JPH02260479A - Laser oscillator - Google Patents

Abstract

PURPOSE:To output a single wavelength light having high peak value of an output pulse stably in high efficiency by detecting a laser light output in such a manner that an exciting light intensity exceeds a threshold value, stopping the operation of a Q switch, and generating a giant pulse. CONSTITUTION:An exciting light intensity is gradually increased by first pulse generating means 28 controlled by a control circuit 27 in a state that a Q switch 22 is driven to oscillate a single wavelength light and to output it from a resonator. This output light is detected by output detecting means 26, the switch 22 is stopped in cooperation with the detection of the output, and a giant pulse is generated. Thus, a single wavelength laser pulse light stable with high output can be oscillated in high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a laser oscillation device that obtains a giant pulse by inserting a Q switch in an optical resonator.

(Prior art) In order to obtain a laser beam that generates a giant pulse,
There is a solid state laser oscillation device l shown in FIG. This laser device 1 includes an optical resonator consisting of a high reflection mirror 2 and an output mirror 3 whose concave mirror portions face each other. For example, a YAG laser rod 4 as a laser medium is inserted between the high reflection mirror 2 and the output mirror 3.

This YAG laser rod 4 is excited by a semiconductor laser beam generated from a semiconductor laser generator 5 as an excitation light generator provided outside the high reflection mirror 2.

The high-reflection mirror 2 has a dielectric multilayer film formed on its reflective surface so that it transmits the semiconductor device laser light and reflects the YAG laser light.

A driving power source 6 for applying voltage is connected to the semiconductor laser generating section 5, and the semiconductor laser generating section 5 is of a driving type? An excitation laser beam is generated by applying a voltage by fi, 6. This excitation laser beam is focused by a focusing optical system 7 inserted between the high reflection mirror 2 and the semiconductor laser generating section 5, and is irradiated onto the laser rod 4. Further, an A10-Q switch element 8 is inserted between the laser rod 4 and the output mirror 3. A Q switch driver 9 is connected to this A10-Q switch cable 8,
A voltage is applied at a predetermined frequency.

The laser oscillation device 1, which is configured as a double series, is controlled as shown in FIG. The driving power source 6 keeps its applied voltage constant and outputs excitation light with a constant light intensity P2. The Q switch driver 9 is RF
(Radio Frequency) Power ^10
- Manually input Q switch Seiko 8. This RF power is outputted for a predetermined minute time 11 at an intensity R2 sufficient to stop laser oscillation, and then is stopped for a predetermined minute time t2. That is, the ^10-Q switch element 8 stops laser oscillation for a period of ti, and then turns the laser into an oscillation state for a period of <12 to output a giant pulse. In addition,
The dashed line in the figure indicates the threshold value for applying jfl power to the laser beam.

When the pulse output of one laser light output in this way is subjected to high-resolution dpj determination, as shown in FIG. 6, due to competition between longitudinal modes caused by oscillation in multiple longitudinal modes, The result is a pulse waveform with overlapping beats. This beat is different for each pulse and therefore the intensity varies from pulse to pulse. As described above, there is a drawback that it is difficult to stabilize the intensity of the output light. Therefore, as shown by the chain line in FIG.
0 into the resonator 2.3, it was difficult to generate a stable second harmonic. Therefore, in order to eliminate the instability of output intensity due to mode competition, it is necessary to make light with a single wavelength and a single longitudinal mode.

Control as shown in FIG. 7 can be performed using a similarly configured laser oscillation device. The control method of this one-noser device is called Briley's single frequency ^10-Q switch pulse oscillation. For example, [G, T, Makc
r and^, 1. Parguson, OpL, Lct.
L.

I3.4 old (19H)]. This 91g4
According to ^10, the excitation light intensity is always kept at a constant value P2
- Set the power level applied to the Q-switch element 8 to R3, which is smaller than R2, set the threshold value to be slightly lower than the gain obtained by the above-mentioned pumping light intensity, and maintain the oscillation state of single wavelength light for a predetermined period of time. After holding L3 ^10-
By stopping the operation of the Q-switch element 8 for a predetermined time L4, a single-wavelength giant pulse is obtained by amplifying the single-wavelength light held during time t3. However, according to the above control, even when the A10-Q switch element 8 is in the operating state, the resonator 2.3
Since the laser beam is oscillated within the chamber, there is a drawback that the inversion position of the laser rod 4 cannot be sufficiently increased. Therefore, the peak power of the output light is lower than in the case of the above-mentioned control. In this way, the output of the laser light is K
In such cases, even if a nonlinear optical element was inserted, the conversion efficiency to the second wave, '8 wave, was low.

Examples of other laser devices will be described with reference to FIGS. 8 and 9. The control method of this dozer device is called a gain switch method, for example [A, Owyung.

G, l? l+adley, P, Isisl+erick,
R, L, Schmltt, anti L, ^.

Rahn, Opt. Lett, 4114 (1985)
].

^10-A Q switch element and a Q switch driver are not provided, and the other O parts are the same as the above laser device. The laser device 11 configured in this way excites the excitation light with an output always higher than the threshold value indicated by the chain line,
During a predetermined time t5, the excitation light is pumped with an output slightly higher than the threshold value, and then, during a predetermined time t6, the excitation light intensity is increased to a predetermined value.

According to such control, during the predetermined time t5, the
Wavelength light is oscillated, and then a predetermined output of a single wavelength can be obtained by amplifying the wavelength t1 by one wavelength for a predetermined time t6. However, in this control, energy cannot be stored in the laser rod like a Q switch, and the population inversion of the laser rod 4 cannot be sufficiently increased, so the peak value of the output YAG laser light output cannot be increased. I couldn't do it.

(Issue 21!1li to be Solved by the Invention) Various devices and their control methods have been developed to generate giant pulses by using Q switches in solid-state laser devices. However, when the peak of the pulse waveform of the laser output is increased, the wavelength of the output laser light becomes unstable. Therefore, a single wavelength light is oscillated by pumping with a power slightly higher than the threshold, and then the pump light intensity is increased to a value significantly higher than the threshold using the pump light generator or the Q switch 1111. A device has been proposed that generates a strong pulse output by controlling the However, even if the solid-state laser medium is excited immediately after oscillating a single wavelength, a sufficiently large population inversion cannot be obtained, so it has been difficult to increase the peak value of the laser output.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a laser oscillation device that can oscillate stable and high-output single-wavelength laser pulse light with high efficiency.

[Structure of the invention]

(Means for solving the problem) A laser medium is inserted into an optical resonator, an excitation light generation section for exciting the laser medium is provided, a drive power source is provided for driving this excitation light generation section, and the drive power source is A first pulse generating means is provided for generating a signal for instructing the output to be increased at a predetermined rate of increase, and for instructing the output of the drive power source to be decreased at a predetermined rate of decrease and further to be stopped. A second pulse generating means for generating a signal is provided, a Q-switch element is inserted into the optical resonator, a Q-switch driver is provided for driving the Q-switch element, and a laser beam output from the optical resonator is provided. A laser oscillation device is provided with a control circuit that continuously controls the first and second pulse generators and the switch driver at a predetermined frequency based on the detection of the laser output by the output detection means. .

(Function) With the Q-switch driven, the first pulse generation means controlled by the control circuit gradually increases the excitation light intensity to oscillate 19-wavelength light, which is output from the resonator. Then, the output detection means detects this output light, and in conjunction with the detection of this output, the Q switch can be stopped and a giant pulse can be generated.

(Example) An example of the present invention will be described with reference to FIGS. 1 to 3. A laser oscillation device 15 shown in the figure includes a resonator consisting of a high reflection mirror 16 and an output mirror 17. The high reflection mirror 16 and the output mirror 17
Both have concave reflecting surfaces and are made of dielectric multilayer films. Furthermore, inside the resonators 16 and 17, a solid laser medium such as YAG laser port/node 1 is provided.
8 has been inserted. This laser rod 18 is excited by a semiconductor laser generator 19 as an excitation light generator provided outside the high reflection mirror 16. This semiconductor laser generator 19 is driven by a drive power source 20. The semiconductor laser light emitted by the semiconductor laser generating section 19 is focused by the focusing optical system 21, transmitted through the high reflection mirror 16, and focused on the laser rod 18. Here, the dielectric multilayer film constituting the reflective surface of the high-reflection mirror 16 reflects the YAG laser light emitted by the laser rod 18 with a high reflectance, and highly transmits the light emitted by the semiconductor laser generating section 19. It is designed to be transparent at a certain rate.

Further, an A10-Q switch element 22 is inserted between the laser rod 14 and the output mirror 17. A Q switch driver 23 is connected to this A10-Q switch element 22.

Further, on the optical path of the output light outside the output mirror 17, a beam splitter 24 is arranged so as to be inclined at a predetermined angle so as to split a small portion of the output YAG laser light. This separated YAG laser light is transmitted through a condensing lens 2.
The light is focused by 5 and is made to enter a light intensity sensor 26 provided approximately at the focal position. Here, the beam splitter 24, condensing lens 25, and light intensity sensor 26 are output detection means.

The signal output section of the light intensity sensor 26, the signal input section of the Q-switch driver, and the signal input section of the drive power source 20 are each controlled by a control circuit 27. This control circuit 27 is provided with a manual switch 27a for starting the entire device. Further, a time counter 27b1 for controlling the frequency of the laser beam is provided. This time counter 2
7b is capable of counting minute amounts of time with high precision.

The control circuit 27 also includes the semiconductor laser generator 1.
First and second pulse generators 28 and 29 are provided which are activated when controlling the two drive power supplies 20. When the first pulse generator 28 receives a signal from the control circuit 27, the first pulse generator 28 generates a pulse signal instructing the drive type lA 20 to start applying voltage and to increase the excitation light intensity at a predetermined increase rate. do. The rate of increase in the excitation light intensity needs to be greater than the rate of energy lost by the laser rod 18 through the spontaneous emission process.

Furthermore, when the control circuit 27 outputs a signal to stop the drive power source, the two second pulse generators decrease the excitation light intensity at a predetermined rate of decrease, and finally stop applying the voltage. Generates pulse number 15 to instruct it to stop.

The above-described control of the excitation light intensity is performed by the control 8 circuit 2.
7, and the first and second pulse generators 28
．． 29 only generates pulse signals.

Furthermore, the control circuit 27 is provided with a third pulse generator 30 that generates a pulse signal for controlling driving and stopping of the Q-switch driver 23 using a constant RF power.

The laser oscillation device 15 configured in this manner is controlled to continuously oscillate laser light, with the following steps as one cycle.

First, oscillation of laser light is started by starting the laser oscillation device 15 using the manual switch 27a.

ST^l in Figure 3? It is T.

Then, as a first step, RF power is applied to the ^10-Q switch cable 22. Here, a predetermined threshold value shown by a chain line in FIG. 2 is determined by the RF power that the Q-switch driver 23 applies to the Q-switch cable 22. As the Q switch 22 is driven, the time counter 27b counts a predetermined minute time t7.

This predetermined minute time t7 is a time determined based on the pulse frequency of the output laser light.

In the second step, the semiconductor laser generator 19 starts emitting excitation light. This excitation light is controlled to increase its light intensity at a predetermined rate of increase.

When the excitation light intensity increases and slightly exceeds the threshold set by the A10-Q switch element 22, the laser beam with the highest gain wavelength (single wavelength light: YAG laser In light, only 1.06u) is 1.06u). [Output from distribution output mirror 17. A portion of this single wavelength light is split by the beam splitter 24, condensed by a condenser lens 25, and then incident on a light intensity sensor 26. The third step is initiated by the detection of this single wavelength light. In the third step, the control circuit °27
The input of RF power to the Q-switch element 22 is stopped, and at the same time, the pumping light intensity starts to decrease. In other words, the third
The pulse generator 30 causes the Q switch driver 23 to
It is controlled to stop the input of RF power to the 10-Q switch cable 22.\.

At the same time, the second pulse generator 29 controls the drive power source 20 to reduce its output at a predetermined rate of decrease, and to stop the output after a predetermined minute time t9.

Then, a predetermined minute time 110 is counted at the same time as the Q switch 22 is stopped and the excitation light intensity starts to decrease. Here, the predetermined minute time 110 is determined by the frequency of the output pulse required for the YAG laser beam.

[7] After the 31st step is completed, the control is performed to perform the 1st step again.

One pulse of laser light output is generated through the first to third steps described above.

In this way, by controlling from the first step to the third step, when the gradually increasing excitation light intensity slightly exceeds 1 to the fortune-telling value, the laser beam of a single wavelength (the wavelength with the highest oscillation output in the laser medium) is activated. Since the excitation during the predetermined time [8] until oscillation or the start of oscillation of this laser beam is pulse-like, the peak t? P1 should be higher than P2 and P in Figures 5, 7 and 9, and R
The F level R0 is also R2 and R3 in Fig. 15 and Fig. 7.
Therefore, the inverted electric potential of the laser rod 4 is larger than that shown in Figs. 7 and 9, and when the Q switch 22 is turned off, a giant pulse of a single wavelength with a high output peak is generated. can.

Note that the resonator 1 of the laser oscillation device 15 as described in -1-
By inserting the nonlinear optical element 31 in 6.1.7,
It is possible to generate stable, single-wavelength second harmonic ^-Q switch pulses with high efficiency that could not be obtained with conventional laser oscillation devices.

This is because the nonlinear optical element 31 has a property that the higher the light intensity of the transmitted light, the higher the efficiency of conversion into harmonic waves.

Note that the present invention is not limited to the above embodiment. For example, in the embodiment described above, the semiconductor laser generating section 19 as an excitation light generating section is provided outside the high reflection mirror 16, but the same effect can be obtained even if it is located on the side of the laser rod 18. In addition, the materials of the laser rod 18, A10-Q switch element 22, nonlinear optical element 7-31, etc. are not limited to (iiJ, etc.). Also, although one semiconductor laser generator is used as the excitation light generator, Not limited to this,
Any excitation light generating section that modulates the excitation light intensity as shown in FIG. 2 may be used. Furthermore, although the rate of increase and decrease of the excitation light intensity are constant, the present invention is not limited to this, and as described above, the excitation light intensity can be increased while advancing the inversion/li of the laser medium. A similar effect can be achieved by controlling a waveform shape that can generate a giant pulse based on a single wavelength light slightly exceeding the threshold of 1'? I can do that.

Further, the first and second pulse generating sections 28.2g may be provided individually, or the present invention is not limited to this, and the first and second pulse generating circuits 28.2g may be provided in one pulse generating section. It is only necessary to provide a -1- stage for generating the first and second pulses.

[light effect]

The excitation light intensity is increased at a predetermined rate of increase, iI (in the process, the inversion of the laser medium is advanced 4i, and the laser beam output with this excitation light intensity exceeding a threshold value is detected, and this laser output By detecting this, it is possible to stop the Q-switch operation and generate a constant pulse.This makes it possible to stabilize single wavelength light with extremely high output pulse peak value compared to conventional structures with high efficiency. can be output.

=1, Brief Description of the Drawings Figures 1 to 3 are examples of the present invention,
Figure 1 shows the schematic configuration of the laser oscillation device. Figure 2 shows time on the horizontal axis and solid-state laser output and R on the vertical axis.
A laser oscillation device input/output diagram showing the oscillation state of laser light by showing F power and excitation light intensity, respectively, FIG. 3 is a flowchart showing control of the laser oscillation device, and FIGS. 4 to 9 are conventional examples, Fig. 4 is a schematic +i-plane diagram showing an example of a laser device, and Fig. 5 shows time on the horizontal axis and solid-state laser output, RF power, and pumping light intensity on the vertical axis, and oscillation of laser light. Figure 6 is an input/output diagram of the laser oscillation device showing the status, with time on the horizontal axis and solid-state laser output on the vertical axis, and output showing the pulse waveform of the solid-state laser output with high resolution 4p1 constant shown in Figure 5. 7 is an input/output diagram when the laser oscillation device shown in FIG. 4 is controlled by another control method, FIG. 8 is a plan view showing the schematic configuration of another laser oscillation device, and FIG. The figure is an input/output diagram showing the input/output state of the laser device shown in FIG. 8, with the horizontal axis representing time and the vertical axis representing solid state L) laser output and excitation light intensity.

15... Laser oscillation device, 16... High reflection mirror 17
...Output mirror 18...Laser rod (laser medium) 19...Semiconductor laser generator (excitation light generator)
20... Drive power supply, 22...^10-Q switch element (Q switch), 23... Q switch driver,
26... Light intensity sensor (output detection means) 27...
- Control circuit, 28... first pulse generating section (first pulse generating means), 29... second pulse generating section (second
pulse generation means).

Claims (1)

[Claims] A high-reflection mirror, an output mirror that faces the high-reflection mirror and forms an optical resonator, a laser medium and a Q-switch element provided between the high-reflection mirror and the output mirror, and a Q-switch element that excites the laser medium. an excitation light generating section for emitting light, a driving power source for causing the excitation light generating section to emit light, and a first pulse generating means for generating a signal instructing the output of the driving power source to increase at a predetermined increase rate. , a second pulse generating means for generating a signal instructing to reduce the output of the drive power source at a predetermined rate and further stop the output;
a Q-switch driver that drives the Q-switch element;
Output detection means for detecting the laser light output from the output mirror, and control for continuously controlling the first and second pulse generators and the Q-switch driver at a predetermined frequency based on the detection of the laser output by the output detection means. A laser oscillation device comprising a circuit.