JPH05121815A - Laser oscillator using injection method - Google Patents

Abstract

PURPOSE:To provide a highly reliable laser oscillator by using an injection method capable of stably producing a smooth laser waveform through injection locking regardless of external influences such as heat CONSTITUTION:The title oscillator has a master laser oscillator 1 and a slave laser oscillator 2. A laser beam 22 from the slave laser oscillator 2 is monitored by means of a detector 10. A micro-driving means 7 such as piezoelectric element is subjected to feedback control by a control means 13 on the basis of the waveform of the laser beam monitored, and the resonator length of the slave laser oscillator 2 is adjusted. For example, a leading edge of the waveform of the laser beam monitored by the detecting means 10 is used to give a start time of oscillation and then an interval from a constant standard time to the start time of oscillation is used as a delay time of oscillation. By the control means 13, the micro-driving means 7 is controlled on the basis of the delay time of oscillation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection type laser oscillator which emits a weak laser beam from a driving side laser oscillator to a driven side laser oscillator and oscillates a strong laser beam of the same quality as the driving side laser beam. Regarding

[0002]

2. Description of the Related Art Conventionally, an injection lock method has been known as a method for obtaining high quality laser light.
This method combines a laser oscillator on the driving side and a laser oscillator on the driven side, introduces a weak seed laser beam from the laser oscillator on the driving side to the laser oscillator on the driven side, and gains a strong laser excitation region on the driven side. Is used to obtain a strong laser beam of the same quality as the laser beam on the driving side. In this method, a smooth laser waveform having a high peak can be obtained from the laser oscillator on the driven side by tuning the oscillation frequency of the laser oscillator on the driving side and the longitudinal mode frequency of the laser oscillator on the driven side. The tuning is obtained by changing the resonator length of the driven-side laser oscillator by a minute driving device. In general, the driving-side laser oscillator is referred to as a master laser and the driven-side laser oscillator is referred to as a slave laser. Therefore, these general names are mainly used below.

FIG. 3 is a block diagram showing an example of a conventional injection type laser oscillator. First, the configuration of this laser oscillator will be described below. In FIG. 3, 1 is a master laser and 2 is a slave laser.
The oscillation longitudinal mode of the master laser 1 is single, and the stabilizer 3 is provided to stabilize the longitudinal mode.

The slave laser 2 reflects the laser light 21 emitted from the master laser 1 and reflects the laser light 21.
Injection mirror 4 introduced on the optical axis of the resonator
And an output mirror 5 and a wavelength selection grating 6 which form a resonator. In this case, the output mirror 5 and the grating 6 are arranged to face each other with a strong laser excitation region inside the slave laser 2 interposed therebetween.

Further, the output mirror 5 of the slave laser 2 is provided with a piezo element 7 and a piezo driver 8 for driving the piezo element 7 as a minute driving device. In order to tune the oscillation mode frequency of the master laser 1 to the longitudinal mode frequency of the slave laser 2, the drive voltage of the piezo driver 8 is changed to drive the piezo element 7.
It is configured to change the cavity length of the slave laser 2.

Further, a beam splitter 9 for dividing the laser beam 22 from the slave laser 2 into two is provided on the resonator optical axis of the slave laser 2. A detector 10 for detecting the waveform of the laser light is arranged on the axis of the laser light 23 on the reflection side of the laser light split and emitted by the beam splitter 9. A transient recorder 11 is connected to the detector 10 to monitor the waveform of the laser light detected by the detector 10. In addition, reference numeral 12 in the drawing denotes a discharge power supply for applying a discharge voltage to the slave laser 2.

Next, the operation of the laser oscillator having the above structure will be described. That is, the laser light 21 emitted from the master laser 1 is introduced onto the optical axis of the resonator of the slave laser 2 via the injection mirror 4. The laser light introduced from the injection mirror 4 passes through the strong laser excitation region inside the slave laser 2, grows in the resonator of the slave laser 2 by the gain of the excitation region, and the strong laser light 2
2 is emitted to the outside.

In the laser oscillator of FIG. 3, the weak laser beam 21 from the master laser 1 is introduced into the slave laser 2 to oscillate the slave laser 2, and the oscillation frequency of the master laser 1 and the longitudinal mode of the slave laser 21. When the frequency is tuned, the drive voltage of the piezo driver 8 is changed and the piezo element 7 is driven to change the resonator length of the slave laser 2.

[0009]

By the way, in the laser oscillator having the above configuration, when the weak laser light 21 from the master laser 1 is introduced into the slave laser 2 and the slave laser 2 is oscillated, Since the oscillation frequency of 1 and the longitudinal mode frequency of the slave laser 2 do not normally match and are slightly deviated, the laser light 22 emitted from the slave laser 2 has a beating waveform. This waveform is obtained by detecting the laser beam 23 reflected from the beam splitter 9 with the detector 10, and is monitored by the transient recorder 11.

In order to make a laser beam having such a beating waveform into a smooth waveform locked with an injection lock, a voltage is applied from the piezo driver 8 to the piezo element 7 of the slave laser 2 to thereby cause the piezo element 7 to move. By driving, the cavity length of the slave laser 2 is changed so that the oscillation frequency of the master laser 1 matches the longitudinal mode of the slave laser 2.

However, if the voltage of the piezo driver 8 is fixed as it is after the above operation, the cavity length of the slave laser 2 changes due to external influences such as changes in room temperature. As a result, the oscillation frequency of the master laser 1 and the longitudinal mode of the slave laser 2 deviate from each other, so that the laser light 22 emitted from the slave laser 2
However, it becomes the beating waveform again. In this case, a voltage is again applied to the piezo element 7 to change the resonator length. However, until the end of this operation, the waveform of the laser light emitted from the slave laser 2 is a beating waveform, and a smooth waveform with injection lock cannot be obtained.

The present invention was proposed in order to solve the problems of the prior art as described above, and its object is to provide a smooth laser waveform with an injection lock regardless of external influences such as heat. It is an object of the present invention to provide a highly reliable injection-type laser oscillator that can be stably obtained at all times.

[0013]

A laser oscillator according to the injection system of the present invention has a driving side laser oscillator and a driven side laser oscillator, and emits a weak seed laser beam from the driving side laser oscillator. A laser beam on the driving side is introduced into the driven side laser oscillator, and a gain of a strong laser excitation region of the driven side laser oscillator is used to obtain a powerful laser beam of the same quality as the driving side laser beam. In the injection type laser oscillator described above, a minute driving means for adjusting the resonator length of the driven side laser oscillator, a detecting means for monitoring the waveform of the laser beam from the driven side laser oscillator, and a monitor by the detecting means. A control means for controlling the minute driving means based on the waveform of the laser beam thus generated is provided.

That is, the injection type laser oscillator of the present invention monitors the laser light from the slave laser (driven side laser oscillator) by the detecting means, and performs feedback control by the control means on the basis of the waveform of the monitored laser light. Is performed and the cavity length of the slave laser is adjusted.

More specifically, the control means sets the rising portion of the waveform of the laser beam monitored by the detection means as the oscillation start time, and the oscillation delay time from a fixed reference time to this oscillation start time. , Is configured to control the minute driving means based on the oscillation delay time.

Further, as the minute driving means, generally,
Piezo elements are used. When the piezo element is used, it is necessary to control the drive voltage appropriately according to the hysteresis characteristic of the piezo element. That is, at the start of control, the drive voltage is always returned to 0V, and then a predetermined drive voltage is applied to control the direction of the minute drive means to be reversed. As the drive voltage of the first step of the control,
It is desirable to apply a voltage having a voltage value that is twice to several tens of times the driving voltage in the normal control step.

[0017]

In the laser oscillator of the present invention having the above-mentioned structure, the fine driving means is appropriately controlled by the control means so as to synchronize the master laser and the slave laser based on the laser waveform monitored by the detecting means. Can be controlled. That is, the laser waveform of the slave laser (driven side laser oscillator) is constantly monitored, and the cavity length is constantly changed appropriately by appropriate control according to this laser waveform, so that a smooth laser waveform with injection lock is obtained. Can always be obtained stably.

For example, the control means obtains the oscillation delay time of the laser light from the laser waveform, and controls the minute driving means so that this oscillation delay time is always a minimum value.
In this case, the reason why the oscillation delay time is always controlled to the minimum value is as follows. That is, when the oscillation frequency of the master laser (driving side laser oscillator) and the longitudinal mode frequency of the slave laser (driven side laser oscillator) match, the oscillation delay time becomes a minimum value and a smooth waveform with injection lock is applied. Is obtained. Also,
When the oscillation frequency of the master laser and the longitudinal mode frequency of the slave laser deviate from each other, the oscillation delay time becomes long, resulting in a beating waveform with a beat and a waveform out of injection lock. Therefore, by controlling the minute drive means by the control means so that the oscillation delay time always becomes the minimum value, a smooth waveform with injection lock can be obtained.

On the other hand, when the piezo element is used as the minute drive means, the drive voltage of the piezo element is always returned to 0 V at the start of control, and then a predetermined drive voltage is applied, whereby the hysteresis characteristic of the piezo element is The position of the piezo element can be largely moved by using the curve when the voltage rises. Also, in order to reverse the direction of the piezo element when controlling the piezo element in minute steps,
As the drive voltage for the first step of the control, it is necessary to apply the drive voltage in the range of twice to several tens of times the step voltage of normal control. The range of this drive voltage is set so that the movement length of the piezo element at the time of reversal becomes substantially the same as the movement length in a minute step near the minimum value.

[0020]

Embodiments of the present invention will be described below with reference to FIGS. 1 and 2. Here, FIG. 1 is a configuration diagram showing an embodiment of a laser oscillator according to the present invention, and FIG. 2 is a characteristic diagram showing a hysteresis curve of a piezo element.

First, the structure of the laser oscillator shown in FIG. 1 will be described. In this embodiment, a continuous oscillation CO ₂ laser is used as the master laser (driving side laser oscillator) 1, and a slave laser (driven side laser oscillator) 2 is used as the slave laser (driven side laser oscillator) 2.
A pulsed TEA CO ₂ laser is used.
Further, the master laser 1 has a grating inside, and wavelength selection is performed. Further, the master laser 1 has a single oscillation longitudinal mode, and the stabilizer 3 is provided as a longitudinal mode stabilizing mechanism.

On the other hand, as is apparent from a comparison between FIGS. 1 and 3, the basic structure of this embodiment is the same as that of the prior art shown in FIG. That is, the slave laser 2 has an injection mirror 4 that introduces the laser light 21 from the master laser 1, an output mirror 5 that constitutes a resonator, and a wavelength selection grating 6. Further, the output mirror 5 is provided with a minute driving device (small driving means).
Piezo element 7 for controlling the resonator length, and this piezo element 7
A piezo driver 8 for driving the is provided. Further, a beam splitter 9 for splitting the laser light 22 emitted from the slave laser 2, a detector (detection means) 10 for detecting the waveform of the laser light 23 on the reflection side, a transient recorder 11, and a discharge power supply 12 are provided. ing.

In addition to the basic structure as described above, the present embodiment further has the following structure. That is, the transient recorder 11 has
A computer (control means) 13 for measuring the oscillation delay time is connected, and the computer 13 passes through a D / A converter 14
It is connected to the piezo driver 8. In this case, the computer 13 is configured to change the drive voltage of the piezo driver 8 to drive the piezo element 7 and change the resonator length of the slave laser 2 based on the measured oscillation delay time. ..

In the laser oscillator of the present invention having the above-mentioned structure, the weak laser light 21 from the master laser 1 is introduced into the slave laser 2 and the slave laser 2
When the oscillation frequency of the master laser 1 and the longitudinal mode frequency of the slave laser 21 are tuned, the following operation is performed. That is, first, a part of the laser light 22 emitted from the slave laser 2 is reflected by the beam splitter 9, the reflected laser light 23 is received by the detector 10, and the laser waveform of the laser waveform is sent to the computer 13 via the transient recorder 11. Send data. At the same time, the waveform of the discharge power source 12 of the slave laser 2 is sent to the transient recorder 11, and the laser waveform data is used as the trigger waveform when sent to the computer 13. Further, the waveform of the discharge power supply 12 is used as the reference time, the time of 50% of the peak value of the laser waveform is the oscillation start time until the rise of the laser waveform, and the oscillation delay time is from the reference time to the oscillation start time. ..

Then, in order to measure the oscillation delay time of the laser light, the slave laser 2 is pulsed. In this case, in order to obtain the minimum value of the oscillation delay time, the piezo element 7 is moved from 0 V to the position where the hysteresis curve is substantially linear as shown in FIG. Is moved in a minute step to a position corresponding to, and the resonator length is changed. Here, when the minimum value of the oscillation delay time is obtained, the piezo element 7 is once returned to 0 V and then moved so as to have the minimum value. While the oscillation delay time does not increase significantly from the minimum value, the piezo element 7
Is moved in the vicinity of the minimum value by a small step. When the oscillation delay time significantly increases from the minimum value, the piezo element 7 is inverted to reverse the direction in which the resonator length changes. Subsequently, the piezo element 7 is moved in small steps near the minimum value of the oscillation delay time. Further, when the piezo element 7 is inverted, in the first step, a voltage value which is 15 times the driving voltage for moving the vicinity of the minimum value is applied due to the hysteresis characteristic of the piezo element 7.

By repeating the above operation, a smooth laser waveform with an injection lock can be obtained as the waveform of the laser beam 22 of the slave laser 2. Even if the cavity length of the slave laser 2 changes due to external influences such as heat, by repeating the above operation, a smooth laser waveform with an injection lock can always be obtained.

In the above embodiment, the beam splitter is arranged outside the output mirror of the slave laser to obtain the monitor light. However, the monitor light is obtained in the vicinity of the injection mirror to obtain the laser light of the slave laser. A configuration for measuring the waveform is also possible. In addition, in the above-described embodiment, when measuring the oscillation delay time, the rise time of the laser beam is set to 50 times the peak value of the laser waveform.
Although the time of the value of% is the oscillation start time of the laser waveform, the oscillation start time can be set freely. For example, an arbitrary two points of the laser waveform (for example, two points of 20% and 80% of the peak value of the waveform) having the peak value of the laser waveform as the oscillation start time are connected to oscillate a point intersecting with the 0 level. A configuration such as the start time is possible.

[0028]

As described above, according to the present invention,
A minute driving means for adjusting the cavity length of the slave laser;
Based on the detection means for monitoring the waveform of the laser light from the slave laser and the waveform of the monitored laser light,
By using the control means for controlling the minute driving means, it is possible to constantly obtain a smooth laser waveform locked with the injection regardless of external influences such as heat. A laser oscillator according to the method can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a laser oscillator by an injection method of the present invention.

FIG. 2 is a characteristic diagram showing a hysteresis curve of a piezo element.

FIG. 3 is a configuration diagram showing an example of a conventionally used injection type laser oscillator.

[Explanation of symbols]

 1 ... Master laser (driving side laser oscillator) 2 ... Slave laser (driven side laser oscillator) 3 ... Stabilizer 4 ... Injection mirror (splitting means) 5 ... Output mirror 6 ... Grating 7 ... Piezo element (fine driving means) 8 ... Piezo Driver 9 ... Beam splitter 10 ... Detector (detection means) 11 ... Transient recorder 12 ... Discharge power supply 13 ... Computer (control means) 14 ... D / A converters 21-23 ... Laser light

Claims (3)

[Claims] 1. A driving-side laser oscillator and a driven-side laser oscillator are provided, wherein the driving-side laser oscillator emits laser light that is a weak seed, and the driving-side laser light is introduced into the driven-side laser oscillator. , Configured to obtain a strong laser beam of the same quality as the laser beam on the driving side by using a gain of a strong laser excitation region of the driven-side laser oscillator,
In the injection type laser oscillator, a minute driving means for adjusting the resonator length of the driven side laser oscillator, a detection means for monitoring the waveform of the laser beam from the driven side laser oscillator, and a laser monitored by the detection means. An injection-type laser oscillator comprising a control means for controlling the minute driving means based on a light waveform. 2. The oscillation delay time, wherein the control means sets the rising portion of the waveform of the laser beam monitored by the detection means as an oscillation start time, and an oscillation delay time from a fixed reference time to the oscillation start time. The laser oscillator of the injection system according to claim 1, wherein the laser oscillator is configured to control the minute driving means based on the above. 3. The minute driving means is a means which is driven by a driving voltage and which does not linearly change with respect to a signal from the outside and has a hysteresis characteristic, and the control means comprises the minute driving means. In the case where the control means controls the drive voltage to always return to 0V at the start of control, and controls to reverse the direction of the minute drive means, The drive voltage of the first step of the control is configured to be applied with a voltage having a voltage value which is twice to several tens of times the drive voltage of the normal control step. Laser oscillator by injection method.