JPS6018983A - Q-switched solid-state laser - Google Patents

Abstract

PURPOSE:To obtain stabilized output by a method wherein a probe laser beam subjected to an amplitude modulation at a period shorter than the fluorescent lifetime of the laser rod of a Q-switched solid-state laser is detected; a component, which synchronizes with the solid-state laser, is extracted from the output, and a Q-switching is started at a point when the output traverses the prescribed value. CONSTITUTION:In addition to the conventional circuits, polarizing plates 11 and 12 have been anew provided at both ends of a laser rod 13 as well as a probe laser 13 has been provided with the laser rod 3 along the optical axis of the resonator and an HPF14 and a detector 15 have been provided between a photo detector 5 and a comparator 7. Moreover, the cut-off frequency of the HPF14 has been chosen between a frequency, which is decided by the inverse number of the fluorescent lifetime of the rod 3, and the modulation frequency of the probe laser beam, and when the probe laser beam is in an ON state, the amplified probe laser beam and the fluorescent are light- received, and in a condition that the probe laser beam is in an OFF state, the fluorescent only is light-received. At this time, the circuit 15 performs the envelope detection of output amplitude of the HPF14 and when the output traverses the threshold value with the comparator, the Q-switching starting signal is generated from a driver 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Q-switched solid-state laser device with high output stability.

In recent years, as the application of Q-switched solid-state lasers to precision processing, measurement, etc. has progressed, Q-switched solid-state laser devices with high output stability have been sought after.

A fluorescent monitor Q-switch method is known as one of the conventional methods for stabilizing laser output.

FIG. 1 shows an example of this conventional method, and FIG. 2 shows a timing chart of its operation. In FIG. 1, a high reflectance reflector 1. Q switch? Element 2.
Laser rod 3. Output mirror 4. Q Sui, Chi Driver 9. A photodetector 5 for detecting the fluorescence from the laser rod 3 to the solid-state laser coming from the excitation unit IO. Amplifier 6. A comparator 7 and a fall detection circuit 8 are added.

In Figure 2, from the top, the fluorescence, comparator output signal,
The waveforms of the Q-switch trigger signal, resonator loss, and Q-switch pulse are shown.

Next, the operation of this conventional device will be explained in more detail with reference to FIG. When the laser rod 3 is excited by the excitation unit 10, energy is accumulated in the laser rod 3 in the form of population inversion. If this energy fluctuates, the energy of the Q-switch pulse will fluctuate. Since the fluorescence intensity from the laser starting level is proportional to the distribution density of the laser starting level, fluctuations in excitation energy appear as changes in the amplitude of the fluorescent light waveform. Therefore, by performing Q-switching under the condition that the fluorescence is constant, that is, the distribution density of the starting level is constant, the Q
Fluctuations in switch pulse energy can be suppressed to a certain degree. In the configuration of this conventional device, the comparator 7 determines the point at which the intensity of fluorescent light reaches a predetermined value.

The falling timing of the pulse generated by the comparator 7 is detected by the falling detection circuit 8, and a Q-switch start signal is sent to the Q-switch driver 9 to start the Q-switch.

However, this conventional device has the following drawbacks. As mentioned above, the fluorescence intensity is proportional to the distribution density of the laser starting level, but does not reflect the distribution density of the laser ending level. For this reason, in a three-level laser, the distribution density of the final level changes greatly with the temperature of the laser rod 3, so the output stability of the laser cannot be improved only with the conventional configuration.

Although it is not as noticeable in a 4-level laser as in a 3-level laser, when the energy difference between the base level and the final laser level is small, the influence of the wetness of the laser rod 30 appears in the output fluctuation. In this case, it may be sufficient to stabilize the temperature of the laser cooling medium, but if the repetition of the Q-switch pulse is changed, the temperature at the center of the laser rod 3, which contributes to laser oscillation, will change, causing output fluctuations. This has the disadvantage of being inconvenient in practice.

Furthermore, the fluorescent light from the laser rod 3 has poor directivity, and the fluorescent light from the periphery of the laser rod 3, which is not related to laser oscillation, mixes with the fluorescent light from the center of the laser rod 3 and is detected by the photodetector. 5. For this reason, if non-uniform excitation is performed within the laser rod 3, fluorescent light will be received from parts that do not contribute to laser oscillation, making it difficult to obtain high ψ output stability. .

An object of the present invention is to provide a Q-switched solid-state laser device that overcomes the above-mentioned drawbacks. According to the present invention, there is no decrease in output stability due to fluctuations in excitation of the laser rod, temperature fluctuations in the laser rod, or changes in repetition rate, and high ψ
A Q-switched solid-state laser device that maintains output stability is obtained.

The Q-switched solid-state laser device of the present invention includes a Q-switched solid-state laser and a probe that emits puss laser light having the same oscillation wavelength as the solid-state laser and whose amplitude is modulated at a cycle sufficiently shorter than the fluorescence lifetime of the laser rod of the solid-state laser. means for making the probe laser beam incident on the laser rod along the optical axis of the laser and the resonator of the solid-state laser; a photodetector that receives the probe laser beam that has passed through the laser rod; and a photodetector that receives the probe laser beam that has passed through the laser rod; The configuration is characterized by comprising a circuit that extracts and detects a signal component from the photodetector, and a circuit that detects a point in time when the output after the detection crosses a predetermined value and generates a Q-switch start signal. ing.

The feature of the present invention is that instead of the conventional method of monitoring the distribution density of the laser starting level, the amplification factor proportional to the population inversion density is directly monitored, and under the condition that this amplification factor is kept constant, the output stability is significantly improved. The purpose is to perform an excellent Q-switch.

Next, the present invention will be explained in detail using the drawings.

FIG. 3 is a block diagram of an embodiment of the present invention, and the structure and names are the same as in FIG. 1 except for the following points.

In FIG. 3, what is newly added to FIG. 1 are polarizing plates 11 and 12 at both ends of the laser rod 3. 10 - blazer 13. on the laser rod 3 along the optical axis of the resonator. A high-pass filter circuit 14 and a detection circuit 15 are provided between the photodetector 5 and the comparator 7. The wavelength of the push laser light is equal to the oscillation wavelength of the laser device,
The light is interrupted for a sufficiently shorter time than the fluorescent life of the laser rod 3.

If the direction of polarization is perpendicular to the direction of polarization of the solid-state laser, the loss due to the polarizing plates 11 and 12 will be reduced.

Further, the photodetector 5 is arranged in the direction in which the probe laser beam that has passed through the laser rod 3 is reflected by the polarizing plate 11 and proceeds. FIG. 4 is a diagram showing a timing chart of signal processing. In Fig. 4, the horizontal axis is time, and the vertical axis is the output of the photodetector, the output of the high-pass filter circuit 14, the output of the detection circuit 15, and the output of the comparator 7, starting from the top. It shows.

The timing after comparator 7 is the same as in the conventional fluorescent monitor Q-switch method. The cutoff frequency of the high-pass filter circuit 14 is selected between the frequency determined by the reciprocal of the fluorescence lifetime of the laser rod 3 and the modulation frequency of the probe laser beam. The light reception signal waveform of the photodetector 5 is the fourth
As shown in the figure, the amplified probe laser light and the fluorescent light from the laser rod 3 appear to overlap. When the probe laser beam is present, the amplified slope laser beam and fluorescent light are received, and when the probe laser beam is off, only the fluorescent light is received. The high-pass filter circuit 14 has the function of removing fluorescent components, as shown in FIG. The detection circuit 15 has the function of performing envelope detection of the output amplitude of the high-pass filter circuit 14, and as a result, it is possible to extract a signal proportional to the amplification factor of the probe laser beam.

In addition, although the above explanation shows an example in which the probe laser beam is modulated intermittently, the same effect can be obtained by using sinusoidal wave modulation.

A configuration diagram of another embodiment of the present invention is shown in FIG.

In FIG. 5, the configuration and names other than the signal processing section between the photodetector 5 and the comparator 7 are the same as in FIG. 3. Fifth
The signal processing section shown in the figure is a differential circuit that outputs a difference signal between the output signals of first and second sample and hold circuits 16 and 17 that sample and hold the output of the photodetector 5 in synchronization with the intermittent period of the probe laser beam. It consists of an amplifier 18. The first sample and hold circuit 16 performs a sample and hold operation when the probe laser beam is present, and the second sample and hold circuit 17 performs a sample and hold operation at a timing when the probe laser beam is cut off. The time constants of the first and second sample and hold circuits are set to be longer than the intermittent period of the probe laser beam, and are set so that the outputs of the first and second sample and hold circuits change smoothly.

FIG. 6 is a diagram showing a timing chart in the configuration of FIG. 5. FIG. 6 shows, from the top, the output of the photodetector 5, the output of the first sample and hold circuit 16, the output of the second sample and hold circuit 17, and the output of the differential amplifier 18.

As shown in FIG. 6, the first sample and hold circuit 16 detects the upper envelope of the output of the photodetector 5, and the second sample and hold circuit 17 detects the lower envelope of the output of the photodetector 5. Output each. The differential amplifier 18 outputs the entire output difference between the first and second sample and hold circuits 16 and 17. In other words, as in the embodiment shown in FIG. 3, only a signal proportional to the amplification factor of the laser rod 3 from which the fluorescent component has been removed can be output. In the embodiment shown in FIG.
sample and hold circuits 16 and 17 and differential amplifier 18
By inserting a low-pass filter circuit in which the intermittent frequency of the probe laser beam is low and the cutoff frequency is higher than the frequency determined by the reciprocal of the fluorescence lifetime,
The population inversion density at the start of oscillation can be determined with higher accuracy.

In addition, in FIGS. 3 and 5, polarizing plates 11 and 12
It is not necessarily necessary to arrange the positions on both sides of the laser rod 3. For example, if one polarizing plate is placed outside the output mirror 4, there is an advantage that alignment of the resonator becomes easier.

The advantages of the present invention other than direct monitoring of population inversion are that the intensity of the probe laser beam can be easily made stronger than the fluorescent light intensity, and that the signal-to-noise ratio of the photodetector output can be increased by using the directivity of the probe laser beam. It is possible to get a high price. 87N
If the ratio can be made high, the timing for starting the Q-switch can be determined more accurately than in the conventional fluorescent monitor Q-switch method, and the output stability can be further improved.

However, if the probe laser beam is concentrated near the center of the laser rod 3 and transmitted, the influence of fluorescence from the periphery of the four parts 1, which was a problem with the conventional fluorescent monitor Q switch method, can be reduced. Therefore, only the population inversion density of the portion contributing to laser oscillation can be monitored with higher accuracy.

In the embodiments shown in FIGS. 3 and 5, the polarizing plates 11 and 12 allow the polarization plane of the Q-switch optical pulse to be directly aligned with the polarization plane of the probe laser beam, so that high-performance branching ability can be achieved. If a similar polarizing plate is used, there is almost no fear that the probe laser 13 and photodetector 5 will be damaged by the Q-switched optical pulse.

The present invention has been explained above using two examples, but
It is also possible to use the pond configuration without losing the EF feature of the present invention of monitoring the amplification amount of the laser rod 3 in real time. For example, if a filter, aperture, or lens to select and receive the probe laser beam is inserted in front of the photodetector 5, as is done in the conventional fluorescent monitor Q-switch method, only the signal can be transmitted. can be measured. Furthermore, an optical isolator can be placed between the probe laser 13 and the solid-state laser to suppress output fluctuations of the probe laser light due to returned light.

Furthermore, in the process of signal processing, it is obvious that an amplifier is placed after the photodetector 5 to increase the s/Iq ratio.

FIG. 1 is a block diagram showing an example of the conventional return monitor Q-switch method, and FIG. 20 is a timing chart showing the operation of the fluorescent monitor Q-switch method shown in FIG. ; Light communication intensity, comparator output signal,
The Q-switch trigger signal resonator loss and the waveform of the Q-switch pulse are shown.

3 and 5 are respectively configuration diagrams of one embodiment of the present invention, and FIGS. 4 and 6 are diagrams showing timing charts of operations in the configurations shown in FIGS. 43 and 5, respectively. be. In Figure 4, from the top, Ml (light, ) (output output, high-pass transmission filter circuit output, detection circuit output, converter output) are shown.
In Fig. 6, from the top, the photodetector output and the first sample and hold circuit are shown.

The output of the second sample and hold circuit, the output of the differential amplifier, and the comparator wide output are shown.

In the figure, 1 is a high reflectance mirror, 2 is a Q-switch element, 3 is a laser rod, 4 is an output bowl, 5 is a photodetector, and 6
is an amplifier, 7 is a comparator, 8 is a falling detection circuit, 9 is a Q-switch driver, 10 is an excitation unit, 1
1 and 12 are deflection plates, 13 is a prism laser, 14 is a high-pass transmission filter, 15 is a detection circuit, 16 is a first sample and hold circuit, 17 is a second sample and hold circuit, and 18 is a differential amplifier 1II11 It is a vessel.

Figure 73 Figure 4

Claims (1)

[Claims] A Q-switched solid-state laser consisting of a Q-switched driver, an excitation unit, a pair of reflecting mirrors, a Q-switched element and a laser rod installed between the reflecting mirrors, and a laser whose oscillation wavelength is the same as that of the solid-state laser; A probe laser that emits a probe laser beam whose amplitude is modulated at a cycle sufficiently shorter than the fluorescence lifetime of the rod; a means for making the probe laser beam incident on the laser rod along the optical axis of a resonator of the solid-state laser; and the laser. A photodetector that receives the probe laser beam that has passed through the rod, a circuit that extracts and detects a signal component from the photodetector that changes with the period, and detects a point in time when the output after the detection cuts off a predetermined value -. A Q-switch solid-state laser device comprising: a circuit for generating a Q-switch start signal.