JPH05259561A - Injection lock tuning control equipment - Google Patents

Abstract

PURPOSE:To obtain an injection lock tuning control equipment of high frequency stability wherein the oscillation frequency of a resonator is stabilized by applying the oscillation frequency of a master laser to the reference. CONSTITUTION:A part of output pluse light from a laser resonator 5 and a part of light from a master laser 1 are led out as the respective monitor lights, and both of the monitor lights are superposed by using a beam splitter 23. The superposed monitor light is measured with a waveform measuring equipment 23. Based on the output thereof, the beat frequency caused by the frequency difference between the output pluse monitor light and the master laser monitor light is detected with a degitizer 25 and an FFT analyzer 26. On the basis of said beat frequency, the tuning states of the output pluse light and the master laser light are judged, and the optical length of the laser resonator 5 is controlled by using feedback mechanism constituted of a computer 27 and a piezocontroller 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuning control device for a laser resonator using an injection lock method.

[0002]

2. Description of the Related Art Generally, a pulsed pump laser oscillator is
Simultaneous oscillation occurs at a plurality of resonance frequencies determined by the optical resonator length of the laser resonator. Several methods have been used to oscillate this at a single frequency, one of which is the injection lock method.

A laser resonator using the injection lock method combines a parent laser (hereinafter referred to as a master laser) and a child laser (hereinafter referred to as a slave laser) to obtain a weak seed from the master laser. The laser light to be transmitted to the slave laser resonator, using the gain of the strong laser excitation region of the slave laser resonator,
A powerful laser beam of the same quality as the master laser beam is obtained.

FIG. 8 shows an example of a conventionally used injection lock type laser resonator. That is, the light of the master laser 1 oscillated at a single frequency in advance is adjusted to a required intensity by the attenuator 2 and injected into the slave laser resonator by the folding mirror 3 and the injection mirror 4. Using this injected master laser light as a seed, pulsed laser oscillation is grown to obtain a strong laser light.

As described above, the injection-lock type laser resonator can oscillate at a frequency determined by the frequency of the master laser. At this time, the oscillation frequency of the master laser and the resonance frequency determined by the cavity length of the slave laser cavity must match (tune). Therefore, the detector 8 for detecting the tuning state of the laser resonator, the feedback mechanism 9 for controlling the optical length of the laser resonator based on the detected signal, and the optical structure of the laser resonator according to the feedback signal. An injection lock tuning controller comprising a resonator length adjusting mechanism 10 for adjusting the length is provided and is configured to be able to control tuning.

By the way, conventionally, the following methods have been used as the method for detecting the tuning state and the feedback control method. (A) A method of performing feedback control so that the intensity of the master laser light output from the output mirror of the slave laser is maximized at the time of tuning, so that the intensity of the master laser light detected by the power meter is maximized. (B) Utilizing the fact that the delay time from the pulse excitation to the start of slave laser oscillation is minimized during tuning so that the slave laser oscillation delay time detected by the waveform measuring instrument is minimized. Feedback control method. (C) The output of the slave laser detected by the waveform measuring instrument (heterodyne measuring instrument) by utilizing that the slave laser oscillates at a plurality of resonance frequencies (longitudinal modes) when deviating from the single frequency oscillation state. Feedback control method to minimize the beat component between the longitudinal modes of the pulse.

[0007]

However, the injection lock tuning control device as described above has the following problems to be solved. That is, the above (a)
The method of detecting the intensity of the master laser light has a drawback that it does not necessarily match the tuning state in the oscillation state because the tuning state is determined during non-oscillation. Also, (b)
The method of detecting the oscillation delay time has a drawback that the oscillation frequency stability is poor because the region where the oscillation delay time is the minimum has a frequency width. Further, the method (c) for detecting beats between longitudinal modes has a drawback that it lacks frequency stability because it only maintains a single frequency oscillation state in which longitudinal mode beats do not appear. As described above, the problem of improving the oscillation frequency stability remains in any of the conventional methods.

The present invention has been proposed in order to solve the above-mentioned drawbacks of the prior art, and its purpose is not only to maintain a single frequency oscillation state, but also to change the oscillation frequency of a master laser oscillation. An object of the present invention is to provide an injection lock tuning controller that stabilizes on the basis of frequency.

[0009]

To achieve the above object, the invention of claim 1 extracts a part of the output pulse light from the laser resonator and a part of the master laser light as respective monitor lights. , An optical system that superimposes both monitor lights, a waveform measuring instrument for measuring the waveform of the superposed monitor lights, and an output based on the output of the waveform measuring instrument, depending on the frequency difference between the pulse monitor light and the master laser monitor light. A feedback mechanism that detects the beat frequency that occurs, determines the tuning state of the output pulse light and the master laser light based on the detected beat frequency, and sends out a signal that controls the optical length of the laser resonator, A resonator length control mechanism for adjusting the optical length of the laser resonator by a control signal is provided.

According to a second aspect of the present invention, in addition to the first aspect of the invention, means for measuring an oscillation delay time from the pulse excitation until the oscillation of the output pulsed light is started, and the waveform measuring instrument. The beat frequency generated by the frequency difference between the output pulse monitor light and the master laser monitor light is detected based on the output of the laser, and the tuning state of the output pulse light and the master laser light is determined based on the detected beat frequency, and the laser resonance In addition to sending a signal to control the optical length of the instrument, in a region below the measurement limit of the beat frequency, a feedback mechanism that sends a control signal that minimizes the oscillation delay time, and this control signal A resonator length control mechanism for adjusting the optical length of the laser resonator is provided.

According to a third aspect of the present invention, a master laser frequency measuring optical system for extracting a part of the master laser light as master laser monitor light, and an output of the master laser frequency measuring optical system are fed back to the master laser, In an injection lock tuning controller equipped with a master laser frequency stabilizing feedback mechanism for stabilizing the frequency of the master laser light, a part of the output pulse light from the laser resonator is used as a monitor light in an optical system for measuring the master laser frequency. An optical system for guiding and an output pulse monitor photodetector for extracting and detecting output pulse monitor light from the master laser frequency measurement optical system,
Based on the output of the output pulse monitor photodetector, the output pulse monitor optical frequency is detected, the tuning state of the output pulse light and the master laser light is determined based on the detected frequency, and the optical frequency of the laser resonator is determined. It is characterized in that a feedback mechanism for sending a signal for controlling the length and a resonator length control mechanism for adjusting the optical length of the laser resonator by the control signal are provided.

[0012]

According to the invention of claim 1 having the above construction,
By measuring a waveform obtained by superimposing a part of the output pulsed light and a part of the master laser light, the frequency difference between the output pulsed light and the master laser light can be detected as the frequency of the beat generated in the measured waveform, By performing feedback control so that the beat frequency is kept constant, the oscillation frequency of the output pulsed light can be kept stable with the oscillation frequency of the master laser as a reference.

According to the second aspect of the present invention, by detecting the frequency difference from the master laser from the beat frequency detected by the waveform measuring instrument, it is possible to suppress malfunction and increase in jitter due to the control of only the oscillation delay time, and further to further improve the beat frequency. By controlling so that the oscillation delay time is minimized under the measurement limit, the oscillation frequency of the output pulsed light can be maintained in a stable state.

According to the third aspect of the present invention, the master laser frequency measurement optical system stabilizes the frequency of the master laser, and the master laser frequency measurement optical system is used to measure the frequency of the output pulsed light. By performing feedback control so as to maintain a constant frequency difference from the oscillation frequency, the oscillation frequency of the output pulsed light can be maintained in a stable state.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings starting from FIG. (1) First Embodiment ... FIGS. 1 and 2 The first embodiment is an embodiment corresponding to the invention of claim 1. In the first embodiment, a master laser monitor light extraction beam splitter 21 is provided on the output side of the master laser 1 via an attenuator 2, and a part of the master laser light is emitted from this monitor light extraction beam splitter 21. Is reflected by and injected into the slave laser discharge unit 5 via the injection mirror 4. The other part of the master laser light is used as the master laser monitor light, and the light extraction beam splitter 21 is used.
To the tuning optics. On the other hand, a slave laser monitor light extraction beam splitter 22 is provided on the output side of the output mirror 6 of the slave laser, and a part of the output pulse light from the slave laser discharge unit 5 becomes slave laser output light. The light is extracted to the outside, and the other part is taken out from the monitor light extraction beam splitter 22 to the tuning control optical system as the monitor light of the slave laser output pulse.

In the tuning control optical system, the master laser monitor light extraction beam splitter 21 and the slave laser monitor light extraction beam splitter 22 are followed by a superimposing beam of monitor light from both beam splitters 21 and 22. Splitter 23
Is provided. A waveform measuring instrument 24 is connected to the latter stage of the beam splitter 23 for superposition, and a digitizer 25 for converting the output signal into a digital signal and an FFT (fast Fourier transform) for frequency analysis are provided on the output side of the waveform measuring instrument 24. ) An analyzer 26, a calculator 27 that calculates and outputs a signal for changing the resonator length so that the obtained beat frequency is constant, a piezo controller 28 that controls a piezo element 29 according to a signal from the calculator 27, and Piezo elements 29 for sequentially changing the resonator length according to the output signal of the piezo controller 28 are sequentially provided.

In the first embodiment having such a structure, the master laser 1 oscillates laser light of a single frequency as shown in FIG. A part of this master laser light is reflected by the master laser monitor light extraction beam splitter 21 and injected into the discharge portion 5 of the slave laser resonator through the injection mirror 4. When the frequency of this master laser light is close to the resonance frequency of the slave laser resonator, the slave laser oscillates at a single frequency at the resonance frequency closest to the master laser frequency. That is, as shown in FIG. 2B, slave laser light having a frequency difference Δf with respect to the master laser light is oscillated.

The slave laser light is extracted from the output mirror 6 to the outside of the slave laser resonator, a part of the light is extracted from the extraction beam splitter 22 as slave laser monitor light, and the superposition beam splitter is further used. Sent to 23. On the other hand, a part of the master laser light is extracted as the master laser monitor light from the master laser monitor light extraction beam splitter 21, and is further sent to the superposition beam splitter 23. When the waveforms of the monitor lights of the master laser and the slave laser, which are superposed by the superposing beam splitter 23, are measured by the waveform measuring device 24, a detection waveform as shown in FIG. 2C is obtained.

The detected waveform signal thus obtained is
When digitized by the digitizer 25 and frequency-analyzed by the FFT analyzer 26, the beat frequency component of the frequency difference between the master laser light and the slave laser light is
It is detected as shown in FIG. Therefore, a signal that keeps the beat frequency thus obtained constant is sent from the computer 27 to the piezo controller 28, and the slave laser resonator length is changed using the piezo element 29. By doing so, the oscillation frequency of the slave laser light can be always maintained at a constant oscillation frequency with the oscillation frequency of the master laser as a reference. In particular, when the resonator length is controlled so that the beat frequency becomes 0 Hz, it is possible to maintain the tuning state in which the oscillation frequency of the slave laser always matches the oscillation frequency of the master laser.

FIG. 3 shows a modification of the first embodiment in which the monitor light of the master laser and the monitor light of the slave laser are taken out from the injection mirror 4. According to this modification, the monitor light of the master laser is taken out as the transmitted light of the injection mirror 4, the output pulse monitor light of the slave laser is taken out as the reflected light of the injection mirror 4, and after being superposed on the injection mirror 4. , And enters the waveform measuring device 24. In the following, the oscillation frequency of the slave laser light can always be kept at a constant oscillation frequency with the oscillation frequency of the master laser as a reference by the same operation as that of the first embodiment.

(2) Second Embodiment ... FIG. 4 The second embodiment is an embodiment corresponding to the invention of claim 2. By the way, in the invention of claim 1 shown in the first embodiment, since the measurement limit frequency is determined by the pulse width,
After the oscillation pulse width becomes shorter and the beat frequency falls below the measurement limit, control becomes impossible and frequency stability deteriorates. Therefore, in the invention of claim 2, in the region below the measurement limit of the beat frequency, the fact that the delay time from the pulse excitation until the oscillation of the slave laser starts is minimized at the time of tuning, Perform more precise control.

This second embodiment has a tuning control optical system similar to that of the first embodiment, and as shown in FIG.
On the output side of the master laser 1, a beam splitter 2 for extracting the master laser monitor light is provided via an attenuator 2.
1 is provided, and a part of the master laser light is reflected by the monitor light extraction beam splitter 21 and injected into the slave laser discharge unit 5 via the injection mirror 4. The other part of the master laser light is extracted from the light extraction beam splitter 21 to the tuning optical system as master laser monitor light. On the other hand, a beam splitter 22 for extracting the slave laser monitor light is provided on the output side of the output mirror 6 of the slave laser, and a part of the output pulse light of the slave laser becomes the slave laser output light and is extracted to the outside of the laser oscillator. The other part is taken out as slave laser monitor light from the monitor light extraction beam splitter 22 to the tuning control optical system.

In the tuning control optical system, the beam splitter 21 for extracting the master laser monitor light and the beam splitter 22 for extracting the slave laser monitor light are arranged at the subsequent stage of the beam splitter for superimposing the monitor lights from both beam splitters 21 and 22. 23 are provided. A waveform measuring instrument 24 is connected to the subsequent stage of the beam splitter 23 for superposition. The digitizer 2 for converting the output signal into a digital signal and measuring the oscillation delay time on the output side of the waveform measuring device 24
5 are provided. An FFT (Fast Fourier Transform) analyzer 26 for frequency analysis and a calculator 27 are sequentially connected to the output side of the digitizer 25. This calculator 27 changes the resonator length so that the beat frequency obtained by the analyzer 26 becomes constant and that the oscillation delay time measured by the digitizer 25 becomes the minimum in the region below the measurement limit of the beat frequency. This is to calculate and output a signal for making the signal. On the output side of the calculator 27, a piezo controller 28 for controlling the piezo element 29 according to the signal from the calculator 27 and a piezo element 29 for changing the resonator length according to the output signal of the piezo controller 28 are sequentially provided. There is.

In the second embodiment having such a structure,
Similar to the first embodiment, when the waveforms of the monitor light of the master laser and the slave laser superposed by the superposing beam splitter 23 are measured by the waveform measuring device 24, a detection waveform as shown in FIG. 2C is obtained. can get. When this detected waveform signal is converted into a digital signal by the digitizer 25 and frequency-analyzed by the FFT analyzer, the beat frequency component of the frequency difference between the master laser light and the slave laser light is detected as shown in FIG. 2 (d). At the same time, the digitizer 25 measures the oscillation delay time from the pulse excitation until the oscillation of the slave laser starts, and the measurement result is sent to the computer 27. Calculator 27
In Fig. 5, in the region where the oscillation frequency difference is larger than the beat frequency measurement limit by heterodyne measurement, a signal that keeps the obtained beat frequency constant is sent from the computer 27 to the piezo controller 28,
The slave laser resonator length is changed using the piezo element 29. On the other hand, in the region below the detection limit of the beat frequency, the computer 27 issues a command to minimize the oscillation delay time and controls the resonator length.

With this configuration, the oscillation frequency of the slave laser light can be kept at a constant oscillation frequency with reference to the oscillation frequency of the master laser with high precision.
In particular, in a conventional device that performs tuning control only by detecting the oscillation delay time, a large oscillation delay time is entered at regular intervals during control, and the variation (jitter) in the oscillation delay time increases, which causes malfunction. It had the drawback of being easy. However, according to this embodiment, the resonator length is controlled in advance so that the beat frequency becomes small,
Since the oscillation delay time is measured below the measurement limit of the beat frequency, malfunctions and increase in jitter due to control of only the oscillation delay time are suppressed, and more precise control is possible. In particular, as shown in FIG. 5, the oscillation delay time has a minimum value at the position where the difference in oscillation frequency is 0. Therefore, the oscillation delay time is measured and the feedback mechanism 9 is set so as to have the minimum value.
By controlling the resonator length control mechanism 10 by means of this, it becomes possible to perform precise synchronization between the master laser light and the slave laser oscillation light.

The invention according to claim 2 is not limited to the embodiment shown in the drawings, but as an optical system or a tuning control optical system for extracting the monitor light from each laser light, as shown in FIG.
It is possible to appropriately employ such as.

(4) Third Embodiment FIG. 6 The third embodiment is an embodiment corresponding to the invention of claim 3. By the way, in the inventions of claim 1 and claim 2,
On the assumption that the oscillation frequency of the master laser is stable, the oscillation frequency of the slave laser is stabilized with reference to the oscillation frequency of the master laser. But,
If the oscillation frequency of the master laser itself is not stabilized, the inventions of the first and second aspects will not be able to obtain sufficient effects. Therefore, the invention of claim 3 stabilizes the oscillation frequency of the master laser so that an excellent effect is exhibited when the oscillation frequency of the slave laser is stabilized with the oscillation frequency of the master laser as a reference. It was done.

In the third embodiment, as shown in FIG.
A beam splitter 31 for extracting a part of the master laser light as a master laser monitor light is provided on the output side of the master laser 1, and the monitor light of the master laser separated by the beam splitter 31 is used as a frequency measurement optical system 32. Have been introduced to. A detector 33 is connected to the frequency measuring optical system 32, and the frequency of the master laser monitor light is measured by the detector 33. The frequency of the measured master laser monitor light is
It is fed back to the master laser 1 by the frequency stabilizing feedback mechanism 34, and the frequency of the master laser light is stabilized based on this feedback information.

On the other hand, on the output side of the slave laser, a beam splitter 41 for extracting a part of the slave laser light as monitor light is provided, and the monitor light from this beam splitter 41 is passed through a reflection mirror 42 to measure the frequency. It is introduced into the optical system 32. The frequency measurement optical system 32 includes a slave laser monitor photodetector 43.
The frequency of the slave laser monitor light is detected by the detector 43, and the feedback mechanism 9 is arranged so that the frequency of the slave laser monitor light detected here and the oscillation frequency of the slave laser maintain a constant frequency difference. By the slave laser cavity length control mechanism 10
Is controlled.

FIG. 7 shows the embodiment of FIG. 6 more specifically, in which a stabilizing etalon 44 is used as the optical system 32 for frequency measurement. In this embodiment, a part of the oscillation light of the master laser 1 is introduced as a monitor light into the stabilizing etalon 44 via the master laser monitor light extraction beam splitter 31 and the beam splitter 45, and the introduced monitor is introduced. The light is extracted by the beam splitter 46 to the detector 33, and its frequency is detected. Here, when the optical length of the stabilized etalon is L and the speed of light is c, when the frequency f _{m of the} master laser is f _m = n · c / 2L (n; positive integer), the transmission of the stabilized etalon Since the characteristic shows a sharp peak, the master laser oscillation frequency is stabilized by the frequency stabilizing feedback mechanism 34 so that the detection intensity of the monitor light becomes maximum.

On the other hand, a part of the output pulse of the slave laser light is extracted by the slave laser monitor light extraction beam splitter 41 as monitor light.
This slave laser monitor light is introduced into the stabilizing etalon 44 via the reflection mirror 42 and the beam splitter 45, and then output to the slave laser monitor photodetector 43 via the beam splitter 46. The feedback mechanism 9 controls the resonator length control mechanism 10 so that the monitor light output intensity from the monitor light detector 43 is maximized. That is, from the characteristics of the stabilized etalon, the oscillation frequency f _s of the slave laser is stabilized at f _s = f _m + m · c / 2L (m; positive integer). As described above, according to the embodiment of FIG. 7, the oscillation frequency of the slave laser can always be kept stable with the oscillation frequency of the master laser as a reference.

[0032]

As described above, the first to third aspects are provided.
In any of the above aspects, since the oscillation frequency of the slave laser is stabilized with the oscillation frequency of the master laser as a reference, it is possible to obtain an injection lock tuning controller with high oscillation frequency stability. In particular, according to the second aspect of the invention, the oscillation frequency can be stabilized even in the region below the measurement limit value of the beat frequency, and the frequency can be stabilized with higher accuracy. Further, in the invention of claim 3, the slave laser oscillation frequency can be stabilized by stabilizing the oscillation frequency of the master laser, and at the same time, the master laser oscillation frequency measuring optical system can be used as it is for the slave laser oscillation frequency measurement. Therefore, it is possible to simplify the optical system.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing an output waveform of each part in the first embodiment of the present invention.

FIG. 3 is a block diagram showing a modification of the embodiment of FIG.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is a graph showing a relationship between an oscillation frequency or an oscillation delay time and a resonator length.

FIG. 6 is a block diagram showing a third embodiment of the present invention.

FIG. 7 is a block diagram showing a specific example of the embodiment of FIG.

FIG. 8 is a block diagram showing an example of a conventional injection lock tuning control device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Master laser 2 ... Attenuator 4 ... Injection mirror 5 ... Slave laser discharge part 6 ... Output mirror 7 ... Rear mirror 21 ... Master laser monitor beam extraction beam splitter 22 ... Master laser monitor beam extraction beam splitter 23 ... Monitor beam overlap Beam splitter for alignment 24 ... Waveform measuring instrument 25 ... Digitizer 26 ... FFT analyzer 27 ... Calculator 28 ... Piezo controller 29 ... Piezo element

Claims (3)

[Claims] 1. An optical system for extracting a part of output pulse light from a laser resonator and a part of master laser light as respective monitor lights and superposing both monitor lights, and a waveform of the superposed monitor lights. A waveform measuring instrument for measuring, detects the beat frequency generated by the frequency difference between the output pulse monitor light and the master laser monitor light based on the output of the waveform measuring instrument, and outputs the pulse light based on the detected beat frequency. And a feedback mechanism that sends out a signal that controls the optical length of the laser resonator by determining the tuning state of the master laser light, and a resonator length control mechanism that adjusts the optical length of the laser resonator by this control signal. An injection lock tuning control device comprising: 2. A means for measuring an oscillation delay time from the pulse excitation until the oscillation of the output pulse light is started, and output pulse monitor light and master laser monitor light based on the output of the waveform measuring instrument. Detects the beat frequency generated by the frequency difference, determines the tuning state of the output pulse light and the master laser light based on the detected beat frequency, and sends a signal for controlling the optical length of the laser resonator, In a region below the measurement limit of the beat frequency, a feedback mechanism that sends a control signal that minimizes the oscillation delay time, and a cavity length control that adjusts the optical length of the laser cavity by this control signal. The injection lock tuning control device according to claim 1, further comprising a mechanism. 3. A master laser frequency measuring optical system for extracting a part of the master laser light as a master laser monitor light, and an output of the master laser frequency measuring optical system is fed back to the master laser to obtain a master laser light frequency. In an injection lock tuning controller equipped with a master laser frequency stabilizing feedback mechanism that stabilizes, an optical system that guides a part of the output pulse light from the laser resonator to the master laser frequency measurement optical system as monitor light, An output pulse monitor photodetector that takes out and detects the output pulse monitor light from the master laser frequency measurement optical system, and detects the output pulse monitor optical frequency based on the output of the output pulse monitor photodetector. Output pulse light based on the frequency and master It is equipped with a feedback mechanism that determines the tuning state of the laser light and sends out a signal that controls the optical length of the laser cavity, and a cavity length control mechanism that adjusts the optical length of the laser cavity with this control signal. An injection lock tuning control device characterized in that