JP2000022254A - Laser oscillation control method and device - Google Patents

Abstract

(57) Abstract: To reliably prevent a temperature change of a photoacoustic optical element due to a change in input intensity of an acoustic wave input to the photoacoustic optical element. A birefringent photoacoustic optical element to which a first acoustic wave is input is arranged in a laser resonator, and a wavelength tunable laser capable of oscillating laser in a predetermined wavelength range is incident on the photoacoustic optical element. Then, in the wavelength selection method of controlling the wavelength according to the frequency of the first acoustic wave, the second acoustic wave is input to the photoacoustic optical element together with the first acoustic wave, and the frequency of the first acoustic wave is Laser oscillation frequency,
The frequency of the second acoustic wave is a frequency at which laser oscillation is not possible, the input intensity value of the first acoustic wave is an input intensity value at which laser oscillation is possible based on the frequency of the first acoustic wave, and the input intensity value of the second acoustic wave is The value is a value obtained by subtracting the input intensity value of the first acoustic wave from the predetermined value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser oscillation control method and apparatus, and more particularly, to a laser oscillation control method and apparatus capable of electronically controlling a laser oscillation wavelength at high speed and with high reliability. About.

[0002]

2. Description of the Related Art As a conventional laser oscillation control device, for example, a laser oscillation control device disclosed in Japanese Patent Application Laid-Open No. 9-172215 is known.

FIG. 1 shows a laser oscillation control device disclosed in FIG. 3 in JP-A-9-172215. In this laser oscillation control device, an emission mirror 112 having a predetermined transmittance is used. And a total reflection mirror 110 constitute a laser resonator.

In the laser resonator, a Ti: Al2O3 laser crystal 14 as a laser medium of a wavelength tunable laser, a photoacoustic optical crystal 100 as a photoacoustic optical element for selecting a wavelength, and a diffraction light correcting prism 28 are sequentially arranged from the emission side mirror 112 to the total reflection mirror 110 side.

A piezoelectric element 22 driven by an RF power supply 20 is attached to the photoacoustic optical crystal 100 as acoustic wave input means. Accordingly, when the piezoelectric element 22 is driven by the RF power source 20 to cause distortion in the piezoelectric element 22, an acoustic wave having a frequency corresponding to the distortion is generated in the photoacoustic optical crystal 100 based on the distortion of the piezoelectric element 22. Will be entered.

The diffracted light correction prism 28 is configured to always emit the diffracted light 106 emitted from the photoacoustic optical crystal 100 in a fixed direction regardless of the wavelength. , Diffraction light correction prism 2
It is configured to reflect the light emitted from 8.

In the above arrangement, the second harmonic of an Nd: YAG laser is used as the excitation laser 24 and Ti:
The Al2O3 laser crystal 14 is excited. Further, the piezoelectric element 22 is driven by controlling the RF frequency input from the RF power supply 20 according to the wavelength of the emitted laser light to be emitted from the emission side mirror 112.

As described above, the photoacoustic optical crystal 10
In the light emitted from the Ti: Al2O3 laser crystal 14 and having a wavelength corresponding to the RF frequency input from the RF power source 20, the light emitted from the Ti: Al2O3 laser crystal 14 is diffracted in a predetermined direction. Then, the light is emitted from the photoacoustic optical element 100 as the diffracted light 106.

Further, the diffracted light 106 diffracted and emitted from the photoacoustic optical crystal 100 in a predetermined direction enters the diffracted light correcting prism 28 and is emitted in a certain direction. The light emitted from the diffraction light correcting prism 28 is reflected by the total reflection mirror 110 and reciprocates in the laser resonator.

[0010] Therefore, the R input from the RF power supply 20
Only the light of the wavelength corresponding to the F frequency is amplified to cause laser oscillation, and only the emitted laser light of the wavelength can be emitted from the laser resonator.

As described above, in the conventional laser oscillation control apparatus, the RF frequency input by the RF power supply 20, that is, the acoustic wave frequency input to the photoacoustic optical crystal 100 is varied so that the RF power supply 20 Only the output laser light having a wavelength corresponding to the input RF frequency, that is, the acoustic wave frequency input to the photoacoustic optical crystal 100 can be selectively emitted.

Incidentally, in the photoacoustic optical crystal 100, the RF input intensity input from the RF power supply 20, that is,
The diffraction efficiency of the photoacoustic optical crystal 100 is affected according to the acoustic wave intensity input to the photoacoustic optical crystal 100, and the RF input intensity, that is, the change in the acoustic wave intensity input to the photoacoustic optical crystal 100 It is known that the output intensity of the emitted laser light changes.

Moreover, the RF input intensity for obtaining the output laser having the highest output intensity, that is, the photoacoustic optical crystal 10
The acoustic wave intensity input to 0 is different depending on the frequency of the emitted laser light and the RF frequency, that is, the acoustic wave frequency input to the photoacoustic optical crystal 100.

When the applicant of the present invention conducted an experiment using the laser oscillation control apparatus shown in FIG. 1, as shown in FIG. 2, for example, the oscillation wavelength of the emitted laser light was about 850 nm to about 1 nm.
At 000 nm, when the RF input intensity is set to 2 W, the output laser light having a higher output intensity can be obtained than when the RF input intensity is set to 1 W, while the oscillation wavelength of the output laser light is about 720 nm to about 720 nm. At 850 nm, setting the RF input intensity to 1 W makes the RF input intensity 2 W
It was possible to obtain outgoing laser light with higher output intensity than that described above.

Therefore, in order to obtain an output laser beam having a high output intensity, every time the RF frequency, ie, the acoustic wave frequency input to the photoacoustic optical crystal is changed, the RF input intensity, ie, the photoacoustic optical It was necessary to change the intensity of the acoustic wave input to the crystal.

However, when the RF input intensity, that is, the intensity of the acoustic wave input to the photoacoustic optical crystal is changed, the temperature of the photoacoustic optical crystal changes due to the absorption of the RF input, that is, the input of the acoustic wave. It has been pointed out that disorder of the refractive index and diffraction angle of the acousto-optic crystal 100 occurs, which adversely affects the oscillation wavelength and output intensity of the emitted laser light.

In particular, when the output intensity of the emitted laser light is controlled to be constant or the wavelength is swept while obtaining the maximum output intensity at each laser oscillation wavelength, the RF input intensity, ie, the light The intensity of the acoustic wave input to the acousto-optic crystal 100 must be changed according to the RF frequency, that is, the frequency of the acoustic wave input to the acousto-optic crystal 100. As a result, a rapid temperature change occurs, and the output intensity of the emitted laser light becomes unstable during high-speed sweep as compared with during low-speed sweep.

Therefore, in the prior art, a thermometer, a thermostat, a heat exchange medium (a heater, a Peltier element) are used in order to suppress a temperature change of the photoacoustic optical crystal which affects the output intensity of the emitted laser light. Such)
It has been realistically considered that the temperature of the photoacoustic optical crystal is controlled by heat conduction from a heat sink by using the method, and the feedback control is performed to stabilize the temperature.

However, the above-mentioned conventional method has the following problems (1) to (3).

(1) Inorganic / organic crystals, which are photoacoustic optical crystals, have poor thermal conductivity, and it is difficult to obtain a uniform heat distribution by external temperature control.

(2) There is a problem in that the speed of heat exchange is low, and it is difficult to control the temperature at a high speed corresponding to the wavelength change frequency (on the order of kHz) of the photoacoustic optical crystal.

(3) In the control by the feedback system, there is a problem that the timing of the temperature control is delayed due to the heat capacity of the thermometer and the heater, and it is impossible to follow the change of the RF frequency.

[0023]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned various problems of the prior art, and has as its object the following (1) to (4). While solving the problems in (3), the temperature of the photoacoustic optical element due to the change in the input intensity of the acoustic wave input to the photoacoustic optical element is reliably prevented, and the emitted laser light is emitted from the photoacoustic optical element. It is an object of the present invention to provide a laser oscillation control method and an apparatus therefor which are not affected by a change in temperature.

[0024]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for reliably preventing a temperature change of a photoacoustic optical element due to a change in input intensity of an acoustic wave input to the photoacoustic optical element. In addition, a second acoustic wave of a second frequency, which is a frequency outside the oscillatable range of the laser medium, is input to the photoacoustic optical element together with a first acoustic wave of the first frequency, which is the oscillation frequency of the emitted laser light. Then, the change in the input intensity of the first acoustic wave for controlling and sweeping the oscillation wavelength at the first frequency is offset by the input intensity of the second acoustic wave, whereby the temperature of the photoacoustic optical element is changed. This is to prevent. This is an active temperature control, which is completely different from control by a feedback method.

That is, according to the first aspect of the present invention, a birefringent photoacoustic optical element to which a first acoustic wave is input is arranged in a laser resonator, and a birefringent photoacoustic element is provided within a predetermined wavelength range. In a wavelength selection method of irradiating a wavelength-tunable laser capable of laser oscillation into the photoacoustic optical element and controlling the wavelength according to the frequency of the first acoustic wave, the first acoustic wave is transmitted to the photoacoustic optical element. And the second acoustic wave is input, the frequency of the first acoustic wave is a frequency at which laser oscillation is possible, the frequency of the second acoustic wave is a frequency at which laser oscillation is not possible, and the input of the first acoustic wave is The intensity value is an input intensity value that allows laser oscillation by the frequency of the first acoustic wave, and the input intensity value of the second acoustic wave is a value obtained by subtracting the input intensity value of the first acoustic wave from a predetermined value. Is something that I tried to do .

Therefore, according to the first aspect of the present invention, the photoacoustic optical element includes the first acoustic wave and the second acoustic wave.
Therefore, even if the input intensity of the first acoustic wave changes, the inside of the photoacoustic optical element is substantially changed even if the input intensity of the first acoustic wave changes. In, no change occurs in the input intensity of the acoustic wave. Therefore, a change in the temperature of the photoacoustic optical element due to a change in the input intensity of the first acoustic wave is prevented, and the possibility that the emitted laser light is affected by the change in the temperature of the photoacoustic optical element can be eliminated.

Here, the input intensity value of the first acoustic wave is set to a desired value in accordance with the frequency of the first acoustic wave, as in the second aspect of the present invention. It may be variable as possible.

The input intensity value of the first acoustic wave is
According to the third aspect of the present invention, an optimal value for laser oscillation can be obtained.

Further, the predetermined value may be changed according to the frequency of the first acoustic wave, as in the invention according to a fourth aspect of the present invention.

That is, there is a possibility that the absorptivity of the acoustic wave of the photoacoustic optical element and the efficiency of conversion into heat differ depending on the frequency of the acoustic wave. For example, the maximum value of the total input intensity of the acoustic wave is 1 W
It is assumed that the heat conversion efficiency at 80 MHz is half of the heat conversion efficiency at 130 MHz. Here, when the frequency of the first acoustic wave is set to 80 MHz or 130 MHz, and the input intensity value of the first acoustic wave is controlled at 0.5 W in each case, the first acoustic wave is considered. The input intensity value of the second acoustic wave given when the frequency of the wave is 80 MHz is 0.5 W, and the frequency of the first acoustic wave is 1
At 30 MHz, the input intensity value of the second acoustic wave, 0.
Twice the strength of 25W is required.

The heat conversion efficiency at the frequency ω of the acoustic wave is e
(ω), the frequency of the first acoustic wave and the input intensity are respectively ω
1, I1, the frequency and input intensity of the second acoustic wave are ω2 and I2, respectively, and the amount of heat generated is h, and the amount of heat h generated at h = e (ω1) × I1 + e (ω2) × I2 So that I1 and I2
It is desirable to control the laser while maintaining the relationship.

However, if e (ω1) and e (ω2) are always approximately equal to arbitrary ω1 and ω2, “I1
By keeping "+ I2" constant, laser control can be performed.

Further, the frequency dependence of the heat conversion efficiency of the photoacoustic optical element varies depending on the size of the element, and so on.
It is preferable that the total input intensity value of the input intensity value of the first acoustic wave and the input intensity value of the second acoustic wave can be set to any value with respect to the frequency of the first acoustic wave.

Further, the frequency of the second acoustic wave is variable according to the frequency of the first acoustic wave within a frequency band where laser oscillation is not possible, as in the invention according to a fifth aspect of the present invention. It may be done.

That is, if the frequency of the first acoustic wave and the frequency of the second acoustic wave are very close to each other, swelling will occur due to the interaction between the acoustic waves.
When such undulation occurs, the laser oscillation intensity is adversely affected.

Also, even when the frequency of the first acoustic wave is far from the frequency of the second acoustic wave, swelling may occur. For example, if the frequencies are 80 MHz and 121 MHz
And the second harmonic of 80 MHz, 240
It is conceivable that an interaction may occur between MHz and 242 MHz, which is the first harmonic of 121 MHz.

For this reason, the frequency of the second acoustic wave is changed to the first
By maintaining the acoustic wave frequency at a value that does not cause undulation, the laser oscillation intensity can be prevented from being adversely affected.

Therefore, it is preferable that the frequency of the second acoustic wave is changed depending on the frequency of the first acoustic wave within a frequency band where laser oscillation is not possible.

According to a sixth aspect of the present invention, there is provided a laser resonator comprising mirrors having a predetermined reflectance facing each other, and a wavelength within a predetermined range provided in the laser resonator. A wavelength tunable laser medium capable of oscillating laser light in a wavelength range, a birefringent photoacoustic optical element disposed in the laser resonator and receiving light emitted from the wavelength tunable laser medium, and a first acoustic wave. First acoustic wave input means for generating a second acoustic wave and inputting the first acoustic wave to the photoacoustic optical element; second acoustic wave input means for generating a second acoustic wave and inputting the second acoustic wave to the photoacoustic optical element; Controlling the acoustic wave input means and the second acoustic wave input means to generate a first acoustic wave having a laser oscillating frequency and an input intensity value in the first acoustic wave input means, Second acoustic wave input means It is obtained as a control means for generating a second acoustic wave having an input intensity value obtained by subtracting the first input intensity value of the acoustic wave from the laser oscillating non frequency and a predetermined value.

Therefore, according to the sixth aspect of the present invention, the first acoustic wave input means and the second acoustic wave input means are controlled by the control means, and the photoacoustic optical element includes: Since the acoustic wave having the input intensity of the predetermined value is always input by the input of the first acoustic wave and the second acoustic wave, even if the input intensity of the first acoustic wave changes,
Substantially, no change occurs in the input intensity of the acoustic wave inside the photoacoustic optical element. Therefore, a change in the temperature of the photoacoustic optical element due to a change in the input intensity of the first acoustic wave is prevented, and the possibility that the emitted laser light is affected by the change in the temperature of the photoacoustic optical element can be eliminated.

Here, the control means sets the input intensity value of the first acoustic wave in a desired state according to the frequency of the first acoustic wave. It can be changed so that it can oscillate.

Further, the control means can set the input intensity value of the first acoustic wave to an optimum value for laser oscillation, as in the invention of claim 8.

[0043] The control means may vary the predetermined value according to the frequency of the first acoustic wave.

That is, there is a possibility that the absorptance of the acoustic wave of the photoacoustic optical element and the conversion efficiency into heat may differ depending on the frequency of the acoustic wave. For example, the maximum value of the total input intensity of the acoustic wave is 1 W
It is assumed that the heat conversion efficiency at 80 MHz is half of the heat conversion efficiency at 130 MHz. Here, when the frequency of the first acoustic wave is set to 80 MHz or 130 MHz, and the input intensity value of the first acoustic wave is controlled at 0.5 W in each case, the first acoustic wave is considered. The input intensity value of the second acoustic wave given when the frequency of the wave is 80 MHz is 0.5 W, and the frequency of the first acoustic wave is 1
At 30 MHz, the input intensity value of the second acoustic wave, 0.
Twice the strength of 25W is required.

The heat conversion efficiency at the frequency ω of the acoustic wave is e
(ω), the frequency of the first acoustic wave and the input intensity are respectively ω
1, I1, the frequency and input intensity of the second acoustic wave are ω2 and I2, respectively, and the amount of heat generated is h, and the amount of heat h generated at h = e (ω1) × I1 + e (ω2) × I2 So that I1 and I2
It is desirable to control the laser while maintaining the relationship.

However, if e (ω1) and e (ω2) are always approximately equal to arbitrary ω1 and ω2, “I1
By keeping "+ I2" constant, laser control can be performed.

Further, the frequency dependence of the heat conversion efficiency of the photoacoustic optical element changes depending on the size of the element, and so on.
It is preferable that the total input intensity value of the input intensity value of the first acoustic wave and the input intensity value of the second acoustic wave can be set to any value with respect to the frequency of the first acoustic wave.

Further, the control means sets the frequency of the second acoustic wave in accordance with the frequency of the first acoustic wave within a frequency band in which laser oscillation is not possible, as in the tenth aspect of the present invention. It can be variable.

That is, if the frequency of the first acoustic wave and the frequency of the second acoustic wave are very close to each other, undulation will occur due to the interaction between the acoustic waves.
When such undulation occurs, the laser oscillation intensity is adversely affected.

Also, even when the frequency of the first acoustic wave and the frequency of the second acoustic wave are far apart, swelling may occur. For example, if the frequencies are 80 MHz and 121 MHz
And the second harmonic of 80 MHz, 240
It is conceivable that an interaction may occur between MHz and 242 MHz, which is the first harmonic of 121 MHz.

For this reason, the frequency of the second acoustic wave is
By maintaining the acoustic wave frequency at a value that does not cause undulation, the laser oscillation intensity can be prevented from being adversely affected.

Therefore, it is preferable that the control means can change the frequency of the second acoustic wave depending on the frequency of the first acoustic wave within a frequency band where laser oscillation is not possible.

[0053]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a laser oscillation control method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a schematic structural explanatory view showing an example of an embodiment of a laser oscillation control device according to the present invention. Regarding the same or equivalent configuration as that of the conventional laser oscillation control device shown in FIG. In order to facilitate understanding, the same reference numerals are used.

In this laser oscillation control device, as in the case of the conventional laser oscillation control device, a laser resonator is constituted by an emission mirror 112 having a predetermined transmittance and a total reflection mirror 110.

In the laser resonator, a Ti: Al2O3 laser crystal 14 as a laser medium of a wavelength tunable laser, a photoacoustic optical crystal 100 as a photoacoustic optical element for selecting a wavelength, and a diffraction light correcting prism 28 are sequentially arranged from the emission side mirror 112 to the total reflection mirror 110 side.

In the photoacoustic optical crystal 100, as an acoustic wave input means, a first RF frequency (for example, 8) corresponding to a wavelength at which the Ti: Al2O3 laser crystal 14 can perform laser oscillation.
0 MHz to 130 MHz. ) That can generate
An F power source 10 and a second RF power source 1 capable of generating a second RF frequency (for example, 60 MHz) corresponding to a wavelength at which the Ti: Al2O3 laser crystal 14 cannot perform laser oscillation.
2, the first RF power source 10 and the second RF power source 1
2 is attached.

Therefore, when the piezoelectric element 22 is driven by the first RF frequency input from the first RF power source 10 to cause the piezoelectric element 22 to be distorted, the piezoelectric element 22 is distorted based on the distortion. Acoustic wave of frequency (first
Acoustic wave) is input to the photoacoustic optical crystal 100.

The diffracted light correcting prism 28 is configured to always emit the diffracted light 106 emitted from the photoacoustic optical crystal 100 in a fixed direction regardless of the wavelength. , Diffraction light correction prism 2
It is configured to reflect the light emitted from 8.

Then, the first RF power source 10 and the second R
The F power supply 12 is connected to an RF power supply control device 13 that controls the first RF power supply 10 and the second RF power supply 12.

The operation of the RF power supply controller 13 is controlled by, for example, a microcomputer. Based on the control of the RF power supply control device 13, the first RF frequency and the first RF input strength input from the first RF power supply 10 to the piezoelectric element 22 are controlled, and the first RF frequency and the first RF input intensity are input from the second RF power supply 12 to the piezoelectric element 22. The second RF frequency and the second RF input strength are controlled.

Here, the first RF power source 10 supplies the piezoelectric element 2
The first RF frequency and the first RF input intensity input to the second 2 and the second RF frequency and the second RF input intensity input to the piezoelectric element 22 from the second RF power supply 12 are set as described below. .

That is, since the light corresponding to the first RF frequency is oscillated by the laser in the Ti: Al 2 O 3 laser crystal 14 and extracted as the output laser light, the first RF frequency corresponds to the frequency of the output laser light as described above. The frequency at which laser oscillation is possible in the Ti: Al2O3 laser crystal 14 (for example, 80 MHz to 130 MHz).
MHz), and the second RF frequency is a frequency at which laser oscillation is impossible in the Ti: Al2O3 laser crystal 14 (for example, 60 MHz). Here, the second RF frequency may be a constant value or may be appropriately changed.

The first RF input intensity is preferably set to an intensity most suitable for laser oscillation at the first RF frequency, but the second RF input intensity is always the sum of the first RF input intensity (total input intensity). It is controlled to be constant.

That is, the sum of the first RF input intensity and the second RF input intensity is controlled so as to always become a preset total input intensity (for example, 2 W). It should be noted that the value of the total input strength can be appropriately set by the user to an arbitrary value.

Hereinafter, the first RF frequency, the second RF frequency,
The first RF input intensity and the second RF input intensity are summarized as follows.

(1) First RF frequency: desired laser oscillation frequency (for example, 80 MHz to 130 MHz) (2) Second RF frequency: frequency at which laser oscillation is not possible (for example, 60 MHz) 3) 1st RF input intensity: optimum value for laser oscillation at the first RF frequency (for example, 0 to 2 W) (4) 2nd RF2 input intensity: 1st R from total input intensity
A subtraction value obtained by subtracting the F input intensity (0 W to 2 W). The frequency of the acoustic wave input to the photoacoustic optical crystal 100 (the frequency of the first acoustic wave) is given by the first RF frequency, and the second RF The frequency of the acoustic wave input to the photoacoustic optical crystal 100 (the frequency of the second acoustic wave) is given by the frequency, and the photoacoustic optical crystal 10 is given by the first RF input intensity.
The input intensity of the acoustic wave (the input intensity of the first acoustic wave) input to 0 is given, and the input intensity of the acoustic wave (the input intensity of the second acoustic wave) input to the photoacoustic optical crystal 100 is given by the second RF input intensity. Input strength).

In the above configuration, the second harmonic of an Nd: YAG laser is used as the excitation laser 24 and Ti:
The Al2O3 laser crystal 14 is excited. Further, the first RF power source 10 is controlled by the RF power source control unit 14 in accordance with the wavelength of the emitted laser light to be emitted from the emission side mirror 112.
Controls the first RF frequency input from the
2 is driven.

As described above, the photoacoustic optical crystal 10
In the light emitted from the Ti: Al2O3 laser crystal 14 and incident in a wide wavelength band, the first RF
The outgoing light of a wavelength corresponding to the first RF frequency input by the power supply 10 is diffracted in a predetermined direction and
It is emitted from the photoacoustic optical element 100 as 06.

Further, the diffracted light 106 diffracted and emitted from the photoacoustic optical crystal 100 in a predetermined direction enters the diffracted light correcting prism 28 and is emitted in a certain direction. The light emitted from the diffraction light correcting prism 28 is reflected by the total reflection mirror 110 and reciprocates in the laser resonator.

Accordingly, only the light of the wavelength corresponding to the first RF frequency inputted by the first RF power supply 10 is amplified to cause laser oscillation, and only the emitted laser light of the wavelength can be emitted from the laser resonator. .

Here, in the laser oscillation control device described above, the first RF power is input by the first RF power supply 10 and the second RF frequency is input by the second RF power supply 12. That is, the second RF frequency is input as the compensation RF input at the second RF input intensity so as to cancel the fluctuation of the first RF input intensity of the first RF frequency used for the wavelength selection of the photoacoustic optical crystal 100, and the first RF input intensity and the second RF input intensity are changed. By always keeping the total value with 2RF input strength constant,
The thermal fluctuation of the photoacoustic optical crystal 100 is suppressed.

That is, in this laser oscillation control device, in order to keep the heat generated by the ultrasonic absorption of the photoacoustic optical crystal 100 constant even during wavelength sweeping, the photoacoustic optical crystal always uses the heat generated by the ultrasonic absorption. 100 is in thermal equilibrium with the outside air.

That is, assuming that the first RF input intensity is “I 1”, the second RF input intensity is “I 2”, and the total input intensity is “I total”, even if the laser is not oscillated by the RF power source control means 14, (I 1 = 0) so that the photoacoustic optical crystal 100 is always in a thermal equilibrium state.
otal ”by the RF power controller 14
The F power supply 12 is controlled. Then, the RF power control means 14
Even when the laser oscillation occurs (I1 ≠ 0), “I” is set so that the photoacoustic optical crystal 100 is always in thermal equilibrium.
1 + I2 = Itotal "
Controls the first RF power supply 10 and the second RF power supply 12.

Although the above is the basic principle, "I2 =
Since “Itotal−I1” is not always optimal,
It is preferable to appropriately adjust the value so that “2” and “Itotal−I1” are substantially equal.

In this way, the intensity of the acoustic wave input to the photoacoustic optical crystal 100 is always kept constant, and a thermal equilibrium state of the photoacoustic optical crystal 100 is realized.

Incidentally, there is a possibility that the absorptance of the acoustic wave of the photoacoustic optical crystal 100 and the conversion efficiency to heat may differ depending on the frequency of the acoustic wave. For example, it is assumed that the maximum value of the total input intensity of the acoustic wave is 1 W, and the heat conversion efficiency at 80 MHz is half of the heat conversion efficiency at 130 MHz. Here, the first RF
When the frequency is set to 80 MHz or 130 MHz, and the first RF input intensity is controlled at 0.5 W in each case, the second RF input intensity given when the first RF frequency is 80 MHz is 0.5 W
Therefore, twice the intensity of 0.25 W which is the second RF input intensity when the first RF frequency is 130 MHz is required.

The heat conversion efficiency at the frequency ω of the acoustic wave is e
(ω), when the first RF frequency and the first RF input intensity are ω1 and I1, respectively, the second RF frequency and the second RF input intensity are ω2 and I2, respectively, and the generated heat amount is h, h = e (ω1) In the case of × I1 + e (ω2) × I2, I1 and I2 are set so that the generated heat quantity h is constant.
It is desirable to control the laser while maintaining the relationship.

However, if e (ω1) and e (ω2) are always approximately equal for arbitrary ω1 and ω2, “I1
By keeping "+ I2" constant, laser control can be performed.

Since the frequency dependence of the heat conversion efficiency of the photoacoustic optical crystal 100 also changes depending on the size of the element, the total input intensity of the first RF input intensity and the second RF input intensity is equal to the first RF frequency. On the other hand, it is preferable that the value can be set at any value.

If the first RF frequency and the second RF frequency are very close to each other, swelling will occur due to the interaction between acoustic waves. When such undulation occurs, the laser oscillation intensity is adversely affected.

Further, even when the first RF frequency is separated from the second RF frequency, swelling may occur.
For example, when the frequencies are 80 MHz and 121 MHz, 240 MHz and 1
An interaction may occur with 242 MHz, which is the first overtone of 21 MHz.

For this reason, if the second RF frequency is kept at a value that does not cause undulation with respect to the first RF frequency,
The laser oscillation intensity can be prevented from being adversely affected.

Therefore, it is preferable that the second RF frequency is changed depending on the first RF frequency within a frequency band where laser oscillation is not possible.

Here, as shown in the graph of FIG. 4, when this laser oscillation control device is not used (in the case “before temperature control” indicated by a solid line), the acoustic wave input to the photoacoustic optical crystal is The effect of the change in the temperature of the photoacoustic optical crystal due to the change in the input intensity appears. When this laser oscillation control device is used (in the case of “after temperature control” indicated by a broken line),
The effect of the temperature change of the photoacoustic optical crystal due to the change of the input intensity of the acoustic wave input to the photoacoustic optical crystal does not appear at all.

In the actual wavelength sweeping method, a table is created by optimizing the input conditions of the second RF power supply 12 for each wavelength experimentally in advance for each wavelength, and a table is created. May be optimized and controlled.

Therefore, according to the above-described embodiment, the following effects (1) to (3) can be obtained.

(1) Since the photoacoustic optical crystal itself generates heat, the temperature distribution in the element can be kept constant regardless of the thermal conductivity.

(2) The amount of heat to be applied can be changed at a high speed regardless of the speed of heat exchange.

(3) Active temperature management is performed instead of feedback, so that there is no timing shift and fluctuations in RF input intensity can be covered.

In the above-described embodiment, the correction prism is provided, but it is needless to say that the correction prism need not be provided.

[0092]

Since the present invention is configured as described above, it is possible to reliably prevent the temperature change of the photoacoustic optical element due to the change of the input intensity of the acoustic wave input to the photoacoustic optical element. As a result, there is an excellent effect that the emitted laser light is not affected by the temperature change of the photoacoustic optical element.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a conventional laser oscillation control device.

FIG. 2 is a graph showing a relationship between a change in an acoustic wave intensity input to a photoacoustic optical crystal and a change in an output intensity of an output laser beam.

FIG. 3 is a schematic configuration explanatory view showing an example of an embodiment of a laser oscillation control device according to the present invention.

FIG. 4 is a graph showing the effect of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 1st RF power supply 12 2nd RF power supply 13 RF power supply control device 14 Ti: Al2O3 laser crystal 22 Piezoelectric element 24 Excitation laser light 28 Diffraction light correction prism 106 Diffraction light 100 Photoacoustic optical crystal 110 Total reflection mirror 112 Emission mirror

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Tashiro 19-1399, Koshiji, Nagamachi, Aoba-ku, Sendai, Miyagi Prefecture F-term in the Photodynamics Research Center, RIKEN (Reference) 5F072 AB20 GG02 HH03 HH05 HH09 JJ05 KK06 KK13 KK18 KK30 MM03 TT12 TT28

Claims (10)

[Claims] 1. A birefringent photoacoustic optical element to which a first acoustic wave is input is disposed in a laser resonator, and a wavelength tunable laser capable of oscillating laser in a predetermined wavelength range is provided by the photoacoustic optical element. In the wavelength selection method of controlling the wavelength according to the frequency of the first acoustic wave, a second acoustic wave is input to the photoacoustic optical element together with the first acoustic wave; The frequency of the acoustic wave is a frequency at which laser oscillation is possible, the frequency of the second acoustic wave is a frequency at which laser oscillation is not possible, and the input intensity value of the first acoustic wave is determined by the frequency of the first acoustic wave. A laser oscillation control method, wherein the input intensity value is an oscillating input value, and the input intensity value of the second acoustic wave is a value obtained by subtracting the input intensity value of the first acoustic wave from a predetermined value. 2. The laser oscillation control method according to claim 1, wherein the input intensity value of the first acoustic wave is set so that the laser can oscillate in a desired state according to the frequency of the first acoustic wave. A laser oscillation control method that is variable. 3. The laser oscillation control method according to claim 1, wherein the input intensity value of the first acoustic wave is an optimal value for laser oscillation. 4. The laser oscillation control method according to claim 1, wherein the predetermined value is variable according to a frequency of the first acoustic wave. Control method. 5. The method according to claim 1, wherein the first, second, third, or fourth aspect is selected.
3. The laser oscillation control method according to claim 1, wherein the frequency of the second acoustic wave is varied according to the frequency of the first acoustic wave within a frequency band where laser oscillation is not possible. 6. A laser resonator constituted by opposed mirrors having a predetermined reflectance, a tunable laser medium capable of oscillating laser in a predetermined wavelength range provided in the laser resonator, A birefringent photoacoustic optical element disposed in a laser resonator and receiving light emitted from the wavelength tunable laser medium; and a second acoustic wave generating a first acoustic wave and inputting the first acoustic wave to the photoacoustic optical element. A first acoustic wave input means, a second acoustic wave input means for generating a second acoustic wave and inputting the generated acoustic wave to the photoacoustic optical element; a first acoustic wave input means and a second acoustic wave input means Controlling the means to cause the first acoustic wave input means to generate a first acoustic wave having a frequency capable of laser oscillation and an input intensity value; And prescribed Laser oscillation control device and a control means for generating a second acoustic wave having an input intensity value obtained by subtracting the input intensity value of the first acoustic wave from. 7. The laser oscillation control device according to claim 6, wherein the control unit sets the input intensity value of the first acoustic wave in a desired state in accordance with the frequency of the first acoustic wave. A laser oscillation control device that can be oscillated. 8. The laser oscillation control device according to claim 6, wherein the control unit sets an input intensity value of the first acoustic wave to an optimal value for laser oscillation. apparatus. 9. The laser oscillation control device according to claim 6, wherein the control unit controls a frequency of the first acoustic wave.
A laser oscillation control device that changes the predetermined value. 10. The laser oscillation control device according to claim 6, wherein the control means sets the frequency of the second acoustic wave within a frequency band in which laser oscillation is not possible. 2. The laser oscillation control device according to claim 1, wherein the laser oscillation control device varies according to the frequency of the first acoustic wave.