JP2001313434A - Q-switch laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable simple suppression of the peak value of a first pulse at a low cost. SOLUTION: When a laser beam 114 is emitted from a solid-state laser medium 101 and an acousto-optic Q switch 104 or the like, a signal level of a high-frequency generator 108 for driving the Q switch 104 is reduced gradually with a prescribed time constant to be given via a time constant deciding unit 112, a time constant selector 111 and a time constant generator 109. Thus, the level of a first pulse of a Q switch pulse train is made substantially equal to that of a second pulse.

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. .

[0004]

However, the above conventional method 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. Therefore, an object of the present invention is to suppress the first pulse with a small-sized and low-cost configuration.

[0005]

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;
A time constant determining unit for determining a time constant to be selected by the time constant selecting unit, wherein the peak value of the first pulse of the Q-switch pulse train is suppressed and a laser oscillation pulse substantially equal to the peak value of the second pulse is provided. It is characterized by obtaining. In the first aspect of the present invention, the Q switch control section may include a high frequency generator and a time constant generator.

According to a second aspect of the present invention, the time constant generating device includes a buffer amplifier and an integrator, the time constant selecting unit includes a D / A converter and a latch circuit, and the time constant determining unit includes An arithmetic processing unit having a memory can be included (the invention of claim 3). Further, the above claims 1 to 3
In the invention, the time constant determining unit can determine the time constant based on at least one of pumping energy to the solid-state laser, pumping energy accumulation time, and Q switching frequency (claim 4). This claim 4
In the present invention, the excitation energy to the solid-state laser can be determined based on a current value of an excitation light source, and the excitation energy accumulation time can be determined based on a time during which a laser oscillation pulse is stopped. Item 5).
Further, in the invention according to claim 5, the time constant determining unit determines the time constant using at least one of a current value of the excitation light source, a time during which a laser oscillation pulse is stopped, and a Q switching frequency. A table for determining can be provided (the invention of claim 6).

According to the first aspect of the present invention, a scanner device capable of dynamically controlling the optical axis of the laser oscillation pulse is provided, and when the first pulse is applied to the scanner device, the first pulse and the second pulse are applied. The generation timing of the first pulse can be adjusted in consideration of the time according to the determined time constant so that the time interval with the pulse becomes an interval corresponding to the Q switching frequency (the invention of claim 7). According to the seventh aspect of the present invention, the scanner device has two X, Y coordinates.
A motor driving device having a laser light reflecting mirror for controlling the axis can be provided (invention of claim 8). In the invention of claim 7 or 8, the trajectory of the optical axis is stored and the same trajectory is stored. Can be used to draw the stored data (the invention of claim 9).

[0008]

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 101 is a solid-state laser medium, 102 is a total reflection mirror, 103 is a transmission 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 high frequency generator, 109 is a time constant generator, 1
10 is a Q switch control device, 111 is a time constant selection device,
Reference numeral 112 denotes a time constant determining device.

That is, the solid-state laser medium 101 is excited by irradiating the solid-state laser medium 101 with the excitation light 113 by using the excitation lamp 105 as a light source, and the laser light is emitted while the acousto-optic Q switch 104 is controlled to transmit the laser light. The total reflection mirror 102 and the transmission reflection mirror 103 are
The laser beam reciprocates along the line 7 to form a continuous oscillation state (CW oscillation mode), 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 a high-frequency generator 108 (for example, 20M).
Hz), and has a function of converting a high-frequency signal into an ultrasonic wave to change optical characteristics and deflect laser light. During a period of receiving a high-frequency input, the laser light deflects and reaches the total reflection mirror 102. The laser oscillation is suppressed by no longer forming the laser resonance path 107, and the excitation energy is accumulated in the laser medium 101 during the suppression of the laser oscillation. The stored energy is reduced by the high frequency power of the Q switch 104 decreasing at a high speed.
The laser oscillates between the total reflection mirror 102 and the transmission reflection mirror 103 at the moment when the laser deflection of the switch is released, and the energy is released at once, resulting in a pulse having a high peak value. 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. 2 shows a time chart of the Q switch pulse. FIG. 6A shows a time chart in the conventional case. When the laser output period signal becomes active, the Q-switch pulse signal gradually decreases in accordance with the time tf to lower the high-frequency output signal, thereby causing virtual laser oscillation. When the threshold value is reached, laser oscillation occurs gradually,
A suppressed first pulse is obtained. At this time, Q
When the switch pulse signal is controlled instantaneously as shown by the dotted line in the figure, the first pulse is not suppressed, and becomes a pulse having a high peak value.

FIG. 3 is an explanatory diagram for explaining the principle of the present invention. That is, the behavior of the first pulse when the Q switch pulse signal is instantaneously changed, and the time tf until the predetermined threshold is reached so that the Q switch pulse signal gradually changes.
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. This will be described with reference to FIG. 3. If the tf time is changed stepwise as shown in FIG. 3, the first pulse changes as shown in the enlarged view. It is clear that the absolute laser output of the first pulse at this time depends on the condition of energy storage in the laser medium, and this tendency is relative under the same condition. However, the state of energy storage in the laser medium can be predicted by carefully collecting data, and absolute level control of the first pulse is possible in any laser output state.

Parts corresponding to the above description of the principle are shown as 108 to 112 in FIG. The Q switch control device 110 includes a time constant generation device 109 for controlling the high frequency generation device 108, a time constant selection device 111 selects a time constant of the time constant generation device 109, and the time constant determination device 112 The time constant selection device 111 is controlled based on various conditions such as the laser excitation state (for example, the current value of an excitation light source such as an arc lamp and a laser diode), the laser oscillation state (for example, excitation energy accumulation time), and the Q switch frequency. Decide the constant and give the command. FIG. 2B shows a timing chart when the control is performed by selecting and determining the time constant as described above. It can be seen that the level of the first pulse is suppressed to the level of the second pulse as compared with the conventional example of FIG.

FIG. 4 shows a specific configuration of the time constant generator 109, the time constant selector 111, and the time constant determiner 112. That is, in the time constant determining device 112, the arithmetic processing unit (CPU) 401 determines the energy accumulation level in real time from the above-described various conditions of the laser output, and calculates the peak value output level of the second pulse from the Q switch frequency. Tf (time constant) of the Q switch pulse signal
Is determined, and the time constant selecting device 111 is instructed by a digital signal. The time constant selecting device 111 is a time constant determining device 11
The digital signal from 2 is latched by a latch circuit 402, and is further subjected to digital / analog conversion by a D / A converter 403, and the input current to the integrator 404 of the time constant generator 109 is determined. The integrator 404 includes a buffer amplifier 405 for offset, gain, and impedance conversion.
, And is output as a Q switch pulse signal. The integrator 404 is reset when the laser output is off, and returns to the initial state. The time constant tf depends on parameters such as the excitation lamp current, the Q switch frequency, and the laser output off time, and the laser absorption characteristics of the workpiece.
Since it is assumed that the time constant is determined empirically, the memory 406 can be prepared inside the time constant determination device 112 and a conversion table for determining tf based on these conditions can be provided.

By the way, the above-described Q-switch laser device is often used in combination with a scanner device for dynamically controlling the emission optical axis of a laser pulse. FIG. 5 is a block diagram showing such an example. The reference numeral 201 in FIG.
The laser beam 114 extracted from the switch laser device is expanded by an expander lens 208 to a beam diameter of about several millimeters to improve condensing on the processing surface of the f-theta lens 209 at the subsequent stage, and a servo motor 20
The density of the laser beam to the total reflection mirror 202 attached to 3,204 is reduced to reduce thermal damage.
The laser beam reflected by the total reflection mirror 202 is guided to the fθ lens 209, and is condensed on the surface of the processing work 207 to contribute to the processing. Note that the scanner device includes all elements except for 201 and 207 in FIG.

The focusing position of the laser beam on the work 207 is controlled by the angles θ _X and θ _Y formed by the respective motor shafts 206 of the servo motors 203 and 204. Workpiece surface in the home position 210, the theta _X position of the optical axis center the laser beam passes through the fθ lens 209, theta is defined as _Y, θ _X, θ _{Y X} amount change on the workpiece 207
It corresponds to Y orthogonal coordinates. The coordinate control device 212 uses the X
Servo controller 205 determines the position of the laser beam in the Y orthogonal coordinates.
At the same time, a command as to whether or not to emit laser light at the coordinate position is issued to the Q-switch laser device 201 as a shutter control signal.

The servo controller 205 determines the above θ _X and θ _Y so as to be at the designated coordinate position, and controls the X-axis and Y-axis servo motors 203 and 204 using these as target values. The coordinate control device 212 stores in advance information about what kind of trajectory the laser light draws on the work surface as a coordinate sequence of XY orthogonal coordinates, and synchronizes the coordinate sequence with an internal clock. Thus, a desired laser beam trajectory can be obtained by reading the data at a constant time interval and continuously instructing the servo control device 205. Coordinate control device 21
2 is issued in response to the processing start signal. The optical axis of the laser light is dynamically controlled, and the coordinate control device 2
Based on a command from 12, the workpiece moves on the work surface.

As described above, when the optical axis of the laser beam moves on the work surface and moves at a constant speed, the firing interval between the first pulse and the second pulse described above is determined by the reciprocal of the Q switch frequency. When the time is shorter or longer than the tq time (see FIG. 2 (a)) represented by the following equation, the laser processing trace unnaturally approaches or separates between the first pulse and the second pulse. Trouble occurs.
FIG. 6 explains this. When the first pulse appears at the position of the solid line or the dotted line as shown in FIG.
Pitch 1 and pitch 2 are irregular. Such a phenomenon undesirably lowers the quality particularly when engraving characters, figures, symbols, codes, and the like.

Therefore, in the present invention, not only the level of the first pulse is suppressed as described above, but also the time interval t1 (see FIG. 2A) between the first pulse and the second pulse is controlled. Therefore, the time required for the first pulse to reach a predetermined laser oscillation threshold value is tf.
Predicted according to time, the CP in the time constant determination device 112
By controlling or adjusting the activation start timing by U, pitch 1 and pitch 2 are made equal to each other as shown in FIG. 6B, regardless of which tf is selected.

[0020]

According to the present invention, the behavior of the first pulse when the Q-switch pulse signal is instantaneously changed, and the time tf (time constant) until the predetermined threshold is reached so as to make a gradual change. While examining the behavior of the first pulse when the value of the pulse width is changed, focusing on the fact that the peak value output of the first pulse changes when tf is approximately in the range of 1 ms to several ms, the method of changing the Q switch pulse signal is described. By appropriately selecting, not only the level of the first pulse is suppressed but also the time interval t1 between the first pulse and the second pulse.
Can also be optimized. As a result, there is an advantage that a high-speed and versatile Q-switch laser device can be provided.

[Brief description of the drawings]

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

FIG. 2 is a time chart for explaining a relationship between a Q switch pulse and a laser output.

FIG. 3 is a diagram illustrating the principle of the present invention.

FIG. 4 is a partial detailed view of FIG. 1;

FIG. 5 is a block diagram showing a Q-switch laser device including a scanner device.

FIG. 6 is an explanatory diagram for explaining a movement locus of a laser beam.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 101 ... Solid-state laser medium, 102, 202 ... Total reflection mirror, 103 ... Transmission reflection mirror, 104 ... Acousto-optic Q switch, 105 ... Excitation lamp, 106 ... Reflector, 107 ... Laser resonator, 108 ... High frequency generator ,
109: time constant generator, 110: Q switch controller, 111: time constant selector, 112: time constant determiner, 113: excitation light, 114: laser light, 201: Q switch laser device, 203: X-axis servo Motor, 204
... Y-axis servo motor, 205 ... servo control device, 206
... Motor shaft, 207 ... Workpiece, 208 ... Expander lens, 209 ... Fθ lens, 210 ... Processing origin, 2
12 ... Coordinate control device.

Claims (9)

[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 selector for selecting a time constant for gradually reducing the high-frequency power signal level; and a time constant determiner for determining a time constant to be selected by the time constant selector. A Q-switched laser device wherein a peak value of one pulse is suppressed to obtain a laser oscillation pulse substantially equal to a peak value of a second pulse. 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 time constant generating device includes a buffer amplifier and an integrator, the time constant selecting unit includes a D / A converter and a latch circuit, and the time constant determining unit includes an arithmetic processing unit having a memory. The Q-switched laser device according to claim 2, comprising a device. 4. The time constant determining unit determines the time constant as an excitation energy to a solid-state laser, an excitation energy accumulation time,
The Q-switched laser device according to any one of claims 1 to 3, wherein the Q-switched laser device is determined based on at least one of the Q switching frequencies. 5. The excitation energy to the solid-state laser is determined based on a current value of an excitation light source, and the excitation energy accumulation time is determined based on a time during which a laser oscillation pulse is stopped. The Q-switch laser device according to claim 4. 6. The time constant determining unit includes a table for determining the time constant using at least one of a current value of the excitation light source, a time during which a laser oscillation pulse is stopped, and a Q switching frequency. The Q-switch laser device according to claim 5, wherein: 7. A scanner device capable of dynamically controlling the optical axis of the laser oscillation pulse, and when the first pulse is given to the scanner device, the time interval between the first pulse and the second pulse is a Q switching frequency. 2. The Q-switched laser device according to claim 1, wherein the generation timing of the first pulse is adjusted in consideration of a time based on the determined time constant so as to have an interval corresponding to the time. 8. The Q-switched laser device according to claim 7, wherein said scanner device comprises a motor drive device having a laser light reflecting mirror for performing two-axis control of X and Y coordinates. 9. The Q-switched laser device according to claim 7, wherein the trajectory of the optical axis is stored, and when the same trajectory is drawn, the stored data is used.