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WO2018211637A1 - Appareil de conversion de longueur d'onde - Google Patents

Appareil de conversion de longueur d'onde Download PDF

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Publication number
WO2018211637A1
WO2018211637A1 PCT/JP2017/018569 JP2017018569W WO2018211637A1 WO 2018211637 A1 WO2018211637 A1 WO 2018211637A1 JP 2017018569 W JP2017018569 W JP 2017018569W WO 2018211637 A1 WO2018211637 A1 WO 2018211637A1
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WIPO (PCT)
Prior art keywords
laser beam
intensity
temperature
shg crystal
crystal
Prior art date
Application number
PCT/JP2017/018569
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English (en)
Japanese (ja)
Inventor
望 平山
智毅 桂
秀則 深堀
Original Assignee
三菱電機株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 三菱電機株式会社 filed Critical 三菱電機株式会社
Priority to KR1020197016176A priority Critical patent/KR102033657B1/ko
Priority to CN201780075736.7A priority patent/CN110050229B/zh
Priority to JP2017557149A priority patent/JP6272597B1/ja
Priority to PCT/JP2017/018569 priority patent/WO2018211637A1/fr
Priority to TW107114684A priority patent/TWI675247B/zh
Publication of WO2018211637A1 publication Critical patent/WO2018211637A1/fr

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/37—Non-linear optics for second-harmonic generation
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/05—Function characteristic wavelength dependent

Definitions

  • the present invention relates to a wavelength converter that outputs harmonics generated in a nonlinear medium.
  • a wavelength conversion device that includes a nonlinear medium that generates a second harmonic of a fundamental wave and a nonlinear medium that generates a third harmonic that is the sum frequency of the fundamental and the second harmonic.
  • the second harmonic is a harmonic having a wavelength that is half the wavelength of the fundamental wave.
  • the third harmonic is a harmonic having a wavelength that is one third of the wavelength of the fundamental wave. It is known that the intensity of the harmonics output from the wavelength converter changes depending on the temperature of the nonlinear medium.
  • the temperature of the nonlinear medium may be controlled so as to improve the intensity of the output harmonic and obtain a stable harmonic.
  • Patent Document 1 discloses a technique for setting the temperature of a second harmonic generation (SHG) crystal based on the output of a third harmonic generation (THG) crystal.
  • the SHG crystal is a nonlinear medium that generates the second harmonic.
  • the THG crystal is a nonlinear medium that generates the third harmonic.
  • the SHG crystal and the THG crystal are formed such that a plurality of peaks of the third harmonic intensity are generated in a correspondence relationship between the temperature of the SHG crystal and the intensity of the third harmonic output from the THG crystal.
  • the temperature of the SHG crystal is set to an intermediate temperature between the temperatures corresponding to a plurality of peaks.
  • the intensity of the third harmonic output is the peak intensity by setting the temperature of the SHG crystal at a temperature other than the temperature corresponding to the peak of the third harmonic intensity. It will be lower. Separately from this, when the temperature of the SHG crystal is set to the temperature corresponding to the peak of the third harmonic intensity, the temperature range of the SHG crystal that can output the third harmonic of an intensity higher than a certain intensity is obtained. Reduced. In this case, the influence on the intensity of the third harmonic due to the change in the temperature of the SHG crystal becomes large. For this reason, it becomes difficult for the wavelength converter to achieve both improvement in the intensity of the output harmonic and stabilization of the intensity of the harmonic.
  • the intensity peak of the third harmonic with respect to the temperature of the SHG crystal is a single peak.
  • the conversion efficiency from the fundamental wave to the second harmonic in the SHG crystal becomes high.
  • the third harmonic intensity peak may change from a single peak to a plurality of peaks. In this case, the intensity of the third harmonic generated in the THG crystal may be lowered due to a decrease in the intensity of the fundamental wave emitted from the SHG crystal.
  • the peak of the third harmonic intensity becomes a plurality of peaks, a change in the intensity of the third harmonic due to a temperature change of the SHG crystal may become large. For this reason, it becomes difficult for the wavelength converter to achieve both improvement in the intensity of the output harmonic and stabilization of the intensity of the harmonic.
  • the present invention has been made in view of the above, and an object of the present invention is to obtain a wavelength conversion device capable of improving and stabilizing the intensity of output harmonics.
  • a wavelength conversion device converts a first beam, which is a pulsed fundamental wave, into a second beam, which is a harmonic wave of the fundamental wave.
  • a second nonlinear medium for generating a third beam based on the first nonlinear medium, the second beam, and the first beam transmitted through the first nonlinear medium, and the first beam Adjusting means for adjusting the conversion efficiency to the second beam is provided.
  • the adjusting means adjusts the conversion efficiency so that the temperature dependence of the intensity of the third beam at the temperature of the first nonlinear medium is a single maximum.
  • the temperature of the first nonlinear medium showing the maximum value and the temperature of the first nonlinear medium showing the maximum value and the temperature of the first nonlinear medium showing the maximum value are maintained the same.
  • the wavelength conversion device according to the present invention has an effect that it is possible to improve and stabilize the intensity of the output harmonics.
  • FIG. 1 is a first diagram illustrating a laser beam in the SHG crystal shown in FIG. 2nd figure explaining the laser beam in the SHG crystal
  • FIG. 1 is a first diagram showing the relationship between the temperature of the SHG crystal shown in FIG. 1 and the intensity of a laser beam.
  • FIG. 2 is a second diagram showing the relationship between the temperature of the SHG crystal shown in FIG. 1 and the intensity of the laser beam.
  • FIG. 3 is a third diagram showing the relationship between the temperature of the SHG crystal shown in FIG. 1 and the intensity of the laser beam.
  • the flowchart which shows the example of the procedure which adjusts the conversion efficiency of the SHG crystal
  • FIG. 10 is a first diagram for explaining a laser beam in the SHG crystal shown in FIG. 2nd figure explaining the laser beam in the SHG crystal shown in FIG.
  • the flowchart which shows the example of the procedure which adjusts the conversion efficiency of the SHG crystal
  • FIG. 1 is a diagram showing a schematic configuration of a wavelength conversion device 1 according to the first embodiment of the present invention.
  • the wavelength conversion device 1 includes a second harmonic generation (SHG) crystal that is a first nonlinear medium that converts a first beam that is a pulsed fundamental wave into a second beam that is a harmonic of the fundamental wave.
  • SHG second harmonic generation
  • TMG third harmonic generation
  • the third beam is the sum frequency of the fundamental wave and the harmonic.
  • the wavelength converter 1 includes a laser light source 10 that emits a laser beam 21 that is a first beam.
  • the wavelength of the laser beam 21 may be referred to as a first wavelength.
  • the first wavelength is 1064 nm.
  • the laser light source 10 is a YAG laser or a YVO4 laser.
  • the YAG laser is a solid-state laser in which yttrium, aluminum, and garnet are used as a laser medium.
  • YVO4 lasers, yttrium laser medium (Yttrium) and vanadium tetraoxide (Vanadium tetraoxide, VO 4) is a solid-state laser used is.
  • the laser light source 10 generates the laser beam 21 by Q switch oscillation.
  • Q-switched oscillation is an oscillation technique for improving the intensity of a laser to be generated by causing oscillation after the number of excited atoms in the laser medium increases.
  • the laser light source 10 may be a solid-state laser other than a YAG laser and a YVO4 laser.
  • the condensing optical system 13 is provided between the laser light source 10 and the SHG crystal 11.
  • the condensing optical system 13 includes a lens 15 that is an optical element for converging the laser beam 21 with the SHG crystal 11.
  • the number of lenses 15 included in the condensing optical system 13 is not limited to one, and may be plural.
  • the SHG crystal 11 When the laser beam 21 from the laser light source 10 is incident, the SHG crystal 11 generates a laser beam 22 that is a second beam.
  • the SHG crystal 11 converts a laser beam 21 that is a fundamental wave into a laser beam 22 that is a second harmonic.
  • the second wavelength which is the wavelength of the laser beam 22 is half of the first wavelength. In the first embodiment, the second wavelength is 532 nm.
  • the SHG crystal 11 emits the generated laser beam 22.
  • the SHG crystal 11 emits the remaining laser beam 21 without being converted into the laser beam 22.
  • an LBO crystal LiB 3 O 5
  • a KTP crystal KTP crystal
  • BBO crystal ⁇ -BaB 2 O 4
  • the condensing optical system 14 is provided between the SHG crystal 11 and the THG crystal 12.
  • the condensing optical system 14 includes a lens 16 that is an optical element for converging the laser beams 21 and 22 with the THG crystal 12.
  • the number of lenses 16 included in the condensing optical system 14 is not limited to one, and may be plural. In the wavelength converter 1, the condensing optical system 14 may not be provided.
  • the THG crystal 12 generates a laser beam 23 which is a third beam based on the laser beam 21 and the laser beam 22 incident from the SHG crystal 11.
  • the THG crystal 12 converts a laser beam 21 that is a fundamental wave and a laser beam 22 that is a second harmonic into a laser beam 23 that is a sum frequency and is a third harmonic.
  • the third wavelength that is the wavelength of the laser beam 23 is one third of the first wavelength. In Embodiment 1, the third wavelength is 355 nm.
  • the THG crystal 12 emits the generated laser beam 23.
  • the THG crystal 12 emits the remaining laser beams 21 and 22 without being converted into the laser beam 23.
  • an LBO crystal As the THG crystal 12, an LBO crystal, a YCOB crystal (YCa 4 O (BO 3 ) 3 ), a BBO crystal, a CLBO crystal (CsLiB 6 O 10 ), or other nonlinear optical crystal is used.
  • the wavelength separation element 17 has a characteristic of transmitting light in a wavelength range including the first wavelength and the second wavelength and reflecting light in a wavelength range including the third wavelength.
  • the wavelength separation element 17 separates the laser beams 21, 22 and 23 from the THG crystal 12 into the laser beam 23 and the laser beams 21 and 22.
  • One example of the wavelength separation element 17 is a dichroic mirror.
  • the wavelength converter 1 emits a laser beam 23 reflected by the wavelength separation element 17.
  • the damper 18 absorbs the laser beams 21 and 22 from the wavelength separation element 17.
  • the laser beams 21 and 22 from the wavelength separation element 17 are converted into thermal energy by the damper 18.
  • the wavelength separation element 17 may have a characteristic of reflecting the first wavelength light and the second wavelength light and transmitting the third wavelength light.
  • the wavelength separation element 17 may be any optical element other than a dichroic mirror as long as it can separate light based on a difference in wavelength.
  • the wavelength separation element 17 may be a prism that separates light using a difference in refractive index of light depending on the wavelength.
  • the wavelength converter 1 includes a temperature controller 24 that controls the temperature of the SHG crystal 11 and a temperature controller 25 that controls the temperature of the THG crystal 12.
  • the temperature controller 24 monitors the temperature of the SHG crystal 11 and adjusts the temperature of the SHG crystal 11 to a preset temperature.
  • the temperature controller 25 monitors the temperature of the THG crystal 12 and adjusts the temperature of the THG crystal 12 to a preset temperature.
  • the temperature controllers 24 and 25 include a Peltier element that is a thermoelectric element that supplies and absorbs heat, and a thermistor that is a temperature sensor. It is assumed that the set temperature of the SHG crystal 11 and the set temperature of the THG crystal 12 can be set independently of each other.
  • the wavelength conversion device 1 includes a moving mechanism 30 that moves the lens 15 that is an optical element for converging the laser beam 21.
  • the moving mechanism 30 is adjusting means for adjusting the conversion efficiency of the SHG crystal 11 from the laser beam 21 to the laser beam 22.
  • the moving mechanism 30 moves the holder 31 that holds the lens 15 in the linear direction.
  • the moving mechanism 30 includes a motor and a mechanism that converts the rotational motion of the motor into linear motion.
  • the control circuit 26 is hardware that controls the entire wavelength conversion device 1 by executing processing according to instructions.
  • the control circuit 26 controls the temperature controller 24 according to the set temperature of the SHG crystal 11.
  • the control circuit 26 controls the temperature controller 25 according to the set temperature of the THG crystal 12.
  • the control circuit 26 controls driving of the laser light source 10 and driving of the moving mechanism 30.
  • the control circuit 26 may be a CPU (Central Processing Unit) or a microcomputer.
  • the photodetector 27 detects the intensity of the laser beam 23 when adjusting the conversion efficiency by the moving mechanism 30.
  • the photodetector 27 is installed at a position where the laser beam 23 from the wavelength conversion device 1 is incident when the conversion efficiency is adjusted by the moving mechanism 30.
  • the photodetector 27 is not limited to the one installed outside the wavelength conversion device 1, and may be one provided inside the wavelength conversion device 1.
  • the wavelength conversion device 1 may include a spectroscopic element that branches a part of the laser beam 23 that travels from the THG crystal 12 toward the outside of the wavelength conversion device 1.
  • the photodetector 27 may detect light branched by the spectroscopic element.
  • Equation (1) The phase mismatch ⁇ k in the generation of the laser beam 22 in the SHG crystal 11 is expressed by the following equation (1).
  • k 1 is the magnitude of the wave number vector of the laser beam
  • k 2 is the magnitude of the wave number vector of the laser beam 22
  • ⁇ 1 is the first wavelength that is the wavelength of the laser beam 21.
  • n 1 is the refractive index of the SHG crystal 11 with respect to the laser beam 21
  • n 2 is the refractive index of the SHG crystal 11 with respect to the laser beam 22.
  • the SHG crystal 11 generates a laser beam 22 in so-called type 1 phase matching when the polarization direction of the fundamental wave and the polarization direction of the second harmonic wave are perpendicular to each other.
  • the conversion efficiency ⁇ of the laser beam 22 in the SHG crystal 11 represents the result of dividing the intensity of the laser beam 22 emitted from the SHG crystal 11 by the intensity of the laser beam 21 incident on the SHG crystal 11.
  • the temperature of the SHG crystal 11 when the phase matching condition is satisfied is referred to as the phase matching temperature of the SHG crystal 11.
  • the phase mismatch ⁇ k expressed by the formula (1) depends on the temperature of the SHG crystal 11.
  • the relationship between the conversion efficiency ⁇ of the laser beam 22 in the SHG crystal 11 and the intensity I 1 of the laser beam 21 in the SHG crystal 11 is expressed by the following equation (2).
  • L is the length of the SHG crystal 11.
  • the relationship represented by the expression (2) is so small that the difference between the intensity of the laser beam 21 incident on the SHG crystal 11 and the intensity of the laser beam 21 emitted from the SHG crystal 11 is negligible. This holds when the conversion efficiency ⁇ is low.
  • the conversion efficiency ⁇ is proportional to the phase mismatch ⁇ k and the intensity I 1 . Since the phase mismatch ⁇ k depends on the temperature of the SHG crystal 11, the conversion efficiency ⁇ depends on the temperature of the SHG crystal 11. Even when the conversion efficiency ⁇ of the laser beam 22 is higher than when the relationship of Expression (2) holds, the conversion efficiency ⁇ depends on the temperature of the SHG crystal 11 and the intensity I 1 of the laser beam 21. It is known. Further, the conversion efficiency of the laser beam 23 in the THG crystal 12 depends on the temperature of the THG crystal 12 and the intensities of the laser beam 21 and the laser beam 22 incident on the THG crystal 12.
  • FIG. 2 is a first diagram illustrating the laser beam 21 in the SHG crystal 11 shown in FIG.
  • the Z axis is an axis parallel to the optical axis of the optical system of the wavelength conversion device 1.
  • the X axis is a horizontal axis.
  • the Y axis is the vertical axis.
  • the central axis 32 represents the center of the light beam of the laser beam 21.
  • the central axis 32 is parallel to the Z axis.
  • the plus Z direction is a direction parallel to the Z axis and is a direction from the incident surface 33 of the SHG crystal 11 toward the emission surface 34.
  • the minus Z direction is opposite to the plus Z direction.
  • the length L is the length of the SHG crystal 11 in the Z-axis direction, and is the length between the entrance surface 33 and the exit surface 34.
  • an effective beam diameter W eff of the laser beam 21 in the SHG crystal 11 is defined.
  • the effective beam diameter W eff is an index indicating the degree of convergence of the laser beam 21 in the SHG crystal 11.
  • w (z) is the beam diameter of the laser beam 21 at the position z in the Z-axis direction.
  • the effective beam diameter W eff represents an average value of the beam diameter w (z) of the laser beam 21 in the SHG crystal 11.
  • the beam diameter w (z) is a D4 ⁇ width that is four times the standard deviation ⁇ of the beam intensity distribution in the X-axis direction or the Y-axis direction.
  • the D4 ⁇ width is defined in the international standard of ISO (International Organization for Standardization) in the beam width.
  • the beam diameter w (z) may be other than the D4 ⁇ width, and may be the full width at half maximum or the 1 / e 2 width.
  • the effective beam diameter W eff may be defined by a definition other than Equation (3).
  • the degree of convergence of the laser beam 21 may be indicated by an index other than the effective beam diameter W eff .
  • the laser beam 21 once converges inside the SHG crystal 11 and then diffuses.
  • the beam diameter w (z) of the laser beam 21 is reduced as it travels from the incident surface 33, and is minimized at the beam waist 35.
  • the beam diameter w (z) expands as it travels from the beam waist 35 to the exit surface 34.
  • a laser beam 21 which is parallel light is incident on the lens 15 shown in FIG.
  • the laser beam 21 incident on the lens 15 is not limited to parallel light, and may be convergent light or diffused light.
  • FIG. 3 is a second diagram for explaining the laser beam 21 in the SHG crystal 11 shown in FIG.
  • the moving mechanism 30 changes the distance between the lens 15 and the SHG crystal 11 by moving the lens 15 in the plus Z direction.
  • the moving mechanism 30 moves the position of the beam waist 35 from the center position of the SHG crystal 11 in the Z-axis direction.
  • the moving mechanism 30 changes the convergence degree of the laser beam 21 in the SHG crystal 11 by moving the lens 15 in the Z-axis direction.
  • the conversion efficiency ⁇ is proportional to the intensity I 1 of the laser beam 21 in the SHG crystal 11.
  • the moving mechanism 30 adjusts the conversion efficiency ⁇ by moving the position of the beam waist 35.
  • the intensity of the laser beam 22 emitted from the SHG crystal 11 is adjusted by adjusting the conversion efficiency ⁇ .
  • the moving mechanism 30 may move each lens 15 separately. A modification in the case where the plurality of lenses 15 are individually moved will be described later.
  • FIG. 4 is a first diagram showing the relationship between the temperature of the SHG crystal 11 shown in FIG. 1 and the intensity of the laser beams 21, 22, and 23.
  • the relationship between the temperature of the SHG crystal 11 and the intensity of the laser beams 21, 22, and 23 is represented by a graph.
  • the horizontal axis of the graph represents the temperature of the SHG crystal 11.
  • the vertical axis represents the intensity of the laser beams 21, 22, and 23.
  • the intensity of the laser beams 21 and 22 shown in FIG. 4 is the intensity of the laser beams 21 and 22 emitted from the SHG crystal 11.
  • the intensity of the laser beam 23 shown in FIG. 4 is the intensity of the laser beam 23 emitted from the THG crystal 12.
  • FIG. 4 shows the relationship between temperature and intensity when the effective beam diameter W eff is the minimum value, that is, when the degree of convergence of the laser beam 21 in the SHG crystal 11 is maximum.
  • the effective beam diameter W eff becomes the minimum value.
  • the intensity of the laser beam 22 emitted from the SHG crystal 11 has a peak.
  • the conversion efficiency ⁇ in the SHG crystal 11 becomes high. The higher the conversion efficiency ⁇ , the more the laser beam 21 is converted into the laser beam 22 in the SHG crystal 11, so that the intensity of the laser beam 21 emitted from the SHG crystal 11 decreases.
  • One peak of the intensity of the laser beam 23, appearing in Tb1 1 is a lower temperature than Ta1. At such a peak, the intensity of the laser beam 23 is Pb1. Moreover, another peak of intensity of the laser beam 23, appearing in Tb1 2 is a temperature higher than Ta1.
  • FIG. 4 shows an example in which the intensity peak of the laser beam 23 is two. The intensity peak of the laser beam 23 may be more than two. Thus, when the effective beam diameter W eff is the minimum, in the correspondence relationship between the temperature of the SHG crystal 11 and the intensity of the laser beam 23, a plurality of intensity peaks of the laser beam 23 appear at a temperature near Ta1. Become.
  • the change in case setting temperature is Ta1 Larger than As the change in the intensity of the laser beams 21 and 22 incident on the THG crystal 12 increases, the change in the intensity of the laser beam 23 emitted from the THG crystal 12 also increases.
  • the wavelength conversion apparatus 1 adjusts the position of the lens 15 by the moving mechanism 30 so that the effective beam diameter W eff becomes a minimum value at the initial stage of adjusting the beam diameter of the laser beam 21.
  • the moving mechanism 30 sets a state in which the intensity peak of the laser beam 23 in the correspondence relationship between the intensity of the laser beam 23 and the temperature of the SHG crystal 11 is a plurality of peaks.
  • the moving mechanism 30 expands the effective beam diameter W eff in the SHG crystal 11 by moving the lens 15 from this state.
  • the adjustment at the initial stage is not limited to the adjustment with the effective beam diameter W eff as the minimum value. In the adjustment in the initial stage, it is only necessary to set a state where the intensity peak of the laser beam 23 is a plurality of peaks, and the effective beam diameter W eff may be set to a value other than the minimum value.
  • FIG. 5 is a second diagram showing the relationship between the temperature of the SHG crystal 11 shown in FIG. 1 and the intensity of the laser beams 21, 22, and 23.
  • FIG. 5 shows the relationship between temperature and intensity when the effective beam diameter W eff is increased from the minimum value.
  • the intensity of the laser beam 22 emitted from the SHG crystal 11 is reduced.
  • the intensity of the laser beam 21 emitted from the SHG crystal 11 increases.
  • the intensity of the laser beam 22 emitted from the SHG crystal 11 has a peak.
  • the intensity of the laser beam 21 emitted from the SHG crystal 11 is higher than the intensity when the temperature is Ta1 in the relationship shown in FIG.
  • the intensity of the laser beam 21 that can be used to generate the laser beam 23 is increased compared to the initial stage, and the laser beam 22 emitted from the THG crystal 12 without being used to generate the laser beam 23. The strength is reduced compared to the initial stage.
  • the intensity peak of the laser beam 23 is one.
  • the peak of the intensity of the laser beam 23 in the correspondence relationship between the intensity of the laser beam 23 emitted from the THG crystal 12 and the temperature of the SHG crystal 11 is made into a single peak by adjustment by the moving mechanism 30.
  • the temperature dependence of the intensity of the laser beam 23 with respect to the temperature of the SHG crystal 11 has a single maximum value due to adjustment by the moving mechanism 30.
  • the temperature dependence is the relationship between the temperature of the nonlinear medium and the beam intensity.
  • the maximum value is the intensity value at the peak in the graph representing the temperature dependence with the temperature of the nonlinear medium as the horizontal axis and the beam intensity as the vertical axis.
  • the moving mechanism 30 adjusts the conversion efficiency ⁇ of the SHG crystal 11 to change the intensity peak of the laser beam 23 from a plurality of peaks to a single peak having a maximum value.
  • the value of the conversion efficiency ⁇ depends on the intensity of the laser beam 21 incident on the SHG crystal 11 or the cross-sectional shape of the laser beam 21.
  • the conversion efficiency ⁇ of the SHG crystal 11 has a certain value
  • the intensity of the laser beam 23 peaks when the temperature of the SHG crystal 11 is Tb2.
  • the maximum value that is the intensity at the peak is Pb2.
  • Tb2 which is the temperature of the SHG crystal 11 when the intensity of the laser beam 23 reaches the maximum value Pb2, and the temperature of the SHG crystal 11 when the intensity of the laser beam 22 emitted from the SHG crystal 11 reaches the maximum value. It is the same as a certain Ta2.
  • the intensity changes of the laser beams 21 and 22 emitted from the SHG crystal 11 are relatively small. Since the change in the intensity of the laser beams 21 and 22 incident on the THG crystal 12 is small, the change in the intensity of the laser beam 23 emitted from the THG crystal 12 is also reduced.
  • FIG. 6 is a third diagram showing the relationship between the temperature of the SHG crystal 11 shown in FIG. 1 and the intensity of the laser beams 21, 22, and 23.
  • FIG. 6 shows the relationship between temperature and intensity when the effective beam diameter W eff is further increased from the state of correspondence shown in FIG.
  • the conversion efficiency ⁇ of the SHG crystal 11 is lower than that in the correspondence relationship shown in FIG.
  • the intensity of the laser beam 22 emitted from the SHG crystal 11 has a peak.
  • Tb3 which is the temperature at which the intensity of the laser beam 23 reaches its peak, is the same as Ta3.
  • the intensity of the laser beam 22 emitted from the SHG crystal 11 is lower than that in the case of FIG. Since the intensity of the laser beam 22 that can be used to generate the laser beam 23 in the THG crystal 12 is reduced, the intensity of the laser beam 23 that is generated in the THG crystal 12 is lower than that in the case of FIG.
  • the intensity peak of the laser beam 23 is one.
  • the intensity of the laser beam 23 generated in the THG crystal 12 is lower than that in the case of FIG. Since Pb3 that is the intensity peak of the laser beam 23 is smaller than Pb2 that is the intensity peak of the laser beam 23 shown in FIG. 5, the relationship of Pb3 ⁇ Pb2 is established.
  • the wavelength converter 1 has a lower intensity of the output laser beam 23 than the case of FIG. 5.
  • the wavelength conversion device 1 adjusts the intensity of the laser beam 23 in the correspondence relationship between the intensity of the laser beam 23 emitted from the THG crystal 12 and the temperature of the SHG crystal 11 by adjustment by the moving mechanism 30.
  • the peak is a single peak.
  • the wavelength conversion apparatus 1 can increase the intensity of the laser beam 23 that can be used to generate the laser beam 23, thereby improving the intensity of the output laser beam 23.
  • the wavelength conversion device 1 uses the temperature at which the intensity of the laser beam 22 reaches a peak as the set temperature of the SHG crystal 11 so that the intensity of the laser beam 23 when there is a temperature change near the set temperature. Can be reduced.
  • FIG. 7 is a flowchart showing an example of a procedure for adjusting the conversion efficiency of the SHG crystal 11 in the first embodiment.
  • step S ⁇ b> 1 the moving mechanism 30 sets a state in which the intensity peak in the correspondence relationship between the intensity of the laser beam 23 that is the third beam and the temperature of the SHG crystal 11 is a plurality of peaks.
  • the correspondence between the intensity of the laser beam 23 and the temperature of the SHG crystal 11 is the correspondence illustrated in FIG.
  • Pmax be the maximum value of the intensity of the laser beam 23 in the state in which the setting in step S1 has been performed.
  • Pmax is the intensity of the laser beam 23 is Pb1 when the temperature of the SHG crystal 11 is Tb1 1.
  • the moving mechanism 30 adjusts the conversion efficiency ⁇ from the laser beam 21 in the SHG crystal 11 to the laser beam 22 as the second beam by expanding the effective beam diameter W eff .
  • the moving mechanism 30 may move the lens 15 in the minus Z direction instead of the plus Z direction. Also in this case, the moving mechanism 30 can expand the effective beam diameter W eff .
  • step S3 the temperature controller 24 controls the temperature of the SHG crystal 11 according to the set temperature, and the photodetector 27 measures the intensity of the laser beam 23 corresponding to the set temperature.
  • the photodetector 27 measures the intensity of the laser beam 23 for each set temperature of the SHG crystal 11.
  • step S4 it is determined whether or not the intensity peak of the laser beam 23 is a single peak in the correspondence relationship between the set temperature of the SHG crystal 11 and the intensity of the laser beam 23 measured by the photodetector 27.
  • step S4 When the intensity peak is not single (step S4: No), since the intensity peak is still a plurality of peaks, the process returns to step S2.
  • the moving mechanism 30 again adjusts the conversion efficiency ⁇ by expanding the effective beam diameter W eff .
  • step S5 it is determined whether or not the peak intensity of the laser beam 23 is greater than or equal to Pmax ⁇ P.
  • ⁇ P is an allowable amount of intensity reduction of the laser beam 23.
  • the correspondence relationship illustrated in FIG. 5 is a correspondence relationship between the intensity of the laser beam 23 and the temperature of the SHG crystal 11 when the peak intensity of the laser beam 23 is Pmax ⁇ P or more.
  • the correspondence illustrated in FIG. 6 is a correspondence between the intensity of the laser beam 23 and the temperature of the SHG crystal 11 when the intensity at the peak of the laser beam 23 is less than Pmax ⁇ P.
  • ⁇ P can be arbitrarily set.
  • step S5 When the intensity at the peak of the laser beam 23 is Pmax ⁇ P or more (step S5: Yes), the control circuit 26 determines that the intensity of the laser beam 23 reaches the set temperature of the SHG crystal 11 at step S6. Set the temperature. Thereby, the wavelength conversion device 1 ends the adjustment of the conversion efficiency ⁇ from the laser beam 21 to the laser beam 22 in the SHG crystal 11.
  • step S7 the moving mechanism 30 moves the lens 15 in the minus Z direction, so that the laser beam in the SHG crystal 11 is obtained.
  • the effective beam diameter W eff of 21 is reduced.
  • the moving mechanism 30 adjusts the conversion efficiency ⁇ in the SHG crystal 11 again by reducing the effective beam diameter W eff . Then, the process returns to step S3.
  • the adjustment of the wavelength conversion device 1 according to the procedure shown in FIG. Such adjustment may be performed at a time other than when the wavelength conversion device 1 is shipped, or may be performed at the time of maintenance of the wavelength conversion device 1.
  • the wavelength conversion device 1 may execute all or part of the function for adjustment according to the procedure shown in FIG. 7 on a program that is analyzed and executed by a CPU or a microcomputer.
  • the wavelength conversion device 1 may include a memory in which a program is stored.
  • the wavelength conversion device 1 may execute all or part of the function for adjustment according to the procedure shown in FIG. 7 on hardware based on wired logic.
  • FIG. 8 is a diagram showing an example of the relationship between the temperature change of the SHG crystal 11 shown in FIG. 1 and the intensity of the laser beam 23.
  • the relationship between the temperature change of the SHG crystal 11 and the intensity of the laser beam 23 is represented by a graph.
  • the horizontal axis of the graph represents the temperature change of the SHG crystal 11.
  • the unit of temperature is Celsius degree.
  • the vertical axis represents the intensity of the laser beam 23 emitted from the THG crystal 12.
  • the unit of intensity is arbitrary.
  • the broken line graph represents the relationship before the adjustment of the wavelength conversion device 1 according to the procedure shown in FIG.
  • the solid line graph represents the relationship after the wavelength converter 1 is adjusted according to the procedure shown in FIG.
  • two peaks appear in the intensity of the laser beam 23 in the relationship before adjustment of the wavelength conversion device 1.
  • One peak appears at a temperature change around ⁇ 0.5 ° C.
  • the intensity at the peak is the maximum value of the intensity of the laser beam 23.
  • Another peak appears at a temperature change around 0.5 ° C.
  • the temperature range of the SHG crystal 11 when the intensity of the laser beam 23 is 90% or more of the maximum value is about ⁇ 0.2 ° C.
  • the wavelength conversion device 1 In the relationship after adjustment of the wavelength conversion device 1, one peak appears in the intensity of the laser beam 23. Such a peak appears in a temperature change near 0 ° C.
  • the temperature range of the SHG crystal 11 when the intensity of the laser beam 23 is 90% or more of the maximum value is about ⁇ 0.6 ° C.
  • the temperature range in which the laser beam 23 with an intensity of 90% or more of the maximum value can be emitted is expanded compared with that before adjustment.
  • the wavelength conversion device 1 can reduce the change in the intensity of the laser beam 23 due to the temperature change of the SHG crystal 11 and can stabilize the intensity of the laser beam 23 by adjustment according to the procedure shown in FIG. .
  • the maximum value of the intensity of the laser beam 23 after adjustment of the wavelength converter 1 is equivalent to the maximum value of the intensity of the laser beam 23 before adjustment.
  • the wavelength conversion device 1 can output a high-intensity laser beam 23 even if adjustment is performed according to the procedure shown in FIG.
  • the SHG crystal 11 is an LBO crystal that performs wavelength conversion under type 1 noncritical phase matching (NCPM) conditions
  • the first wavelength of the laser beam 21 is 1064 nm
  • the set temperature of the SHG crystal 11 is about 150 ° C.
  • the walk-off which is a deviation in the traveling direction between the fundamental wave and the harmonic wave
  • the wavelength conversion device 1 can stabilize the intensity of the laser beam 23 and output a high-intensity laser beam 23 even when the temperature of the SHG crystal 11 is likely to change.
  • the wavelength conversion device 1 adjusts the intensity peak of the laser beam 23 as a single peak by the moving mechanism 30 that moves the lens 15.
  • the wavelength conversion device 1 can reduce the change in the intensity of the laser beam 23 due to the temperature change of the SHG crystal 11 by adjustment by the moving mechanism 30. Further, the wavelength conversion device 1 can output a high-intensity laser beam 23. Thereby, the wavelength converter 1 has the effect that the intensity
  • FIG. 9 is a view showing a modification of the adjustment by the moving mechanism 30 shown in FIG. In the modification, the moving mechanism 30 adjusts the conversion efficiency ⁇ from the laser beam 21 to the laser beam 22 in the SHG crystal 11 by changing the beam diameter of the laser beam 21 in the SHG crystal 11.
  • the wavelength conversion device 1 includes a condensing optical system 36 including a plurality of lenses 15 instead of the condensing optical system 13 shown in FIG.
  • the condensing optical system 36 shown in FIG. 9 includes three lenses 15A, 15B, and 15C that are optical elements. Each lens 15A, 15B, 15C is held by a holder 31.
  • the moving mechanism 30 can individually move the lenses 15A, 15B, and 15C in the Z-axis direction.
  • the moving mechanism 30 enables each of the lenses 15A, 15B, and 15C to be individually moved so that the beam diameter at the beam waist 35 can be expanded and reduced without moving the beam waist 35.
  • the number of optical elements provided in the condensing optical system 36 is not limited to three, and may be two or four or more.
  • the moving mechanism 30 changes the effective beam diameter W eff by changing the beam diameter of the laser beam 21 in the SHG crystal 11. Also in the modified example, the wavelength converter 1 can be adjusted by the moving mechanism 30 as in the case of moving the beam waist 35.
  • FIG. FIG. 10 is a diagram showing a schematic configuration of the wavelength conversion device 40 according to the second embodiment of the present invention.
  • the wavelength conversion device 40 is provided with a moving mechanism 41 for moving the SHG crystal 11 as the first nonlinear medium, instead of the moving mechanism 30 for moving the lens 15 shown in FIG.
  • the same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.
  • the moving mechanism 41 is an adjusting means for adjusting the conversion efficiency from the laser beam 21 to the laser beam 22 in the SHG crystal 11.
  • the moving mechanism 41 moves the holder 42 holding the SHG crystal 11 in the linear direction.
  • the moving mechanism 41 includes a motor and a mechanism that converts the rotational motion of the motor into linear motion.
  • the control circuit 26 controls driving of the moving mechanism 41.
  • FIG. 11 is a first diagram for explaining the laser beam 21 in the SHG crystal 11 shown in FIG.
  • FIG. 12 is a second diagram for explaining the laser beam 21 in the SHG crystal 11 shown in FIG.
  • the moving mechanism 41 moves the SHG crystal 11 in the plus Z direction from the state shown in FIG. 11, the position of the beam waist 35 in the SHG crystal 11 moves in the minus Z direction. By moving the beam waist 35, the effective beam diameter W eff increases compared to the state shown in FIG. Thus, the moving mechanism 41 changes the convergence degree of the laser beam 21 in the SHG crystal 11 by moving the SHG crystal 11 in the Z-axis direction. In the second embodiment, the moving mechanism 41 can change the degree of convergence of the laser beam 21 in the SHG crystal 11 without changing the spread of the laser beam 21 after the SHG crystal 11.
  • FIG. 13 is a flowchart showing an example of a procedure for adjusting the conversion efficiency of the SHG crystal 11 in the second embodiment.
  • the moving mechanism 41 shown in FIG. 11 sets the position of the SHG crystal 11 such that the position of the beam waist 35 is the center position of the SHG crystal 11 in the Z-axis direction, and the effective beam diameter of the laser beam 21 in the SHG crystal 11. Let W eff be the minimum value.
  • the moving mechanism 41 sets a state in which the intensity peaks in the correspondence relationship between the intensity of the laser beam 23 that is the third beam and the temperature of the SHG crystal 11 are a plurality of peaks.
  • the correspondence between the intensity of the laser beam 23 and the temperature of the SHG crystal 11 is the correspondence illustrated in FIG.
  • the maximum value of the intensity of the laser beam 23 in the state where the setting in step S11 has been performed is defined as Pmax.
  • step S12 the moving mechanism 41 extends the effective beam diameter W eff of the laser beam 21 as the first beam in the SHG crystal 11 by moving the SHG crystal 11 in the minus Z direction.
  • the moving mechanism 41 adjusts the conversion efficiency ⁇ from the laser beam 21 in the SHG crystal 11 to the laser beam 22 as the second beam by expanding the effective beam diameter W eff .
  • the moving mechanism 41 may move the SHG crystal 11 in the plus Z direction instead of the minus Z direction. Also in this case, the moving mechanism 41 can expand the effective beam diameter W eff .
  • step S13 the temperature controller 24 controls the temperature of the SHG crystal 11 according to the set temperature, and the photodetector 27 measures the intensity of the laser beam 23 corresponding to the set temperature.
  • the photodetector 27 measures the intensity of the laser beam 23 for each set temperature of the SHG crystal 11.
  • step S14 it is determined whether or not the intensity peak of the laser beam 23 is a single peak in the correspondence relationship between the set temperature of the SHG crystal 11 and the intensity of the laser beam 23 measured by the photodetector 27.
  • step S14 When the intensity peak is not single (step S14: No), since the intensity peak is still a plurality of peaks, the process returns to step S12.
  • the moving mechanism 41 again adjusts the conversion efficiency ⁇ by expanding the effective beam diameter W eff .
  • step S14 When the intensity peak is single (step S14: Yes), the process proceeds to step S15.
  • step S15 it is determined whether or not the peak intensity of the laser beam 23 is equal to or greater than Pmax ⁇ P.
  • step S15 When the intensity at the peak of the laser beam 23 is Pmax ⁇ P or more (step S15: Yes), the control circuit 26 determines that the intensity of the laser beam 23 reaches the set temperature of the SHG crystal 11 in step S16. Set the temperature. Thereby, the wavelength conversion device 40 ends the adjustment of the conversion efficiency ⁇ from the laser beam 21 to the laser beam 22 in the SHG crystal 11.
  • step S17 the moving mechanism 41 moves the SHG crystal 11 in the plus Z direction, thereby causing the laser in the SHG crystal 11 to move.
  • the effective beam diameter W eff of the beam 21 is reduced.
  • the moving mechanism 41 adjusts the conversion efficiency ⁇ in the SHG crystal 11 again by reducing the effective beam diameter W eff . Then, the process returns to step S13.
  • the wavelength conversion device 40 adjusts the intensity peak of the laser beam 23 as a single peak by the moving mechanism 41 that moves the SHG crystal 11.
  • the wavelength conversion device 40 can reduce the change in the intensity of the laser beam 23 due to the temperature change of the SHG crystal 11 by adjustment by the moving mechanism 41. Further, the wavelength conversion device 40 can output a high-intensity laser beam 23. Thereby, the wavelength converter 40 has an effect that the strength and the stability of the output harmonic can be improved.
  • FIG. 14 is a diagram illustrating a schematic configuration of the wavelength conversion device 50 according to the third embodiment of the present invention.
  • the SHG crystal 11 that is the first nonlinear medium and the THG crystal 12 that is the second nonlinear medium are provided inside the optical resonator 61.
  • the same parts as those in the first and second embodiments are denoted by the same reference numerals, and redundant description is omitted.
  • the wavelength conversion device 50 includes an excitation light source 51 that emits excitation light 60 and a laser medium 56 that is excited by the excitation light 60 and emits a laser beam 21 that is a first beam and a pulsed laser beam.
  • the wavelength conversion device 50 includes an optical resonator 61 in which a laser medium 56, an SHG crystal 11, and a THG crystal 12 are disposed.
  • the two resonance mirrors 55 and 59 constitute an optical resonator 61.
  • the excitation light source 51 is a semiconductor laser. In the third embodiment, it is assumed that the wavelength of the excitation light 60 is 808 nm.
  • the control circuit 26 controls driving of the excitation light source 51.
  • the excitation light 60 emitted from the excitation light source 51 propagates through the optical fiber 52.
  • the excitation optical system 54 converges the excitation light 60 emitted from the emission end 53 of the optical fiber 52.
  • the resonant mirror 55 has a characteristic of transmitting light in a wavelength region including the wavelength of the excitation light 60 and reflecting light in a wavelength region including the first wavelength and the second wavelength.
  • the resonant mirror 55 transmits the excitation light 60 from the excitation optical system 54.
  • the laser medium 56, the Q switch element 57, the wavelength separation element 58, the THG crystal 12, and the SHG crystal 11 are provided in the optical path between the two resonance mirrors 55 and 59.
  • the laser medium 56 enters an excited state due to absorption of the excitation light 60, and spontaneously emitted light is generated as the energy state transitions from the excited state.
  • the laser medium 56 amplifies spontaneous emission light reciprocating between the two resonant mirrors 55 and 59 by stimulated emission, and emits a laser beam 21 that is a fundamental wave.
  • the laser medium 56 is a YAG crystal or YVO4 crystal that is a laser crystal doped with neodymium or ytterbium.
  • the Q switch element 57 generates the laser beam 21 by Q switch oscillation.
  • the Q switch element 57 may not be provided.
  • the wavelength separation element 58 is provided between the Q switch element 57 and the THG crystal 12.
  • the wavelength separation element 58 has a characteristic of transmitting light in a wavelength region including the third wavelength and reflecting light in a wavelength region including the first wavelength and the second wavelength.
  • the wavelength separation element 58 separates the laser beams 21, 22 and 23 from the THG crystal 12 into the laser beam 23 and the laser beams 21 and 22. Further, the wavelength separation element 58 advances the laser beams 21 and 22 from the Q switch element 57 to the THG crystal 12.
  • One example of the wavelength separation element 58 is a dichroic mirror.
  • the wavelength conversion device 50 emits the laser beam 23 that has passed through the wavelength separation element 58.
  • the wavelength separation element 58 may have a characteristic of reflecting the light of the third wavelength and transmitting the light of the first wavelength and the light of the second wavelength.
  • the wavelength separation element 58 may be any optical element other than a dichroic mirror as long as it can separate light based on a difference in wavelength.
  • the wavelength separation element 58 may be a prism that separates light using a difference in refractive index of light depending on the wavelength.
  • the resonant mirror 59 has a characteristic of reflecting light in a wavelength region including the first wavelength and the second wavelength.
  • Laser beams 21 and 22 from the resonance mirror 59 and laser beams 21 and 22 from the THG crystal 12 are incident on the SHG crystal 11.
  • the SHG crystal 11 converts the laser beam 21 into a laser beam 22 that is a second beam and a pulsed laser beam.
  • the SHG crystal 11 emits the generated laser beam 22 and the remaining laser beam 21 without being converted into the laser beam 22.
  • the SHG crystal 11 transmits the laser beam 22 incident from the THG crystal 12 or the resonance mirror 59.
  • the laser beams 21 and 22 from the wavelength separation element 58 and the laser beams 21 and 22 from the SHG crystal 11 are incident on the THG crystal 12.
  • the THG crystal 12 converts the laser beams 21 and 22 into a laser beam 23 which is a third beam and a pulse laser beam.
  • the THG crystal 12 emits the generated laser beam 23 and the remaining laser beams 21 and 22 without being converted into the laser beam 23.
  • the laser beams 21 and 22 reciprocate between the two resonance mirrors 55 and 59.
  • the two resonant mirrors 55 and 59 may have a curved surface shape with a radius of curvature so as to form a beam waist with the SHG crystal 11.
  • the wavelength conversion device 50 includes a moving mechanism 41 for moving the SHG crystal 11 as in the second embodiment.
  • the moving mechanism 41 as adjusting means adjusts the conversion efficiency from the laser beam 21 to the laser beam 22 in the SHG crystal 11 by moving the SHG crystal 11.
  • the wavelength conversion device 50 may include the moving mechanism 30 shown in FIG. 1 instead of the moving mechanism 41.
  • the moving mechanism 30 as the adjusting means adjusts the conversion efficiency ⁇ in the SHG crystal 11 by moving the lens 15 that is an optical element for converging the laser beam 21, as in the first embodiment.
  • the moving mechanism 30 may adjust the conversion efficiency ⁇ by individually moving the plurality of lenses 15 that are optical elements.
  • the wavelength conversion device 50 has an effect that it is possible to improve and stabilize the intensity of the output harmonic, as in the first and second embodiments.
  • FIG. 15 is a diagram illustrating a schematic configuration of the wavelength conversion device 70 according to the fourth embodiment of the present invention.
  • the wavelength conversion device 70 is provided with a pulse laser light source 71 and a frequency controller 72 instead of the laser light source 10 in the second embodiment shown in FIG.
  • the configurations other than the pulse laser light source 71 and the frequency controller 72 in the wavelength conversion device 70 are the same as the configurations other than the laser light source 10 in the wavelength conversion device 40 according to the second embodiment.
  • the same parts as those in the first and second embodiments are denoted by the same reference numerals, and redundant description is omitted.
  • the pulse laser light source 71 is a laser light source that emits a laser beam 21 that is a first beam and a pulse laser beam.
  • the frequency controller 72 controls a pulse oscillation frequency that is a frequency at which the laser beam 21 is emitted from the pulse laser light source 71 by adjusting the drive timing of the pulse laser light source 71.
  • the control circuit 26 controls the frequency controller 72.
  • the SHG crystal 11 converts the laser beam 21 into a laser beam 22 that is a second beam and a pulsed laser beam.
  • the THG crystal 12 converts the laser beams 21 and 22 into a laser beam 23 which is a third beam and a pulse laser beam.
  • the wavelength conversion device 70 includes a moving mechanism 41 for moving the SHG crystal 11 as in the second embodiment.
  • the moving mechanism 41 is adjusting means for adjusting the conversion efficiency ⁇ from the laser beam 21 to the laser beam 22 in the SHG crystal 11 by moving the SHG crystal 11.
  • the moving mechanism 41 adjusts the conversion efficiency ⁇ when the pulse oscillation frequency of the laser beam 21 is changed, in addition to adjusting the conversion efficiency ⁇ as in the second embodiment.
  • the moving mechanism 41 adjusts the conversion efficiency ⁇ so that the temperature dependence of the intensity of the laser beam 23 at the temperature of the SHG crystal 11 has a single maximum value.
  • the temperature of the SHG crystal 11 showing the maximum value and the temperature of the SHG crystal 11 showing the maximum intensity of the laser beam 22 are kept the same.
  • the intensity of the laser beam 21 for each pulse emitted from the pulse laser light source 71 decreases as the pulse oscillation frequency increases.
  • the intensity of the laser beam 21 incident on the SHG crystal 11 decreases due to an increase in the pulse oscillation frequency
  • the conversion efficiency ⁇ from the laser beam 21 to the laser beam 22 in the SHG crystal 11 decreases.
  • the intensity of the laser beam 21 for each pulse emitted from the pulse laser light source 71 increases as the pulse oscillation frequency decreases.
  • the conversion efficiency ⁇ from the laser beam 21 to the laser beam 22 in the SHG crystal 11 increases.
  • the wavelength converter 70 is adjusted according to the procedure shown in FIG. 13 when F1, which is a certain value, is set to the pulse oscillation frequency.
  • F1 which is a certain value
  • the conversion efficiency ⁇ from the laser beam 21 to the laser beam 22 in the SHG crystal 11 Becomes lower.
  • the intensity peak of the laser beam 23 is a single peak, while the maximum value of the intensity of the laser beam 23 may be lower than Pmax. In this case, the intensity of the laser beam 23 output from the wavelength conversion device 70 may be low.
  • the wavelength conversion device 70 makes it possible to readjust the conversion efficiency ⁇ in the SHG crystal 11 by the procedure shown in FIG. 13 when the pulse oscillation frequency is changed to F2, which is higher than F1 at the time of past adjustment. Since the intensity peak of the laser beam 23 is maintained as a single peak, in the readjustment, the steps from Step S11 to Step S14 shown in FIG. May be.
  • the wavelength converter 70 adjusted according to the procedure shown in FIG. 13, when the pulse oscillation frequency is changed to F3 which is lower than F1, conversion from the laser beam 21 to the laser beam 22 in the SHG crystal 11 is performed.
  • the efficiency ⁇ increases.
  • the intensity peak of the laser beam 23 may change from a single peak to a plurality of peaks.
  • the intensity of the laser beam 23 generated by the THG crystal 12 may decrease.
  • the intensity peak of the laser beam 23 becomes a plurality of peaks, the intensity change of the laser beam 23 due to the temperature change of the SHG crystal 11 may become large.
  • the wavelength conversion device 70 can readjust the conversion efficiency ⁇ in the SHG crystal 11 by the procedure shown in FIG. Since the intensity peak of the laser beam 23 may change from a single peak to a plurality of peaks, in the readjustment, the procedure from step S11 is performed as in the second embodiment.
  • the wavelength conversion device 70 can output the high-intensity laser beam 23 by adjusting the conversion efficiency ⁇ in the SHG crystal 11 again when the pulse oscillation frequency is changed. A change in intensity of the laser beam 23 due to a temperature change can be reduced.
  • the wavelength conversion device 70 may include the moving mechanism 30 shown in FIG. 1 instead of the moving mechanism 41.
  • the wavelength converter 70 is provided with a pulse laser light source 71 and a frequency controller 72 instead of the laser light source 10 in the first embodiment shown in FIG.
  • the configurations other than the pulse laser light source 71 and the frequency controller 72 in the wavelength conversion device 70 are the same as the configurations other than the laser light source 10 in the wavelength conversion device 1 according to the first embodiment.
  • the moving mechanism 30 that is an adjusting means moves the lens 15 that is an optical element that converges the laser beam 21 from the laser beam 21 in the SHG crystal 11 when the frequency at which the laser beam 21 is emitted is changed.
  • the conversion efficiency ⁇ to the laser beam 22 is adjusted. Similar to the first embodiment, the moving mechanism 30 moves the position of the beam waist 35 as shown in FIGS. 2 and 3 to change the effective beam diameter W eff of the laser beam 21 in the SHG crystal 11. Thereby, the moving mechanism 30 adjusts the conversion efficiency ⁇ .
  • the moving mechanism 30 may individually move the plurality of lenses 15 that are optical elements.
  • the moving mechanism 30 individually moves the lenses 15A, 15B, and 15C in the Z-axis direction in the condensing optical system 36 including the three lenses 15A, 15B, and 15C.
  • the moving mechanism 30 enables each of the lenses 15 ⁇ / b> A, 15 ⁇ / b> B, and 15 ⁇ / b> C to be individually moved to expand and reduce the beam diameter at the beam waist 35.
  • the moving mechanism 30 changes the effective beam diameter W eff of the laser beam 21 in the SHG crystal 11 without moving the beam waist 35. Thereby, the moving mechanism 30 adjusts the conversion efficiency ⁇ .
  • the wavelength conversion device 50 according to the third embodiment may readjust the conversion efficiency ⁇ similarly to the wavelength conversion device 70 according to the fourth embodiment when the frequency of the Q switch oscillation in the Q switch element 57 is changed.
  • the moving mechanism 41 or the moving mechanism 30 that is the adjusting means of the wavelength conversion device 50 adjusts the conversion efficiency ⁇ when the frequency at which the laser beam 21 is emitted is changed.
  • the wavelength conversion device 50 can output a high-intensity laser beam 23 and can reduce a change in the intensity of the laser beam 23 due to a temperature change of the SHG crystal 11.
  • the wavelength conversion device 70 adjusts the conversion efficiency ⁇ by the adjusting means when the frequency at which the laser beam 21 is emitted is changed.
  • the wavelength conversion device 70 can reduce the change in the intensity of the laser beam 23 due to the temperature change of the SHG crystal 11 by adjusting the conversion efficiency ⁇ . Further, the wavelength conversion device 70 can output a high-intensity laser beam 23. As a result, the wavelength conversion device 70 has an effect that it is possible to improve and stabilize the intensity of the output harmonics.
  • the configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

La présente invention concerne un appareil de conversion de longueur d'onde (1) comprenant : un premier milieu non linéaire (11) qui convertit un premier faisceau (21) qui est une onde de base oscillée par impulsions en un deuxième faisceau (22) qui est une onde harmonique de l'onde de base ; un deuxième milieu non linéaire (12) qui produit un troisième faisceau (23) sur la base du deuxième faisceau et du premier faisceau transmis à travers le premier milieu non linéaire ; et un moyen de réglage (30) permettant de régler l'efficacité de conversion du premier faisceau dans le deuxième faisceau. Lorsque la fréquence d'oscillation d'impulsion du premier faisceau est modifiée, le moyen de réglage maintient, par réglage de l'efficacité de conversion, un état dans lequel la dépendance à la température de l'intensité du troisième faisceau à la température du premier milieu non linéaire présente une valeur maximale unique, et dans lequel la température du premier milieu non linéaire présentant une valeur maximale et la température du premier milieu non linéaire à laquelle l'intensité du second faisceau présente une valeur maximale, sont égales.
PCT/JP2017/018569 2017-05-17 2017-05-17 Appareil de conversion de longueur d'onde WO2018211637A1 (fr)

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PCT/JP2017/018569 WO2018211637A1 (fr) 2017-05-17 2017-05-17 Appareil de conversion de longueur d'onde
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