JP2007294498A - Pulse laser apparatus and method for generating pulse laser beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide pulse laser equipment which can produce a harmonic laser beam having a controlled pulse width. <P>SOLUTION: The pulse laser equipment comprises an optical resonator; a laser medium arranged in the optical resonator; an apparatus for exciting the laser medium; a Q switch for switching a first state where the quality factor Q of the optical resonator is relatively high and a second state where the Q is relatively low; a wavelength conversion element arranged in the optical resonator while including a nonlinear optical crystal and generating a harmonic of a basic wave emitted from the laser medium under the first state; a thermoregulator for varying the temperature of the wavelength conversion element; and a controller for storing the correspondence between the temperature of the wavelength conversion element and the pulse width of a harmonic generated from the wavelength conversion element along with a target pulse width, and controlling the thermoregulator such that the temperature of the wavelength conversion element becomes a target temperature corresponding to a target pulse width obtained from the correspondence. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pulse laser device and a pulse laser beam generation method, and more particularly to a pulse laser device and a pulse laser beam generation method that generate harmonics using a wavelength conversion element.

  A pulsed laser light source that emits a harmonic laser beam is used for laser processing (see, for example, Patent Document 1). In such a laser light source, a fundamental wave emitted from a laser medium is converted into a harmonic by a wavelength conversion element. A nonlinear optical crystal is used as the wavelength conversion element.

  As one method for maximizing the output of the harmonic laser beam, temperature phase matching is used. In temperature phase matching, the temperature of the wavelength conversion element is maintained at a temperature that maximizes the output of the harmonic laser beam.

JP 2005-136218 A

  In some cases, laser processing may be performed by controlling the pulse width to a desired value. However, the pulse width is not controlled in the conventional laser light source as described above.

  An object of the present invention is to provide a pulse laser apparatus and a pulse laser beam generation method capable of obtaining a harmonic laser beam with a controlled pulse width.

  According to a first aspect of the present invention, an optical resonator, a laser medium disposed in the optical resonator, a pumping device that supplies power for pumping the laser medium, and a quality factor of the optical resonator A Q switch that switches between a first state having a relatively high Q and a second state having a relatively low Q; and a non-linear optical crystal disposed in the optical resonator, wherein the laser medium is in the first state. A wavelength conversion element that generates a harmonic wave of the fundamental wave, a temperature controller that changes a temperature of the wavelength conversion element, a temperature of the wavelength conversion element, and the wavelength conversion element. The pulse width temperature dependency that is a correspondence relationship with the pulse width of the generated harmonics is stored, the target pulse width is stored, and the temperature of the wavelength conversion element is obtained from the pulse width temperature dependency. The target temperature corresponding to the target pulse width and In so that the pulse laser apparatus is provided with a control unit that performs first control for controlling the temperature controller.

  According to a second aspect of the present invention, an optical resonator, a laser medium disposed in the optical resonator, a pumping device that supplies power for pumping the laser medium, and a quality factor of the optical resonator A Q switch that switches between a first state having a relatively high Q and a second state having a relatively low Q; and a non-linear optical crystal disposed in the optical resonator, wherein the laser medium is in the first state. A wavelength conversion element that generates a harmonic of the fundamental wave, a temperature controller that changes a temperature of the wavelength conversion element, and a pulse of the harmonic generated by the wavelength conversion element. A pulse width measuring device for measuring the width and an allowable range of the pulse width are stored, and it is determined whether the pulse width measured by the pulse width measuring device is out of the allowable range, and measured by the pulse width measuring device. The measured pulse width is within the allowable range Control that changes the temperature of the wavelength conversion element so that the pulse width of the harmonics generated by the wavelength conversion element becomes a value within the allowable range by controlling the temperature controller when it is off A pulsed laser device is provided.

  According to a third aspect of the present invention, (a) a wavelength conversion element including a nonlinear optical crystal is provided, a fundamental wave emitted from a laser medium is converted into a harmonic by the wavelength conversion element, A step of preparing a pulse laser device that emits a pulse laser beam; and (b) a correspondence relationship between a temperature of the wavelength conversion element and a pulse width of a harmonic generated by the wavelength conversion element for the pulse laser device. Measuring a pulse width temperature dependency; and (c) determining a target temperature of the wavelength conversion element corresponding to a target pulse width based on the pulse width temperature dependency measured in the step (b). (D) A step of controlling the temperature of the wavelength conversion element so as to be the target temperature determined in the step (c) is provided.

  According to a fourth aspect of the present invention, (a) a wavelength conversion element including a nonlinear optical crystal is provided, a fundamental wave emitted from a laser medium is converted into a harmonic by the wavelength conversion element, A step of preparing a pulse laser device for emitting a pulse laser beam; (b) a step of measuring a pulse width of the pulse laser beam emitted from the pulse laser device; and (c) a value measured in the step (b). A step of determining whether or not the pulse width is out of a predetermined allowable range; and (d) when the pulse width is out of the allowable range in the step (c), the pulse laser device emits the pulse width. And a step of changing the temperature of the wavelength conversion element so that the pulse width of the pulse laser beam falls within the allowable range.

  According to the pulse laser device and the pulse laser beam generation method of the first and third aspects, the pulse width is controlled by controlling the temperature of the wavelength conversion element so as to be the target temperature obtained from the pulse width temperature dependency. Can be controlled.

  According to the pulse laser device and the pulse laser beam generation method of the second and fourth aspects, the pulse width is controlled by controlling the temperature of the wavelength conversion element so that the pulse width falls within an allowable range based on the measurement result of the pulse width. The width can be controlled.

  A pulse laser apparatus according to an embodiment of the present invention will be described with reference to FIG. The reflecting mirrors 1 a to 1 d constitute the optical resonator 1, and the reflecting mirrors 1 a and 1 d define both ends of the optical resonator 1. The reflecting mirrors 1a to 1d are arranged so that the light reflected by the reflecting mirror 1a is sequentially reflected by the reflecting mirrors 1b and 1c and enters the reflecting mirror 1d. A laser medium 2 and a Q switch 3 are disposed between the reflecting mirrors 1a to 1b. For example, a YLF rod is used as the laser medium 2.

  The excitation source 5 is composed of a diode laser, for example. The laser medium 2 is excited by the laser beam incident from the excitation source 5. The control device 100 controls the power of the laser beam emitted from the excitation source 5. The control device 100 is configured using, for example, a personal computer.

The wavelength conversion element 4 is arranged between the reflecting mirrors 1c to 1d. As the wavelength conversion element 4, a crystal having a nonlinear optical effect, for example, a lithium triborate (LiB ₃ O ₅ ) crystal (LBO crystal) is used. By making the fundamental wave emitted from the laser medium 2 enter the wavelength conversion element 4, the second harmonic of this fundamental wave can be generated. For example, a fundamental wave having a wavelength of 1054 nm is emitted from the laser medium 2 composed of a YLF rod, and a second harmonic having a wavelength of 527 nm is generated by the wavelength conversion element 4.

  The reflecting mirror 1c is a dichroic mirror that reflects the fundamental wave and transmits the second harmonic. The reflecting mirror 1d reflects both the fundamental wave and the second harmonic. Since the second harmonic wave passes through the dichroic mirror 1c and is emitted out of the optical resonator 1, it does not enter the reflecting mirrors 1a and 1b. The reflecting mirrors 1a and 1b reflect the fundamental wave.

  The Q switch 23 switches between a state where the quality factor Q of the optical resonator 1 is relatively low and a state where the quality factor Q is relatively high (a relatively high state is referred to as an on state). In the ON state, a fundamental wave is emitted from the laser medium 2 by stimulated emission, the fundamental wave is converted into the second harmonic by the wavelength conversion element 4, and the second harmonic is emitted from the dichroic mirror 1c to the outside of the optical resonator 1. (Laser oscillation in the on state)

  The control device 100 sends an opportunity signal sig to the Q switch 3. The Q switch 3 is turned on at a predetermined repetition frequency (for example, 1 kHz) by the trigger signal sig, and a second harmonic pulse laser beam L1 having a predetermined repetition frequency is emitted from the dichroic mirror 1c.

  The temperature controller 6 changes the temperature of the wavelength conversion element 4. For example, a heater is used as the temperature controller 6. In addition, you may use what can perform both heating and cooling, such as a Peltier element, as the temperature regulator 6. FIG. The control device 100 controls the temperature regulator 6 so that the wavelength conversion element 4 has a desired temperature.

  The reflecting mirror 1d that defines one end of the optical resonator 1 reflects both the fundamental wave and the second harmonic, but there is leakage light L2 that passes through the reflecting mirror 1d. The leaked light L2 enters the filter 7. The filter 7 transmits the second harmonic wave without transmitting the fundamental wave. The second harmonic transmitted through the filter 7 enters the photodetector 8.

  The photodetector 8 generates an electrical signal corresponding to the power of incident light and outputs it to the oscilloscope 9. The oscilloscope 9 measures the pulse width of the second harmonic component of the leakage light L2 based on the input electrical signal. This pulse width is equal to the pulse width of the pulse laser beam L1 emitted from the dichroic mirror 1c. Data corresponding to the pulse width measured by the oscilloscope 9 is input to the control device 100.

  The pulse laser beam L1 emitted from the dichroic mirror 1c enters the sorting optical system 20. The sorting optical system 20 sorts the pulse laser beam L1 into an optical path incident on the workpiece 21 and an optical path incident on the power meter 10. As the sorting optical system 20, for example, a galvanometer mirror can be used. The control device 100 controls the sorting optical system 20. The power meter 10 measures the average power of the incident pulse laser beam. The average power measured by the power meter 10 is energy emitted from the dichroic mirror 1c per unit time. Data corresponding to the average power measured by the power meter 10 is input to the control device 100.

  FIG. 2 is a graph showing an example of data obtained by measuring the dependence of the average power of the pulse laser beam L1 on the temperature of the wavelength conversion element 4 and the dependence of the pulse width of the pulse laser beam L1 on the temperature of the wavelength conversion element 4. is there. The laser medium 2 is a YLF rod, and the wavelength conversion element 4 is an LBO crystal. The horizontal axis of the graph is the temperature of the wavelength conversion element 4 expressed in Fahrenheit, the vertical axis on the left side of the graph is the average power expressed in W units, and the vertical axis on the right side of the graph is the pulse width expressed in ns units. . A curve C1 shows the temperature dependence of the average power, and a curve C2 shows the temperature dependence of the pulse width. The power supplied from the excitation source 5 to the laser medium 2 is constant.

  First, the temperature dependence of average power will be described. The average power is 21.0 W, the maximum around 324.5 degrees Fahrenheit. The maximum average power is called maximum power. The range of 323.0 degrees to 325.8 degrees Fahrenheit (range A shown in the figure) is a temperature range in which an average power of 95% or more of the maximum power is always obtained. Whether the temperature is higher or lower than range A, only an average power lower than 95% of the maximum power can be obtained.

  The average power of the pulse laser beam L1 corresponds to the conversion efficiency from the fundamental wave to the second harmonic by the wavelength conversion element 4. The higher the average power of the pulse laser beam L1, the higher the conversion efficiency to the second harmonic, and the lower the average power, the lower the conversion efficiency to the second harmonic. By reducing the conversion efficiency to the second harmonic, the power of the fundamental wave in the optical resonator 1 is relatively increased. This can cause damage to the optical resonator. In order to keep the output of the pulse laser beam L1 at a high level and prevent damage to the apparatus, it is preferable to keep the temperature of the wavelength conversion element 4 within the range A.

  Next, the temperature dependence of the pulse width within the range A will be described. The pulse width varies within the range A, is relatively short near both ends of the range A, and is relatively long near the center of the range A. The shortest pulse width within the range A is 150 ns, which is obtained at 323.0 degrees Fahrenheit. The longest pulse width within the range A is 195 ns, and is obtained around 324.5 degrees Fahrenheit.

  As described above, by changing the temperature of the wavelength conversion element 4 within a temperature range in which an average power level close to the maximum power is obtained, the pulse width can be increased while maintaining a high average power level and suppressing damage to the apparatus. You can see that it can be changed. In the example shown in FIG. 2, the pulse width can be changed from 150 ns to 195 ns by changing the temperature of the wavelength conversion element 4 within the range A.

  Note that one pulse of the laser beam is emitted during the period in which the Q switch 3 is turned on once. The period for which the Q switch 3 is turned on is set to be sufficiently longer than the pulse width (for example, about 5 μs).

  Next, a pulse width control method using the pulse laser device of the embodiment will be described. First, the dependence of the average power of the pulse laser beam L1 on the temperature of the wavelength conversion element 4 and the dependence of the pulse width of the pulse laser beam L1 on the temperature of the wavelength conversion element 4 are measured. These measurement data are stored in the control device 100.

  Next, the maximum power is obtained based on the temperature dependence of the average power, and a certain percentage or more of the maximum power is defined as an average power allowable range (referred to as a power allowable range). The lower limit of the power allowable range is set to 95% of the maximum power, for example. Further, a temperature range corresponding to the power allowable range is obtained based on the temperature dependence of the average power. The power allowable range and the temperature range corresponding to the power allowable range are stored in the control device 100.

  Next, a desired pulse width (referred to as a target pulse width) is input to the control device 100. The control device 100 detects the temperature of the wavelength conversion element corresponding to the target pulse width based on the temperature dependence of the pulse width. Furthermore, the control device 100 determines whether or not the temperature corresponding to the detected target pulse width is included in the temperature range corresponding to the power allowable range.

  When the temperature corresponding to the detected target pulse width is included in the temperature range corresponding to the power allowable range, the temperature corresponding to the detected target pulse width is determined as the target temperature. By controlling the temperature of the wavelength conversion element 4 to the target temperature, the pulse width is controlled to be the target pulse width. Note that if the temperature corresponding to the detected target pulse width is not included in the temperature range corresponding to the allowable power range, the control device 100 issues a warning.

  In some cases, a plurality of temperatures of the wavelength conversion elements corresponding to the target pulse width are detected. In such a case, it is determined whether each of a plurality of detected temperatures is included in a temperature range corresponding to the power allowable range. When there are a plurality of temperatures determined to be included in the temperature range corresponding to the power allowable range, any one of them can be selected as the target temperature. For example, the lowest temperature among the temperatures determined to be included in the temperature range corresponding to the power allowable range can be selected as the target temperature.

  For example, consider the temperature dependence of the average power and pulse width shown in FIG. When 95% or more of the maximum power is set as the allowable power range, the temperature range A is a temperature range corresponding to the allowable power range. The target pulse width is set to 170 ns. Two temperatures corresponding to a pulse width of 170 ns exist in the range A: 323.4 degrees Fahrenheit and 325.5 degrees Fahrenheit. Therefore, for example, the target temperature can be 323.4 degrees Fahrenheit.

  Based on the temperature dependence of the pulse width, a pulse width range (referred to as a pulse width variable range) obtained at a temperature within the temperature range corresponding to the allowable power range can be obtained. The target pulse width needs to be included in the pulse width variable range. If the pulse width variable range is obtained in advance, the target pulse width can be selected from this range. For example, in the temperature dependence of the pulse width shown in FIG. 2, the pulse width variable range is from 150 ns to 195 ns.

  Note that the temperature dependence of the pulse width may change over time due to deterioration of the optical components. For this reason, as the temperature dependence of the pulse width stored in the control device 100 (referred to as a reference characteristic) is measured and the time when the pulse laser beam is actually emitted is separated, the pulse width is increased. There is a concern that the accuracy of control deteriorates.

  Next, a method for controlling the pulse width satisfactorily even when the temperature dependence of the pulse width changes with time will be described. First, the target temperature of the wavelength conversion element 4 is determined based on the reference characteristics by the method as described above, and the temperature of the wavelength conversion element 4 is controlled to the target temperature. However, when the temperature dependence of the pulse width changes with time, the pulse width at the target temperature may deviate from the target pulse width.

  Next, the pulse width at the target temperature is measured by the oscilloscope 9. The control device 100 stores an allowable range of the pulse width including the target pulse width. The control device 100 determines whether the pulse width at the target temperature is a value within the allowable range. If the pulse width is within the allowable range, the temperature of the wavelength conversion element 4 is maintained as it is.

  If the pulse width is out of the allowable range, the control to cancel the temperature of the wavelength conversion element 4 to the target temperature obtained based on the reference characteristics is canceled, and the wavelength is converted by a sufficiently small amount (for example, 0.1 degree Fahrenheit). The temperature of the element 4 is raised and the pulse width is measured again. If the measurement result approaches the target pulse width, the temperature of the wavelength conversion element 4 is further increased until the pulse width falls within the allowable range. When the pulse width deviates from the target pulse width by increasing the temperature of the wavelength conversion element 4, the pulse width is brought closer to the target pulse width by decreasing the temperature of the wavelength conversion element 4, and the pulse width is within the allowable range. Just keep it.

  Thus, by performing feedback control for adjusting the temperature of the wavelength conversion element 4 based on the measurement result of the pulse width, the pulse width can be brought close to the target pulse width. The target temperature determined from the reference characteristics can be used as the initial temperature of the wavelength conversion element 4 when performing such feedback control.

  Even if the temperature is kept constant, there is a possibility that the pulse width fluctuates with time and falls outside the allowable range. In such a case as well, the temperature of the wavelength conversion element 4 is adjusted based on the measurement result of the pulse width. By performing the feedback control to be adjusted, the pulse width can be maintained within an allowable range.

  If necessary, the reference characteristic may be updated by measuring the reference characteristic again at a predetermined frequency. If it is immediately after measuring the reference characteristic, the pulse width at the target temperature determined based on the reference characteristic is sufficiently close to the target pulse width.

  As described above, by using the pulse laser device of the embodiment, a harmonic pulse laser beam whose pulse width is controlled to a desired value can be obtained. In addition, the pulse width can be kept constant over time. Since the pulse width can be controlled to a desired value, when a plurality of pulse laser devices of the embodiment are used, the pulse widths of the plurality of pulse laser devices can be made equal. It is also possible to control the pulse width to change with time.

  Note that by changing the temperature of the wavelength conversion element 4, the average power also changes with the pulse width. As described above, the apparatus may be damaged due to a decrease in the average power of the pulsed laser beam L1.

  Next, a method for preventing such damage will be described. When laser processing is performed by the pulse laser apparatus of the embodiment, the distribution optical system 20 distributes the pulse laser beam L1 to the optical path incident on the workpiece 21.

  During the processing, the distribution optical system 20 distributes the pulse laser beam L1 to the optical path incident on the power meter 10 and measures the average power. The control device 100 determines whether or not the measured average power is equal to or higher than the lower limit value of the allowable power range, and issues a warning if the measured average power is lower than the lower limit value of the allowable power range. In this way, damage to the device due to a decrease in average power is prevented.

  In the pulse laser device having the temperature dependence of the average power shown in FIG. 2, for example, the average power range corresponding to the temperature range A is the power allowable range. When the temperature of the wavelength conversion element 4 is out of the range A, the average power is lower than the allowable range. Comparing the range of decrease in average power from the upper limit of range A to a temperature about 0.5 degrees Fahrenheit and the range of decrease in average power from the lower limit of range A to a temperature about 0.5 degrees Fahrenheit, The range of decrease on the upper side of range A is larger than the range of decrease on the lower side of range A.

  Consider the case where the temperature dependence of the pulse width shown in FIG. 2 is used as a reference characteristic. For example, if the target pulse width is 170 ns, the target temperature of the wavelength conversion element 4 can be selected from 323.4 degrees Fahrenheit on the relatively low temperature side and 325.5 degrees Fahrenheit on the relatively high temperature side. .

  However, when the target temperature on the relatively high temperature side is selected as the initial temperature and the feedback control of the temperature of the wavelength conversion element 4 is performed, the target temperature on the relatively low temperature side is selected as the initial temperature. Therefore, the temperature of the wavelength conversion element 4 tends to be higher than the range A than when feedback control is performed. Due to this, it is considered that selecting the target temperature on the relatively high temperature side has a higher risk of increasing the average power reduction range. Therefore, selecting a target temperature on the relatively low temperature side can reduce the risk of equipment damage due to a decrease in average power.

  Next, a method for adjusting the average power of the pulsed laser beam L1 by changing the power supplied from the excitation source 5 to the laser medium 2 will be described. When the power of the laser beam incident on the laser medium 2 from the excitation source 5 is increased, the power of the pulse laser beam L1 can be increased, and when the power of the laser beam incident on the laser medium 2 from the excitation source 5 is decreased. The power of the pulse laser beam L1 can be reduced.

  The control device 100 stores a desired average power (referred to as a target power) of the pulse laser beam L1. The control device 100 compares the measured average power of the pulse laser beam L1 with the target power, and when the measured average power is lower than the target power, the average power of the pulse laser beam L1 approaches the target power. When the power of the laser beam incident on the laser medium 2 is increased and the measured average power of the pulse laser beam L1 is higher than the target power, the laser is adjusted so that the average power of the pulse laser beam L1 approaches the target power. The power of the laser beam incident on the medium 2 is reduced. In this way, the average power of the pulse laser beam L1 can be adjusted.

  Consider the pulse laser apparatus having the temperature dependence of the average power and pulse width shown in FIG. For example, the average power when the pulse width is 150 ns (323.0 degrees Fahrenheit) is slightly lower than the average power when the pulse width is 195 ns (324.5 degrees Fahrenheit). By adjusting the average power as described above, the average power of the pulse widths 150 ns and 195 ns can be made equal.

  The pulse energy is determined by a formula of pulse energy = average power / repetition frequency, and can be estimated by a formula of pulse energy = pulse width × peak power. For example, the peak power can be changed by changing the pulse width under the condition that the average power and the repetition frequency are constant (that is, under the condition that the pulse energy is constant). Increasing the pulse width decreases the peak power, and decreasing the pulse width increases the peak power.

  Also, for example, the peak power can be changed by changing the pulse energy under the condition that the pulse width is constant. If the pulse energy increases, the peak power increases, and if the pulse energy decreases, the peak power also decreases.

  Similarly to the LBO crystal, the wavelength conversion element of the pulse laser apparatus of the embodiment is applicable to any nonlinear optical crystal (nonlinear optical crystal capable of temperature phase matching) in which the conversion efficiency from the fundamental wave to the harmonic can be controlled by temperature. It can be used as Although the dependence of the pulse width on the wavelength conversion element temperature is considered to vary depending on the type of crystal, as with the LBO crystal, the temperature of the wavelength conversion element is changed within a temperature range in which an average power above a certain level can be secured. Thus, it may be possible to change the pulse width.

  In the above embodiment, YLF is used as the laser medium. However, other laser mediums such as YAG can be used.

  In the above embodiment, the diode laser is used as the excitation source of the laser medium. However, other excitation sources such as a flash lamp may be used.

  For safety, a shutter capable of preventing laser oscillation may be disposed in the optical resonator of the pulse laser device as necessary.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

It is the schematic of the pulse laser apparatus by the Example of this invention. It is a graph which shows the dependence with respect to the temperature of the wavelength conversion element of the average power of a pulse laser beam, and the dependence with respect to the temperature of the wavelength conversion element of the pulse width of a pulse laser beam.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a-1d Reflector 2 Laser medium 3 Q switch 4 Wavelength conversion element 5 Excitation source 6 Temperature controller 7 Filter 8 Photo detector 9 Oscilloscope 10 Power meter 20 Sorting optical system 21 Object 100 Control apparatus L1 Pulse laser beam L2 Leakage light

Claims (11)

An optical resonator;
A laser medium disposed in the optical resonator;
An excitation device for supplying power for exciting the laser medium;
A Q switch for switching between a first state in which the quality factor Q of the optical resonator is relatively high and a second state in which the quality factor Q is relatively low;
A wavelength conversion element that is disposed in the optical resonator, includes a nonlinear optical crystal, and receives a fundamental wave emitted from the laser medium in the first state, and generates a harmonic of the fundamental wave;
A temperature controller for changing the temperature of the wavelength conversion element;
Stores the pulse width temperature dependency, which is the correspondence between the temperature of the wavelength conversion element and the pulse width of the harmonic generated by the wavelength conversion element, and stores the target pulse width, and the temperature of the wavelength conversion element is And a control device that performs a first control for controlling the temperature regulator so as to achieve a target temperature corresponding to the target pulse width obtained from the pulse width temperature dependency. Furthermore, having a pulse width measuring device for measuring the pulse width of the harmonics generated by the wavelength conversion element,
The control device stores an allowable range of a pulse width including the target pulse width, and the first pulse width measured by the pulse width measuring device in a state where the first control is performed is the pulse width. If the first pulse width is out of the allowable range of the pulse width, the first control is canceled and the temperature regulator is controlled. 2. The second control according to claim 1, wherein the second control is performed to change the temperature of the wavelength conversion element so that the pulse width of the harmonics generated by the wavelength conversion element becomes a value within an allowable range of the pulse width. Pulse laser device.   The control device stores power temperature dependency that is a correspondence relationship between the temperature of the wavelength conversion element and the power of the harmonics generated by the wavelength conversion element, and the harmonics generated by the wavelength conversion element. The temperature range corresponding to the allowable range of power obtained from the allowable range of power and the power temperature dependency is stored, and the target temperature is determined so as to be included in the temperature range. Pulse laser device.   4. The control device according to claim 3, wherein when a plurality of temperatures corresponding to the target pulse width are included in the temperature range, the control device selects the lowest temperature among the plurality of temperatures as the target temperature. 5. Pulse laser device. Furthermore, having a power measuring device for measuring the power of the harmonics generated by the wavelength conversion element,
The control device stores an allowable range of power, determines whether or not the power measured by the power measuring device is out of the allowable range, and issues a warning when the power is out of the allowable range. Item 3. The pulse laser device according to Item 1 or 2. Furthermore, having a power measuring device for measuring the power of the harmonics generated by the wavelength conversion element,
The control device stores a target power, and controls the excitation device to increase the power supplied to the laser medium when the power measured by the power measuring device is lower than the target power, 3. The pulse laser device according to claim 1, wherein when the power measured by a power measuring device is higher than the target power, the excitation device is controlled so as to reduce the power supplied to the laser medium. An optical resonator;
A laser medium disposed in the optical resonator;
An excitation device for supplying power for exciting the laser medium;
A Q switch for switching between a first state in which the quality factor Q of the optical resonator is relatively high and a second state in which the quality factor Q is relatively low;
A wavelength conversion element that is disposed in the optical resonator, includes a nonlinear optical crystal, receives a fundamental wave emitted from the laser medium in the first state, and generates a harmonic of the fundamental wave;
A temperature controller for changing the temperature of the wavelength conversion element;
A pulse width measuring device for measuring the pulse width of the harmonic generated by the wavelength conversion element;
The allowable range of the pulse width is stored, it is determined whether the pulse width measured by the pulse width measuring device is out of the allowable range, and the pulse width measured by the pulse width measuring device is out of the allowable range. A control device that controls the temperature controller to change the temperature of the wavelength conversion element so that the pulse width of the harmonics generated by the wavelength conversion element is within the allowable range. And a pulse laser device. (A) A pulse laser device having a wavelength conversion element including a nonlinear optical crystal, converting a fundamental wave emitted from a laser medium into a harmonic by the wavelength conversion element, and emitting a pulse laser beam of the harmonic is prepared. And a process of
(B) for the pulse laser device, measuring a pulse width temperature dependency which is a correspondence relationship between the temperature of the wavelength conversion element and the pulse width of a harmonic generated by the wavelength conversion element;
(C) determining a target temperature of the wavelength conversion element corresponding to a target pulse width based on the pulse width temperature dependency measured in the step (b);
(D) A pulse laser beam generation method including a step of controlling the temperature of the wavelength conversion element so as to be the target temperature determined in the step (c). further,
(E) for the pulse laser device, measuring power temperature dependency which is a correspondence relationship between the temperature of the wavelength conversion element and the power of the harmonics generated by the wavelength conversion element;
(F) based on the power temperature dependency measured in the step (e), obtaining a power allowable range and a temperature range corresponding to the allowable range,
The pulse laser beam generation method according to claim 8, wherein in the step (c), the target temperature is determined so as to be included in the temperature range determined in the step (f).   In the step (c), when a plurality of temperatures corresponding to the target pulse width are included in the temperature range determined in the step (f), the lowest temperature among the plurality of temperatures is set as the target temperature. The pulse laser beam generation method according to claim 9, wherein the pulse laser beam generation method is selected as a temperature. (A) A pulse laser device having a wavelength conversion element including a nonlinear optical crystal, converting a fundamental wave emitted from a laser medium into a harmonic by the wavelength conversion element, and emitting a pulse laser beam of the harmonic is prepared. And a process of
(B) measuring the pulse width of the pulse laser beam emitted from the pulse laser device;
(C) determining whether or not the pulse width measured in the step (b) is out of a predetermined allowable range;
(D) When the pulse width is out of the allowable range in the step (c), the wavelength conversion element is adjusted so that the pulse width of the pulse laser beam emitted from the pulse laser device is within the allowable range. And a method of generating a pulsed laser beam.

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