0 recovers within the range of the minimum allowable value P5 to the maximum allowable value P2 (ST33). At this time, the nonlinear crystal 63 is in a state 53 in which the burn-in has further progressed.

  Thus, if the recovery of the 3ω output P0 by adjusting the temperature of the nonlinear crystal is repeated a plurality of times, the 3ω output P0 may not recover to the minimum allowable value P5 even if the temperature of the nonlinear crystal is adjusted. In this case, the non-linear crystal has a lifetime and is replaced. When the 3ω output P0 does not recover to the minimum allowable value P1, it may be determined that the life of the non-linear crystal is determined and replaced. Further, when the 3ω output P0 is larger than the maximum allowable value P2, the current adjustment flow is performed because the 3ω output P0 is excessively output.

  In this embodiment, the 3ω output P0 of the UV laser L3 is measured while the external shutter 12 is closed. However, the 3ω output P0 of the UV laser L3 is measured while the external shutter 12 is open. Good. In this case, a photoelectric element such as a photodiode is provided on the optical path of the UV laser L3. As a result, the UV laser output can be measured while the external shutter 12 is open (while the UV laser L3 is output to the outside of the laser oscillator 101). With this configuration, since the UV laser output can be constantly monitored, it is possible to quickly detect a decrease in the UV laser output and quickly adjust the temperature of the nonlinear crystal.

  Further, the harmonic laser generated by the laser oscillator 101 is not limited to the green laser L2 or the UV laser L3. The laser oscillator 101 may generate an X harmonic laser (X is a natural number of 2 or more) using the infrared laser L1. In this case, in the laser oscillator 101, a nonlinear crystal that generates an X-wave laser and a temperature controller that adjusts the temperature of the nonlinear crystal are arranged.

In this case, the calculation unit 19 adjusts the temperature of the nonlinear crystal based on the laser output (the most downstream laser output) of the harmonic laser output from the nonlinear crystal arranged on the most downstream side.
When the most downstream laser output becomes smaller than a desired value (for example, the minimum allowable values P1, P5), the calculation unit 19 adjusts the temperature of the nonlinear crystal in order from the temperature controller arranged on the downstream side. Let it be done. The magnitude relationship between the minimum allowable values P1, P5, and P7 is not limited to the above-described relationship. For example, the minimum allowable value may be P1 = P5 = P7.

  As described above, according to the first embodiment, the temperature of the nonlinear crystal is adjusted even when the 3ω output P0 is reduced during the use of the nonlinear crystal, so that the wavelength conversion efficiency is improved and the beam passing through the nonlinear crystal is performed. The usable time (wavelength conversion time) at a point can be extended. As a result, the 3ω output P0 can be recovered to the minimum allowable value P1, and as a result, the wavelength conversion efficiency can be maintained at a high efficiency over a long period of time. Therefore, the lifetime of the laser oscillator 101 is extended.

  Further, when adjusting the temperature of the nonlinear crystal, the temperature is adjusted first from the THG crystal 10 on the downstream side, so that the temperature can be adjusted efficiently. Further, when adjusting the temperature of the nonlinear crystal, the temperature adjustment of the THG crystal 10 and the temperature adjustment of the SHG crystal 9 are repeated a plurality of times in order, so that the THG crystal 10 and the SHG crystal 9 are adjusted to appropriate temperatures. Is possible. Therefore, a desired 3ω output P0 can be ensured. Further, when the 3ω output P0 is larger than a predetermined value, the LD current to the LD 4 is adjusted, so that useless power consumption can be prevented.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, when the temperature of the nonlinear crystal is adjusted and the 3ω output P0 does not recover to the minimum allowable value P5, the laser beam passing point in the nonlinear crystal is moved.

  FIG. 10 is a diagram showing the configuration of the laser oscillator according to the second embodiment of the present invention. Of the constituent elements in FIG. 10, the constituent elements that achieve the same functions as those of the laser oscillator 101 of the first embodiment shown in FIG.

  The laser oscillator 102 according to the present embodiment includes a THG crystal moving mechanism 14 in addition to the components included in the laser oscillator 101. The THG crystal moving mechanism 14 is connected to the calculation unit 19 and moves the THG crystal 10 according to an instruction from the calculation unit 19. The THG crystal moving mechanism 14 moves the laser beam passing point in the nonlinear crystal by moving the THG crystal 10. The THG crystal moving mechanism 14 of the present embodiment moves the laser beam passing point in the nonlinear crystal stepwise with respect to the THG crystal 10.

  FIG. 11 is a flowchart showing an operation procedure of the laser oscillator according to the second embodiment. In addition, the description of the processing similar to the processing described in FIG. 2 (Embodiment 1) in the processing in FIG. 11 is omitted.

  When the output of the UV laser L3 is started, the laser oscillator 102 determines the magnitude of the 3ω output P0, the current adjustment flow, the temperature adjustment of the nonlinear crystal, the magnitude of the ω output P, and the like by the same processing procedure as the laser oscillator 101. I do. Specifically, the processing of steps S800 to S890 shown in FIG. 11 is performed by the same processing procedure as the processing of steps S100 to 190 shown in FIG.

  The computing unit 19 determines the magnitude of the 3ω output P0 measured by the 3ω power monitor 13 (step S880). In this case, when the 3ω output P0 is smaller than the minimum allowable value P5 (step S880, P0 <P5), the calculation unit 19 determines that the 3ω output P0 is insufficient. Then, the calculation unit 19 instructs the THG crystal moving mechanism 14 to move the laser beam passing point.

  The THG crystal moving mechanism 14 moves the laser beam passing point (point) of the nonlinear crystal (THG crystal 10) in accordance with an instruction from the calculation unit 19 (step S900). The THG crystal moving mechanism 14 moves the laser beam passing point by a predetermined distance in order to move the laser beam passing point in the nonlinear crystal stepwise.

  Then, the calculation unit 19 sets the number N of use points (number of step movements) N of the nonlinear crystal to N = N + 1 (step S910). Here, N is a natural number. The number of use points of the nonlinear crystal is the number of movements of the laser beam passing point, and the THG crystal 10 can move the laser beam passing point up to a predetermined number of times.

  Thereafter, the calculation unit 19 sends an instruction to the SHG temperature controller 17 and the THG temperature controller 18 so as to adjust the temperature of the nonlinear crystal. Thereby, the SHG temperature controller 17 and the THG temperature controller 18 adjust the temperature of the SHG crystal 9 and the THG crystal 10, respectively. For example, the temperature adjustment of the nonlinear crystals (SHG crystal 9 and THG crystal 10) is performed by the processing procedure described in FIG. 4 (step S920).

  After the temperature of the nonlinear crystal is adjusted, the 3ω power monitor 13 measures the UV laser output of the UV laser L3. Then, the UV laser output (3ω output P0) measured by the 3ω power monitor 13 is sent to the calculation unit 19 of the control device 20.

  The computing unit 19 determines the magnitude of the 3ω output P0 measured by the 3ω power monitor 13 (step S930). The allowable range of the UV laser output here is P7 or more and P2 or less (the minimum allowable value is P7 and the maximum allowable value is P2). The minimum allowable value P7 is slightly larger than the minimum allowable value P5. As a result, it is possible to determine whether or not the 3ω output P0 is within the allowable range under slightly strict conditions than before the movement of the laser beam passing point.

  If P0 is within the allowable range (step S930, P7 ≦ P0 ≦ P2), the calculation unit 19 determines that the automatic output adjustment is unnecessary. In this case, a message such as “automatic output adjustment completed” is displayed on the display device or the like (step S110).

  When the 3ω output P0 is larger than the maximum allowable value P2 (step S930, P0> P2), the calculation unit 19 determines that the 3ω output P0 is excessive. And the calculating part 19 performs an electric current adjustment flow (step S940). The current adjustment flow here is a processing flow similar to the processing flow in step S120.

  In the laser oscillator 102, the processes in steps S930 and S940 are repeated until the 3ω output P0 satisfies P0 ≦ P2. When the 3ω output P0 satisfies P7 ≦ P0 ≦ P2, the process of step S110 is performed.

  When the 3ω output P0 is smaller than the minimum allowable value P7 (step S930, P0 <P7), the calculation unit 19 determines that the 3ω output P0 is insufficient. In this case, the calculation unit 19 determines whether or not the number of used points of the nonlinear crystal exceeds the upper limit value of the number of points (step S950).

  For example, when the laser beam passing point can be moved up to Nx times for the nonlinear crystal, the upper limit value of the number of points is Nx (for example, 9 times). In this case, the calculation unit 19 compares the number N of points used in the nonlinear crystal with the upper limit value Nx of the number of points.

  When the use point number N of the nonlinear crystal is equal to or less than the upper limit value Nx of the number of points (step S950, N ≦ Nx), the laser oscillator 102 repeats the processes from step S900 to S950 until N> Nx.

  In this case, if P7 ≦ P0 ≦ P2 in the process of step S930, a message such as “automatic output adjustment completion” is displayed on the display device or the like (step S110). If P0> P2, the current adjustment flow is performed (step S940). When the use point number N of the nonlinear crystal becomes larger than the upper limit value Nx of the number of points (step S950, N> Nx), a message such as “oscillator life, replacement” is displayed on the display device (step S960). Then, the SHG crystal 9 and the THG crystal 10 are exchanged.

  FIG. 12 is a diagram for explaining a change in 3ω output accompanying temperature adjustment according to the second embodiment. In FIG. 12, the horizontal axis represents the oscillation time of the laser beam (UV laser L3), and the vertical axis represents 3ω output. The overlapping description of the output change characteristic Px and the output change characteristic Px similar to the states 50 to 53 of the nonlinear crystal 63 and the states 50 to 53 of the nonlinear crystal 63 shown in FIG.

  At the start of use of the SHG crystal 9 and the THG crystal 10, which are nonlinear crystals, the 3ω output P0 is within the range of the minimum allowable value P1 to the maximum allowable value P2. Thereafter, if the nonlinear crystal is continuously used, the 3ω output P0 is lowered. When the 3ω output P0 becomes smaller than the minimum allowable value P1, the temperature of the nonlinear crystal is adjusted, whereby the 3ω output P0 recovers within the range of the minimum allowable value P5 to the maximum allowable value P2. In the nonlinear crystal, the output of the UV laser L3 and the temperature adjustment of the nonlinear crystal are repeated (ST31 to ST33). Thereby, the non-linear crystal 63 is burned and changes from the state 50 to the state 53.

  Thus, if the recovery of the 3ω output P0 by adjusting the temperature of the nonlinear crystal is repeated a plurality of times, the 3ω output P0 may not recover to the minimum allowable value P5 even if the temperature of the nonlinear crystal is adjusted. In this case, in the present embodiment, a laser beam passing point moving process is performed. As a result, the 3ω output P0 recovers within the range of the minimum allowable value P7 to the maximum allowable value P2 (ST34). As a result, the laser beam passing point of the nonlinear crystal 63 is in a state 54 where no seizure occurs. The change characteristic of the 3ω output P0 at this time shows the same characteristic as the output change characteristic Px until ST33, and thereafter becomes the output change characteristic Py (recovery by movement) from the process of ST34.

  In the present embodiment, the temperature adjustment process of the nonlinear crystal and the process of moving the laser beam passing point when the 3ω output P0 does not recover to the minimum allowable value P5 even if the temperature of the nonlinear crystal is adjusted are repeated. Is called.

  In this embodiment, the case where the laser beam passing point in the nonlinear crystal is moved stepwise has been described. However, the THG crystal moving mechanism 14 sets the laser beam passing point in the nonlinear crystal relative to the THG crystal 10. It may be moved continuously. In this case, the output of the UV laser L3 is performed while moving the laser beam passing point.

  As described above, according to the second embodiment, the laser beam passing point is moved when the 3ω output P0 cannot be recovered to the desired value even if the temperature of the nonlinear crystal is adjusted, so that the 3ω output P0 is recovered to the desired value. It becomes possible. Therefore, the wavelength conversion efficiency can be maintained at a high efficiency over a long period.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIG. In the third embodiment, when the laser beam passing point is moved, if the 3ω output P0 cannot be recovered to a desired value even if the laser beam passing point is moved a predetermined number of times, the automatic output adjustment is stopped.

  In the present embodiment, automatic output adjustment of the UV laser L3 is performed using the laser oscillator 102 described in the second embodiment. The laser oscillator 102 of the present embodiment is different from the laser oscillator 102 described in the second embodiment in the operation of the calculation unit 19 (instructions to the SHG temperature controller 17 and the THG temperature controller 18).

  FIG. 13 is a flowchart showing an operation procedure of the laser oscillator according to the third embodiment. Note that the description of the processing in FIG. 13 that is the same as the processing described in FIG. 2 (Embodiment 1) and the processing that is the same as the processing described in FIG. 11 (Embodiment 2) are omitted. .

  When the output of the UV laser L3 is started, the laser oscillator 102 determines the magnitude of the 3ω output P0, the current adjustment flow, the temperature adjustment of the nonlinear crystal, the magnitude of the ω output P, and the like by the same processing procedure as the laser oscillator 101. I do. Specifically, the processing in steps S800 to S890 shown in FIG. 13 is performed by the same processing procedure as the processing in steps S100 to 190 shown in FIG.

  The computing unit 19 determines the magnitude of the 3ω output P0 measured by the 3ω power monitor 13 (step S880). In this case, when the 3ω output P0 is smaller than the minimum allowable value P5 (step S880, P0 <P5), the calculation unit 19 determines that the 3ω output P0 is insufficient. Then, the number of continuous movements is initialized (n = 0) (step S895). The number of continuous movements here is the number of times the laser beam passing point has been moved before the 3ω output P0 is restored to a desired value.

  The calculation unit 19 instructs the THG crystal moving mechanism 14 to move the laser beam passing point. The THG crystal moving mechanism 14 moves the laser beam passing point (point) of the nonlinear crystal (THG crystal 10) in accordance with an instruction from the calculation unit 19 (step S900).

  Then, the calculation unit 19 sets the number of consecutive movements n to n = n + 1, and sets the number N of use points of the nonlinear crystal to N = N + 1 (step S905). Thereafter, the calculation unit 19 sends an instruction to the SHG temperature controller 17 and the THG temperature controller 18 so as to adjust the temperature of the nonlinear crystal. Thereby, the SHG temperature controller 17 and the THG temperature controller 18 adjust the temperature of the SHG crystal 9 and the THG crystal 10, respectively. For example, the temperature adjustment of the nonlinear crystal is performed by the processing procedure described in FIG. 4 (step S920).

  After the temperature of the nonlinear crystal is adjusted, the 3ω power monitor 13 measures the UV laser output of the UV laser L3. Then, the UV laser output (3ω output P0) measured by the 3ω power monitor 13 is sent to the calculation unit 19 of the control device 20.

  The computing unit 19 determines the magnitude of the 3ω output P0 measured by the 3ω power monitor 13 (step S930). Here, it is assumed that the allowable range of the UV laser output is P7 or more and P2 or less.

  If P0 is within the allowable range (step S930, P7 ≦ P0 ≦ P2), the calculation unit 19 determines that the automatic output adjustment is unnecessary. In this case, a message such as “automatic output adjustment completed” is displayed on the display device or the like (step S110).

  When the 3ω output P0 is larger than the maximum allowable value P2 (step S930, P0> P2), the calculation unit 19 determines that the 3ω output P0 is excessive. And the calculating part 19 performs an electric current adjustment flow (step S940). The current adjustment flow here is a processing flow similar to the processing flow in step S120.

  In the laser oscillator 102, the processes in steps S930 and S940 are repeated until the 3ω output P0 satisfies P0 ≦ P2. When the 3ω output P0 satisfies P7 ≦ P0 ≦ P2, the process of step S110 is performed.

  When the 3ω output P0 is smaller than the minimum allowable value P7 (step S930, P0 <P7), the calculation unit 19 determines that the 3ω output P0 is insufficient. In this case, the calculation unit 19 determines whether or not the number of used points of the nonlinear crystal exceeds the upper limit value Nx of the number of points (step S950). In other words, the calculation unit 19 compares the number N of used points of the nonlinear crystal with the upper limit value Nx of the number of points.

  When the use point number N of the nonlinear crystal is equal to or less than the upper limit value Nx of the number of points (step S950, N ≦ Nx), the calculation unit 19 determines whether or not the continuous movement number n exceeds the upper limit value of the continuous movement number. (Step S955).

  For example, when a laser beam passage point is allowed up to n0 times for a nonlinear crystal, the upper limit value of the number of continuous movements is n0 (for example, 3 times). In this case, the computing unit 19 compares the number of continuous movements n with the upper limit value n0 of the number of continuous movements. The laser oscillator 102 repeats the processing from steps S900 to S955 until n> n0.

  In this case, if P7 ≦ P0 ≦ P2 in the process of step S930, a message such as “automatic output adjustment completion” is displayed on the display device or the like (step S110). If P0> P2, the current adjustment flow is performed (step S940). If N> Nx, a message such as “oscillator life, replacement” is displayed on the display device or the like (step S960).

  When the number of continuous movements n is larger than the upper limit value n0 of the number of continuous movements (step S970, n> n0), a message such as “automatic output adjustment incomplete” is displayed on the display device (step S970). Then, the automatic output adjustment of the UV laser L3 is stopped.

  Thereafter, the flow described with reference to FIG. 13 is started from the beginning as necessary. At this time, the use point number N of the non-linear crystal is not initialized, and the use point number N counted up to the previous time is used as it is. On the other hand, the number of consecutive movements n is initialized (n = 0) in step S895, and then starts counting.

  As described above, according to the third embodiment, when the temperature of the nonlinear crystal is adjusted to the upper limit value n0 times of the continuous movement and the 3ω output P0 cannot be recovered to the desired value, the automatic output adjustment of the UV laser L3 is temporarily performed. Since it is canceled, automatic output adjustment when there is little recovery potential of the 3ω output P0 can be avoided. Therefore, it is possible to efficiently perform the automatic output adjustment of the UV laser L3 and the nonlinear crystal exchange process.

  As described above, the harmonic laser oscillator according to the present invention is suitable for the output of a harmonic laser using a nonlinear crystal.

DESCRIPTION OF SYMBOLS 1 ω power monitor 5 YAG rod 6 Q switch 9 SHG crystal 10 THG crystal 13 3ω power monitor 14 THG crystal moving mechanism 15 LD power source 17 SHG temperature controller 18 THG temperature controller 19 arithmetic unit 20 controller 63 nonlinear crystal 101, 102 Laser oscillator L1 Infrared laser L2 Green laser L3 UV laser

Claims (7)

A fundamental wave output unit that outputs a fundamental wave laser by exciting the laser medium;
When the fundamental laser is irradiated, a wavelength converter that converts the wavelength of the fundamental laser and outputs a harmonic laser;
A temperature adjustment unit for adjusting the temperature of the wavelength conversion unit;
Based on the output value of the harmonic laser output from the wavelength conversion unit, a control unit for controlling the temperature adjustment unit,
With
After the initial temperature of the wavelength conversion unit is adjusted, the fundamental wave output unit starts output of the fundamental wave laser and the wavelength conversion unit starts output of the harmonic laser,
When the output value to the outside of the harmonic laser becomes smaller than a first minimum allowable value after the wavelength converter starts the output of the harmonic laser, the control unit is configured to output the harmonic laser. The harmonic laser oscillator is characterized in that the temperature adjustment unit adjusts the temperature so that the output value of becomes higher than a second minimum allowable value. The wavelength converter includes a first nonlinear crystal that generates a first harmonic laser having a wavelength that is a first natural number times that of the fundamental laser, and a second natural number that is twice that of the fundamental laser. A second nonlinear crystal that produces a second harmonic laser having a wavelength;
The temperature adjustment unit includes a first temperature adjustment unit that adjusts the temperature of the first nonlinear crystal, and a second temperature adjustment unit that adjusts the temperature of the second nonlinear crystal,
The second nonlinear crystal is disposed on the downstream side, which is the output side of the first harmonic laser, with respect to the first nonlinear crystal,
The control unit causes the first temperature adjusting unit to adjust the temperature of the first nonlinear crystal after causing the second temperature adjusting unit to adjust the temperature of the second nonlinear crystal. 2. The harmonic laser oscillator according to claim 1, wherein an output value to the outside of the second harmonic laser is made larger than the second minimum allowable value. 3.   The control unit causes the second temperature adjustment unit to adjust the temperature of the second nonlinear crystal, and causes the first temperature adjustment unit to adjust the temperature of the first nonlinear crystal; The harmonic laser according to claim 2, wherein an output value to the outside of the second harmonic laser is made larger than the second minimum allowable value by repeating a plurality of times in order. Oscillator.   The first nonlinear crystal is an SHG crystal that generates a second harmonic laser using the fundamental laser, and the second nonlinear crystal includes the fundamental laser and the second harmonic laser. 4. The harmonic laser oscillator according to claim 2, wherein the harmonic laser oscillator is a THG crystal that generates a third harmonic laser. A power supply for adjusting the output value of the fundamental laser;
The control unit, when the output value of the harmonic laser becomes larger than a first maximum allowable value after the wavelength converter starts the output of the harmonic laser, the output value of the harmonic laser 5. The harmonic laser oscillator according to claim 1, wherein the power supply unit is configured to adjust an output value of the fundamental laser so that is smaller than a second maximum allowable value. 6.   The control unit, when the output value of the fundamental laser becomes smaller than a third minimum allowable value after the wavelength conversion unit starts output of the harmonic laser, the output value of the harmonic laser 6. The harmonic laser oscillator according to claim 1, wherein the temperature adjustment unit is configured to perform temperature adjustment such that is greater than the second minimum allowable value. 7. A moving mechanism for moving a beam passing point through which the beam of the first harmonic laser passes in the second nonlinear crystal;
The control unit causes the second temperature adjustment unit to adjust the temperature of the second nonlinear crystal, and causes the first temperature adjustment unit to adjust the temperature of the first nonlinear crystal; , When the output value to the outside of the second harmonic laser does not become larger than the second minimum allowable value even if the above is repeated a plurality of times, the beam passing point is moved to the moving mechanism. The harmonic laser oscillator according to any one of claims 3 to 6, wherein the harmonic laser oscillator is provided.

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