JP2973673B2 - Q switch laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser marking for evaporating, melting and discoloring a metal, semiconductor or plastic by thermal energy obtained by converging a Q-switched laser pulse having a very high peak value. The present invention relates to a Q-switch laser device suitable for use in a device or a thin film resistor trimming device.

[0002]

2. Description of the Related Art 1) A solid-state laser device using a Q switch is used for precision machining such as marking and trimming by using a laser pulse having a high peak value. This is a high-peak laser pulse generated by emitting the population inversion energy in the laser medium accumulated while the oscillation is turned off at the same time as the oscillation is turned on. Note that the population inversion energy gradually increases when the oscillation is off, and 0.5 to 1.
It is almost saturated in ms. Q switch repetition frequency is 2
When the frequency is higher than KHz, the population inversion energy is low without reaching saturation. Since the laser pulse increases as the population inversion energy increases, in applications where the repetition frequency of the Q switch is increased, the peak value of the first Q switch pulse turned on from the oscillation off state There is a risk that a large processing mark is left only at this point, the quality is deteriorated in the case of marking, and the substrate is damaged in the case of trimming.

2) By the way, when the population inversion value is large at the time of accumulation, the value at the time of emission is also a large value. Therefore, the population distribution value to be accumulated next becomes small and the value at the time of emission becomes small. As a result, the inverted distribution value alternately repeats the magnitude, and the peak value of the Q switch pulse repeats the magnitude alternately. Such a phenomenon becomes more remarkable as the repetition frequency of the Q switch becomes higher, and not only a desired Q switch pulse frequency cannot be obtained, but also the processing becomes unstable.
Therefore, in order to solve the above-mentioned problem 1), for example, a method disclosed in Japanese Patent Publication No. 63-30791 has been proposed (hereinafter, also referred to as Conventional Method 1). This is because the drive power to the Q switch is reduced immediately before the Q switch pulse is generated, the applied loss of the Q switch is reduced, weak continuous oscillation is caused, and a part of the saturated population inversion energy is released. , The peak value of the first pulse is suppressed. Further, as a method for solving the above problem 2), for example, a method in which the optical axes of the laser medium, the output mirror, and the total reflection mirror are slightly deviated and the inversion distribution value when the Q switch pulse is generated is moderate. (Hereinafter, also referred to as Conventional Method 2).

[0004]

However, in the conventional method 1, since the weak continuous oscillation is caused by lowering the driving power to the Q switch, the processed material is thermally deteriorated by the weak continuous oscillation. There is a possibility that damage may be caused by plastics or the like which are easily changed. Further, when the repetition frequency of the Q switch is high, the fluctuation of the Q switch pulse peak value cannot be suppressed, and there is a problem that stable machining cannot be performed. On the other hand, the conventional method 2 has a problem that it can be applied only to a specific frequency and is not practical. Therefore, an object of the present invention is to reduce the peak value of the first pulse and to generate a laser beam having a stable peak value even with a Q switch having a high repetition frequency.

[0005]

According to a first aspect of the present invention, a total reflection mirror and an output mirror are arranged so as to sandwich a laser medium to be excited by an excitation means, and a resonance system is provided. A Q-switch laser device configured to provide an acousto-optic Q-switch on the optical axis of the resonance system and take out a Q-switch pulse from the output mirror, wherein the second total reflection is different from the total reflection mirror and the output mirror. A mirror and a second output mirror are provided, and a pair of partially transmitting mirrors are arranged on the optical axis of the second total reflection mirror, the second output mirror, and the laser medium so as to sandwich the laser medium. To form a second resonance system, and the second resonance system emits energy so that the population inversion energy of the laser medium when the Q switch pulse is not generated is constant. 1 pulse Kept low contributing inversion amount vibration suppressing peak value of the first pulse, a peak value is substantially constant Q
It is characterized by obtaining a switch pulse.

In the second invention, a total reflection mirror and an output mirror are arranged so as to sandwich the laser medium excited by the excitation means to form a resonance system, and the acousto-optic Q is placed on the optical axis of the resonance system.
In a Q-switch laser device for providing a switch and extracting a Q-switch pulse from the output mirror, a second output mirror separate from the output mirror, a partial transmission mirror is provided, and the laser medium and a total reflection mirror are provided. And a second resonance system including a second output mirror and a partial transmission mirror, and the energy is controlled by the second resonance system so that the population inversion energy of the laser medium when the Q switch pulse is not generated is constant. And the peak value of the first pulse is suppressed by suppressing the inversion distribution amount contributing to the first pulse oscillation of the Q switch pulse to obtain a Q switch pulse having a substantially constant peak value. .

In a third aspect based on the first or second aspect, a second acousto-optic Q switch is provided in the second resonance system, and a repetition frequency of the already provided acousto-optic Q switch is provided. The driving power of the second acousto-optic Q switch is changed in accordance with the following. In a fourth aspect based on the first or second aspect, a second acousto-optic Q switch is provided in the second resonance system, and a pulse is generated by the acousto-optic Q switch already provided. The second time at a predetermined repetition frequency
Is driven.

[0008]

The inversion distribution amount accumulated in the laser medium during the stop period of the Q switch pulse is emitted by another resonance system sharing the laser medium during the stop period, and the emission amount is controlled. The peak value of the Q switch pulse is stabilized by making the inversion distribution amount substantially constant, and the practicality is enhanced.

[0009]

FIG. 1 is a block diagram showing a first embodiment of the present invention. In the figure, 1 is a laser medium, 2 is an excitation lamp, 3 is a cavity (container), 4a and 4b are first and second reflectors, 5a and 5b are first and second output mirrors, and 6a is a first output mirror.
Q switch, 7a and 7b are first and second partial transmission mirrors, 8 is a laser absorber, 9a is a mixer, 10a is an amplifier, HP
Represents high-frequency power, MS represents a modulation signal, RS represents laser light (also simply referred to as laser), and QP represents a Q switch pulse. That is, the laser medium 1 disposed between the first total reflection mirror 4a and the first output mirror 5a is housed in the cavity 3 for efficiently condensing the light from the excitation lamp 2 therein. I have. The first total reflection mirror 4a is usually 9
The first output mirror 5a has a reflection characteristic of 9.8% or more.
Those with 0% reflection and 10% transmission are used. The first output mirror 5a, the first total reflection mirror 4a, and the laser medium 1 constitute a first resonator or a resonance system, amplify the laser, and output the laser from the first output mirror 5a. You. Further, between the first total reflection mirror 4a and the first output mirror 5a, the first partially transmitting mirror 7a and the second partially transmitting mirror 7b are arranged so as to sandwich the laser medium 1 on their optical axes. Is arranged.
The partially reflected light from these partially transmitting mirrors 7a and 7b is transmitted to the second output mirror 5b and the second total reflection mirror 4b and the laser medium 1
And the optical axis thereof is adjusted so as to constitute the second resonator.

A first Q switch 6a is arranged between the first partial transmission mirror 7a and the first output mirror 5a.
The Q-switch 6a changes the optical path by bonding a piezoelectric element to a crystal such as fused quartz and applying a high-frequency voltage of several tens of MHz to the piezoelectric element. Then, the high frequency power HP and the modulation signal MS are combined by the mixer 9a, and the Q switch 6a is controlled by the signal amplified by the amplifier 10a, thereby controlling the on / off of the laser oscillation. The excitation lamp 2 is continuously lit even while the laser oscillation is off, whereby energy is accumulated in the laser medium 1 and the population inversion energy increases. With the increased population inversion energy, the optical path change by the Q switch is released at the same time when the modulation signal is turned on, and oscillation occurs. In this manner, a laser output having a high peak value, that is, a so-called Q switch pulse is output by turning on and off the Q switch.

FIG. 2 is a waveform chart for explaining the operation of the Q-switch laser device. This is because the second reflecting mirror 4b, the second output mirror 5b, the first and second partially transmitting mirrors 7a and 7
3 and FIG. 3 (b) shows an example of a population inversion distribution waveform of the conventional device and FIG. 3 (b) shows an example of a Q-switch pulse waveform thereof. It is shown in (c). That is, FIG.
Prior to time t0 when no modulation pulse is given as in (a), the population inversion energy is at a high level in a saturated state as shown in (b) of the figure. Thereafter, when oscillation occurs due to the first modulation pulse, the first Q switch pulse becomes a pulse higher than the normal peak value as indicated by P1 in FIG.

On the other hand, in the embodiment shown in FIG. 1, while the Q switch 6a is off, the first output mirror 5a and the second
Even when the oscillation with respect to b is stopped, the inversion distribution energy is gradually accumulated and exceeds the resonance threshold value constituted by the second partial transmission mirror 7b and the second total reflection mirror 4b. Oscillation occurs. This oscillation is guided to the laser absorber 8 through the partial transmission mirrors 7a and 7b, and disappears as heat.
Since the resonance threshold formed by the second total reflection mirror 4b is constant, the value of the population inversion at which continuous (CW) oscillation starts is substantially constant, and Q1 to Q6 in FIG. ,
As shown by Q7 to Q12, the output of the Q switch pulse is substantially constant. Q1 to Q6 indicate Q switch pulses when the repetition frequency is relatively low, and Q7 to Q12
Indicates a Q switch pulse when the repetition frequency is relatively high.

FIG. 4 shows a second embodiment of the present invention. As is clear from the figure, this embodiment is configured by removing the second partially transmitting mirror 7b and the second reflecting mirror 4b from the one shown in FIG. That is, a second partial mirror 7a and a second output mirror 5b are provided on the optical axis of a first resonance system including the first total reflection mirror 4a, the first output mirror 5a, and the laser medium 1. The resonator is arranged. Even in such a case, as shown in FIG.
The Q switch pulse can be made substantially constant.

FIG. 5 is a block diagram showing a third embodiment of the present invention, and FIG. 6 is a waveform diagram for explaining its operation. This embodiment is different from the one shown in FIG.
Is characterized in that a second Q switch 6b is provided between the partial transmission mirror 7a and the second output mirror 5b, and the laser medium 1 and the first reflection mirror 4a are not shown. This means that the amplification factor of the amplifier 10c is changed by, for example, changing the resistance R by the voltage V corresponding to the frequency of the modulation pulse MS, and the high-frequency power HP1 is changed accordingly. Through the second Q switch 6b. Here, the second Q switch 6b
Are the second output mirror 5b and the laser medium 1, not shown.
The threshold value of the continuous oscillator constituted by the first reflecting mirror 4a can be controlled.

As a result, the driving of the second Q switch 6b as shown in FIG. 6B according to the frequency f1, f2, f3 (f3>f1> f2) of the modulated pulse as shown in FIG. The power is changed and the second Q switch pulse
Therefore, the value of the population inversion becomes substantially constant, and the output of the Q switch pulse becomes substantially constant as shown by Q1 to Q12 in FIG. In particular, when the frequency of the modulation pulse is high, conventionally, as shown in FIG.
7 to P12 occur, but in this embodiment, when the population inversion exceeds a certain value, continuous oscillation can be generated and this can be kept constant.
That is, a switch pulse can be obtained.

FIG. 7 is a block diagram showing a fourth embodiment of the present invention, and FIG. 8 is a waveform chart for explaining its operation. In this embodiment, a second Q switch 6b is provided between the first partially transmitting mirror 7a and the second output mirror 5b as in the case of FIG.
The feature is that the harmonic power HP1 modulated by the second modulation pulse MS1 is guided to this. This second
As shown in FIG. 8B, the modulation pulse MS1 is supplied to the second Q switch 6b while the first modulation pulse MS shown in FIG. 8A is not supplied. This allows
By generating a Q switch pulse from the second Q switch 6b and outputting the output to the laser absorber 8,
The value of the population inversion by the laser medium 1 is made substantially constant as shown in FIG.

[0017]

According to the present invention, the inversion distribution amount accumulated in the laser medium during the stop period of the Q switch pulse can be calculated as follows.
During the stop period, the laser medium is emitted by another shared resonance system, and the amount of the emission is controlled to stabilize the peak value of the Q switch pulse by making the population inversion approximately constant. The peak value of the first pulse does not become excessive even in the case of marking on a heat-sensitive material such as a plastic or a mold package, and as a result, there is obtained an advantage that high quality marking without drilling or burning is possible. In addition, in drilling and discoloring of metal using a high-frequency Q switch pulse, the output of the Q switch pulse is constant, so that there is an advantage that uniform processing can be performed excellently.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a waveform chart for comparing and explaining the device shown in FIG. 1 and a conventional device.

FIG. 3 is a block diagram showing a conventional device.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is a block diagram showing a third embodiment of the present invention.

FIG. 6 is a waveform chart for explaining the operation of FIG. 5;

FIG. 7 is a block diagram showing a fourth embodiment of the present invention.

FIG. 8 is a waveform chart for explaining the operation of FIG. 7;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser medium, 2 ... Excitation lamp, 3 ... Cavity, 4
a, 4b: reflecting mirror, 5a, 5b: output mirror, 6a, 6b ...
Q switch, 7a, 7b: partial transmission mirror, 8: laser absorber, 9a, 9b: mixer, 10a, 10b: amplifier.

Claims (4)

(57) [Claims] 1. A resonance system is constructed by arranging a total reflection mirror and an output mirror so as to sandwich a laser medium excited by an excitation means, and an acousto-optic Q switch is provided on an optical axis of the resonance system. In a Q-switch laser device for extracting a Q-switch pulse from the output mirror, a second total reflection mirror and a second output mirror different from the total reflection mirror and the output mirror are provided. A pair of partially transmitting mirrors are arranged on the optical axis of the second output mirror and the laser medium so as to sandwich the laser medium to form a second resonance system, and the Q switch pulse is not generated. The energy is emitted by the second resonance system so that the inversion distribution energy of the laser medium at the time becomes constant, and the inversion distribution amount contributing to the first pulse oscillation of the Q switch pulse is suppressed to be low, so that the peak of the first pulse Suppress value , Q-switched laser apparatus characterized by peak to obtain a substantially constant Q-switched pulse. 2. A resonance system is constructed by arranging a total reflection mirror and an output mirror so as to sandwich a laser medium excited by an excitation means, and an acousto-optic Q switch is provided on an optical axis of the resonance system. A Q-switch laser device for extracting a Q-switch pulse from the output mirror, further comprising a second output mirror separate from the output mirror, a partial transmission mirror, the laser medium, a total reflection mirror, and a second output mirror. And a second resonance system comprising a partially transmitting mirror, wherein energy is emitted by the second resonance system so that the population inversion energy of the laser medium when the Q switch pulse is not generated becomes constant. The amount of inversion distribution contributing to the first pulse oscillation of the Q switch pulse is suppressed low, and the peak value of the first pulse is suppressed, so that the Q value is almost constant.
A Q-switch laser device for obtaining a switch pulse. 3. A second acousto-optic Q switch is provided in the second resonance system, and the second acousto-optic Q switch is provided in accordance with a repetition frequency of an already provided acousto-optic Q switch. 3. The Q-switched laser device according to claim 1, wherein the driving power is changed. 4. A second acousto-optic Q switch is provided in the second resonance system, and the pulse is not generated by the already provided acousto-optic Q switch at a predetermined repetition frequency. 3. The Q-switched laser device according to claim 1, wherein the second acousto-optic Q-switch is driven.