JP2002252403A - Laser oscillator and its laser pulse control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable laser pulse with high peak power not depending on excited light strength, a Q switch frequency, and the like. SOLUTION: A high frequency signal which is applied to a Q switch is set by a high frequency signal setting means depending on a desirable laser output or the Q switch frequency, and the set high frequency signal is applied to the Q switch. Energy accumulated in a solid laser medium is increased by an exciting light source, and a laser optical detection means detects a start of a laser oscillation by exceeding a laser oscillation threshold which can restrict the laser oscillation according to the high frequency signal. A minimum RF signal power value which can halt the laser oscillation is calculated by detecting the laser output, and the high frequency signal to be applied next is controlled so as to be close thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser oscillator for controlling a laser output pulse emitted from a laser oscillator and a method for controlling a laser pulse.
More specifically, the present invention relates to a pulse control method for stably outputting a laser pulse in a solid-state laser device that performs an oscillation operation using a Q switch.

[0002]

2. Description of the Related Art Laser devices are used for marking, trimming,
It is used for processing applications such as cutting and welding. A solid-state laser such as a YAG laser can change continuous oscillation to high-speed repetitive pulse oscillation having a high peak output value (peak value) by using a Q switch. In general, an acousto-optic Q switch utilizing Bragg diffraction by ultrasonic waves is used in a YAG laser. 2. Description of the Related Art In a laser oscillator for performing a processing operation by a laser such as a laser marking, the laser is turned on / off using a Q switch to control an internal loss of a resonator.

FIG. 1 is a schematic diagram of a laser oscillator. The laser oscillator shown in FIG. 1 includes a solid-state laser medium 1, an excitation light source 2 for exciting the solid-state laser medium 1, a Q switch 3 disposed on one of the solid-state laser medium 1, a total reflection mirror 4, An output mirror 5 is provided on the other side. The Q switch 3 is arranged facing one end face so as to be located on the optical axis of the laser beam emitted from the solid-state laser medium 1. The total reflection mirror 4 and the output mirror 5 are disposed so as to face each other via the solid-state laser medium 1 so as to be able to repeatedly reflect light therebetween, and constitute a resonator for amplifying light. Further, a mechanical shutter 6 is disposed as necessary at a position where the optical axis can be blocked so that light emitted from the solid-state laser medium 1 can be blocked. Further, if necessary, the scanner unit scans the surface of the object with laser light passing through the output mirror 5 to perform desired processing.

An output mirror 5 partially permeable is provided on an extension line connecting the solid-state laser medium 1 and the Q switch 3, and a high frequency signal power is applied to the Q switch 3 to stop laser oscillation. When the Q switch 3 is turned on when the switch is turned on, the solid state laser medium 1 is excited by optical excitation when the Q switch 3 is on to store energy, and the Q switch 3 is turned on.
At the time of FF, laser oscillation occurs instantaneously between the output mirror 5 and the total reflection mirror 4, and a part of the laser light is output from the output mirror 5. On the output side of the laser beam of the output mirror 5, a scanner unit for controlling a processing position can be provided.

FIGS. 14A and 14B show an example of a galvano scanner optical system. FIG. 14A is a side view of a scanner section, and FIG. 14B is a plan view. An X mirror 15 which is two movable mirrors for directing the laser beam from the output mirror 5 downward and scanning in the XY directions is provided inside the scanner unit.
An X and Y mirror 15Y is built in. An Fθ lens 17 as a condenser lens is attached to an emission portion of the scanner unit, and an object (not shown) is disposed at a focal position of the lens. Coordinates X and Y shown in FIG. 14B indicate coordinate axes of the processing plane. The scanner section shown in FIG. 1 includes a beam expander 14 for enlarging the beam diameter of a laser beam, and an X
A mirror 15X, a Y mirror 15Y, and an X scanner 1 for driving and controlling each of these galvano-scanner mirrors 15
It has a 6X, Y scanner 16Y and an Fθ lens 17 as a condenser lens. As the galvano-scanner mirror 15, a mirror made of a transparent base material and a dielectric multilayer film is used.

A laser beam oscillated from a laser oscillator is incident on a beam expander 14 as shown by an arrow,
It is enlarged to a desired magnification. The processing position in the X direction and the Y direction of the expanded laser light is controlled by an X mirror 15X and a Y mirror 15Y whose angles are controlled by an X scanner 16X and a Y scanner 16Y. ON / OFF of laser light and X
Desired laser processing and marking can be performed by position control by the scanner 16X and the Y scanner 16Y.

FIG. 2 shows an example of the Q switch. The Q switch 3 has a synthetic quartz glass 7 as an acousto-optic Q switch.
A piezoelectric element 8 is often used. The acousto-optic Q switch 3 shown in FIG. 1 is connected to a piezoelectric transducer with a high-frequency power supply 9 and applies high-frequency (Radio Frequency, hereinafter referred to as “RF”) signal power, which is a high frequency of several tens of MHz, to produce quartz. An elastic wave can be generated inside. As the frequency of the applied RF signal power, 20 MHz and 24 MHz are mainly used. When no RF signal power is applied to the piezoelectric element 8, the laser light inside the resonator passes through the Q switch 3 as shown in FIG. On the other hand, as shown in FIG. 2B, when an RF signal power is applied to the piezoelectric body to generate an elastic wave inside the quartz, a difference in refractive index occurs due to the density of the elastic wave, and a diffraction grating is formed. By diffracting the light with this diffraction grating, a loss can be generated in the resonator, and the laser output can be controlled.

When a high-frequency electric signal of, for example, 24 MHz and 50 W is applied to the piezoelectric element 8, the high-frequency electric signal is converted into an ultrasonic wave by the piezo effect. The ultrasonic wave propagates in the quartz glass 7 and a periodic refractive index distribution is generated in the quartz glass 7 by a photoelastic effect. When light is incident at an appropriate angle, the light incident at the Bragg angle is
An acousto-optic effect of being diffracted as shown in FIG.

That is, by applying an RF signal power to vibrate the piezoelectric body to generate an elastic wave and block the laser beam passing through the Q switch 3, a loss can be generated in the resonator as a result. As the RF signal power increases, the loss of the resonator can be increased and the laser output can be suppressed, so that the laser output can be controlled by adjusting the RF signal power. If the resonator loss is further increased, laser oscillation is suppressed, and finally the output is stopped. Here, the minimum RF signal at which laser output can be stopped is defined as an RF signal power threshold.

FIG. 3 shows the relationship between the RF signal and the waveform of the laser output pulse. FIG. 3A is a schematic waveform of the RF signal, and the Q switch 3 is turned ON at this amplitude. Actual RF
Although the waveform of the signal is a sine wave shape, for simplicity in the figure, a box-like shape is shown except for a part on the left side. When the amplitude of the RF signal is 0, that is, when the Q switch 3 is off, the laser output is turned on, and a pulse as shown in FIG.

[0011] As shown in FIG.
Laser output by repeating ON / OFF of the oscillation
Can be pulsed. RF signal power Q switch
Resonator applied to switch 3 to stop laser oscillation
When a loss occurs, the Q switch 3 is
Is turned off. On the other hand, the RF signal applied to the Q switch 3
Signal power is low or 0W, the Q switch
When the switch 3 is turned off, the laser is turned on. Repeat this state
By doing so, it is possible to control ON / OFF of the laser oscillation.
Wear. That is, a certain time (for example, several
μsec) for T_onAnd turn off the laser
T for a certain time_offAs T_onAnd T _offRepeat
To generate the laser output in a pulse
it can. T_offThe time interval of pulse generation is controlled by
Possible, T_offThe longer the length of the
Since the stored energy increases, the
Speaking power increases.

During the period when the laser is off, excitation energy is stored in the solid-state laser medium. When the laser is turned on, the stored energy is output as pulsed laser light. For example, when a YAG crystal is used for the solid-state laser medium 1 and constant excitation energy is continuously applied to the YAG rod, the energy stored in the YAG rod increases with time and saturates to a value determined by the excitation energy. As shown in FIG. 4, when the repetition frequency of ON / OFF by the Q switch 3, that is, the Q switch frequency becomes lower than 1 kHz as shown in FIG. 4A, the energy stored in the YAG rod during the laser OFF period. Is saturated, and the laser output becomes maximum as shown in FIG. R at higher repetition frequency
When the F signal power is applied, the time for accumulating energy is shortened, so that the output energy per pulse decreases as the repetition frequency increases. The threshold changes depending on the energy stored in the solid-state laser medium,
The threshold increases as the stored energy increases. Even at the same excitation energy, the threshold value changes depending on the Q switch frequency. The threshold value also changes depending on the type of crystal used for the solid-state laser medium.

[0013]

As the RF signal power applied to the Q switch 3 increases, the magnitude of the elastic wave generated inside the synthetic quartz glass 7 of the Q switch 3 increases. Of the incident light that is diffracted, the amount of diffracted light that is diffracted increases, and the loss of the resonator also increases.

However, the RF signal power is sharply increased
Even when F, the elastic wave inside the quartz glass 7 does not disappear immediately but gradually attenuates and disappears, so that the diffracted light does not become zero and the resonator loss remains for a while.

FIG. 5 shows (a) an RF signal, (b) a resonator loss, and (c) and (d) waveforms of respective laser outputs when the laser power is high and low.
Here, zeta residual resonator loss at the moment the RF signal is turned OFF zeta _A, RF signals resonator loss at ON state
_B , the threshold at which laser oscillation starts when the laser power is high is ζ _S , and the threshold at which laser oscillation starts when the laser power is low and the Q switch frequency is high is _{Ｗ W}
And

As shown in FIG. 5B, the resonator loss is R
Immediately from the moment the F signal becomes 0 0 not, after once lowered to zeta _B under the influence of the residual acoustic waves, gradually decay toward zero. The time until the resonator loss is from 0 to when the RF signal becomes 0 and T _R.

[0017] When Fig. 5 (c) laser power as shown in is strong, since larger than the threshold value zeta _S is zeta _B which laser oscillation is started immediately resonator loss threshold value or steeply OFF the RF signal since the lower than this zeta _B through the zeta _S, laser oscillation is started immediately. Therefore, ζ _B
The larger the value of _S is, the less affected by the residual elastic wave remaining for a while.

[0018] However Figure 5 when the laser power as shown in (d) is weak Q-switching frequency is high, if the laser power is smaller than a threshold zeta _W that laser oscillation is initiated zeta _B specifically Then, change the RF signal to O
Even in the case of FF, the resonator loss does not decrease to the threshold value _ＷW , and the laser is not immediately oscillated. After resonator loss was reduced in zeta _B, gradually decreases with time, the threshold zeta
_The laser oscillation starts when _W is reached.
Since the waveform of the resonator loss below zeta _B is unstable, the laser oscillation pulse also becomes unstable. Time to reach the threshold zeta _W is not fixed to a constant, and because the waveform of the resonator loss is unstable, the laser oscillation becomes unstable in zeta _W vicinity. Furthermore, since the waveform of the resonator loss is not steep but continues gently, the pulse width is increased, and the peak power is also reduced. When the laser power is weak as described above, not only does the start of laser oscillation be delayed, but also the laser output waveform does not become a sharp pulse, resulting in a weak pulse having a wide half width. Further, since the peak power and the pulse width of each pulse fluctuate and become unstable, there is a problem that printing is not stable when the laser power is weak.

The present invention has been developed to prevent such adverse effects. An important object of the present invention is to obtain a laser pulse having a stable peak power irrespective of the laser intensity and the Q-switch frequency. It is an object of the present invention to provide a laser oscillator and a laser pulse control method thereof.

[0020]

In order to solve the above-mentioned problems, a laser oscillator according to a first aspect of the present invention comprises: a solid-state laser medium; an excitation light source for exciting the solid-state laser medium; Driving means for driving the excitation light source, a total reflection mirror positioned on the optical axis of laser light emitted from the solid-state laser medium, and an output facing the total reflection mirror via the solid-state laser medium A mirror, arranged between the total reflection mirror and the output mirror, on the optical axis of the excitation laser light emitted from the solid-state laser medium, and pulsating the excitation laser light by applying a high-frequency signal power. And a Q switch for turning on. Further, the laser oscillator includes a high-frequency signal setting unit that sets a predetermined high-frequency signal power determined based on a desired laser output, and the energy stored in the solid-state laser medium excited by the excitation light source is the predetermined high-frequency signal power. Laser light detecting means for detecting that laser oscillation has begun beyond a laser oscillation threshold value at which laser oscillation can be suppressed by the high frequency signal power, and reducing the high frequency signal power based on a detection signal from the laser light detecting means. A high-frequency signal applying means for causing the high-frequency signal to be applied.

According to a second aspect of the present invention, in the laser oscillator according to the first aspect, when the high frequency signal applying means reduces the high frequency signal power, the amplitude of the high frequency signal is reduced. It is characterized by sharp attenuation.

Further, in the laser oscillator according to the third aspect of the present invention, in addition to the features of the first aspect, when the high-frequency signal applying means reduces the high-frequency signal power, the amplitude of the high-frequency signal is reduced. It is characterized in that it is attenuated in a slope shape.

Further, in the laser oscillator according to a fourth aspect of the present invention, in addition to the features of the first aspect, when the high frequency signal applying means reduces the high frequency signal power, the amplitude of the high frequency signal is reduced. Is exponentially attenuated.

Further, in the laser oscillator according to a fifth aspect of the present invention, in addition to the features of the first aspect, when the high frequency signal applying means reduces the high frequency signal power, the amplitude of the high frequency signal is reduced. It is characterized in that it is attenuated stepwise.

Further, in the laser oscillator described in claim 6 of the present invention, in addition to the features of claim 1, the phase of the high-frequency signal is reduced when the high-frequency signal applying means reduces the high-frequency signal power. , The cavity loss inside the Q switch is forcibly attenuated.

Furthermore, a laser oscillator according to a seventh aspect of the present invention includes a solid-state laser medium, an excitation light source for exciting the solid-state laser medium, and a driving unit for driving the excitation light source. And a total reflection mirror located on the optical axis of laser light emitted from the solid-state laser medium,
An output mirror that faces the total reflection mirror via the solid-state laser medium, disposed on the optical axis of the excitation laser light emitted from the solid-state laser medium between the total reflection mirror and the output mirror, and A Q-switch is provided for pulse-oscillating the excitation laser light when high-frequency signal power is applied. Further, the laser oscillator sets high-frequency signal application time to a predetermined high-frequency signal ON time according to the Q-switch frequency and sets a predetermined high-frequency signal power determined by a desired laser output, and high-frequency signal setting means, A laser light detecting means for detecting that laser energy has been started when the energy stored in the solid-state laser medium excited by the excitation light source exceeds a laser oscillation threshold capable of suppressing laser oscillation by the predetermined high-frequency signal power When,
A timer for measuring the time from the detection of the laser beam to the passage of the high-frequency signal ON time based on the detection signal from the laser beam detector; and the high-frequency signal set value according to the time measured by the timer. It has high frequency signal adjusting means for adjusting.

Further, in the laser oscillator according to the eighth aspect of the present invention, in addition to the features of the first to seventh aspects, the energy stored in the solid-state laser medium before the application of the high-frequency signal power. It is characterized by further comprising an initializing means for discharging and lowering.

Further, according to a laser pulse control method for a laser oscillator according to claim 8 of the present invention, the step of setting the high frequency signal power applied to the Q switch by the high frequency signal setting means based on a desired laser output. Applying the high-frequency signal power set by the high-frequency signal setting means to a Q-switch; and a laser capable of increasing the energy stored in the solid-state laser medium by the excitation light source and suppressing laser oscillation by the high-frequency signal power. A step of detecting the start of laser oscillation beyond the oscillation threshold by the laser light detecting means, and calculating a minimum high-frequency signal value at which laser oscillation can be stopped by detecting the laser output by the laser light detecting means. And controlling the next applied high-frequency signal power so as to approach it.

Further, according to a laser pulse control method for a laser oscillator according to a tenth aspect of the present invention, the high frequency signal power applied to the Q switch by the high frequency signal setting means is determined by a predetermined laser output. Setting the high-frequency signal power value, starting the application of the predetermined high-frequency signal power to the Q switch, and increasing the energy stored in the solid-state laser medium by the excitation light source to increase the energy of the predetermined high-frequency signal power. Detecting by a laser light detecting means that laser oscillation has started beyond a laser oscillation threshold value at which laser oscillation can be suppressed, and the high frequency signal power based on a detection signal from the laser light detecting means by a high frequency signal applying means. A step of reducing the value.

Further, in the laser pulse control method for a laser oscillator according to claim 11 of the present invention, the application time of the high frequency signal power is set to a predetermined high frequency signal ON time by the high frequency signal setting means in accordance with the Q switch frequency. Setting, setting a high-frequency signal power according to the output energy, applying the predetermined high-frequency signal power to the Q switch, and increasing energy stored in the solid-state laser medium by the excitation light source. Detecting by a laser light detecting means that laser oscillation has started beyond a laser oscillation threshold value at which laser oscillation can be suppressed by the predetermined high-frequency signal power; and detecting a laser beam based on a detection signal from the laser light detecting means. The high-frequency signal is turned on from the time of detection
A step of measuring the time until the passage of time by means of a timer;
A step of adjusting the high-frequency signal set value by the high-frequency signal adjusting means according to the time measured by the time measuring means.

The strength of the laser power output by the laser oscillator is specified by a user who uses the laser oscillator. Generally, when the laser power is high, the threshold value of the resonator loss due to the Q switch at which laser oscillation starts is large, and when the laser power is low, the threshold value is small. When the laser power is strong, the loss threshold is high as described above. Therefore, the loss threshold is large with respect to the residual loss when the RF signal power is sharply set to 0, and the problem is hardly affected by the residual loss. Does not occur. But for weak laser power,
That is, when the remaining resonator loss when the RF signal power is sharply set to 0 is equal to or larger than the threshold, the laser output becomes unstable when the resonator loss gradually decreases with an unstable waveform.

It is considered that these are caused by applying an unnecessary RF signal power to the Q switch when the laser is stopped. Generally, when stopping the laser output, the amplitude of the RF signal is set to the maximum value in order to surely stop the laser, or an RF signal power sufficiently larger than the minimum RF signal power that can stop the laser output is applied. Was. In other words, the control is performed with the RF signal power near the maximum and the RF signal applied excessively to the Q switch.

The present inventor has paid attention to this point, and has provided a method for controlling the RF signal power while keeping it to a necessary minimum.
By not applying extra energy to the Q switch, Q
Since it is considered that most of the energy applied to the switch is used to suppress laser oscillation, the effect of elastic waves remaining in the resonator when the Q switch is released can be minimized. Further, by detecting and controlling the leaked laser beam, the laser oscillation threshold value at which the laser can be stopped can be accurately grasped, and optimal control according to the state of the apparatus and individual differences can be performed. In addition, laser oscillation can be promptly obtained without waiting until the influence of the residual resonator loss is reduced as in the related art, so that an agile laser oscillator excellent in responsiveness is provided.

[0034]

Embodiments of the present invention will be described below with reference to the drawings. However, the following embodiments illustrate a laser oscillator for embodying the technical idea of the present invention and a laser pulse control method thereof, and the present invention describes the laser oscillator and the laser pulse control method thereof as follows. Not specific.

Further, in this specification, in order to facilitate understanding of the claims, the numbers corresponding to the members shown in the embodiments are added to the members shown in the column of "Means for Solving the Problems". ing. However, the members described in the claims are not limited to the members of the embodiments.

The size and positional relationship of the members shown in the drawings may be exaggerated for clarity. For example, the waveforms shown in the figures do not accurately represent the peak value or pulse width of each pulse. In particular, the peak value of the minute output is shown large in each figure in order to make it easy to understand that there is a minute laser output that does not affect the object to be processed. Also, on the time axis, the changed part is similarly shown large for the sake of explanation. Furthermore, the actual RF signal waveform is sinusoidal,
In some figures, they are simulated by an envelope for simplicity.

FIGS. 6 to 10 show RF applied to the Q switch.
A method for stably obtaining a laser output pulse by fixing the signal amplitude to a fixed value, detecting the start of laser output leakage, and lowering the RF signal power will be described. In these figures, (a) is the RF signal applied to the Q switch, (b)
Shows the resonator loss, (c) shows the stored energy stored in the solid-state laser medium 1, and (d) shows the outline of the laser output waveform.

Embodiment 1 FIG. 6 shows a state where pulse control is performed by a laser oscillator according to Embodiment 1 of the present invention.

The power value of the high-frequency signal is determined by the laser output. The RF signal power changes according to an arbitrary laser output set by the user, that is, the peak power of one pulse. For example, when the laser output is high, RF to suppress this
The signal power has a large value.

On the other hand, the excitation energy, which is the energy required to excite the solid-state laser medium 1, is determined by the excitation light source. For example, when exciting a YAG rod with an LD, increasing the amount of current flowing through the LD increases the excitation energy. As the excitation energy increases, the peak power also increases.

Further, the Q switch frequency fluctuates due to the excitation energy. As energy increases, Y
Since the energy is quickly stored in the AG rod and the time until the energy is released is also shortened, high-speed switching with a short time interval between pulses results. When a high scan speed is required, if the Q switch frequency is low, the distance between the dots by the laser pulse becomes long, and the visibility deteriorates. For example, in the case of performing printing in which metal is deeply engraved with a laser using a YAG crystal, a Q switch frequency of about 10 kHz is set. The Q switch frequency is set by Q switch frequency setting means. The user can check the print result to determine whether the Q switch frequency is appropriate.

The user compares the results of the sample printing, and sets desired conditions according to the scanning speed of required printing and processing, the degree of overlap between laser spots, and the like. The setting is performed using an input device such as a touch panel in the operation unit of the laser oscillator. As a specification method, the user may directly input a desired value as a numerical value or the like into the apparatus.However, the apparatus specifies a print result that has a desired result from a plurality of sample print results, and the apparatus side performs based on the specification. A method of reading the corresponding setting may be used. When the sample print result is selected, the peak power and Q switch frequency at the time of performing the print are determined,
The setting of the RF signal is also determined based on this.

The intensity of the excitation energy is set by the excitation energy setting means. For example, in the case of a laser marker that excites the solid-state laser medium 1 using an LD, the excitation energy setting means can control the intensity of the excitation energy by adjusting the value of the current flowing through the LD.

Further, the power value of the RF signal applied to the Q switch is set by the calculation means inside the laser marker based on the laser output set by the user. This value is
The F signal power value is _PRF .

Before applying the RF signal power,
To release the energy stored in the solid state laser medium
Can also be scheduled. For example, accumulation using initialization means
Initialize the energy to 0 or a value close to 0
Then, the application of the RF signal is started. Or drop to 0
It is not necessary to do so, but it is only necessary to lower it to a predetermined value.
In addition, a method that does not perform initialization can be adopted. RF
The power when the signal is ON is P _RFTo hold. P_RFWith laser
The laser oscillation threshold value at which oscillation can be stopped is E_sAnd

As time passes, the energy stored in the solid-state laser medium gradually increases as shown in FIG. Beyond E _s gain is increased by a predetermined time after the stored energy, it is impossible to stop the laser oscillation by the resonator loss shown in FIG. 6 (b) by the RF signal of FIG. 6 (a). As a result, the laser beam starts to leak as shown in FIG. The time until leakage starts is constant for each laser pulse, which determines the Q-switch frequency. When the RF signal power is constant, the time to start to leak becomes faster as the excitation energy becomes stronger,
The Q switch frequency will be higher. In this case, only the Q-switch frequency is increased without changing the output of each laser pulse. On the other hand, when the excitation energy is constant and the RF signal power value decreases, the laser pulse output decreases and the Q-switch frequency increases. It is also possible to record the time until the start of leakage and calculate the stored energy based on the recorded time.

[0047] Since the stored energy amount of the laser light is emitted to be released is lost, the laser beam below the E _s is stopped again. Therefore, the laser output at this time is very short. In addition, the peak power of the leak light is weaker than the laser pulse output thereafter, and therefore does not affect the workpiece.

On the other hand, the start of the laser output is detected by the laser light detecting element 12 constituting the laser light detecting means. When detecting the start of laser light leakage, the laser light detecting element 12 sharply reduces the RF signal power to 0 by, for example, instructing the control means 13 of a processing control signal. Then, the Q switch is opened and the laser output is emitted immediately. The stored energy attenuates with the laser output as shown in FIG. At this time, since the laser oscillation is suppressed by the minimum energy in the resonator, the elastic wave is attenuated when the Q switch is opened, and the resonator loss due to the residual wave is minimized.

[0049] In this method of Example 1, since securing the RF signal power to a constant value P _RF, there is a merit capable of controlling the peak power as a laser output corresponding to this value to a constant value. Even if unstable excitation energy for some reason, the pulse oscillation is performed at all times exceeds the E _s, even in the time until the pulse oscillation is started may be around, peak power It will be constant. As described above, an excellent feature that the energy of the laser pulse output every time can be accurately and constantly controlled can be realized.
Further, since only a minimum resonator loss for stopping oscillation due to stored energy is given to the Q switch, there is an advantage that a high peak power can be stably generated without being affected by a residual resonator loss.

Embodiment 2 Next, Embodiment 2 of the present invention will be described with reference to FIG. In this method, similarly to the first embodiment, the RF signal power applied to the Q switch is set to a constant value determined by the excitation energy and the Q switch frequency, and is set as the RF signal power value P _RF .

Before applying the RF power, if necessary,
By releasing energy stored in a solid-state laser medium
You can also. For example, by using initialization
After initializing the lugies and setting them to 0 or a value close to 0,
The application of the RF signal power is started. Or drop to 0
It is not necessary to do so, but it is only necessary to lower it to a predetermined value.
In addition, a method that does not perform initialization can be adopted. RF
The power when the signal is ON is P _RFTo hold. P_RFWith laser
The laser oscillation threshold value at which oscillation can be stopped is E_sAnd

As time passes, the energy stored in the solid-state laser medium gradually increases as shown in FIG. The gain by the accumulated energy after a predetermined time exceeds high becomes E _s, it is impossible to stop the laser oscillation by the resonator loss shown in FIG. 7 (b) by the RF signal of FIG. 7 (a). As a result, the laser light starts to leak as shown in FIG. The time until leakage starts is constant for each laser pulse, which determines the Q-switch frequency. When the RF signal power is constant, the time to start to leak becomes faster as the excitation energy becomes stronger,
The Q switch frequency will be higher. In this case, only the Q-switch frequency is increased without changing the output of each laser pulse. On the other hand, when the excitation energy is constant and the RF signal power value decreases, the laser pulse output decreases and the Q-switch frequency increases. It is also possible to record the time until the start of leakage and calculate the stored energy based on the recorded time.

[0053] Since the stored energy amount of the laser light is emitted to be released is lost, the laser beam below the E _s is stopped again. Therefore, the laser output at this time is very short. In addition, the peak power of the leak light is weaker than the laser pulse output thereafter, and therefore does not affect the workpiece.

On the other hand, the start of the laser output is detected by the laser light detecting element 12. Laser light detecting element 12
When detecting the start of laser light leakage, the RF signal power is attenuated by instructing the processing means 13 to the control means 13 or the like. In FIG. 7A, attenuation is performed by inclining linearly. The method is not limited to this, and although not shown, a method of attenuating in the form of an exponential function, a method of attenuating in a stepwise manner, or the like may be used.

As a result of attenuating the RF signal power, the laser oscillation threshold value is lowered, so that the Q switch is opened, and FIG.
Laser output is started as shown in (d). Further, the stored energy also decreases with the laser output as shown in FIG. In this method, the resonator loss gradually decreases as shown in FIG. 7B, so that the laser output also has a gentle waveform as compared with the first embodiment. Even with this method, the peak power and pulse width of one pulse can be accurately controlled without the influence of the residual resonator loss.

The method of approaching 0 while gradually reducing the RF signal power is not limited to the method described above. For example, a method of decreasing in proportion to time, a method of decreasing exponentially, a stepwise decrease, a plurality of stepwise decreases, a stepwise decrease, and then a slope decrease can be used.

[Embodiment 3] In the method of Embodiment 3 shown in FIG. 8, the start of laser beam leakage is detected by the laser beam detector 12 and the RF signal power is gradually reduced. Is shifted from a constant RF signal power phase. By shifting the phase, the elastic wave in the resonator is forcibly suppressed, so that the influence of the residual resonator loss can be further suppressed and the peak output can be controlled with high accuracy. In FIG. 8A, the RF signal power is reduced linearly in proportion to time, but may be reduced exponentially.

[Embodiment 4] In the method of Embodiment 4 shown in FIG. 9, the start of laser beam leakage is detected by the laser beam detecting element 12 and the RF signal power is gradually reduced. After decreasing the initial value of the RF signal power, the RF signal power is attenuated with time. The degree to which the initial value is reduced is set according to the resonator loss. Even with this method, the peak power and pulse width of one pulse can be accurately controlled without the influence of the residual resonator loss. Also, as above
The RF signal power attenuation may be reduced exponentially.

[Embodiment 5] In the method of Embodiment 5 shown in FIG. 10, the start of laser beam leakage is detected by the laser beam detecting element 12 and the RF signal power is gradually reduced. In addition, the initial value of the RF signal power is reduced and the phase is shifted to attenuate. As described above, the degree to which the initial value is reduced can be set according to the resonator loss, and the attenuation of the RF signal power can be reduced exponentially. According to this method, the pulse output can be controlled with high precision by further minimizing the influence of the residual resonator loss.

[Embodiment 6] In the above embodiment, the amplitude of the RF signal power is fixed to a constant value.
As shown in FIG. 1, the control is performed with the application time of the RF signal kept constant.

First, similarly to the above, the user sets a desired Q-switch frequency and intensity of the excitation energy. By setting the Q-switching frequency by the user, determines the RF signal application time to the RF signal ON time T _{o n} is a predetermined constant value in the laser marker inside the computing means. Further, the RF signal power is _set to an initial value _PRF0 according to the magnitude of the excitation energy and the Q switch frequency.

Thereafter, processing is started based on the processing start signal. The initial value P _RF0 of the RF signal power is changed by the RF signal applying means for a certain period of time as shown in FIG.
_{Apply to} the Q switch during _on . Laser oscillation is R
Suppressed by the resonator loss (b) generated by the F signal,
Meanwhile, the solid-state laser medium 1 is set by the excitation energy setting means.
The energy added to the body accumulates. The energy stored in the solid-state laser medium 1 over time is shown in FIG.
It gradually increases as shown in FIG.

In the first RF signal application cycle to the Q switch, the RF signal power initial value P fixed at a constant value
_{If the} limit at which laser oscillation can be stopped by the resonator loss (b) caused by _RF0 (a) is a laser oscillation threshold initial value _Es0 (c), the gain due to the energy accumulated in the solid-state laser medium 1 is When it becomes higher and exceeds _Es0 , laser oscillation cannot be stopped, and laser light starts to be emitted.

When the laser beam is emitted, the accumulated energy corresponding to the emitted laser beam is lost, so that the laser beam falls below E _{s 0} and is stopped again. Therefore, the laser output at this time is very short. Also, the laser power is extremely weak and does not affect the object to be processed.

On the other hand, the start of laser output is detected by the laser light detecting element 12. And using clock means, RF signal and T _on elapsed since the detected time measures the time dt until it is stopped.

After the lapse of T _on , the RF signal applying means stops the application of the RF signal and sets the signal to 0. Then, the Q switch is opened, and a laser output is obtained as shown in FIG.

On the other hand, the time dt measured by the timing means
, The amplitude of the RF signal power P _RF1 to be applied next time is set. If dt is long, while maintaining a constant RF signal ON time _{T on} the next RF signal applied cycle, the RF signal power _{P RF1} larger than the initial value _{P RF0,} the initial value _E lasing threshold _{E s1 s0} So that Then, since the laser oscillation can be suppressed even for a larger amount of stored energy, the time dt 'during which the laser oscillation can be stopped becomes longer, and the time until the laser output is detected by the laser light detecting element 12 can be delayed from the previous dt. it can. Further, control is performed so that the next time dt ″ becomes shorter than dt ′, and finally dt approaches 0.

[0068] If there is no lasing within T _on time conversely, determines that it can not laser oscillation RF signal power is too strong, the RF signal power as the next time the RF signal applied to lower the lasing threshold E _s reduce the P _RF. These RF signal power P _RF of reduction range, gains can be set arbitrarily. For example, based on the previous RF signal power P _RF , a predetermined coefficient (such as 0.8 or 1.2) is added to this.
, A method of adding or subtracting a predetermined value such as 1W or 2W, or a method of adjusting the width to a value corresponding to the value of dt by a preset table or calculation.

The increase width and the decrease width for adjusting the amplitude of the RF signal power can be selected as appropriate. For example, a table based on actual measured values is set in advance, and the fluctuation width is selected in accordance with the table, or the predetermined width is set to a numerical value. Or a method of multiplying and decreasing the amplitude by a predetermined coefficient. An appropriate value may be obtained by calculation.

As described above, the amplitude of the RF signal power is adjusted by the RF signal applying means in accordance with the time measured by the time measuring means, and the control is performed so that dt approaches 0. However, the peak power and energy of one pulse can be accurately controlled without the influence of the residual resonator loss. In particular, the laser light detecting element 12
According to the embodiment of the present invention in which feedback control is performed according to an actual output by using the apparatus, it is possible to accurately perform optimal control according to an apparatus, a use environment, and conditions. And so on.

[Embodiment 7] The embodiment 7 is different from the above-described embodiment in that even during the period when the laser output is stopped, the minute output that does not damage the target workpiece is intentionally continued. In addition, accurate control is performed by minimizing the stored energy and the resonator loss so that laser oscillation is suppressed. FIG. 12 shows how a Q-switching is performed at a predetermined Q-switch frequency by this method to obtain a pulsed laser output.
Shown in

FIG. 12 shows the relationship between the amplitude (a) of the RF signal power and the laser output (b). As shown in FIG. 12B, in a section where the laser output is paused, the RF signal power is adjusted so that the laser output becomes the last value while the laser light is detected by the laser light detecting element 12. .

The amplitude of the RF signal power at this time increases the RF signal power to suppress laser oscillation when the laser output is detected. Then, the laser oscillation is stopped and no energy is emitted to the outside, so that the excitation energy generated by the excitation means such as the excitation light source is accumulated in the solid-state laser medium 1. As a result, the stored energy increases (not shown), and when it reaches an amount that cannot be suppressed by the previously increased RF signal power, the laser output is emitted to the outside again. When this is detected by the laser light detecting element 12, the RF signal power is further increased, the laser output is stopped, and the stored energy increases. By such repetition, the RF signal power has a waveform that gradually increases as shown in FIG.

When the laser output is restarted in accordance with the Q switch frequency f _Q , the RF signal applying means switches to R
By setting the F signal power to 0 and opening the Q switch, a laser output is obtained.

The magnitude of the minute laser output is shown in FIG.
Although it is shown large for the sake of explanation, it is actually an output that does not affect the workpiece. The RF signal applying means controls the micro laser output based on the signal of the laser light detecting element 12 so as to be within a range that does not hinder processing. If necessary, in order to eliminate the minute laser output, the value of the RF signal power to be applied may be set to a slightly higher value in consideration of a margin than the calculated value, so that laser output leakage can be avoided.

According to this method, the stored energy during the laser output suspension period by the Q switch can be grasped by detecting the laser light, so that the RF signal power can be controlled to the optimum RF signal power according to the increase of the stored energy. For this reason, the energy of each laser pulse can be controlled to be constant and precisely, and stable laser oscillation with high peak power can be obtained.

The first embodiment shows a method of detecting leaked light and turning off the Q switch 3. According to this method,
It is also possible to carry out the processing without affecting the workpiece during processing. However, before processing, the time during which light leakage occurs is measured by a time-measuring means, and the Q switch 3
Can also be controlled. In this case, processing can be performed more efficiently than when processing is performed while generating leakage light. In the seventh embodiment, more efficient processing can be performed by controlling in advance so that the dt becomes the minimum RF signal power of 0.

FIG. 13 is a schematic diagram for detecting leaked light in a state where laser light is cut off in a system using a laser processing machine as a laser oscillator. The laser oscillator shown in the figure has a solid-state laser medium 1, a Q switch 3 and a mechanical shutter 6B on one end face with the optical axis aligned with the medium.
The total reflection mirrors 4 are arranged. Control means 13 for controlling the RF signal power applied to the Q switch 3 is connected thereto.

On the other side, an output mirror 5 for extracting a part of the laser output, a half mirror 10, and a mechanical shutter 6
A is provided. The mechanical shutter 6 </ b> A is arranged at a position where the laser light passes through the half mirror 10. Further, a laser wavelength filter 11 for extracting a laser wavelength and a laser light detecting element 12 are provided at the reflection destination of the half mirror 10.

The reflectance of the half mirror 10 can be set to, for example, 1% or less so as not to hinder the processing operation. At the position of the reflection destination of the half mirror 10, a laser wavelength filter 11 that passes only the laser wavelength is provided to eliminate the influence of the excitation light. Alternatively, the laser wavelength filter 11 may be a filter that removes only the excitation light other than the laser wavelength. Alternatively, it is also possible to adopt a configuration in which the half mirror 10 has a filter function and is also used.

The laser light passing through the laser wavelength filter 11 is detected by a laser light detecting element 12 such as a photodiode. The sensitivity of the laser light detecting element 12 is set to the maximum sensitivity at which spontaneous emission light from the solid-state laser medium is not received. In addition, by utilizing the differential waveform of the detection output, it is possible to remove components such as the excitation light and the spontaneous emission light by the excitation light source 2. Although the laser output is not constant and unstable, the excitation light emitted from an LD or the like is always constant. On the other hand, these DC components are cut to extract only the AC component, and the desired laser light is extracted. Can be accurately detected. The laser light detecting element 12 may be installed immediately after the total reflection mirror 4 or when the X mirror 15X in the optical system shown in FIG. 14 is a mirror in which a dielectric multilayer reflective film is formed on a transparent substrate. Immediately after 15X or the like is also possible. Further, in the embodiment of the present invention, since the processing can be performed while detecting the leakage light, the mechanical shutter 6A shown in FIG. 13 may not be provided.

On the other hand, as the excitation light source 2, an excitation lamp, a semiconductor laser, or the like can be used. Solid-state laser medium 1
For example, a YAG crystal or the like can be used. The solid-state laser medium 1 is excited by the excitation light source 2, emits laser light, is amplified by a resonator composed of the total reflection mirror 4 and the output mirror 5, and emits a laser output from the output mirror 5 side.

It is not necessary for the total reflection mirror 4 to reflect light of all wavelengths, and it is sufficient that the total reflection mirror 4 has a characteristic of totally reflecting light of a wavelength of emitted light determined by the solid-state laser medium 1 used. For example, when using a YAG crystal, 1
A total reflection mirror 4 that reflects almost 100% of light having a wavelength of 064 nm and transmits light of other wavelengths can be used.

The control means 13 applies R to the Q switch 3
Control the F signal. The control means is composed of an electronic component such as a CPU, and the RF is determined based on a desired laser output.
A circuit for generating and controlling a signal is provided, and functions as a high-frequency signal setting unit, a high-frequency signal applying unit, and a high-frequency signal adjusting unit. The specific circuit configuration and arrangement of the control unit 13 can be appropriately changed as needed.

[0085]

As described above, according to the laser oscillator and the laser pulse control method of the present invention, it is possible to obtain a stable laser pulse having a high peak power independent of the intensity of the excitation light and the Q switch frequency. Can be. That is, the laser oscillator and the laser pulse control method of the present invention set the RF signal power to an optimum value by making the parameter constant based on a predetermined criterion and feeding back the obtained laser light result. Because. For example, by controlling the amplitude of the RF signal power to a constant power value or fixing the application time to a constant value, and performing control in accordance with the result of the laser output based on these reference values, accurate The operation becomes possible, and the peak power and pulse width of the laser output can be controlled. In addition, since control can be performed so as to always operate under the conditions according to the use situation, there is also a merit that optimal control can be maintained in response to the influence of deterioration with time of the excitation energy.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a laser oscillator according to one embodiment of the present invention.

FIG. 2 is a schematic side view showing an example of a Q switch.

FIG. 3 is a schematic waveform diagram showing states of an RF signal and a laser oscillation output when a Q switch frequency is high.

FIG. 4 is a schematic waveform diagram showing states of an RF signal and a laser oscillation output when a Q-switch frequency is low.

FIG. 5 shows the relationship between R and R when the laser power is strong and weak.
Schematic waveform diagram showing waveforms of F signal, resonator loss, and laser output

FIG. 6 is a schematic waveform diagram showing waveforms of an RF signal, a resonator loss, and a laser output of the laser oscillator according to the first embodiment of the present invention.

FIG. 7 is a schematic waveform diagram showing waveforms of an RF signal, a resonator loss, and a laser output of the laser oscillator according to the second embodiment of the present invention.

FIG. 8 is a schematic waveform diagram showing waveforms of an RF signal, a resonator loss, and a laser output of a laser oscillator according to a third embodiment of the present invention.

FIG. 9 is a schematic waveform diagram showing waveforms of an RF signal, a resonator loss, and a laser output of a laser oscillator according to a fourth embodiment of the present invention.

FIG. 10 shows an RF of a laser oscillator according to a fifth embodiment of the present invention.
Schematic waveform diagram showing signal, resonator loss, and laser output waveforms

FIG. 11 illustrates an RF of the laser oscillator according to the sixth embodiment of the present invention.
Schematic waveform diagram showing signal, resonator loss, and laser output waveforms

FIG. 12 illustrates an RF of a laser oscillator according to a seventh embodiment of the present invention.
Schematic waveform diagram showing signal and laser output waveforms

FIG. 13 illustrates a laser oscillator according to an embodiment of the present invention;
Schematic diagram showing the state of measuring the threshold

FIG. 14 is a schematic diagram showing a scanner unit of a laser oscillator using a conventional galvano scanner.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Solid-state laser medium 2 ... Excitation light source 3 ... Q switch 4 ... Total reflection mirror 5 ... Output mirror 6 ... Mechanical shutter 6A ... Mechanical shutter 6B ... Mechanical shutter 7 ... Synthetic quartz glass 8 ... Piezoelectric element 9 ... High frequency power supply 10 Half mirror 11 Laser wavelength filter 12 Laser light detecting element 13 Control means 14 Beam expander 15 Galvano scanner mirror 15X X mirror 15Y Y mirror 16X X scanner 16Y Y scanner 17 Fθ lens

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F072 AB01 GG02 HH02 HH07 JJ05 MM08 MM09 MM11 SS06 YY06 YY07

Claims (11)

[Claims] 1. A solid-state laser medium, an excitation light source for exciting the solid-state laser medium, a driving unit for driving the excitation light source, and an optical axis of laser light emitted from the solid-state laser medium A total reflection mirror positioned above, an output mirror facing the total reflection mirror via the solid-state laser medium, and pump laser light emitted from the solid-state laser medium between the total reflection mirror and the output mirror A laser oscillator provided with a Q-switch that is arranged on the optical axis of the laser beam and that oscillates the excitation laser light by applying a high-frequency signal power, wherein the predetermined high-frequency signal power is determined based on a desired laser output. High-frequency signal setting means for setting energy stored in the solid-state laser medium excited by the excitation light source by the predetermined high-frequency signal power. Laser light detection means for detecting that laser oscillation has started beyond a laser oscillation threshold value capable of suppressing laser oscillation, and high-frequency signal application means for reducing the high-frequency signal power based on a detection signal from the laser light detection means Laser oscillator having 2. The laser oscillator according to claim 1, wherein said high-frequency signal applying means sharply attenuates the amplitude of said high-frequency signal when lowering said high-frequency signal power. 3. The laser oscillator according to claim 1, wherein said high-frequency signal application means attenuates the amplitude of said high-frequency signal in a slope when lowering said high-frequency signal power. 4. The laser oscillator according to claim 1, wherein said high frequency signal applying means attenuates the amplitude of said high frequency signal exponentially when lowering said high frequency signal power. 5. The laser oscillator according to claim 1, wherein the high-frequency signal applying means attenuates the amplitude of the high-frequency signal stepwise when lowering the high-frequency signal power. 6. A high frequency signal applying means for forcibly attenuating a resonator loss inside the Q switch by shifting a phase of the high frequency signal when lowering the high frequency signal power. 2. The laser oscillator according to 1. 7. A solid-state laser medium, an excitation light source for exciting the solid-state laser medium, driving means for driving the excitation light source, and an optical axis of laser light emitted from the solid-state laser medium A total reflection mirror located above, an output mirror facing the total reflection mirror via the solid laser medium, and an excitation laser beam emitted from the solid laser medium between the total reflection mirror and the output mirror A laser oscillator having a Q-switch that is arranged on the optical axis of the device and that oscillates the excitation laser light by applying a high-frequency signal power. High-frequency signal setting means for setting a signal ON time and setting a predetermined high-frequency signal power determined by a desired laser output; A laser light detecting means for detecting that laser energy is started when the energy stored in the solid-state laser medium exceeds a laser oscillation threshold value at which laser oscillation can be suppressed by the predetermined high-frequency signal power, and the laser light detecting means And a high-frequency signal adjustment unit that adjusts the high-frequency signal set value according to the time measured by the time-measurement unit. A laser oscillator having means. 8. An apparatus according to claim 1, further comprising an initialization means for releasing energy stored in said solid-state laser medium to reduce the energy before applying a high-frequency signal power.
8. The laser oscillator according to any one of claims 7 to 7. 9. A method for controlling a laser pulse of a laser oscillator, comprising: setting high-frequency signal power applied to a Q switch by high-frequency signal setting means based on a desired laser output; Applying the high-frequency signal power to the Q switch, and starting the laser oscillation when the energy stored in the solid-state laser medium by the excitation light source increases and exceeds the laser oscillation threshold value at which laser oscillation can be suppressed by the high-frequency signal power. A step of detecting that the laser light is detected by the laser light detecting means, and calculating a minimum high-frequency signal value at which laser oscillation can be stopped by detecting a laser output by the laser light detecting means,
A laser pulse control method for a laser oscillator, comprising a step of controlling a high-frequency signal power to be applied next to approach this. 10. A method for controlling a laser pulse of a laser oscillator, comprising: setting a high-frequency signal power applied to a Q switch to a predetermined high-frequency signal power value determined by a desired laser output by a high-frequency signal setting means. A step of starting to apply the predetermined high-frequency signal power to the Q switch; and setting a laser oscillation threshold at which energy stored in the solid-state laser medium by the excitation light source increases and laser oscillation can be suppressed by the predetermined high-frequency signal power. A laser oscillator having a step of detecting the start of laser oscillation by exceeding the threshold, and a step of lowering the high-frequency signal power value based on a detection signal from the laser light detecting means by a high-frequency signal applying means. Laser pulse control method. 11. A method for controlling a laser pulse of a laser oscillator, comprising: setting a high-frequency signal power application time to a predetermined high-frequency signal ON time according to a Q-switch frequency by a high-frequency signal setting means; Setting the high-frequency signal power, applying the predetermined high-frequency signal power to the Q switch, increasing the energy stored in the solid-state laser medium by the excitation light source, and causing the laser oscillation by the predetermined high-frequency signal power Detecting the start of laser oscillation by exceeding a laser oscillation threshold value capable of suppressing laser light, and elapse of the high-frequency signal ON time from the time of laser light detection based on a detection signal from the laser light detection means. Measuring the time until the time by the time measuring means, and the time according to the time measured by the time measuring means. A laser pulse control method for a laser oscillator, comprising a step of adjusting a frequency signal set value by a high frequency signal adjusting means.