JPS6317236B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Q-switch laser device.

Q-switches are known as a technology that converts the oscillation of solid-state lasers into narrow pulses with extremely high peak output values, and are an essential technology for applications such as precision processing of laser light, laser radar, and nonlinear optics. ing. Q-switching methods include mechanical, electro-optical, acousto-optic, and photochemical methods, each with its own characteristics in terms of repetition frequency, switching speed, magnitude of dynamic loss, ease of construction, etc. Because of this, it can be used most appropriately depending on the purpose.

When considering the application of precision machining, which has been increasing dramatically in recent years, there is a need to increase machining speed, shorten processing time, and reduce production costs. The most practical and widely used.

The acousto-optic method is also called an ultrasonic Q-switch and is developed by RBChesler.
Submitted by et al. and published in the journal ``Proceedings
Proceedings
of the IEEE)” Volume 58. No. 12 (December 1970)
As described in detail on page 1899, a phase diffraction grating created by traveling longitudinal ultrasonic waves in a fused silica plate is used as an optical modulator. Typically, a phase grating is attached to a transducer (electro-acoustic transducer) such as an X-cut quartz plate glued to a fused silica plate.
It is formed by applying a high frequency electric field of about 40 MHz, and the Q switch is realized by modulating this high frequency electric field in a pulse manner. In this Q-switch method, the repetition frequency and on/off control of the Q-switch pulse is performed purely electrically by a modulation circuit that modulates a high-frequency electric field, so that a Q-switch pulse with a high repetition frequency and a narrow width can be obtained.

For example, Nd, a continuously pumped solid-state laser:
When applied to a YAG laser, a repetition frequency of 10 KHz and a pulse width of about 100 ns can be obtained.

However, when obtaining high-repetition Q-switch pulses using this ultrasonic Q-switch, the biggest drawback is that the peak output value decreases with the repetition frequency.
Because the fluorescence lifetime of YAG crystal is approximately 230μsec,
The peak value remains constant at a repetition frequency up to about 2KHz, and thereafter decreases in proportion to the repetition frequency.

When applying to precision machining, such as thin film resistor trimming, the repetition frequency is
When the frequency exceeds 2KHz, the peak value of the first Q-switch pulse that turns the laser beam from the OFF state to the ON state is large, leaving a deep and large machining trajectory in this area, which may cause damage to the board.

An object of the present invention is to provide a Q-switch laser device that can gradually widen the modulation pulse width of an applied high-frequency electric field when a Q-switch occurs and maintain a constant peak pulse width in an acousto-optic Q-switch method. .

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows a schematic configuration of an embodiment of the present invention, and FIG. 2 schematically shows signal waveforms and Q switch pulse waveforms.

A solid-state laser material 11 includes an excitation light source 12 and a condenser 1
3 and placed in a laser resonator composed of reflecting mirrors 14 and 15. On the other hand, an acousto-optic light modulator 16 placed in this laser resonator for pulsating laser oscillation has an ultrasonic phase diffraction grating 18 in an ultrasonic cell 17 made of a fused silica plate.
It is composed of an electroacoustic transducer 19 that forms a. A high frequency signal from a high frequency driver 20 is applied to this electroacoustic transducer 19 . The high frequency driver 20 is composed of an oscillator 21 that oscillates at VHF, for example, 40 MHz, a pulse modulation circuit 22, a modulation signal generation circuit 23, and a high frequency amplification circuit 24.
controlled by.

Next, the relationship among the Q-switch control external signal 25, the modulation signal generation circuit 23, and the Q-switch pulse waveform will be explained using the diagram. In FIG. 2, the horizontal axis represents time, and the vertical axis represents relative signal strength.

The waveform 101 of the Q switch control external signal 25 is Q
It is maintained at a low level for the time the switch occurs.
As a result, the modulation signal generation circuit 23 changes like a waveform 104 with a predetermined period and pulse width. The waveform 102 is a modulation signal waveform according to the prior art, and is normally used with a pulse width T of 6 μs and a cycle number of ms or less. Q switch pulse waveform 103 obtained if the period is less than 0.5ms
becomes a pulse oscillation with a high peak value only for the first pulse, because the modulation signal waveform 102
While laser oscillation is at a high level, laser oscillation is suppressed and energy is accumulated, but only the first pulse is at a high level for a long time, and the energy is accumulated until it is completely saturated. The peak value of the first pulse of the Q-switch pulse waveform 103 is easily 10 times or more compared to the second and subsequent pulses, which has a serious impact on applications such as precision machining. The modulated signal waveform 104 according to the present invention differs from the conventional waveform 102 in that the pulse width T' at the rising edge is not constant, and the Q
From the time the switch control external signal waveform 101 becomes low level, it gradually spreads to a constant value of approximately
Controlled to 6μs. For this reason, the peak value of the Q switch pulse waveform 105 gradually rises for the first few pulses. The reason for this is that if the pulse width of the modulation signal waveform 104 is narrow, a loss is caused to the Q-switch oscillation that has started, equivalently creating a state in which the optical shutter cannot be opened completely. As a result, the peak value of the conventional first Q switch pulse is prevented from becoming abnormally high, and a Q switch pulse train having approximately the same peak value can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention, and FIG. 2 schematically shows signal waveforms and Q-switch pulse waveforms. 11 is a solid-state laser material, 12 is an excitation light source, 13 is a condenser, 14, 15
16 is an acousto-optic light modulator, 17 is an ultrasonic cell, 18 is an ultrasonic phase diffraction grating, 19 is an electroacoustic transducer, 20 is a high frequency driver, 21 is a VHF oscillator, 22 is a pulse modulation circuit, 23 is a modulation signal generation circuit, 24 is a high frequency amplification circuit, 25 is a Q switch control external signal,
101 is a Q switch control external signal waveform, 102 is a modulation signal waveform according to the prior art, 103 is a Q switch pulse waveform according to the prior art, 104 is a modulation signal waveform according to the present invention, and 105 is a Q switch pulse waveform obtained by the present invention. It is.

Claims (1)

[Claims] 1. In a Q-switch laser device in which a continuously pumped solid-state laser is oscillated with Q-switch pulses by an acousto-optic Q-switch method, an acousto-optic Q-switch element and an acousto-optic Q-switch element with a sufficient amount to form a phase diffraction grating are provided. a high-frequency signal source that generates a high-frequency signal at a certain frequency; the high-frequency signal is modulated with a pulse signal having a predetermined period and a pulse width that gradually increases until it reaches a certain width; and the high-frequency signal is cut off according to the pulse width. The modulation circuit includes a modulation circuit that generates a drive signal, and means for supplying the drive signal to the acousto-optic Q-switch element, suppresses the peak value of the first pulse of the Q-switch pulse, and maintains the peak value substantially constant. A Q-switch laser device characterized in that it obtains a Q-switch pulse train.