JP2015095536A - Pulse laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pulse laser device capable of outputting a pulse having pulse energy that is stable even if environmental temperature changes or secular change occurs, regardless of whether it is a giant pulse.SOLUTION: A pulse laser device includes a semiconductor laser 1 generating the exciting light, a solid laser medium 2 generating laser light in response to the exciting light from the semiconductor laser, a RF signal generating section 5 for generating a RF signal, an acoustic optical element 3 for modulating the laser light generated in the solid laser medium in accordance with the RF signal generated in the RF signal generating section, and a resonator 10 constituted by sandwiching the solid laser medium and acoustic optical element between mirrors. When the repetition period of pulse is longer than the fluorescence lifetime of the solid laser medium, the RF signal generating section controls the power of the RF signal to a predetermined value at least for the fluorescence lifetime.

Description

  The present invention relates to a pulse laser device that performs stabilization control of an RF (Radio Frequency) signal necessary for a Q-switched pulse laser, and in particular, APC (Auto Power Control) depending on a fluorescence lifetime of a solid-state laser medium and an OFF time of an RF signal. The present invention relates to a pulsed laser apparatus that performs

  As a conventional pulse laser device, for example, the one described in Patent Document 1 is known.

  This pulse laser device includes a semiconductor laser that generates excitation light, a solid-state laser medium that generates laser light in response to the excitation light, an acoustooptic device that modulates laser light generated by the solid-state laser medium, and an RF signal. An RF signal generation unit that generates and supplies the acoustooptic element, a resonator configured by sandwiching a solid-state laser medium and the acoustooptic element between mirrors, and a control circuit that maintains the RF signal power at a predetermined value. ing.

  This predetermined value is a value set on the basis of the minimum RF signal power that causes an allowable variation by measuring the variation of the pulse laser with respect to the power of the RF signal by changing the power of the RF signal.

  As described above, in Patent Document 1, when a giant pulse having a long pulse repetition period is generated, power saving and miniaturization are realized by minimizing the RF signal while monitoring variations in pulse energy. .

JP 2012-129220 A

  However, in the pulse laser device described in Patent Document 1, when the environmental temperature changes abruptly, the variation due to temperature increases, and this cannot be dealt with.

  In the case of a pulse that is not a giant pulse, that is, when the pulse repetition period is short, the configuration of Patent Document 1 cannot cope with it.

  An object of the present invention is to provide a pulse laser device capable of outputting a pulse having stable pulse energy regardless of whether it is a giant pulse or not even if an environmental temperature change or a change with time occurs.

  In order to solve the above problems, the invention of claim 1 generates a semiconductor laser that generates excitation light, a solid-state laser medium that generates laser light in response to excitation light from the semiconductor laser, and an RF signal. An RF signal generation unit, an acousto-optic device that modulates laser light generated by the solid-state laser medium according to the RF signal generated by the RF signal generation unit, and the solid-state laser medium and the acousto-optic device are mirrored. The RF signal generation unit, when the pulse repetition period is longer than the fluorescence lifetime of the solid-state laser medium, the RF signal power is predetermined for at least a time longer than the fluorescence lifetime. It is characterized by being controlled to a value.

  According to a second aspect of the present invention, there is provided a semiconductor laser that generates pumping light, a solid-state laser medium that generates laser light in response to pumping light from the semiconductor laser, an RF signal generation unit that generates an RF signal, and the RF signal An acoustooptic device that modulates laser light generated by the solid-state laser medium according to an RF signal generated by the generator, and a resonator configured by sandwiching the solid-state laser medium and the acoustooptic device with a mirror. The RF signal generation unit controls the power of the RF signal to a predetermined value during the ON period of the RF signal when the pulse repetition period is shorter than the fluorescence lifetime of the solid-state laser medium.

  According to a third aspect of the present invention, there is provided a semiconductor laser that generates excitation light, a solid-state laser medium that generates laser light in response to excitation light from the semiconductor laser, an RF signal generation unit that generates an RF signal, and the RF signal An acoustooptic device that modulates laser light generated by the solid-state laser medium according to an RF signal generated by the generator, and a resonator configured by sandwiching the solid-state laser medium and the acoustooptic device with a mirror. The RF signal generation unit controls the power of the RF signal to a predetermined value by feedback, and a time constant for determining the speed of the feedback is set to be equal to or longer than an OFF period of the RF signal. .

  According to the pulse laser device of the present invention, when the pulse repetition period is longer than the fluorescence lifetime of the solid-state laser medium, the RF signal power is controlled to a predetermined value for at least a time longer than the fluorescence lifetime, or the pulse repetition is performed. When the period is shorter than the fluorescence lifetime of the solid-state laser medium, the RF signal power is controlled to a predetermined value during the ON period of the RF signal, or the RF signal power is controlled to a predetermined value by feedback and the feedback speed is increased. Since the time constant to be determined is set to be longer than the off period of the RF signal, a pulse having stable pulse energy can be output regardless of whether it is a giant pulse or not even if the ambient temperature changes or changes with time. A pulse laser device can be provided.

It is a figure which shows the principle of operation of an acoustooptic device. It is a figure which shows the relationship between laser medium excitation time and pulse energy. It is a block diagram which shows the structure of the pulse laser apparatus which concerns on Example 1 of this invention. It is a figure which shows the structural example of the RF signal generation part in the pulse laser apparatus which concerns on Example 1 of this invention. It is a timing chart for demonstrating operation | movement of the pulse laser apparatus which concerns on Example 1 of this invention. It is a timing chart for demonstrating operation | movement of the pulse laser apparatus which concerns on Example 2 of this invention. It is a block diagram which shows the main structures of the pulse laser apparatus which concerns on Example 3 of this invention.

  Hereinafter, embodiments of the pulse laser device of the present invention will be described in detail with reference to the drawings.

  First, the operation principle of the acoustooptic device will be described with reference to FIG. When an acoustic wave is present in the acoustooptic device, it acts like a grating. This is called an acoustooptic effect. Incident laser light is diffracted by passing through the grating.

  By supplying an RF signal to the acoustooptic device, an acoustic wave is generated in the device as shown in FIG. As shown in FIG. 1B, the loss of the resonator is reduced and the pulse laser is generated at the timing when the supply of the RF signal is stopped. That is, a pulse laser can be output by controlling on / off of the RF signal.

  Also, the pulse energy increases monotonously with the time when the laser medium is excited. As shown in FIG. 2, the pulse energy becomes substantially the same level because it is in an equilibrium state even when excited for a time longer than the fluorescence lifetime.

  For this reason, when a giant pulse is output, APC control of the RF signal is performed at least during the fluorescence lifetime of the fixed laser medium, and the power of the RF signal is controlled to a predetermined value even if environmental temperature changes or changes with time occur. Thus, a pulse having stable pulse energy can be generated. Details of the present invention will be described in Example 1.

  If the RF signal is not a giant pulse, APC control is performed during the on period of the RF signal, and APC control is stopped only during the off period of the RF signal. Details of the present invention will be described in a second embodiment.

  Further, by setting the time constant of the feedback of APC control to be longer than the OFF period of the RF signal, a pulse having stable pulse energy can be generated. Details of the present invention will be described in a second embodiment.

  FIG. 3 is a block diagram showing a configuration of the pulse laser apparatus according to the first embodiment of the present invention. The pulse laser device 100 includes a semiconductor laser 1, a solid-state laser medium 2, an acoustooptic device 3, two mirrors 4, and an RF signal generator 5.

  Note that a resonator 10 is a portion configured by sandwiching the solid-state laser medium 2 and the acoustooptic device 3 between two mirrors 4.

  The semiconductor laser 1 generates excitation light. The excitation light generated by the semiconductor laser 1 is applied to the solid-state laser medium 2 through the mirror 4.

  The solid-state laser medium 2 is a material that causes laser oscillation. For example, in a solid-state laser called a YAG laser, materials such as yttrium, aluminum, and garnet (Yttrium Aluminum Garnet) are used. This solid-state laser medium 2 generates stimulated emission light when irradiated with excitation light from the semiconductor laser 1. The stimulated emission light generated by the solid-state laser medium 2 is sent to the acousto-optic device 3.

  The acoustooptic device 3 constitutes a Q switch and controls the pulse energy by modulating the fundamental wave of the stimulated emission light generated in the solid-state laser medium 2 in accordance with the RF signal sent from the RF signal generator 5. A pulse laser with a narrow peak and a large peak is output.

  The RF signal generation unit 5 generates an RF signal and sends it to the acoustooptic device 3. When the pulse repetition period is longer than the fluorescence lifetime of the solid-state laser medium, the RF signal generation unit 5 performs APC control for controlling the RF signal power to a predetermined value at least for a time longer than the fluorescence lifetime.

  FIG. 4 is a diagram illustrating a configuration example of the RF signal generation unit in the pulse laser apparatus according to the first embodiment of the present invention. As shown in FIG. 4, the RF signal generation unit 5 includes an RF generation unit 51, an RF amplifier 52, a detection circuit 53, and an RF control unit 54.

  The RF generator 51 generates an RF signal and outputs the RF signal to the RF amplifier 52. The RF amplifier 52 amplifies the RF signal from the RF generator 51 and supplies it to the acoustooptic device 3 as an RF signal output.

  The detection circuit 53 detects the power of the RF signal amplified by the RF amplifier 52 and outputs it to the RF control unit 54. That is, the power of the RF signal is fed back to the RF control unit 54.

  The RF control unit 54 sets the amplification factor of the RF amplifier 52 based on the power of the RF signal detected by the detection circuit 53, and performs APC control for controlling the power of the RF signal to be a predetermined value.

  Next, the operation of the pulse laser apparatus according to Embodiment 1 of the present invention configured as described above will be described in detail with reference to the timing chart shown in FIG.

  First, when the pulse laser device 100 is activated, the semiconductor laser 1 generates excitation light and irradiates the solid-state laser medium 2. Thereby, the solid-state laser medium 2 generates stimulated emission light and sends it to the acoustooptic device 3. In parallel with this, the RF signal generator 5 generates an RF signal and gives it to the acoustooptic device 3.

  As shown in FIG. 5, when the pulse repetition period T (for example, times t4 to t7) is longer than the fluorescence lifetime τ of the solid-state laser medium 2, that is, in the case of a giant pulse, as described in FIG. When excited for the above time, pulses having substantially the same energy can be generated. For this reason, the RF signal subjected to APC control is supplied to the acoustooptic device 3 for at least the period of the fluorescence lifetime τ until the RF signal changes from on to off.

  That is, the RF signal generation unit 5 performs APC control for controlling the power of the RF signal to a predetermined value at least for a time longer than the fluorescence lifetime.

  Further, in the ON period of the RF signal output from the RF signal generation unit 5 (for example, times t2 to t4), the loss in the resonator is larger than the gain and laser oscillation is not performed, and the gain of the solid-state laser medium 2 is increased. Going up. When the RF signal is turned off from this state, laser oscillation is enabled from the fall, and a pulsed laser is output from the solid laser medium 2 having the maximum gain via the acoustooptic device 3. .

  As described above, according to the pulse laser device according to the first embodiment of the present invention, when the pulse repetition period T is longer than the fluorescence lifetime τ of the solid-state laser medium 2, the RF signal is output for at least a time longer than the fluorescence lifetime. Since the power is controlled to a predetermined value, a pulse having stable pulse energy can be output regardless of whether the pulse is a giant pulse, even if an environmental temperature change or a change with time occurs.

  FIG. 6 is a timing chart for explaining the operation of the pulse laser apparatus according to the second embodiment of the present invention. In the pulse laser apparatus according to the second embodiment, as shown in FIG. 6, the pulse repetition period T is shorter than the fluorescence lifetime τ of the solid-state laser medium 2, that is, not the giant pulse.

  Since the pulse repetition period T is shorter than the fluorescence lifetime τ, when the APC control is always performed on the RF signal, the APC control is performed by the average power of the RF signal. If the off period of the RF signal is constant, the power of the on period of the RF signal varies depending on the pulse frequency, and a desired pulse energy cannot be obtained.

  Therefore, stable pulse energy can be obtained by starting APC control simultaneously with the turning on of the RF signal and stopping the APC control simultaneously with (or immediately before) turning off the RF signal.

  For this reason, the RF signal generation unit 5 performs APC control for controlling the power of the RF signal to a predetermined value during the ON period of the RF signal (for example, times t12 to t13) as shown in FIG.

  As described above, according to the pulse laser apparatus of the second embodiment, the RF signal generation unit 5 determines that the RF signal ON period, the RF signal of the RF signal, when the pulse repetition period T is shorter than the fluorescence lifetime τ of the solid-state laser medium 2. Since the power is controlled to a predetermined value, it is possible to provide a pulse laser device capable of outputting a pulse having stable pulse energy regardless of whether it is a giant pulse or not even if an environmental temperature change or a change with time occurs. .

  Further, the RF signal generation unit 5 may control the power of the RF signal to a predetermined value by feedback and set the time constant for determining the feedback speed to be equal to or longer than the off period of the RF signal.

  The time constant for determining the feedback speed is, for example, the time constant RC provided by the resistor R and the capacitor C provided in the detection circuit 53 and the RF control unit 54 shown in FIG.

  As described above, since the time constant for determining the feedback speed is set to be longer than the OFF period of the RF signal, the fluctuation of the power of the RF signal due to the OFF period of the RF signal can be ignored. As a result, regardless of whether the pulse is a giant pulse, a pulse having stable pulse energy can be output even if an environmental temperature change or a change with time occurs.

  FIG. 7 is a block diagram showing the main configuration of the pulse laser apparatus according to Embodiment 3 of the present invention. In the pulse laser device according to the third embodiment shown in FIG. 7, the semiconductor laser 1, the mirror 4, and the solid laser medium 2 are omitted for simplification, but the semiconductor laser 1, the mirror 4, and the solid laser medium 2 are These are the same as those shown in FIG.

  In FIG. 7, a vibration sensor 6 is attached to the acoustooptic device 3. This vibration sensor 6 detects the vibration of the acoustooptic device 3.

  The RF signal generation unit 5a includes an RF generation unit 51, an RF amplifier 52, and an RF control unit 54a. The RF generator 51 and the RF amplifier 52 are the same as those shown in FIG.

  The RF control unit 54a performs APC control for controlling the power of the RF signal to a predetermined value by controlling the vibration output of the acoustooptic device 3 detected by the vibration sensor 6 to be a constant value.

  That is, by using the vibration sensor 6, the RF signal generation unit 5 can perform APC control of the RF signal.

  The APC control of the RF signal by the vibration sensor 6 can also be applied to the pulse laser device according to the first embodiment or the pulse laser device according to the second embodiment.

  The present invention can be used in a pulse laser device that requires adjustment of pulse energy without depending on temperature change of a laser diode or power of an RF signal.

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Solid state laser medium 3 Acousto-optic device 4 Mirror 5 RF signal generation part 6 Vibration sensor 51 RF generation part 52 RF amplifier 53 Detection circuit 54, 54a RF control part

Claims (4)

A semiconductor laser that generates excitation light;
A solid-state laser medium that generates laser light in response to excitation light from the semiconductor laser;
An RF signal generator for generating an RF signal;
An acoustooptic device that modulates laser light generated in the solid-state laser medium in accordance with the RF signal generated by the RF signal generator;
A resonator configured by sandwiching the solid-state laser medium and the acoustooptic device with a mirror,
The RF signal generation unit controls the power of the RF signal to a predetermined value at least for a time longer than the fluorescence lifetime when the pulse repetition period is longer than the fluorescence lifetime of the solid-state laser medium. apparatus. A semiconductor laser that generates excitation light;
A solid-state laser medium that generates laser light in response to excitation light from the semiconductor laser;
An RF signal generator for generating an RF signal;
An acoustooptic device that modulates laser light generated in the solid-state laser medium in accordance with the RF signal generated by the RF signal generator;
A resonator configured by sandwiching the solid-state laser medium and the acoustooptic device with a mirror,
When the pulse repetition period is shorter than the fluorescence lifetime of the solid-state laser medium, the RF signal generation unit controls the power of the RF signal to a predetermined value during the ON period of the RF signal. . A semiconductor laser that generates excitation light;
A solid-state laser medium that generates laser light in response to excitation light from the semiconductor laser;
An RF signal generator for generating an RF signal;
An acoustooptic device that modulates laser light generated in the solid-state laser medium in accordance with the RF signal generated by the RF signal generator;
A resonator configured by sandwiching the solid-state laser medium and the acoustooptic device with a mirror,
The RF signal generation unit controls the power of the RF signal to a predetermined value by feedback, and a time constant for determining the feedback speed is set to be equal to or longer than an OFF period of the RF signal. apparatus. A vibration sensor attached to the acoustooptic element and detecting vibration of the acoustooptic element,
The RF signal generation unit controls the power of the RF signal to a predetermined value by controlling the vibration output of the acoustooptic element detected by the vibration sensor to be a constant value. The pulse laser device according to any one of claims 1 to 3.

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