JP2002208750A - Laser oscillator and laser pulse control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a first pulse and a train of following pulses in a solid laser oscillator, using a Q-switch. SOLUTION: The laser oscillator comprises a solid laser medium 1, an exciting power source 2, an output mirror 5, a total reflection mirror 4, and a Q-switch 3. The waveform of an RF signal applied to the Q-switch is adjusted according to the laser output power or the frequency of the Q-switch 3. For example, the initial value of the RF signal starting the laser oscillation is set near to an RF threshold to attenuate it along an exponential slope, thereby suppressing a train of laser output pulses first outputted from the laser oscillator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser oscillator that performs pulse oscillation using a Q switch. More specifically, the present invention relates to a laser oscillator for controlling a laser output pulse group output first from a laser oscillator and a method for controlling the laser pulse.

[0002]

2. Description of the Related Art Laser oscillators are used for processing applications such as marking, trimming, cutting, and welding. YAG
A solid-state laser oscillator such as a laser can change continuous oscillation to high-speed repetitive pulse oscillation having a high peak output value (peak value) by using a Q switch.

FIG. 1 is a schematic diagram of a laser oscillator. The laser oscillator shown in this figure includes a solid-state laser medium 1 and
An excitation light source 2 for exciting a solid-state laser medium 1;
Q switch 3 arranged on one side of solid-state laser medium 1
, A total reflection mirror 4 and an output mirror 5 arranged on the other side
It has. The Q switch 3 is disposed 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. Furthermore, solid laser medium 1
A mechanical shutter 6 is disposed as needed at a position where the optical axis can be blocked so that light emitted from the shutter can be blocked. Further, the laser beam passing through the output mirror 5 is scanned on the surface of the object by the scanner unit as necessary,
Perform desired processing.

A partially transparent output mirror 5 is provided on an extension line connecting the solid-state laser medium 1 and the Q switch 3, and excites the solid-state laser medium 1 by optical excitation when the Q switch 3 is ON. To store energy, and the Q switch 3
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. 23A and 23B show an example of a galvano scanner optical system. FIG. 23A is a side view of the scanner unit, and FIG. 23B is a plan view. Inside the scanner section,
An X mirror 22X and a Y mirror 22Y, which are two movable mirrors for directing the laser light from the output mirror 5 downward and scanning in the XY directions, are incorporated. In addition, the output part of the scanner unit includes a condensing lens Fθ
A lens 24 is mounted, and an object (not shown) is arranged at the focal position of the lens.

An acousto-optic Q switch utilizing Bragg diffraction by ultrasonic waves is generally used for 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, an on / off operation of a laser in which an internal loss of a resonator is controlled using a Q switch is performed.

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, 20 MHz and 24 MHz are mainly used.

As shown in FIG. 2A, when no RF power is applied to the piezoelectric element 8, the laser light inside the resonator passes through the Q switch 3. On the other hand, when an RF power is applied to the piezoelectric body to generate an elastic wave inside the quartz as shown in FIG. 2B, a difference in refractive index is generated 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 a piezoelectric element, the high-frequency electric signal is converted into an ultrasonic wave by a piezo effect. The ultrasonic waves propagate in the quartz glass, and a periodic refractive index distribution is generated in the quartz glass due to the photoelastic effect. When light is made incident at an appropriate angle (Bragg angle), an acousto-optic effect is produced in which the incident light is diffracted.

That is, an RF wave is applied to vibrate the piezoelectric body to generate an elastic wave, which becomes a diffraction grating and blocks the laser beam passing through the Q switch. As a result, loss occurs in the resonator. be able to. As the RF 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 power. When the resonator loss is further increased, the laser oscillation is suppressed and the output is finally stopped.

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. Although the actual RF signal waveform oscillates in a sine wave shape as shown in the enlarged view, in the figure, only the envelope is shown for simplification. The Q switch of the rectangular RF signal is turned ON / OFF at this amplitude. When the amplitude of the RF signal is 0,
Since the Q switch is opened and turned on, a pulsed laser as shown in FIG. 3B is output. At this time, the Q switch is repeatedly driven to oscillate by the ON / OFF of the RF signal, and the frequency at which the laser pulse is output is determined. Hereinafter, this frequency is referred to as a Q switch frequency.

[0011]

When a certain amount of excitation energy is continuously applied to the solid-state laser medium, if the oscillation frequency of the ON / OFF repetition of the Q switch is equal to or lower than a predetermined value, the energy is accumulated during the laser output OFF. Energy is saturated. The predetermined frequency differs depending on the solid-state laser medium to be used.
In this case, the Q-switch oscillation frequency saturates at 1 kHz.
At an oscillation frequency higher than this, the time during which energy is stored in the solid-state laser medium is shortened, so that the energy per pulse decreases as the Q-switch oscillation frequency increases.

When processing is performed by using a laser pulse with a high oscillation frequency, a phenomenon occurs in which the energy of the first pulse for starting processing becomes abnormally large as compared with other pulses. This is called a giant pulse or a first pulse, and since only the portion at the start of processing is processed with high energy, there is a problem in processing such as laser marking.

In order to avoid this, for example, Japanese Patent Application Laid-Open
Japanese Patent Application Publication No. 0-52069 discloses a method in which a Q switch is gradually turned off at the start of machining to make a continuous oscillation state and then perform a repetitive oscillation operation.

Japanese Patent Application Laid-Open No. 7-74422 discloses a method of estimating the inversion distribution by measuring the excitation energy to estimate the peak power, and controlling the Q switch in a closed loop based on the actually measured peak power.

Further, Japanese Patent Application Laid-Open No. 54-16200 discloses a method of gradually lowering the RF output to 0 V over a plurality of pulses at the start of processing.

However, the method of performing the repetitive oscillating operation after the continuous oscillating operation is performed once has a problem that processing different from other parts is performed at the start of processing. In this method, by gradually turning off the Q switch, the laser output is gradually increased. If the object to be processed is metal, for example, the laser is not processed unless the power of the laser output once in a continuous oscillation state is large, so that there is little problem. However, when processing into resin or the like that is sensitive to energy per pulse, processing may be performed even at a peak output lower than the specified value. there were. As described above, there is a disadvantage in that, depending on a processing target, processing in a continuous oscillation state different from processing in a steady state is performed at the start.

Further, the peak power is estimated by estimating the population inversion from the excitation energy, and Q
The method of controlling the switches in a closed loop has a problem that it is difficult to accurately estimate the peak power and to perform accurate control. The population inversion depends on the absorption coefficient of the solid-state laser medium, that is, the proportion of light emitted from the excitation light source that is absorbed by the solid-state laser medium. However, there is a problem that the population inversion cannot be accurately estimated because there are individual differences in the absorption coefficient of the solid-state laser medium.

Further, it is considered that it is very difficult to realize the method using the acousto-optic device in the method using the acousto-optic device in the method of controlling the Q switch by judging that the laser has reached the peak. This is because acousto-optic devices are not suitable for high-speed driving.

Furthermore, in the method of gradually lowering the RF output to 0 V over a plurality of pulses at the start of processing, the first pulse can be reduced, but the first pulse can be reduced according to the change in the laser output and Q switch frequency. It is difficult to achieve optimal control, and it is difficult to accurately control the second, third and subsequent pulses even if the first pulse can be controlled. As described above, the conventional fast pulse suppression control has disadvantages, and has a problem in practical use.

The present invention has been developed to prevent such adverse effects. An important object of the present invention is to provide a laser oscillator capable of obtaining a laser pulse having a stable peak power irrespective of laser intensity, Q switch frequency, and the like.

[0021]

According to a first aspect of the present invention, there is provided a laser oscillator, a solid-state laser medium, an excitation light source for exciting the solid-state laser medium, and light emitted from the solid-state laser medium. A total reflection mirror positioned on the optical axis of the laser light; an output mirror facing the total reflection mirror via the solid laser medium; and an output mirror from the solid laser medium between the total reflection mirror and the output mirror. A Q-switch that is arranged on the optical axis of the laser to be radiated and oscillates the laser light in a pulsed manner. The laser oscillator further includes Q switch frequency setting means for setting a frequency of a high frequency signal applied to the Q switch;
Threshold setting means for setting a threshold based on the minimum high-frequency signal value capable of cutting off the laser output from the laser oscillator, and the threshold setting means being set to keep the laser output constant at the start of laser oscillation. An initial value setting means is provided for setting an initial value of a high-frequency signal at the start of laser oscillation based on the threshold value and the Q switch frequency set by the Q switch frequency setting means.

According to a second aspect of the present invention, in the laser oscillator, the initial value setting means sets an initial value of the high frequency signal to a value smaller than the threshold value.

In the laser oscillator according to a third aspect of the present invention, the high frequency signal is gradually attenuated from an initial value so that the laser oscillator further holds a laser output pulse group at the start of laser oscillation. A damping means is provided.

Further, in the laser oscillator according to a fourth aspect of the present invention, the attenuating means attenuates the high-frequency signal exponentially from an initial value.

Further, the laser oscillator according to the fifth aspect of the present invention is further characterized by further comprising a laser output detection sensor for measuring a high frequency signal threshold value.

Further, according to a laser pulse control method for controlling a pulse group output from a laser oscillator at the start of oscillation according to a sixth aspect of the present invention, a Q switch for setting a frequency of a high frequency signal applied to the Q switch is provided. A step of setting a frequency, a step of setting a threshold that is a minimum high-frequency signal value capable of cutting off a laser output from the laser oscillator, and a threshold set to keep the laser output constant at the start of laser oscillation. And setting an initial value of a high-frequency signal at the start of laser oscillation based on the Q-switch frequency and the Q-switch frequency.

Further, in the laser pulse control method according to the present invention, the step of setting the threshold value of the high-frequency signal includes the step of measuring the threshold value with a laser output detection sensor. .

Further, in the laser pulse control method according to the present invention, the step of setting the threshold value of the high frequency signal includes a step of estimating the threshold value based on the excitation energy.

Further, the laser pulse control method according to the ninth aspect of the present invention includes a step of detecting an abnormality in the optical system of the laser oscillator by comparing the measured value and the estimated value of the high frequency signal threshold. It is characterized by.

Further, in the laser pulse control method according to claim 10 of the present invention, the high-frequency signal is exponentially shifted from an initial value so as to keep a laser output pulse group at the start of laser oscillation constant. The method further includes the step of attenuating.

According to the laser oscillator and the laser pulse control method of the present invention, the first pulse is suppressed and the initial pulse output such as the second and third pulses following the first pulse is controlled so that the peak of each pulse is controlled. And a stable and good laser output can be obtained.
In particular, even if the object to be laser-processed is delicate and can be processed even with a weak laser output, it can be processed with a stable output from the time of laser oscillation, thereby enabling high-precision processing.

According to the present invention, the initial value of the RF signal is adjusted according to the RF threshold value and the Q switch frequency, and the slope waveform at which the RF signal attenuates is exponentially attenuated to stabilize the pulse at the start of machining. Succeeded.

In this specification, the first laser output pulse group output from the laser oscillator includes not only the first pulse but also the second, third and subsequent laser output pulses. In addition, "starting" or "starting" or "starting" or "outputting first" means not only the first laser oscillation when using a laser oscillator or a laser processing machine, but also printing and processing. This also means that the laser oscillation is temporarily restarted from a stopped state.

[0034]

Embodiments of the present invention will be described below with reference to the drawings. However, the following examples illustrate a laser oscillator and a laser oscillation method for embodying the technical idea of the present invention, and the present invention does not specify the laser oscillator and the laser oscillation method as follows. .

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.

Hereinafter, the laser oscillator and the like shown in the present invention are partially exaggerated for explanation.
It does not always correspond to what accurately represents the actual positional relationship, distance, size, and the like.

FIG. 1 shows a schematic configuration of a laser oscillator according to one embodiment of the present invention. This laser oscillator indicates a laser processing machine. In the figure, when no RF signal is applied to the Q switch 3 arranged in the laser oscillator, laser oscillation is possible and laser light is output. That is, when the high-frequency signal is OFF, the Q switch 3 is open, that is, ON, so that the oscillated laser is reflected between the output mirror and the total reflection mirror, and repeats inside the resonator. The reflected laser light is output to the outside. This state is referred to as CW (Continuous Wav
e) Called oscillation.

When the RF power applied to the Q switch 3 is gradually increased, the resonator loss gradually increases,
Since the Q switch 3 gradually closes, the laser output decreases. When the RF power is further increased and reaches a predetermined power value, the oscillation stops. The RF power at which the oscillation of the laser stops is referred to as an “RF threshold” in this specification.

R when the laser is completely stopped
The F threshold value is determined to be a value proportional to the laser output during CW oscillation. Increasing the laser output also increases the RF threshold, and decreasing the laser output decreases the RF threshold. The state where the laser is completely stopped here means
This refers to a state in which laser oscillation is disabled due to the loss of the Q switch and the amount of energy stored in the solid-state laser medium is saturated.

The energy of one pulse can be considered to be the energy stored in the solid state laser medium while the Q switch is operating and the laser is stopped. When a YAG rod is used as the solid-state laser medium, the stored energy is saturated when the Q-switch frequency is 1 kHz or less. Therefore, when the RF signal is sharply set to 0 from a completely stopped state, first, In the emitted laser pulse and each subsequent pulse, the output magnitude and energy are equal.

On the other hand, when the Q-switch frequency is 1 kHz or more, the energy storage time becomes shorter as the Q-switch frequency becomes higher, so that the stored energy becomes smaller. As a result, the energy of one pulse becomes smaller.
From a state where the laser is completely stopped, a Q of 1 kHz or more
When pulse oscillation is performed at the switch frequency, the first laser pulse and the pulse in the steady state are made equal to each other by changing the pulse size according to the Q switch frequency from the state where the energy is saturated. Energy must be released in a coordinated manner. In order to release a certain amount of energy from a state in which more than necessary energy is stored, it is necessary to limit the energy to be released by giving a loss even during the release of energy.

Referring to FIG. 4, the laser is oscillated and a laser pulse is output by lowering the RF signal to a predetermined value equal to or lower than the RF threshold value from a completely stopped state. The predetermined value for generating the first pulse is
Let it be “RF initial value”. The magnitude of the pulse is determined by the difference between the RF initial value and the RF threshold. RF initial value and R
The smaller the difference between the F thresholds, the smaller the magnitude of the output pulse. When the RF initial value is set to 0, the RF initial value and R
Since the difference between the F thresholds is maximum, a giant pulse is generated.

To stably process from the start of processing,
It is necessary to change the setting of the RF initial value according to the Q switch frequency. When the Q switch frequency is 1 kHz or less, R
By setting the F initial value to 0 and setting the difference between the RF initial value and the RF threshold smaller as the Q switch frequency increases, the first pulse can be made equal to the pulse size at the time of steady output.

On the other hand, CW without changing the Q switch frequency
If the laser output at the time of oscillation is increased, the RF threshold value when the laser is completely stopped is also increased. Therefore, unless the RF initial value is changed, the difference between the RF threshold value and the RF initial value increases. Therefore, it is necessary to increase the RF initial value to the extent that the size of the first pulse is the same as the pulse in a steady state, that is, the output value of one pulse when stable laser output is performed.

Assuming that the laser is not completely stopped, consider the case of a YAG rod as in the above example. It is assumed that the time during which the laser is stopped is 1 msec or less, and the time during which energy can be accumulated by Q switching is shorter than the time during which the laser is stopped. For example, when the Q switch frequency is 50 kHz, the time during which the Q switch is opened to generate a pulse is 5 μsec.
, The energy storage time per pulse is 1
This is 5 μsec. In the operation at the Q switch frequency, when the processing is temporarily interrupted for 0.5 msec, the stored energy is not saturated but becomes larger than the energy required for one pulse. The RF threshold value in such a state becomes smaller than the RF threshold value when the laser is completely stopped. Therefore, when the laser processing is stopped, the RF initial value is set to be proportional to a certain elapsed time (1 msec in the case of YAG) after the processing is stopped, or exponentially or geometrically. Adjustment to increase the size is required. In this case, if the difference between the RF threshold value determined by the elapsed time after the processing is stopped and the RF initial value is controlled to be the energy required for one pulse, stable processing can be performed regardless of the processing interruption time.

The measurement of the threshold value of the RF signal when the laser oscillation starts is measured before using the laser oscillator. FIG. 9 is a schematic diagram for detecting a threshold value 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, a mechanical shutter 6B, and a total reflection mirror 4 arranged on one end face with its optical axis aligned with the solid-state laser medium 1, respectively. The Q switch 3 has RF applied to it.
A Q switch control circuit 19 for generating a signal is connected.

On the other side, an output mirror 5, a half mirror 10, and a mechanical shutter 6A for extracting a part of the laser output are provided. The mechanical shutter 6 </ b> A is disposed at a position where the laser light passes through the half mirror 10. Further, a laser wavelength transmission filter 11 for extracting a laser wavelength and a laser output detection sensor 12 are provided at the reflection destination of the half mirror 10. Laser output detection sensor 1
The arrangement of 2 is not limited to this, and for example, it may be provided on the optical axis of the total reflection mirror 4 so as to detect the leakage light from the total reflection mirror 4.

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 the wavelength of the emitted light determined by the solid-state laser medium 1 used. For example, when a YAG crystal is used, 106
It is possible to use a total reflection mirror 4 that reflects almost 100% of light having a wavelength of 4 nm and transmits light of other wavelengths.

The reflectance of the half mirror 10 can be set to 1% or less so as not to hinder the processing operation. Half mirror 10
In order to eliminate the influence of the excitation light, a laser wavelength transmission filter 11 that allows only the excited laser wavelength to pass is provided at the position of the reflection destination. Alternatively, the laser wavelength transmission 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 transmission filter 11 is detected by a laser output detection sensor 12. The laser output detection sensor 12 is a photodiode,
It is composed of a photodetector such as a photocoupler or a CCD, and can also be used as a sensor for detecting a failure of the Q switch 3. The sensitivity of the laser output detection sensor 12 is the maximum sensitivity that does not receive spontaneous emission light from the solid-state laser crystal.

On the other hand, as the excitation light source 2, an excitation lamp, a semiconductor laser or the like can be used. For the solid laser medium 1, a YAG crystal or the like can be used. Although the example of FIG. 1 describes the case where a YAG rod is used as the solid-state laser medium, the laser oscillator of the present invention is not limited to a YAG laser. Also, as the excitation light source 2, an excitation lamp, a semiconductor laser (LD), or the like can be used. These excitation light sources 2 include excitation lamp currents,
A driving means for driving by applying an excitation LD current or the like is provided. In the laser oscillator shown in FIG. 1, a solid-state laser medium 1 is excited by a pumping light source 2, a laser beam is emitted and amplified by a resonator constituted by a total reflection mirror 4 and an output mirror 5, and a laser output from the output mirror 5 side. Is released.

When a normal processing operation is performed using this laser processing machine, both mechanical shutters 6A and 6B are opened. To completely shut off the laser, the mechanical shutter 6B is closed to shut off the light. At this time, the mechanical shutter 6A may be closed.

When detecting the RF threshold, first, the RF power applied to the Q switch 3 is set to the maximum value. At this time, the laser output is stopped by closing the mechanical shutter 6A, and the mechanical shutter 6B is opened. Then, the RF value is gradually reduced, and it is monitored whether or not an output is detected by the laser output detection sensor 12. When the Q switch 3 is gradually released and the laser output is emitted, the output is emitted from the resonator through the output mirror 5. This output is partially reflected by the half mirror 10 and reaches the laser output detection sensor 12 through the laser wavelength transmission filter 11. The RF signal value when the output is generated in the laser output detection sensor 12 is the RF threshold.

The RF threshold value varies depending on the laser power. For example, when the laser power emitted from the solid-state laser medium 1 is large, the RF threshold value is large, and when the laser power is low, the RF threshold value is low.

The RF threshold value can be measured in advance for each set current of the excitation light source, and the laser control system can hold data as a setting table. However, the RF threshold value also fluctuates due to deterioration of the excitation light source and deterioration of the Q switch 3 with use conditions and aging. In addition, since the control accuracy is reduced due to the variation due to individual differences, it is possible for the user to perform the measurement again as needed. Alternatively, an RF threshold value for each excitation light current value is actually measured, and the obtained data can be stored as a table.

Alternatively, in addition to actually measuring the RF threshold,
It can also be estimated by calculation. When the RF threshold is obtained by calculation, there is a method of calculating the excitation energy from the excitation light source drive current or the like, and obtaining the RF threshold corresponding to the excitation energy based on a table or calculation. Alternatively, the threshold value can be estimated based on a predetermined calculation formula by inputting the environmental temperature, the type of the solid-state laser medium, and the like. The calculation of the threshold value is automatically performed inside the apparatus without the user's awareness. Further, the control may be a combination of an actually measured value and a calculated value.

On the other hand, abnormality of the laser oscillator can be detected by comparing the measured value with the setting table or the calculated value. RF calculated from known excitation energy
By comparing the threshold value with the actually measured RF threshold value, it is possible to monitor the state of the optical member constituting the laser oscillator, such as the life of the excitation medium, the breakage or contamination of the Q switch 3, and the like.

The RF threshold is set and measured according to the above procedure while the processing operation is not performed, for example, immediately after the setting of the excitation light is changed or immediately after the processing operation is performed. RF
The setting of the threshold is performed by a Q switch control circuit 19 composed of a CPU or the like. R obtained by measurement and calculation
The F threshold is input to a Q switch control circuit 19 that controls an RF signal applied to the Q switch.

The Q switch control circuit 19 outputs the RF signal O
Q to set the frequency of the pulse output by N / OFF
Switch frequency setting means, threshold setting means for setting a threshold from a minimum high-frequency signal value at which laser output can be cut off, initial setting of an RF signal based on a threshold set to keep laser output constant and a Q switch frequency It functions as an initial value setting means for setting a value and an attenuating means for gradually attenuating the RF signal from the initial value. The Q switch control circuit 19 includes a circuit that generates and controls an RF signal, and is configured by electronic components such as a CPU. Q
The specific circuit configuration and arrangement of the switch control circuit 19 can be appropriately changed as needed.

The threshold value set by the threshold value setting means is an RF threshold value which is the minimum RF signal at which laser oscillation can be stopped, or a value determined based on the RF threshold value. For example, a value slightly lower than the RF threshold may be set as the threshold.

FIG. 10 is a block diagram of a Q switch control circuit 19 for applying an RF signal to the Q switch 3. This circuit turns on / off the RF signal at a cycle corresponding to the Q switch frequency when the processing of the laser oscillator is started. A slope waveform generating circuit 1 so that the RF signal amplitude is gradually reduced to 0 during the Q switch opening time of the RF signal after the processing is started, that is, in a section where the Q switch is turned off.
The RF signal applied to the Q switch 3 is determined based on the waveform generated in Step 3. Figure 1 shows the output waveform of each block.
6 (a) to 6 (d).

The processing control circuit 18 receives the processing start signal shown in FIG. 16A, outputs a slope waveform generation start instruction signal to the slope waveform generation circuit 13, and outputs an RF signal modulation start instruction signal to the high frequency modulation circuit 15. Send.

On the other hand, the high-frequency generation circuit 14 generates a high-frequency signal R for applying an ultrasonic wave to the quartz of the Q switch 3.
Generate a source waveform for the F signal. For example, in this embodiment, 24
MHz sinusoidal signal. And the high frequency generating circuit 14
Sends an output signal as shown in FIG.

The high-frequency modulation circuit 15 generates the ON / OFF cycle control according to the Q-switch frequency of the RF signal, the control of the time width in the OFF section, the RF signal amplitude in the OFF section, and the like by the slope waveform generation circuit 13. FIG.
In accordance with the slope waveform shown in FIG. 16C, control is performed to modulate the RF signal into a waveform shown in FIG. Here, the Q switch frequency for turning on / off the Q switch, the RF threshold, and the like are determined by conditions such as the Q switch frequency and laser output desired by the user. When these are determined, the RF threshold value, which is the minimum RF signal that can cut off the laser output from the laser oscillator, is determined. Based on these data, the high-frequency modulation circuit 1
5 forms the RF signal waveform.

The slope waveform generating circuit 13 has the configuration shown in FIG.
An exponentially attenuated waveform as shown in (c) is generated. In order to obtain this waveform, the slope waveform generation circuit 13
Generates, for example, discrete data composed of geometric series having a common ratio of 1 or less in a time series and performs D / A conversion. Alternatively, a similar waveform can be obtained using an analog circuit. When the control of the RF output for the slope waveform is non-linear,
It is necessary to generate a slope waveform corrected for nonlinearity. Alternatively, a waveform in which discrete geometric series are connected by a line segment, a waveform in which the geometric series is attenuated in a stepwise manner, and a waveform in which the geometric series becomes smaller each time the Q switch is turned off are described above. May be used as the slope waveform.

An RF signal modulated into a slope waveform shown in FIG. 16D is output from the high-frequency modulation circuit 15 based on the modulation signal shown in FIG. . This slope waveform signal is shown in FIG.
The signal is amplified by the high-frequency amplifier circuit 16 of zero, and is applied to the Q switch 3 after impedance matching is obtained by the impedance matching circuit 17. Thus, the Q switch 3 is driven in response to the RF signal from the high frequency modulation circuit 15. As described above, the Q switch frequency is set by the Q switch control circuit 19 shown in FIG. Also,
The initial value of the RF signal and the common ratio at the time of attenuation are also set.

According to the present invention, first pulses are suppressed by adjusting the RF initial value at the start of processing according to the laser output. As a result, a stable first pulse output can be obtained even when the Q switch frequency is high, and processing and printing of the print start position can be performed as desired. Hereinafter, a method of controlling the first pulse will be described.

[First Pulse Suppression Method] FIGS. 3 to 5 are schematic diagrams showing waveforms of laser pulse output with respect to the amplitude of the RF signal. These figures show a state where the amplitude of the RF signal is gradually reduced from the maximum value over a plurality of pulses in order to suppress the first pulse.

In each figure, (a) shows the envelope of the waveform of the RF signal. The actual waveform oscillates at a high frequency in a sine wave shape as shown in the enlarged view of FIG. In each figure, the magnitude of the RF threshold value according to each laser output is indicated by an arrow. The laser can be stopped by setting the maximum value of the RF signal to an amplitude larger than the RF threshold.
When the RF signal shown in (a) is at the maximum value, the Q switch is turned off, so that the laser pulse shown in (b) is not output. When the RF signal falls below the RF threshold, Q
The switch is opened at a rate corresponding to the RF value, and a laser pulse is output. When the laser output is stopped by the Q switching operation, the amplitude of the RF signal is set to a value slightly larger than the RF threshold value in order to prevent leakage when the Q switch is turned on.

FIG. 3 shows the amplitude at which the RF signal starts to decrease, that is, the initial value of the RF signal at the start of processing.
The method for setting the RF maximum value is shown. In this method, since the RF signal is at or above the RF threshold at the time of processing start,
As shown in FIG. 3B, the first laser pulse cannot be generated.

On the other hand, as shown in FIG. 4, when the difference between the RF initial value and the RF threshold value at the start of the reduction of the RF signal is in an optimum state (including the case where the RF signal coincides with each other), the output is stable from the start of processing. Laser oscillation appears.

FIG. 5 shows a case where the laser output is smaller than the case shown in FIG. In this case, since the RF threshold value becomes smaller in accordance with the laser output, it is necessary to reduce the RF initial value at the start of processing.

The present invention further adjusts the RF initial value according to the Q-switch frequency. FIG. 6 shows the laser pulse output when the Q switch frequency is low. If the Q-switch frequency is below a predetermined value, the energy stored while the laser is off saturates. For example, when the solid laser medium is a YAG rod, the energy is saturated when the Q switch frequency is lower than 1 kHz as described above. Therefore, in this case, the energy of all the pulses is maximized, and pulses having the same magnitude as the first pulse continue as shown in FIG. 6B. Therefore, it is not necessary to suppress the first pulse.

However, as the time from the opening of the Q switch to the next opening, that is, as the Q switch frequency increases and the interval between the pulses decreases, the energy is output before the energy is saturated. Therefore, the energy per pulse is reduced, and the difference between the high peak value of the first pulse and the pulse in the steady state is enlarged. In other words, the peak value of the pulse tends to decrease as the Q-switch frequency increases. 6 to 8, it is observed that the peak value of (b) decreases as the Q switch frequency of (a) increases. 6 to 8 show how the peak value of the pulse generally decreases as the Q-switch frequency increases, and as described above, the pulse width and the height of the peak value are accurate. Not.

The laser output set by the user of the laser processing machine determines the RF threshold value for completely stopping the laser. An RF initial value is determined based on the RF threshold value and the setting of the Q switch frequency by the user. The RF initial value is determined such that the magnitude of the first pulse generated according to the difference from the RF threshold is equal to the magnitude of the pulse in a steady state determined by the laser power and the Q switch frequency.

The higher the Q-switch frequency, the greater the difference between the first pulse and the steady-state pulse, thus increasing the necessity for fast pulse control. When the peak value decreases, the RF threshold value also decreases as described above. Therefore, it is necessary to change the RF initial value accordingly.
In the present invention, when the Q-switch frequency is relatively low, the RF initial value at which the RF amplitude starts to decrease is reduced as shown in FIG. 7, and when the Q-switch frequency is high, the RF initial value is reduced as shown in FIG. I'm making it big. By varying the RF initial value in accordance with the Q switch frequency in this way, the feature that the first pulse can be suppressed to the optimum value at any Q switch frequency is realized.

[Control Method After Second Pulse] By adjusting the initial value at which the amplitude of the RF signal attenuates, it is possible to adjust the peak power of the first pulse to be the same as the peak power of the pulse in the steady state. It is. However, this method alone cannot control the first pulse, but cannot adjust the peak power of the second, third and subsequent pulses. This is because the magnitude of the peak power of the second and subsequent pulses is determined by the slope of the slope at which the RF signal decreases.

Hereinafter, a case of a slope waveform in which the RF signal decreases in proportion to time will be described with reference to FIGS. The case where the slope waveform is proportional to time is, for example, a case where the slope waveform generating circuit 13 in the block diagram of FIG. 10 inputs a waveform that decreases in proportion to time.

When the Q-switch frequency is high as shown in FIG. 11, it is considered that the RF signal is attenuated with a slope waveform as shown in FIG. As described above, when the Q-switch frequency is higher than the predetermined frequency, the energy accumulated in the solid-state laser medium cannot be completely consumed by the first pulse.

The first pulse in FIG. 11B can have the same peak power as the pulse in the steady state by adjusting the RF initial value as described above. Before the start of processing, the energy stored in the solid-state laser medium is saturated, and in this state, the RF threshold value at which laser oscillation can be stopped becomes the maximum value.

Since the energy stored by the first pulse oscillation is released, the energy stored in the solid-state laser medium decreases. By the way, the energy increases during the rest period between the first and second laser oscillations, that is, the operation period of the Q switch, but does not reach the saturation state. In this state, the RF threshold at which the second laser oscillation can be stopped is smaller than the RF threshold in the saturated state (first).

When the attenuation slope of the RF signal decreases in proportion to time, the slope determines the peak value of the second pulse. If the slope of the slope is set so that the RF signal amplitude in the second oscillation section is equal to or slightly smaller than the RF threshold value of the second pulse, the second pulse is not output or the first pulse is not output. Is also smaller. As a result, the energy emitted from the solid-state laser medium is reduced, and the energy is accumulated during the next Q-switch operation section, so that the RF threshold value of the third pulse becomes larger than the RF signal amplitude. In other words, since the amplitude of the RF signal is smaller than the RF threshold,
A state in which laser oscillation is sufficiently possible is obtained. Therefore, 3
The peak value of the second pulse is higher than the peak value in the steady state. Therefore, the peak values of the output pulses are not aligned, and particularly in the above example, the third peak value becomes large, which hinders processing.

On the other hand, by making the slope of the slope gentle as shown in FIG. 12, the rate of decrease of the RF signal amplitude with respect to the rate of decrease of the RF threshold value in each pulse can be prevented from increasing. It is possible that the pulse does not exceed the magnitude of the steady state pulse. However, in this method, as shown in FIG. 12B, some pulses following the first pulse are smaller than the pulses in the steady state, and there is a problem that machining immediately after the start of machining becomes weak.

On the other hand, as shown in FIG. 13, when the slope of the slope is made steeper so that the magnitude of the second pulse can be made the same as that of the first pulse, the R of the third pulse is increased.
When the RF amplitude with respect to the F threshold becomes too small, the peak value becomes too large. in this way,
R of Q switch OFF section in slope shape proportional to time
In the method of controlling the F signal amplitude, it is difficult to generate a pulse having a uniform peak value from the start of processing.

In order to solve such a problem, according to the present invention, an exponential function exp (r
A slope formed by an exponential function where r in t) is 1 or less is used. At the time of actual use, a discrete value group composed of a geometric series having a common ratio of 1 or less can be used, and does not need to be a continuous value. For example, when the first term, which is the first value of the slope, is 1, and the common ratio is 0.95, the first data is 1,
The second data is 1 × 0.95 = 0.95, the third data is 0.95 × 0.95 = 0.925, the fourth data is 0.9025 × 0.95 = 0.857375,.
・ Create a slope function consisting of discrete values so that
An exponential function slope can be created by performing / A conversion or the like.

As a method for creating such data, C
A method of performing calculation using a PU, a method of storing data calculated in advance in a memory, and sequentially calling and using the data may be considered. By performing D / A conversion on the data thus obtained, a slope waveform can be obtained. Alternatively, a similar slope waveform may be generated by configuring an analog circuit. The present invention is not limited to the method for obtaining the slope waveform, and any other slope waveform generation method currently used or developed in the future can be appropriately adopted.

As shown in FIG. 14, by attenuating the RF signal amplitude exponentially as shown by a broken line in the Q switch OFF section from the start of processing, appropriate control of the first pulse and subsequent pulses is achieved. I do. By attenuating exponentially, the value of the RF signal amplitude for each Q switch OFF decreases at a constant rate. By optimally setting this ratio, the peak value of each pulse can be output stably. As described with reference to FIG. 14, when the emission energy of one pulse is constant, the stored energy is emitted at a constant rate and decreases at each output of the pulse, so that the RF threshold value decreases at a constant rate. Since the RF value of each pulse decreases at a constant rate in accordance with this, a stable pulse can be obtained from the first pulse.

Experiments have confirmed that the use of the slope that attenuates in a geometric series shown in FIG. 14 properly controls the first pulse and subsequent pulses. Although the detailed principle is not clear, it may be that the fact that the ratio of the RF amplitudes that generate an arbitrary pulse and the immediately succeeding pulse is always the same leads to a uniform consumption of pulse energy and a uniform peak value. is expected. Assuming that the common ratio of the geometric series is r, the magnitude of the RF signal that generates the second pulse is r (<1) times that of the RF signal that generates the first pulse. Also the third R
The F signal is r times as large as the second RF signal.

When an exponential slope waveform is generated using an analog circuit, the value of r can be reduced by decreasing the slope time, and can be increased to approach 1 by increasing the slope time. The common ratio is adjusted to an optimum value according to the Q switch frequency and the laser power. It is most certain that the optimum value of the common ratio is measured by actually driving the apparatus. However, it is also possible to store the measured value in advance and select the optimum value based on this data.

As described above, according to the present invention, it is possible to control the initial value of the RF signal at the start of the slope to control the first pulse to be equal to the magnitude of the pulse in the steady state, and to control the common ratio or the slope time. Can control the magnitude of the second and subsequent pulses, and can obtain a uniform pulse output.

Further, as a result of experiments, it was confirmed that the first pulse in each laser output can be suppressed according to this method even when the same slope waveform is used. This is expected to be achieved because the ratio of RF amplitudes between adjacent pulses is the same even with different laser outputs. For example, FIG. 15 shows an example in which the laser output pulse is reduced using the slope waveform of FIG.
Shown in In this case, since the laser pulse output becomes low, the RF threshold becomes small accordingly. Therefore, although the pulse is not output until the slope falls below the RF threshold,
The peak value of the output pulse can be controlled to be constant. In the example of FIG. 15, the first and second pulses are not output, but a constant laser output is obtained after the third pulse.

Thus, even if the laser output decreases and the RF threshold value changes, the control of the first pulse is maintained. Therefore, in the case of processing that does not cause a problem even if some pulses are not output immediately after the start of processing, the feature that the first pulse can be controlled while keeping the slope waveform constant regardless of the laser output is realized. .

On the other hand, depending on whether the start of the laser pulse control is immediately before or immediately after the pulse oscillation, R
The F initial value may be changed. For example, the initial value for attenuating the RF signal may be set to a value slightly larger than the RF threshold value so that the first pulse is not generated at the start of the laser pulse control. In this case, in order to surely stop the laser oscillation at the start of the first pulse control, the RF
The initial value is set to a value slightly larger than the RF threshold value, and the RF signal is controlled so as to be attenuated so that the next and subsequent laser oscillations can be obtained.

[Feedback Control] Next, as another embodiment of the present invention, a method of performing feedback control based on laser output when controlling an RF signal will be described. In the following embodiments, the laser oscillation is detected using the laser light detection element 12 during the processing operation, and the RF signal is adjusted based on the detected laser light to stabilize the first pulse.

FIGS. 17 to 22 show (a) a processing control signal,
(B) RF signal and (c) laser output waveforms are shown schematically. The waveforms shown in the figures of these embodiments are exaggerated for explanation, and 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 easily understand that there is a minute laser output that does not affect the object to be processed. In the same manner, on the time axis, the changed part is similarly shown large for the sake of explanation.

FIGS. 17 to 19 illustrate a procedure for starting the laser oscillation by lowering the RF signal from the state where the laser oscillation is completely stopped. Here, the RF threshold when the energy stored in the solid-state laser medium 1 is saturated is defined as an RF saturation threshold.

In the embodiment shown in FIG. 17, laser oscillation is performed in a state where the energy stored in the solid-state laser medium 1 is saturated or close to it. As shown in FIG. 17A, when the laser oscillation is stopped, the RF signal is at the maximum value or a high value that can sufficiently stop the laser oscillation.
Is activated to prevent laser oscillation. When the control means 13 issues a processing start control signal for starting laser processing from the state where laser oscillation is stopped (t ₁ ), the RF signal starts to gradually decrease in response to this. When the RF signal drops below the RF saturation threshold (t
₂ ), laser oscillation starts. When the laser output is started, the energy stored in the solid-state laser medium 1 decreases by the amount of the output of the laser, so that the RF threshold slightly decreases from the RF saturation threshold. As a result of the lowering of the RF threshold, the RF signal becomes larger than the RF threshold, and the laser oscillation is stopped again. At this time, the laser output is extremely small and extremely weak without affecting the object to be processed.

The laser light detecting element 12 detects this slight laser output (t ₃ ), and records the RF signal value at this point in the control means 13 as an RF signal threshold. And R
The laser output is started by rapidly lowering the F signal to the RF initial value (t ₄ ). In the first pulse output generated at this time, since the RF signal was close to the RF threshold, the loss of the resonator was quickly reduced due to the reduction of the RF signal, and a stable output was obtained without the influence of the residual resonator loss. When the RF signal is returned to the maximum value or a sufficiently high value again, the laser output is stopped (t ₅ ). Thereafter, ON / OFF of the Q switch 3 is repeated at a cycle corresponding to the designated Q switch frequency, and the RF signal when the Q switch 3 is opened is gradually reduced. As a method of reducing the RF signal, the method of the above-described embodiment can be appropriately used. The RF initial value at which the RF signal is sharply reduced is determined according to the recorded RF threshold and the Q switch frequency in order to suppress the first pulse.

As described above, at the time of laser processing, RF
The method of obtaining the RF threshold value by gradually lowering the signal and detecting the time point at which the laser output is started enables appropriate control according to the amount of energy stored in the solid-state laser medium 1 and more accurately. A controlled laser oscillation can be obtained.

Next, the embodiment shown in FIG. 18 will be described. As in FIG. 17, when the laser oscillation is stopped, as shown in FIG. 18A, the RF switch operates the Q switch 3 at the maximum value or a sufficiently high value to prevent the laser oscillation. When the control means 13 issues a processing control signal for starting laser processing from the laser oscillation stop state (t ₁ ), the RF signal is gradually attenuated in response thereto. The method of attenuation is
The RF signal is reduced in proportion to time or at a fixed rate so that laser pulses can be obtained at the required period.
The method of the above-described embodiment can be appropriately used. RF signal is R
When it falls below the F saturation threshold (t ₂ ), laser oscillation starts. As in FIG. 17, when the laser output is started, the energy stored in the solid-state laser medium 1 decreases by an amount corresponding to the output of the laser, so that the RF threshold slightly decreases from the RF saturation threshold. As a result of the lowering of the RF threshold, the RF signal becomes larger than the RF threshold, and the laser oscillation is stopped again. Therefore, the laser output at this time is very small and instantaneous, and does not affect the workpiece. When this laser output is detected by the laser light detecting element 12 (t ₃ ), the RF signal is reduced to such an extent that a desired peak power can be generated (t ₄ ).

After the pulse is generated, the RF signal is returned to the original state, that is, to the attenuation waveform (t ₅ ). The RF threshold value at this time is lower than the RF saturation threshold value due to the loss of energy. When the RF signal that decreases in accordance with the attenuation waveform becomes equal to or less than the RF threshold value after one pulse is output (t ₆ ), the minute laser output is emitted again. This was detected in the same manner that the laser light detecting element 12, lowering the RF signal to the extent that it is possible to generate a desired peak power (t _7). Hereafter, Q
By turning ON / OFF the switch 3 repeatedly, a steady state is established. Note that the steady state refers to a state in which the RF threshold is reduced as the energy stored in the solid-state laser medium 1 is released by reducing the RF power, and the RF threshold does not decrease any more.

As described above, in the embodiment of FIG. 18, the RF threshold value is monitored every moment by detecting the minute laser output so that the RF threshold value decreases from the RF saturation threshold value to the RF threshold value in the steady state. The RF signal is attenuated accordingly. In this method, Q near the current RF threshold
Since the switch is operated, in other words, control is performed using the last resonator loss that suppresses laser oscillation, accurate control is performed and a stable pulse is obtained.

Next, the embodiment shown in FIG. 19 will be described. In this embodiment, unlike in FIGS. 17 and 18, laser oscillation is not completely stopped even when processing is stopped, and laser oscillation is performed so as not to hinder processing. In other words, the RF threshold is constantly monitored by intentionally outputting a very small laser. Therefore, it is possible to always perform the optimal control according to the RF threshold. After the processing is started, the above-described methods of FIGS. 17 and 18 can be used. FIG. 19 shows an example using the method of FIG.

Next, the embodiment shown in FIG. 20 will be described.
In FIGS. 17 to 19, a description has been given of the case where the laser processing is shifted from the stop to the start. However, in the embodiment of FIG. 20, the shift from the laser processing to the stop is described. As shown in FIG. 20B, the RF signal at the time of laser processing has an amplitude at which laser output can be stopped and a minimum amplitude of Q.
Repeated at switch frequency, Q switch 3 ON
/ OFF is being performed. In FIG. 20A, when the machining control signal is interrupted and machining stop is instructed by the control means 13,
RF signal (b) to stop laser output (c)
Increase. At this time, the RF signal is controlled so as not to completely suppress the laser oscillation but to emit a very small laser output that does not affect the workpiece. When the RF signal is controlled so that a very small laser output leaks while being detected by the laser light detecting element 12, the energy accumulated in the solid-state laser medium 1 gradually increases, and the leaked laser light increases. When it is detected that the leakage laser light has increased, R
The laser output is suppressed by increasing the F signal. Since the portion of the laser output that is not output to the outside is stored as energy, the energy further increases, and as a result, the laser output starts to leak again. Then, it is necessary to further increase the RF signal. For the above reasons, the RF signal gradually increases as shown in FIG.

To stop the laser output only, R
It is sufficient to increase the F signal, but there is a problem in that the state inside the resonator cannot be determined simply by increasing the F signal. That is, it cannot be determined whether the laser output is stopped near the RF threshold value by the minimum RF signal or whether the RF signal completely suppresses laser oscillation with sufficient power. In the former case, the effect of the residual resonator loss is extremely small because the energy is minimum, but in the latter case, the energy is high and the effect of the residual resonator loss cannot be ignored if the Q switch 3 is suddenly opened.

For this reason, in FIG. 20, the RF signal is controlled so as to intentionally emit a very small laser output to minimize the energy so as to achieve the former state. In other words, the method of this embodiment controls the laser oscillation at a value close to the RF threshold while monitoring the RF threshold. As described above, since the RF signal is controlled in accordance with the increase of the stored excitation energy after the laser stop by the Q switch 3, the control of the Q switch 3 when restarting the laser processing can be always performed from the RF threshold. Fig. 21
As shown in (1), a stable pulse can be obtained even when the machining is restarted.

In particular, when the period from the stop to the restart is short, for example, even if the YAG rod of the solid laser medium 1 is not saturated for 1 ms or less, operations such as stable processing and printing can be performed. As described above, even when the excitation energy is not completely saturated, the RF signal is always controlled to the RF threshold value according to the accumulated energy when laser processing is started again. Appropriate fast pulse control can be performed using the method of the example.

In the above-described embodiment, the case of the pulse oscillation in which the laser output is output in the form of a pulse has been mainly described.
In the embodiment shown in FIG. 22, an example will be described in which the present invention is used to obtain a CW oscillation output in which a laser is continuously oscillated instead of a pulse. In the case of the CW oscillation, similarly to the QCW oscillation, if the RF signal is sharply set to 0, there is a problem that the laser power at the first rise is not stabilized due to the influence of the residual resonator loss. For this reason, in FIG. 22, after receiving the processing control signal (a), the RF signal (b) is gradually reduced. When the RF signal falls below the RF saturation threshold, the laser output (c) starts to oscillate. However, the RF signal is continuously controlled so that the laser output becomes a value within a predetermined range without abrupt change of the RF signal, and accumulation is performed. It releases the energy that was given. According to this method, since the stored energy is not released at a stroke, a laser output by CW oscillation with a stable rising can be obtained.

A stable pulsed laser beam can be obtained by the above method, and this laser output is used for laser marking and laser processing. FIG. 23 schematically shows a galvano scanner optical system for controlling a laser processing position. FIG. 23A is a side view of the scanner unit of the laser oscillator, and FIG. FIG. 23 (b)
Indicate the coordinate axes of the machining plane. The scanner section shown in FIG. 1 includes a beam expander 21 for expanding a beam diameter of a laser beam, and an X mirror 22X and a Y mirror 22Y constituting a galvano scanner mirror 22.
And an X scanner 16X and a Y scanner 16Y for driving and controlling these galvano scanner mirrors 22, respectively.
And an Fθ lens 24 as a condenser lens. As the galvano-scanner mirror 22, a mirror made of a transparent base material and a dielectric multilayer film is used.

The laser light oscillated from the laser oscillator is incident on the beam expander 21 as shown by the arrow, and is expanded to a desired magnification. The expanded laser light is converted into an X beam by an X mirror 22X and a Y mirror 22Y whose angles are controlled by an X scanner 16X and a Y scanner 16Y.
The processing position in the direction and the Y direction is controlled. O of laser light
N / OFF and X scanner 23X, Y scanner 23Y
The desired laser processing and marking can be performed by the position control based on.

When processing is performed with a laser oscillator using a galvano scanner mirror, the laser beam described in the embodiment of the present invention is disposed behind the galvano scanner mirror 22 on the optical axis of the laser. The laser light detection element 12 which is a detection sensor can be used.

The laser light detecting element 12 receives the light transmitted through the galvano scanner mirror 22. The method of detecting laser light with the laser light detecting element 12 is shown in FIG.
As shown in FIG. 3, since a sensor for detecting a failure of the Q-switch provided in the laser oscillator can be used as the laser light detecting element 12, there is an advantage that it can be realized by using an existing mechanism.

Prior to the control of the RF signal, the control is performed in a state where the processing surface is shielded from light by a light shielding means such as a mechanical shutter 6 before the processing is started, and the RF signal corresponding to the Q switch frequency or the excitation energy is controlled. Value and waveform can be optimized. An RF threshold or the like may be measured, and an optimal initial value may be calculated based on this value. Further, the data obtained at this time can be stored in a table or the like, and the actual machining operation can be started based on this value. The configuration of FIG. 9 described above can be used for an optical system for setting RF signal control parameters. In a normal processing operation, the mechanical shutter 6 is open. When setting the RF signal control parameters, the control shown in FIGS. 17 to 22 is performed with the mechanical shutter 6 closed, and the parameters are set optimally and stored in a storage unit (not shown, connected to the control unit 13). Is performed), and processing is performed based on the settings. The above operation is performed while the processing operation is not performed, for example, immediately after the setting of the excitation light is changed or immediately after the processing operation is performed, and the RF threshold value is set.

In the laser oscillator and the laser pulse control method according to the embodiment of the present invention, not only a method of setting each value such as an RF threshold value by blocking light with a mechanical shutter 6 or the like, but also a work such as an actual printing process. While the laser light detecting element 12 detects the minute laser output, the value when the laser light starts to leak can be recorded as the RF threshold value. For this reason, the measurement before processing becomes unnecessary, and the merit that the RF threshold value is automatically calculated in the apparatus and can be used conveniently can be enjoyed.

According to the method of the above embodiment, a first pulse having a stable peak power can be obtained irrespective of the excitation light intensity, the Q switch frequency, and the like. In addition, as a result of being able to perform optimal and accurate control according to the state of the apparatus, there is also an advantage that the influence of deterioration with time of the excitation energy can be avoided. In general, various conditions and excitation energies of a laser beam machine may fluctuate irrespective of a user's setting, for example, due to fluctuations in cooling water temperature, environmental temperature, and the like. In the above embodiment, the laser beam machine is automatically controlled so that the leakage light of the small laser output is detected by the feedback control, and the laser beam machine is automatically controlled so as to be constant according to the strength as well as the presence or absence of the laser beam. Operation can be expected.

Further, since no special mechanism or circuit for realizing the embodiment of the present invention is required, a merit in cost can be enjoyed. Furthermore, even when the processing is started again after the processing is stopped and before the excitation energy is saturated, a first pulse having a stable peak power can be obtained. In addition, even during machining by CW oscillation, machining without the influence of the first pulse at the time of rising can be performed.

[0117]

The laser oscillator and the laser pulse control method of the present invention are characterized in that the pulse output at the initial stage of oscillation is stabilized by adjusting the initial RF value and the slope. Thereby, regardless of the power of the laser, for example, even when the laser power is weak, a laser pulse having a stable peak power can be obtained, and high-precision processing can be performed. In particular, even when the output laser power is weak, it is possible to prevent the output pulse from becoming unstable and to achieve a feature that each pulse can be obtained with a desired stable peak power. This is because the laser oscillator and the laser pulse control method of the present invention are configured to adjust the amplitude of the RF signal for turning on the Q switch according to the laser output.

The present invention is characterized in that first pulses are suppressed by first adjusting the RF initial value at the start of processing according to the laser output. As a result, even when the Q-switch frequency is high, it is possible to obtain a stable and high-quality first pulse output by controlling the initial pulse of oscillation, and to perform delicate processing according to the processing target, such as printing directly on a semiconductor silicon chip. , Can be printed.

Further, according to the present invention, when the Q switch is opened, R
By gradually reducing the F signal, a method of controlling the second, third and subsequent pulses following the first pulse is realized. In particular, by applying an exponential slope, a stable output can be obtained with simple control regardless of the RF initial value. It is difficult to control the second and subsequent pulses using a linear slope. However, if a geometric series curve is used, the characteristic that the second and subsequent pulses are suppressed and the peak values are uniform is used. Things. According to this method, the peak value can be stabilized by adjusting the common ratio while keeping the RF initial value constant, so that control can be simplified. In particular, it is possible to avoid the problem that the threshold value fluctuates in the next pulse because the first laser output is not oscillated. This method has the advantage that the peak value of the pulse can be controlled by simple control without adjusting the RF initial value, if the processing does not cause a problem even if oscillation of several pulses from the first pulse does not occur.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration 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 shows an RF when an RF signal initial value is set to an RF maximum value.
Schematic waveform diagram showing the waveform of the laser pulse output with respect to the signal amplitude

FIG. 4 is a schematic waveform diagram showing a waveform of a laser pulse output with respect to an amplitude of an RF signal when an RF signal initial value is set as an RF threshold value.

FIG. 5 is a schematic waveform diagram showing the waveform of a laser pulse output with respect to the amplitude of an RF signal when the laser output is low.

FIG. 6 is a schematic waveform diagram showing a waveform of a laser pulse output with respect to an amplitude of an RF signal when a Q-switch frequency is low.

FIG. 7 is a schematic waveform diagram showing a waveform of a laser pulse output with respect to an amplitude of an RF signal when a Q-switch frequency is relatively low.

FIG. 8 is a schematic waveform diagram showing the waveform of a laser pulse output with respect to the amplitude of an RF signal when the Q-switch frequency is high.

FIG. 9 is a schematic diagram showing a state where an RF threshold value is measured by a laser oscillator according to an embodiment of the present invention.

FIG. 10 is a block diagram showing an example of a Q switch control circuit for applying an RF signal to a Q switch in the laser oscillator according to one embodiment of the present invention.

FIG. 11 is a graph showing an R signal when the RF signal is attenuated in a slope shape;
Schematic waveform diagram showing the waveform of the laser pulse output with respect to the amplitude of the F signal

FIG. 12 is a graph showing R when the slope of the RF signal is made gentle;
Schematic waveform diagram showing the waveform of the laser pulse output with respect to the amplitude of the F signal

FIG. 13 shows an RF signal when the slope of the RF signal is steep.
Schematic waveform diagram showing waveform of laser pulse output with respect to signal amplitude

FIG. 14 is a schematic waveform diagram showing a waveform of a laser pulse output with respect to an amplitude of an RF signal when an exponentially attenuating slope according to one embodiment of the present invention is used

FIG. 15 is a schematic waveform diagram showing the waveform of a laser pulse output with respect to the amplitude of an RF signal when an exponentially attenuating slope according to one embodiment of the present invention is used

FIG. 16 is a schematic waveform diagram showing a signal waveform in each block of FIG. 10;

FIG. 17 is a schematic waveform diagram showing waveforms of a processing control signal, an RF signal, and a laser output of a laser oscillator according to another embodiment of the present invention.

FIG. 18 is a schematic waveform diagram showing waveforms of a processing control signal, an RF signal, and a laser output of a laser oscillator according to another embodiment of the present invention.

FIG. 19 is a schematic waveform diagram showing waveforms of a processing control signal, an RF signal, and a laser output of a laser oscillator according to another embodiment of the present invention.

FIG. 20 is a schematic waveform diagram showing waveforms of a processing control signal, an RF signal, and a laser output of a laser oscillator according to another embodiment of the present invention.

FIG. 21 is a schematic waveform diagram showing waveforms of a processing control signal, an RF signal, and a laser output of a laser oscillator according to another embodiment of the present invention.

FIG. 22 is a schematic waveform diagram showing waveforms of a processing control signal, an RF signal, and a laser output of a laser oscillator according to another embodiment of the present invention.

FIG. 23 is a schematic diagram showing a scanner unit of a laser oscillator using a galvano scanner according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Solid 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 transmission filter 12 Laser output detection sensor 13 Slope waveform generation circuit 14 High frequency generation circuit 15 High frequency modulation circuit 16 High frequency amplification circuit 17 Impedance matching circuit 18 Processing control circuit 19 … Q switch control circuit 21… Beam expander 22… Galvano scanner mirror 22X… X mirror 22Y… Y mirror 23X… X scanner 23Y… Y scanner 24… Fθ lens

Claims (10)

[Claims] A solid-state laser medium; an excitation light source for exciting the solid-state laser medium; a total reflection mirror positioned on an optical axis of laser light emitted from the solid-state laser medium; An output mirror opposed to the total reflection mirror via a mirror, and a laser beam arranged between the total reflection mirror and the output mirror on an optical axis of a laser emitted from the solid-state laser medium, thereby causing the laser light to oscillate. In a laser oscillator having a Q switch, based on a Q switch frequency setting means for setting a frequency of a high frequency signal applied to the Q switch, and a minimum high frequency signal value capable of cutting off a laser output from the laser oscillator. Threshold setting means for setting a threshold, and the threshold setting means for maintaining a constant laser output at the start of laser oscillation. Laser oscillator comprising an initial value setting means for setting an initial value of the laser oscillation start time of the high-frequency signal based on the Q-switching frequency set by the set threshold the Q-switching frequency setting means by. 2. The laser oscillator according to claim 1, wherein said initial value setting means sets an initial value of said high-frequency signal to a value smaller than said threshold value. 3. The laser oscillator according to claim 1, further comprising an attenuating means for gradually attenuating the high-frequency signal from an initial value so as to keep a laser output pulse group at the start of laser oscillation constant. 4. The attenuating means attenuates the high-frequency signal exponentially from an initial value.
The described laser oscillator. 5. The laser oscillator according to claim 1, wherein the laser oscillator further includes a laser output detection sensor for measuring a high-frequency signal threshold. 6. A laser pulse control method for controlling a pulse group output from a laser oscillator at the start of oscillation, comprising: setting a Q switch frequency for setting a frequency of a high frequency signal applied to a Q switch; Setting a threshold value that is a minimum high-frequency signal value at which laser output from the laser oscillator can be cut off; A laser pulse control method including a step of setting an initial value of a high-frequency signal at the start of oscillation. 7. The laser pulse control method according to claim 6, wherein the step of setting the threshold value of the high-frequency signal includes the step of measuring the threshold value with a laser output detection sensor. 8. The laser pulse control method according to claim 6, wherein the step of setting the threshold of the high-frequency signal includes the step of estimating the threshold based on the excitation energy. 9. The laser pulse control method according to claim 7, further comprising a step of comparing the measured value of the high-frequency signal threshold value with the estimated value to detect an abnormality in the optical system of the laser oscillator. 10. The laser pulse according to claim 6, further comprising a step of exponentially attenuating the high-frequency signal from an initial value so as to keep a laser output pulse group at the start of laser oscillation constant. Control method.