JPH1197783A - Q switched pulse laser driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate the pulse laser of narrow width without emitting diffracted light to the outer part of a resonator by installing plural Q switches in the resonator of a laser oscillator and driving the Q switches at arbitrary delay time. SOLUTION: A first A/O element 4 is arranged on a total reflection mirror 2-side in the resonator constituted of a total reflection mirror 2 and an outgoing mirror 3. A second A/O element 5 is arranged on an outgoing mirror 3-side. The A/O elements 4 and 5 arc connected to a control signal generation part 8 through high frequency modulation signal generation parts (signal parts) 6 and 7. The control signal generation part 8 generates a control signal C1 and gives it to the signal part 6. Then, it generates a control signal C2 delayed from the control signal C1 and gives it to the control part 7. The signal part 6 turns on/off a high frequency modulation signal (modulation) Mrf1 in accordance with the control signal C1 and the signal part 7 turns on/off modulation Mrf2 in accordance with the control signal C2 and generates pulse laser. Then, pulse laser width is adjusted by adjusting delay time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Q-switch pulse laser driving method capable of keeping the pulse width constant even when the pulse repetition frequency is increased, and relates to a pulse laser device, a laser processing machine, a laser welding machine, and a laser. It is useful when applied to a measuring device or the like.

[0002]

2. Description of the Related Art One of methods for generating pulsed light from a laser oscillator is a Q-switch method for changing the quality (Q) of a resonator by changing the loss in the resonator. Q
The principle of the switch method is as follows. By setting the loss in the resonator sufficiently higher than the threshold value of laser oscillation, it becomes possible to suppress stimulated emission and achieve a population inversion in the active medium to a high value. Therefore, from a state where the loss in the resonator is sufficiently higher than the threshold value of the laser oscillation, when the loss in the resonator is rapidly reduced, the threshold gain of the laser oscillation also decreases. Since the high population inversion in the active medium is maintained, stimulated emission grows rapidly in the resonator, and the energy effective as the population inversion is emitted as a single pulsed laser.

The Q switch method is roughly classified into the following (1) to (3). (1) A mechanical Q-switch method for changing a resonator mirror. (2) E / O Q switch method using an electro-optical element (E / O element). (3) A using an acousto-optic device (hereinafter referred to as A / O device)
/ OQ switch method.

Here, based on FIGS. 3 to 7, an A / O that can be applied as a pulse laser oscillator for high output and high repetition will be described.
The Q switch method will be described.

FIG. 3 shows a configuration of an A / OQ switch CW-YAG laser oscillator. In this laser oscillator, YAG
A total reflection mirror 2 and an output mirror 3 are arranged as resonators on both sides of a cavity 1 containing a crystal and its excitation source system,
An A / O element 4 is inserted and arranged between the resonator mirrors 2 and 3.

A high-frequency modulation signal generator 6 is connected to the A / O element 4, and a control signal generator 8 is connected to the high-frequency modulation signal generator 6. The control signal generator 8 generates a control signal C1 for the A / OQ switch and supplies it to the high frequency modulation signal generator 6. The high-frequency modulation signal generating section 6 outputs a high-frequency modulation signal Mrf.
1 to apply the high-frequency modulation signal Mrf1 to the A / O element 4 according to the control signal C1, or stop the application.

[0007] In a pulse operation having an average output of several tens of watts and a repetition frequency exceeding several kHz, CW (continuous wave) excitation is employed as an excitation source system of the YAG crystal. Therefore, in the standard state where the A / O element 4 is removed from FIG.
The continuous oscillation is performed in the AG crystal.

The A / O element 4 is composed of a vibrator and, for example, quartz. When the quartz is vibrated at a high frequency using the vibrator, an ultrasonic wave is transmitted into the quartz. Due to this ultrasonic wave, a refractive index is formed in the quartz, and the quartz can function as a diffraction grating. Therefore, the laser beam incident at a certain angle θ in the quartz to which the ultrasonic wave is transmitted has its optical path bent by 2θ by diffraction. On the other hand, in quartz where ultrasonic waves are not transmitted, the laser beam goes straight.

Utilizing this diffraction action, it becomes possible to resonate or suppress the resonance of the laser light between the resonator mirrors 2 and 3, and it can serve as a Q switch.

FIG. 4 shows a timing chart of each of the Q switch, the inversion distribution, and the laser pulse waveform. That is, (1) When the control signal C1 of the A / O element 4 is input, the high-frequency modulation signal Mrf1 that has been applied up to now is opened (stopping application) by the high-frequency modulation signal generation unit 6, so that the inside of the resonator is , And the population inversion n (t) starts to decrease. In the laser pulse waveform, the pulse laser intensity P (t) increases with a decrease in the population inversion n (t), but reaches the peak intensity when the threshold value n _{t of the} population inversion is reached,
Thereafter, the pulse laser intensity P (t) decreases. (2) The high-frequency modulation signal Mrf1 is transmitted to the high-frequency modulation signal generator 6
Is applied again, the optical axis is diffracted at the A / O element 4 to suppress stimulated emission. Therefore, the population inversion n (t) is increased by continuous excitation, and the repetition frequency of the laser pulse is low. In this case, it reaches the limit value n∞ of the population inversion. (3) where the pulse width t _p is the population inversion of the values n _i immediately opening of the high-frequency modulated signal Mrf1 to A / O element 4 (the maximum value of the inversion: In Figure 4 n _i = N∞) and The value n _f of the population inversion after re-application of the high frequency modulation signal Mrf1 (the minimum value of the population inversion), the threshold value n _{t of the} population inversion and the resonator life τ _c are expressed by the following _equation (1).

[0011]

## EQU1 ## t _p = τ _c (n _i −n _f ) / [n _i −n _t ｛1
+ Ln (n _i / n _t )}], where τ _c = L / {c (1-R)}, L is the resonator length,
c is the speed of light, and R is the reflectance of the output mirror 3.

Next, FIG. 5 shows a timing chart of the Q switch, the inversion distribution, and the laser pulse waveform when the repetition frequency F of the laser pulse is increased. That is,
When the repetition frequency of the laser pulse is increased, the value n _i ′ of the population inversion immediately after opening the high-frequency modulation signal Mrf1 and the value n _f ′ of the population inversion after re-application of the high-frequency modulation signal Mrf1 are: _{n i '<n i, n} f'> a n _f. Therefore, 'as it is seen from Equation 1, than the pulse width t _p when the repetition frequency is low, t _p' pulse width t _p> t _p
And spread.

FIG. 6 shows an A / OQ switch CW-YAG laser.
3 shows the repetition frequency dependence of the pulse width of the laser. Roughly
And the pulse width t until the repetition frequency F reaches about 1 kHz._p
Is about 100 nsec (nanosecond), which is higher than 1 kHz
Pulse width t at high repetition frequency _p’Is gradually expanding
Good.

An increase in the pulse width due to an increase in the repetition frequency is problematic in various applications including laser processing. For example, the machinability decreases due to the increase in the pulse width.

Next, as a method of keeping the pulse width constant even when the repetition frequency is increased, as shown in FIG. 7, in addition to the A / O element 4 inside the resonator, the A / O element is also provided outside the resonator. An A / OQ switch CW-YAG laser oscillator provided with the element 9 is exemplified.

In the laser oscillator shown in FIG. 7, in addition to the A / O element 4, high-frequency modulation signal generator 6, and control signal generator 8 inside the resonator shown in FIG. 9, a high-frequency modulation signal generator 10, and a delay circuit 12.

The delay circuit 12 delays the control signal C1 at a timing delayed by Δt from the A / O element 4 inside the resonator, and supplies the control signal C2 obtained thereby to the high-frequency modulation signal generator 10. The high-frequency modulation signal generator 10 generates the high-frequency modulation signal Mrf2, and applies the high-frequency modulation signal Mrf2 to the A / OQ element 9 outside the resonator according to the control signal C2, or stops the application.

The operation of the laser oscillator shown in FIG.
As in the case of FIG. 3, a pulse laser is generated by the A / O element 4 inside the resonator, but a part of the pulse laser 13 emitted from the resonator is cut out by the A / O element 9 outside the resonator. The pulse width is kept constant. In other words, the front part of the pulse laser 13 emitted from the resonator is excluded as the diffracted light 11 by the A / O element 9 outside the resonator to reduce the pulse width.

However, the addition of the A / O element 9 outside the resonator leads to an increase in the size of the device (laser oscillator). Further, since the remaining laser obtained by cutting out a part of the pulse laser 13 emitted from the resonator is emitted as the diffracted light 11,
This needs to be absorbed by a damper or the like outside the resonator. Further, the diffracted light 11 wastes energy.

The above-mentioned problem exists not only in the A / OQ switching method but also in the mechanical Q switching method and the E / OQ switching method.

[0021]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art without increasing the size of the apparatus.
Another object of the present invention is to provide a Q-switch pulse laser driving method capable of generating a narrow pulse laser without emitting diffracted light to the outside of the resonator.

[0022]

A Q-switch pulse laser driving method for solving the above-mentioned problems is as follows. (1) A plurality of Q-switches are installed in one resonator of a laser oscillator, and each Q-switch is set to an arbitrary delay. It is characterized by being driven by time,
(2) Alternatively, A / O in one resonator of laser oscillator
It is characterized by installing a plurality of Q switches using elements, and driving the signal of each A / O element with an arbitrary delay time.
(3) Alternatively, the delay time is determined within a range in which the signals of the respective A / O elements overlap in time series. (4) Alternatively, the plurality of A / O elements in the resonator are determined.
The pulse width of the generated pulse laser is adjusted by adjusting the delay time of the Q switch timing of the O element.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for driving a Q-switched pulse laser according to an embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a configuration of an A / OQ switch type YAG laser oscillator according to the present embodiment, and FIG. 2 shows a timing chart of each of a Q switch, a population inversion, and a laser pulse waveform.

In the laser oscillator shown in FIG. 1, a total reflection mirror 2 and a main mirror 3 are provided as resonator mirrors so as to face a cavity 1 containing a YAG crystal and its excitation source system. The first and second two A / O elements (acousto-optic elements) 4, 5 are provided in the resonator formed by the total reflection mirror 2 and the main mirror 3, and the first A / O element 4 The second A / O element 5 is disposed on the optical axis with the second A / O element 5 disposed on the reflection mirror 2 side and on the output mirror 3 side. High-frequency modulation signal generators 6 and 7 are connected to the respective A / O elements 4 and 5, and the respective high-frequency modulation signal generators 6 and 7 share a common control signal generator 8
It is connected to the.

The control signal generator 8 generates a control signal C1 for the first A / O element 4 and supplies the control signal C1 to the high-frequency modulation signal generator 6, and the second A / O element 5 delayed by Δt from the control signal C1. Is generated and given to the high-frequency modulation signal generator 7. The high-frequency modulation signal generator 6 generates a high-frequency modulation signal Mrf1, and generates a first A / O signal according to the control signal C1.
The high frequency modulation signal Mrf1 is applied to the Q element 4 or the application is stopped. The high-frequency modulation signal generator 7 generates a high-frequency modulation signal Mrf2, and outputs a second high-frequency modulation signal Mrf2 according to the control signal C2.
The high frequency modulation signal Mrf2 is applied to the A / OQ element 5 or the application is stopped.

Next, the operation will be described with reference to FIG. In addition,
In FIG. 2, C1 and Mrf1 indicate a control signal and a high frequency modulation signal for the first A / O element 4, and C2 and Mrf2 indicate the second A / O element.
5 shows a control signal and a high-frequency modulation signal for the O element 5.
Further, n (t) indicates a change in the population inversion, and P (t) indicates a pulse laser waveform. n∞ shows limits of inversion, the maximum value of n _i is the population inversion, the minimum value of n _f inversion, the n _t a population inversion threshold.

(1) In response to the control signal C1 of the first A / O element 4, the A / O element 4 is released from the high frequency modulation signal Mrf1 that has been applied. That is, the high-frequency modulation signal generator 6 stops applying the high-frequency modulation signal Mrf1. (2) On the other hand, after a lapse of a certain delay time Δt in the control signal generating section 8, the control signal C2 of the second A / O element 5 causes the A / O
The element 5 is released from the high-frequency modulation signal Mrf2 applied up to now. That is, the high-frequency modulation signal generator 7 stops applying the high-frequency modulation signal Mrf2. (3) From the time when the second A / O element 5 is released from the high-frequency modulation signal Mrf2, the loss of the resonator decreases, stimulated emission in the resonator starts, and a pulse laser is generated. That is, when the population inversion n (t) starts to decrease, the pulse laser intensity P (t) increases, but when the threshold value n _{t of the} population inversion is reached, the peak intensity is reached, and thereafter the pulse laser intensity P (t)
(t) decreases. (4) Next, the high-frequency modulation signal Mrf1 is supplied to the first A / O element 4.
Is applied again, the loss of the resonator increases,
The pulse laser disappears. That is, since the stimulated emission is suppressed by diffracting the optical axis at the first A / O element 4, the population inversion n (t) is increased by continuous excitation. (5) Therefore, since the pulse width t _p of the pulse laser is determined in accordance with the time ΔT in which the first A / O element 4 is a second A / O element 5 is released from the high frequency modulated signal at the same time, high-frequency (in other words, the delay time between the control signal C1 control signal C2) modulated signal Mrf1 and high frequency modulated signal delay time between Mrf2 by arbitrarily altering the Delta] t, can be controlled pulse width t _p of the pulse laser and is a possible also increasing the pulse repetition frequency constant pulse width t _p to a narrow value.

In this example, as described above, the control signal generator 8
, The high-frequency modulation signal Mrf1 and the high-frequency modulation signal Mrf2 are delayed and driven by the delay time Δt between the control signal C1 and the control signal C2.

Further, in this embodiment, the control signal generating unit 8 has been adjusted can configure the delay time Delta] t, by arbitrarily adjusting the delay time Delta] t, of the pulse laser pulse width t _p
Can be adjusted arbitrarily. Further, the control signal generator 8 includes a high frequency modulation signal Mrf1 and a high frequency modulation signal Mrf2.
The delay time Δt is determined in a range where the values overlap.

Further, in the present embodiment, the control signal generator 8 has an automatic mode. That is, from the number 1 or FIG. 6, the relationship between the repetition frequency and the delay time Δt of the control signal C1 necessary for the pulse width of the pulse laser with a certain desired constant value is known, the desired value t _p in addition to setting, automatically changing the delay time Δt in accordance with the repetition frequency of the control signal C1 based on this relationship, there always to a constant pulse width t _p regardless repetition frequency of the pulse laser .

The above description relates to a method of driving a Q-switched pulse laser in a laser oscillator using an A / O Q-switch. A laser oscillator using a mechanical Q-switch or an E / O (electro-optical element) Q-switch. Similarly, by applying the present invention, it is possible to drive a plurality of Q switches in one resonator with an arbitrary delay time and arbitrarily control the pulse width of the pulse laser.
Even if the pulse repetition frequency is increased, the pulse width can be kept constant.

[0032]

According to the Q-switched pulse laser driving method according to the first aspect of the present invention, a plurality of Q-switches are installed in one resonator of a laser oscillator, and each Q-switch is set to an arbitrary delay time. , Which controls the difference in population inversion within the resonator, and controls the pulse width of the pulse laser within the resonator. Therefore, a pulse laser with a controlled pulse width can be directly extracted from the resonator. Therefore, unlike the related art, there is no need for a Q switch outside the resonator, so that the device does not increase in size. Further, since no diffracted light is emitted to the outside of the resonator, no damper or the like is required, and there is no waste of energy.

According to the Q-switch pulse laser driving method according to the second aspect of the present invention, a Q-switch using an acousto-optical element (hereinafter referred to as an A / O element) in one resonator of a laser oscillator is provided. Since a plurality of A / O elements are installed and the signals of each A / O element are driven with an arbitrary delay time, the present invention is effectively applied to a pulse laser oscillator for high output and high repetition. Of course, similarly to the above, the difference of the population inversion in the resonator is controlled, and the pulse width of the pulse laser is controlled in the resonator, so that the pulse laser with the controlled pulse width can be directly extracted from the resonator. Since a Q switch is not required outside the resonator unlike the related art, the device does not increase in size. Further, since no diffracted light is emitted to the outside of the resonator, no damper or the like is required, and there is no waste of energy.

According to the Q-switch pulse laser driving method according to the third aspect of the present invention, the delay time is determined within a range where the signals of the respective A / O elements overlap in time series. A pulse laser can always be generated.

According to the Q-switched pulse laser driving method according to the fourth aspect of the present invention, the plurality of A /
Since the pulse width of the generated pulse laser is adjusted by adjusting the delay time of the Q switch timing of the O element, an arbitrary pulse width can be obtained.

[Brief description of the drawings]

FIG. 1 shows an A / OQ switch type Y according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating a configuration of an AG laser oscillator.

FIG. 2 is a diagram showing a timing chart of each of a Q switch, a population inversion, and a laser pulse waveform in a Q switch pulse laser driving method according to an embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional A / OQ switch type YAG laser oscillator.

FIG. 4 is a diagram showing a timing chart of each of a Q switch, a population inversion, and a laser pulse waveform in a conventional Q switch pulse laser driving method.

FIG. 5 is a diagram showing a timing chart of each of a conventional Q switch, a population inversion, and a laser pulse waveform when the pulse repetition frequency is high.

FIG. 6 is a diagram showing the repetition frequency dependence of a conventional pulse width.

FIG. 7 is a diagram showing a conventional laser oscillator in which a Q switch is added outside the resonator.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 cavity 2 total reflection mirror 3 emission mirror 4, 5 A / O element 6, 7 high-frequency modulation signal generator 8 control signal generator C1 control signal for A / O element 4 C2 control signal for A / O element 5 Mrf1 A / High frequency modulation signal of O element 4 Mrf2 High frequency modulation signal of A / O element 5

Claims (4)

[Claims] 1. A method of driving a Q-switched pulse laser, wherein a plurality of Q-switches are provided in one resonator of a laser oscillator, and each Q-switch is driven with an arbitrary delay time. 2. A plurality of Q-switches using an acousto-optic device (hereinafter, referred to as an A / O device) are provided in one resonator of a laser oscillator, and a signal of each A / O device is arbitrarily delayed. And a Q-switched pulse laser driving method. 3. The method of driving a Q-switched pulse laser according to claim 2, wherein the delay time is determined within a range in which signals of the respective A / O elements overlap in time series. 4. The pulse width of a generated pulse laser is adjusted by adjusting a delay time of a Q-switch timing of the plurality of A / O elements in a resonator. The method for driving a Q-switched pulse laser according to the above.