JPS6366074B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Q-switch laser with improved reproducibility of optical pulses.

In order to obtain high-output Q-switched optical pulses from a solid-state laser, it is necessary to use a pulse excitation method.If mode-locking method is also used, it is possible to further increase the output power and make the output optical pulses extremely short. can. In large-scale systems such as laser fusion and distance measurement using artificial satellites, which require high-power and short Q-switch light pulses, in order to improve the reliability of the entire system,
It is necessary to improve the reproducibility of the output and emission timing of the Q-switch light pulse, which is the light source, more than ever before.

Conventionally, a laser oscillator capable of producing relatively stable Q-switched optical pulses was developed by Mr. Kuizenga in Optics Communicatior, Vol. 22,
The method described on pages 156 to 160 is to reproduce the population inversion just before Q switching by forming a stable continuous oscillation state (pre-oscillation state) with low output in advance before performing active Q switching. An oscillator that improves the performance is known.

However, this method does not have any active stabilization means to keep the optical output constant other than keeping the excitation lamp current constant, and the heat applied to the laser resonator from the outside in the pre-oscillation state is target,
Relaxation vibrations induced by mechanical, electrical, etc. fluctuations cannot be prevented. Since such relaxation oscillations occur randomly over time, there is a finite probability that relaxation oscillations will occur just before Q-switching, and in that case, the photon density and population inversion, which are the initial conditions for Q-switching, will fluctuate greatly from their steady values. do. However, the peak value of the Q-switched optical pulse strongly depends on the initial conditions of the population inversion, and the time from the start of active Q-switching until the optical pulse intensity reaches its peak value is inverted with the photon density. Since it strongly depends on the initial conditions of both density and density, if relaxation oscillation occurs immediately before Q-switching, the reproducibility of the output and emission timing of the Q-switched light pulse will be greatly impaired.

Conventionally, in order to suppress relaxation oscillation in a continuous oscillation state such as the pre-oscillation state mentioned above, it has been thought that a method of providing resonator loss proportional to the increase/decrease in optical output using negative feedback may be effective. If installed independently, it is expensive, and as a result of suppressing the growth of the optical pulse during Q-switching, it becomes difficult to obtain a high Q-switching output.

An object of the present invention is to suppress the relaxation oscillation in the preliminary oscillation state of the above method using a simple configuration, to keep the optical output and inverted population just before the Q switch constant, and to reproduce the output and output timing of the output Q switch pulse. The object of the present invention is to provide a laser with improved performance without compromising output.

According to the present invention, there is provided a Q-switch means consisting of a Q-switch element, a power source for supplying power for driving the Q-switch element, and a high-speed switch for switching the driving power, and the Q-switch means is configured to open the high-speed switch. A Q-switched solid-state laser is provided with a pre-excitation means for the laser rod to maintain a low-output pre-oscillation state before Q-switching, and further includes an optical output detector and a low-frequency component extracted from the detector output signal. and a modulator for modulating the power for driving the Q-switch element by the output signal from the filter, and the modulator is used for driving the Q-switch element. An output stabilized Q-switch laser is obtained, which is characterized in that it is installed between a power source that supplies electric power and the high-speed switch.

Hereinafter, specific embodiments of the present invention will be described in detail using the drawings.

The figure is a configuration diagram of an embodiment of the present invention. Nd：
A solid laser rod 1, typically made of YAG, is excited by an excitation lamp 3, and a laser resonator is constituted by a total reflection mirror 2 and an output mirror 2'. An ultrasonic Q-switch element 4 is inserted into the resonator. In a normal Q-switch laser, the driving device for the Q-switch element 4 includes an RF power source 9 for generating drive power for the ultrasonic Q-switch element 4, and a Q-switch from the RF power source 9.
It is composed of a high-speed switch 10 that switches constant RF power applied to the switch element 4. In the present invention, a modulator 8 is further installed between the RF power source 9 and the high speed switch 10 for modulating the drive power of the Q switch element with an electric signal proportional to the output of the laser. Specifically, a double balanced mixer operating in the RF frequency band is used as this modulator. The specific modulation signal is created by the following additional circuit. The output signal of the photodetector 5, which receives a part of the laser output, is appropriately amplified by the amplifier 6, and the low frequency component of at least 1 KHz or less is removed from the output signal by the condenser 7, and an AC signal is sent to the modulator. Add to 8. Furthermore, DC
The operating point of the modulator 8 is set by the voltage of the bias circuit 11. The modulation signal thus obtained provides a resonator loss proportional to the laser output, and the output is stabilized by negative feedback.

The above-mentioned additional circuit to the normal Q-switch element drive circuit is operable when the switch 10 is closed, that is, when the resonator loss is high. If the excitation means is used to excite the oscillation threshold, which has increased in response to the resonator loss, a preliminary oscillation state can be obtained before the Q switch.
The additional circuit significantly suppresses fluctuations in the output of the oscillated light, and significantly stabilizes the output immediately before the Q switch and the population inversion.

In the above-mentioned method by Mr. Keisinger, the lamp lighting current waveform during pulse excitation is normally controlled to be a rectangular waveform with a width of several milliseconds. At this time, if the additional circuit responds to a steady change in optical output determined by the current waveform, a steady oscillation state cannot be obtained. at least
It is necessary to remove low frequency components below 1KHz.
The capacity of the capacitor 7 constituting the filter of the additional circuit is selected according to this purpose.

On the other hand, when the high-speed switch 10 opens and enters the so-called Q-switching state, the loop generated by this additional circuit for suppressing fluctuations in optical output is automatically opened at the same time. It is not suppressed by additional circuitry.

As mentioned above, this system has a compact structure in which the output stabilizing means is incorporated into the Q switch means in the form of an additional circuit, and it also has several advantages that cannot be realized when both means are installed independently. It also has an effect. The first effect is that duplication of the Q-switch element and the RF power supply for driving the Q-switch element can be avoided, making it more compact and economical.In addition, it also has the secondary effect of increasing the Q-switch output by shortening the resonator length. This is a point that can be obtained. Second, in the output stabilization means using negative feedback, the resonator loss as a bias that is necessary for normal operation is no longer necessary in the present invention because active loss for Q switching can be used. The point is that there is no decrease in the Q switch output. The third point is that when an output stabilization circuit is installed independently, it is necessary to open and close that circuit at the same time as the Q switching drive circuit, and it is necessary to devise ways to synchronize the switching of both circuits. In contrast, the present invention has the advantage that synchronization can be achieved automatically since a common switch is used.

Note that it is of course permissible to make changes to the configuration of the embodiments of the present invention without departing from the purpose of the present invention.

For example, it is possible to use a Potsukel cell Q-switch device instead of the ultrasonic Q-switch element used in the present invention. In that case, specifically, 4 in the figure is a combination of a polarizer and a Potsukel cell, and 8 in the figure is To connect 7, 9, and 10, 9 in the figure should be changed to a DC high voltage power supply via an output resistor, respectively.
The bias circuit 11 in the figure becomes unnecessary.

Furthermore, the configuration of the present invention functions effectively even when active mode-locking means is inserted into the resonator, and exhibits a remarkable effect in suppressing relaxation oscillations that occur due to detuning during mode-locking, for example. .

[Brief explanation of drawings]

The figure is a configuration diagram showing an embodiment of the present invention. 1...Solid laser rod, 2...Total reflection mirror, 2'
... Output mirror, 3... Excitation lamp, 4... Ultrasonic Q-switch element, 5... Photodetector, 6... Amplifier, 7... Capacitor, 8... Modulator, 9... RF power supply, 10... High speed switch, 11... DC bias circuit, 12...Lamp current control power supply.

Claims (1)

[Claims] 1 Q switch means consisting of a Q switch element, a power source for supplying power for driving the Q switch element, and a high speed switch for switching the driving power; A Q-switched solid-state laser includes a pre-excitation means for a laser rod for maintaining a pre-oscillation state of the laser rod, further comprising: a detector for optical output; a filter for cutting low frequency components from the detector output signal; an additional circuit comprising a modulator for modulating power for driving the Q-switch element by an output signal; An output stabilized Q-switch laser characterized by being installed between.