JP2001332791A - Q switch laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a conversion table determining a time constant for suppressing the peak value of a first pulse easily and accurately. SOLUTION: When a laser output 115 is obtained through a solid state laser medium 101, an acoustoptic Q switch 104, and the like, signal level from a high frequency generator 113 for driving the acoustoptic Q switch 104 is lowered gradually at a specified time constant provided through a CPU 110, a time constant selector 111 and a time constant generator 112 such that the first pulse in a Q switch pulse train has a level substantially same as that of the second pulse. A laser output detector 116 for monitoring the laser output 115 is provided and a conversion table for determining the time constant can be formed easily and accurately in a memory 114 based on the output therefrom.

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 type laser output device having a solid-state laser device and an acousto-optic Q switch, and more particularly, to control of a first pulse (also referred to as a first pulse) of a Q-switch pulse train. The present invention relates to a Q-switched laser device capable of performing the following.

[0002]

2. Description of the Related Art A Q-switch laser device of this kind can be used for a wide range of applications such as precision machining, marking, and trimming because an extremely large laser peak value can be obtained instantaneously.
In this device, during the period when laser oscillation is suppressed by the Q switch, laser excitation energy is accumulated in the solid-state laser medium, and the first pulse that starts laser oscillation is:
It is known that the output becomes extremely large with respect to the laser peak value after the second pulse, and the location of the first pulse with respect to the object irradiated with the laser light is compared with the location after the second pulse. Heterogeneous processing / engraving / trimming.

To solve the problem of the first pulse of such a Q-switch laser device, for example, Japanese Patent Publication No. 63-030791, Japanese Patent Application Laid-Open No. 10-313145.
And JP-A-11-354876. Japanese Patent Publication No. 63-030791 discloses a technique for reducing the temperature to a level that does not cause a thermal change on the surface of an object to be laser-irradiated by causing weak continuous oscillation with accumulated excitation energy. JP Hei 10
JP-A-313145 has a laser emission port dedicated to a first pulse, and discharges the first pulse out of a processing surface. Japanese Patent Application Laid-Open No. 11-354876 discloses a technique in which light energy is completely emitted by a suppressed first pulse, and the first pulse of a Q-switch pulse train is suppressed to a negligible level with respect to a second pulse. .

However, the above-mentioned conventional system has the following problems. 1) Since the first pulse is applied to the surface of the object to be laser-irradiated while being suppressed, a material having a large laser absorptivity, a material having poor thermal conductivity, or a material that responds sensitively to laser light (for example, a photosensitive material) Then, a surface change that cannot be ignored is generated. 2) Since the period during which the first pulse is suppressed or discharged does not contribute to the processing, the time during which the first pulse is controlled becomes a loss in the entire processing time, and the laser oscillation / stop is frequently repeated in general in use. However, this loss time increases to a level that cannot be ignored in terms of production efficiency. 3) A Q switch for discharging the first pulse out of the processing surface is separately required.

The applicant has proposed the following Q-switched laser device (Japanese Patent Application No. 12-1300).
No. 57: hereinafter also simply referred to as a proposed device). FIG. 4 is a block diagram showing such a proposed device. In the figure, 1
01 is a solid-state laser medium, 102 is a total reflection mirror, 10
3 is a transmission type reflection mirror, 104 is an acousto-optic Q switch, 105 is an excitation lamp, 106 is a reflector, 107
Is a laser resonator, 108 is a Q switch control device, 111
Is a time constant selecting device, 112 is a time constant generating device, 113 is a high frequency generating device, 115 is a laser beam (laser output),
Reference numeral 10 denotes a time constant determining device.

That is, during the period when the solid-state laser medium 101 is excited by irradiating the solid-state laser medium 101 with excitation light using the excitation lamp 105 as a light source and the acousto-optic Q switch 104 is controlled to transmit the laser light, Reflective mirror 10
By reciprocating between the transmission mirror 2 and the transmission-type reflection mirror 103 along the laser resonance path 107, a continuous oscillation state (CW oscillation mode) is obtained, and a part of the light is output from the transmission-type reflection mirror 103 in the laser emission direction. Generally, in order to obtain a larger laser output, a Q-switch pulse modulation is added and used for processing or the like. The reflector 106 is an excitation lamp 1
05 is a reflecting device for efficiently supplying the light of No. 05 to the solid-state laser medium 101, 101, 104, 105 and 1
06 and the like are cooled by a cooling device (not shown) as necessary.

The acousto-optic Q switch 104 receives a high-frequency output from the high-frequency generator 113 (for example, 20M).
Hz), and has a function of converting a high-frequency signal into an ultrasonic wave to change optical characteristics and deflect the laser light 115. During a period of receiving a high-frequency input, the laser light is deflected to the total reflection mirror 102. Laser oscillation is suppressed by no longer reaching the laser resonance path 107, and excitation energy is accumulated in the laser medium 101 during the suppression of laser oscillation.

The stored energy is transferred to the Q switch 10
4 at a high speed, the total reflection mirror 1 is turned off at the moment when the laser deflection of the Q switch is released.
Oscillation occurs between the transmission mirror 02 and the transmission-type reflection mirror 103, energy is released at once, and a pulse having a high peak value is obtained.
The energy of this pulse has the characteristic that it increases as the pumping energy increases, and when laser oscillation is suppressed for a long time while pumping is continued and an oscillation pulse is output at a certain Q switch frequency, the first pulse is used. One shot is a laser pulse having a large peak value, and thereafter becomes a small laser pulse because it becomes the excitation energy after the excitation energy is once emitted.

FIG. 5 shows a time chart of the Q switch pulse. When the laser output period signal shown in FIG. 5A becomes active, the Q-switch pulse signal gradually decreases as shown in FIG. 5B according to the time tf, and the high-frequency output signal decreases as shown in FIG. 5C. Then, when the laser oscillation reaches a virtual laser oscillation threshold, the laser oscillation is gradually performed, so that the suppressed first pulse as shown in FIG. At this time, if the Q switch pulse signal is instantaneously controlled, the first pulse is not suppressed, and becomes a pulse having a high peak value.

That is, the behavior of the first pulse when the Q switch pulse signal is instantaneously changed, and the time tf required to reach a predetermined threshold value so as to make a gradual change.
When examining the behavior of the first pulse when the (time constant) is changed, an intermediate tf (about 1 ms to several μs) is considered.
It has been found through various experiments that the peak value output of the first pulse changes within the range. That is,
When the tf time is changed stepwise as shown in (1) and (2), the first pulse changes as in (d), and the first pulse output becomes smaller as the tf time becomes longer. It can be seen that the peak values of the first pulse and the second pulse can be made substantially equal.

The part corresponding to the above-mentioned principle explanation is shown in FIG.
In this case, they are mainly shown as 108 to 113 and 210. The Q switch control device 108
3, a time constant selecting device 111 selects a time constant of the time constant generating device 112, and a time constant determining device 210 instructs the time constant selecting device 111 to perform laser excitation. State (for example, current value of an excitation light source such as an arc lamp or a laser diode), laser oscillation state (for example, excitation energy accumulation time), Q
The time constant is determined from various conditions such as the switch frequency, and a command is issued. At this time, a memory can be prepared inside the time constant determining device 210, and a conversion table for determining tf based on these various conditions can be provided.

[0012]

In the above proposed device,
A time constant for making the peak values of the first pulse and the second pulse substantially equal is determined by a conversion table using at least one of the current value of the excitation light source, the time during which the oscillation pulse is suppressed, and the Q switch frequency. However, in preparing this conversion table, it is necessary to collect a large amount of detailed data under the respective conditions of the excitation lamp current value, the Q switch frequency, and the laser output off time. There is a problem of doing.
In addition, since the conversion table is created by irradiating the object to be laser-irradiated with a laser and visually comparing the dot size (processing state) of the first pulse and the second pulse, the optimum time constant can be accurately determined. Difficult to seek.

Further, the absolute laser output of the first pulse is determined by the energy storage condition in the laser medium, that is, the excitation energy and the storage time of the excitation energy. In the case of a YAG laser lamp, the first pulse is stably controlled to be substantially equal to the second pulse over a long period of time because, in the case of a lamp of a YAG laser, the initial pulse decreases by about 10 to 30% near the life time. There is also a problem that can not be. Accordingly, an object of the present invention is to facilitate creation of a conversion table and to control a first pulse in a long term so as to be stable and substantially equal to a second pulse.

[0014]

In order to solve the above-mentioned problems, according to the present invention, in a Q-switched laser device in which a solid-state laser to be continuously excited is Q-switched pulse-oscillated by an acousto-optic Q-switch, A Q switch control section for gradually reducing a high frequency power signal level for driving the optical Q switch with a predetermined time constant;
A time constant selection unit capable of selecting a time constant for gradually reducing the high-frequency power signal level in a switch control unit;
An arithmetic processing unit for determining a time constant to be selected by the time constant selection unit and a laser output detector for monitoring a laser output are provided, and a peak value of a first pulse of a Q-switch pulse train is suppressed to produce a second pulse. A laser oscillation pulse substantially equal to the peak value of the laser beam is obtained, and the laser output can be monitored.

In the first aspect of the present invention, the Q-switch control unit may include a high-frequency generator and a time constant generator (the second aspect of the present invention), or the arithmetic processing unit may include: A table for determining the time constant using at least one of the current value of the excitation light source of the solid-state laser, the time during which the laser oscillation pulse is stopped, and the Q switching frequency can be provided (the invention of claim 3). According to the third aspect of the invention, the table can be created based on the laser output measured by the laser output detector (the fourth aspect of the invention). This claim 4
In the present invention, the current value of the excitation light source can be corrected according to the amount of change between the laser output measured at the time of creating the table and the laser output measured at the time of actual laser irradiation. invention).

[0016]

FIG. 1 is a block diagram showing an embodiment of the present invention. In contrast to the proposed device shown in FIG.
The feature is that a laser output detector 116 for monitoring the power of the laser is added. The reflector 106 is not shown here, and the CPU 110 is used as a time constant determining device.
The CPU 110 is also used for controlling the lamp power supply 118. Hereinafter, the difference will be mainly described. Based on the power detection signal from the laser output detector 116, the CPU 110 creates a conversion table of the time constant tf using the excitation lamp current value, the Q switch frequency, and the laser output off time as parameters, and stores it in the memory 114. This conversion table is created by comparing the output of the first pulse with the output per unit pulse after the second pulse, calculating the amount of change, and obtaining a time constant tf that eliminates the amount of change.

FIG. 2 is a time chart when the conversion table is created, and FIG. After setting the parameters (see step S1 of FIG. 3), tf = 0 to measure the unsuppressed fast pulse output.
The laser output period is activated (without delay) (see step S2 in FIG. 3). At this time, an output detection valid signal as shown in FIG. 2 is given to the laser output detector 116 in FIG. 1 so that only the first pulse output P1 can be measured (see step S3 in FIG. 3). Next, tf
When = 0, the laser output period is activated, an output detection valid signal as shown in FIG. 2 is given, and the average output P _AV after the second pulse is measured (see step S4 in FIG. 3).

The output energy P [J / pulse]
= Average output P _AV [W] / Q switch frequency [Hz] The output P2 per unit pulse after the second pulse is calculated from the relational expression (see step S5 in FIG. 3),
After increasing the value of tf according to the fluctuation amount of P1 and P2,
P1 and P2 are measured again, and if there is a variation, tf is further increased (see steps S3 to S7 in FIG. 3). Then, by gradually increasing the value of tf until P1 = P2, an optimum time constant tf for a predetermined laser parameter can be obtained (see step S8 in FIG. 3), and the same applies to other laser parameters. The conversion table is created by performing the operations of (1) and (2) and storing the results in the memories (steps S9 and S9 in FIG. 3).
10).

Next, a method of controlling the first pulse stably for a long period will be described. In FIG. 1, since the excitation energy of the excitation lamp 105 is determined by the lamp current 117, the decrease in the excitation energy due to the deterioration of the lamp is compensated by controlling the lamp current 117 from the CPU 110 via the lamp power supply 118. I do. The deterioration of the laser output due to aging is mainly caused by the deterioration of the excitation lamp 105. For example, the average output P _AV after the second pulse measured at the time of creating the above-mentioned tf conversion table and the average output at the time of laser output The CPU
By comparing at 110, the amount of change is calculated. Then, the CPU 110 controls the lamp current 11 according to the variation.
By correcting the command value of 7, the excitation energy is kept constant. Furthermore, if the average power is measured during continuous laser irradiation and the lamp current is controlled, the fluctuation of the excitation energy can be automatically corrected, and as a result, the first pulse can be controlled stably in the long term almost equal to the second pulse. become. Note that the value of the lamp current used for determining the time constant tf is a value before correction.

[0020]

According to the present invention, the conversion table for determining the time constant for suppressing the peak value output of the first pulse can be obtained easily and accurately, and the first pulse can be stably obtained for a long period of time. It is possible to control up to a peak value substantially equal to the second pulse. As a result, Q
The processing, engraving, and trimming performance of the switch laser device can be further improved.

[Brief description of the drawings]

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

FIG. 2 is a time chart when the conversion table of FIG. 1 is created.

FIG. 3 is a flowchart when the conversion table of FIG. 1 is created.

FIG. 4 is a block diagram showing a proposal device.

FIG. 5 is a time chart illustrating a relationship between a Q switch pulse and a laser output.

[Explanation of symbols]

101: solid laser medium, 102: total reflection mirror, 1
03: transmissive reflection mirror, 104: acousto-optic Q switch, 105: excitation lamp, 106: reflector, 107
... Laser resonance path, 108 ... Q switch control device, 110
... CPU, 111 ... time constant selection device, 112 ... time constant generation device, 113 ... high frequency generation device, 114 ... memory, 1
15: laser light (laser output), 210: time constant determining device.

Claims (5)

[Claims] 1. An acousto-optic Q laser for continuously exciting a solid-state laser.
A Q-switch laser device that oscillates a Q-switch pulse by a switch, comprising: a Q-switch control unit that gradually reduces a high-frequency power signal level for driving the acousto-optic Q switch by a predetermined time constant; A time constant selection unit capable of selecting a time constant for gradually reducing the high-frequency power signal level, an arithmetic processing unit for determining a time constant to be selected by the time constant selection unit, and a laser output detection for monitoring a laser output A peak value of the first pulse of the Q switch pulse train is suppressed to obtain a laser oscillation pulse substantially equal to the peak value of the second pulse, and the laser output can be monitored. Switch laser device. 2. The device according to claim 1, wherein the Q switch control unit includes a high frequency generator and a time constant generator.
6. The Q-switched laser device according to item 1. 3. The arithmetic processing unit according to claim 1, wherein the time constant is determined using at least one of a current value of an excitation light source of the solid-state laser, a time during which a laser oscillation pulse is stopped, and a Q switching frequency. 2. The Q-switched laser device according to claim 1, comprising: 4. The Q-switched laser device according to claim 3, wherein the table is created based on a laser output measured by the laser output detector. 5. A current value of the excitation light source is corrected according to a variation between a laser output measured at the time of creating the table and a laser output measured at the time of actual laser irradiation. 6. The Q-switched laser device according to item 1.