JP2013205426A - Solid-state laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state laser device capable of improving the stability of third harmonic wave output for optimal temperature change of second harmonic wave.SOLUTION: The solid-state laser device comprises: a semiconductor laser 1 generating a laser beam; a solid laser medium 2 excited by the laser beam outputted from the semiconductor laser 1; an SHG element 4 and a THG element 5 which are arranged in an optical resonator including the solid laser medium 2 and output a third harmonic wave of a fundamental wave, generated in the optical resonator; and a temperature adjustment part 9 controlling the temperatures of the SHG element 4 and the THG element 5. The lengths of the SHG element 4 and the THG element 5 are set so that a plurality of output peaks of the THG element 5 for the temperature of the SHG element 4 can be obtained.

Description

  The present invention relates to a solid-state laser device, and more particularly to a solid-state laser device that outputs a third harmonic.

  Conventionally, a solid-state laser device capable of stabilizing the peak intensity of the third harmonic pulse output is known (Patent Document 1). The solid-state laser device described in Patent Document 1 that outputs the third harmonic includes a second harmonic generation crystal element (hereinafter referred to as an SHG element) that outputs the second harmonic, and a third harmonic. And a third harmonic generation crystal element (hereinafter referred to as a THG element) for output.

  The third harmonic output from the THG element is a sum frequency of the second harmonic obtained by converting the fundamental wave by the SHG element and the residual fundamental wave transmitted without being converted by the SHG element.

  FIG. 4 is a diagram showing the characteristics of the SHG output and the residual fundamental wave output with respect to the SHG element temperature when the SHG element length is 2 mm. FIG. 5 is a graph showing the THG output characteristics with respect to the SHG element temperature when the SHG element length is 2 mm and the THG element length is 10 mm. As can be seen from FIG. 4, when the SHG output and the residual fundamental wave output with respect to the SHG element temperature are measured, the residual fundamental wave output becomes the minimum value at the temperature at which the SHG output becomes the maximum value.

  When the SHG element is as short as 2 mm, when the sum frequency mixing is performed with the THG element, the fundamental wave is always sufficiently present. Therefore, the THG output characteristic depends on the SHG output characteristic, and the SHG output characteristic shown in FIG. The peak and the peak of the THG output characteristic shown in FIG. 5 substantially coincide with each other and become a single peak.

JP 2010-251448 A

  However, as shown in FIG. 5, since the rate of change of the THG output with respect to the SHG temperature change is large, when the SHG optimum temperature changes from a preset temperature due to environmental changes, it becomes a factor that the output is greatly reduced.

  In the case of a continuous wave drive laser, there is a method of stabilizing the output by automatically adjusting the drive current by an output feedback mechanism using a photodiode. However, in a pulse drive laser with a variable repetition frequency, when the repetition frequency changes from a single shot to several kHz or more, the average power changes greatly even if the pulse energy is constant. For this reason, since the dynamic range of the photodiode is insufficient, automatic output stabilization by the photodiode is difficult.

  The subject of this invention is providing the solid-state laser apparatus which can improve the stability of the 3rd harmonic output with respect to a 2nd harmonic optimal temperature change.

  In order to solve the above problems, a solid-state laser device according to the present invention includes a semiconductor laser that generates laser light, a solid-state laser medium that is excited by laser light output from the semiconductor laser, and the solid-state laser medium. A second harmonic generation crystal and a third harmonic generation crystal disposed in the optical resonator for outputting the third harmonic of the fundamental wave generated in the optical resonator, and the second harmonic A temperature adjusting unit that controls the temperatures of the wave generating crystal and the third harmonic generating crystal, and the peak of the third harmonic generating crystal output with respect to the temperature of the second harmonic generating crystal is The length of each of the second harmonic generation crystal and the third harmonic generation crystal is set so as to obtain a plurality.

  Further, the temperature adjusting unit sets the temperature of the second harmonic generation crystal to a temperature intermediate between a plurality of peak temperatures of the third harmonic generation crystal output.

  According to the solid-state laser device of the present invention, the second harmonic generation crystal and the third harmonic wave are obtained so that a plurality of peaks of the third harmonic generation crystal output with respect to the temperature of the second harmonic generation crystal are obtained. Since the lengths of the generating crystals are set, the stability of the third harmonic output with respect to the second harmonic optimum temperature change can be improved.

It is a block diagram which shows the structure of the solid-state laser apparatus which concerns on Example 1 of this invention. It is a figure which shows the characteristic of SHG output and a residual fundamental wave output with respect to SHG element temperature in case the SHG element length in the solid-state laser apparatus which concerns on Example 1 of this invention is 5 mm. It is a figure which shows the characteristic of the THG output with respect to SHG element temperature when the SHG element length in the solid-state laser apparatus which concerns on Example 1 of this invention is 5 mm, and a THG element length is 10 mm. It is a figure which shows the characteristic of SHG output and a residual fundamental wave output with respect to SHG element temperature when the SHG element length in the conventional solid-state laser apparatus is 2 mm. It is a figure which shows the characteristic of the THG output with respect to SHG element temperature when the SHG element length in the conventional solid-state laser apparatus is 2 mm and the THG element length is 10 mm.

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

  FIG. 1 is a block diagram showing a configuration of a solid-state laser apparatus according to Embodiment 1 of the present invention. This solid-state laser device includes a semiconductor laser 1, a solid-state laser medium 2, two mirrors 3, an SHG element 4, a THG element 5, a beam splitter 6, a photodetector 7, a readout circuit 8, a temperature adjustment unit 9, and a temperature adjustment unit 9. CPU (Central Processing Unit) 10 having

  A portion composed of the solid-state laser medium 2, the two mirrors 3, the SHG element 4, and the THG element 5 is called a resonator 20.

  The semiconductor laser 1 is constituted by a laser diode, for example, and generates laser light. Laser light generated by the semiconductor laser 1 passes through one mirror 3 and is irradiated onto the solid-state laser medium 2.

  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. The solid-state laser medium 2 generates stimulated emission light when irradiated with laser light from the semiconductor laser 1. The stimulated emission light generated by the solid-state laser medium 2 is sent to the SHG element 4.

  The SHG element 4 is LBO (type 1), and generates a second harmonic from the fundamental wave from the solid-state laser medium 2. The THG element 5 is LBO (type 2), generates a third harmonic from the fundamental wave and the second harmonic generated by the SHG element 4, and guides it to the beam splitter 6 through the other mirror 3.

  The beam splitter 6 transmits the fundamental wave and the second harmonic and outputs it as a pulse laser, reflects the third harmonic and guides it to the photodetector 7. The photodetector 7 detects the third harmonic from the beam splitter 6. The readout circuit 8 reads out the third harmonic detected by the photodetector 7 and outputs the pulse energy or power of the third harmonic to the temperature adjustment unit 9.

  The temperature adjustment unit 9 controls the temperature of each of the SHG element 4 and the THG element 5.

Further, the temperature adjustment unit 9 sets the temperature of the SHG element 4 to a temperature intermediate between the two peaks of the THG output based on the pulse energy or power of the third harmonic from the readout circuit 8.

  Next, the operation of the solid-state laser device according to the first embodiment of the present invention configured as described above will be described.

  FIG. 2 is a diagram showing the characteristics of the SHG output and the residual fundamental wave output with respect to the SHG element temperature when the SHG element length in the solid-state laser apparatus according to Example 1 of the present invention is 5 mm. FIG. 3 is a graph showing the THG output characteristics with respect to the SHG element temperature when the SHG element length is 5 mm and the THG element length is 10 mm in the solid-state laser device according to the first embodiment of the present invention.

  As shown in FIG. 2, when the SHG element 4 is lengthened to 5 mm, the conversion efficiency from the fundamental wave to the SHG is improved, the SHG output is increased, and the residual fundamental wave output that is transmitted through the SHG element without being reduced is decreased. To do. At this time, the fundamental wave sufficient for sum frequency mixing does not remain near the temperature at which the SHG output reaches a peak, and the THG output depends on the residual fundamental wave output.

  As shown in FIG. 3, the peak of the THG output characteristic with respect to the SHG temperature depends on the temperature deviating from the peak temperature of the SHG output. This temperature is a temperature at which the residual fundamental wave output is sufficiently present with respect to the SHG output, and there are two locations on both sides of the peak temperature of the SHG output as shown in FIG. There are two THG output peaks at 30 ° C. and 38 ° C.

  In this case, the SHG element temperature is not set to one of the two peak temperatures of the THG output, but the temperature adjustment unit 9 sets the control temperature of the SHG element 4 to an intermediate temperature between the two peaks of the THG element 5. Set to ° C.

  As a result, the allowable range of the SHG element temperature at which a value greater than a certain value (for example, 80%) with respect to the maximum value of the THG output is obtained is set to one of the two peaks, or the SHG element length is short and the THG output characteristics are single. More than the peak case. Therefore, the stability of the THG output with respect to the SHG optimum temperature change can be improved. That is, the output fluctuation with respect to the temperature change is suppressed to be small, and the stability is improved.

  In the conventional example shown in FIG. 5, when the SHG temperature is set to 33 ° C., the temperature range in which 100 μJ or more is obtained is ± 3 ° C. On the other hand, in Example 1 shown in FIG. 3, when the SHG temperature is set to 34 ° C., the temperature range in which 100 μJ or more is obtained is ± 5 ° C. Therefore, the stability against environmental temperature changes can be improved without using the automatic output stabilization function.

  In addition, this invention is not limited to the solid-state laser apparatus of Example 1 mentioned above. In Example 1, there are two THG output peaks as shown in FIG. 3, but when there are three or more THG output peaks, the control temperature of the SHG element 4 is set to three or more peaks. The temperature may be set to an intermediate temperature.

  In the first embodiment, the length of the SHG element 4 is 5 mm. However, the length of the SHG element 4 is not limited to 5 mm, and there are a plurality of output peaks of the THG element 5 with respect to the temperature of the SHG element 4. What is necessary is just to set each length of the SHG element 4 and the THG element 5 so that it may be obtained.

  The present invention can be used for a solid-state pulse laser device.

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Solid-state laser medium 3 Mirror 4 SHG element 5 THG element 6 Beam splitter 7 Photo detector 8 Reading circuit 9 Temperature adjustment part 10 CPU

Claims (2)

A semiconductor laser for generating laser light;
A solid-state laser medium excited by laser light output from the semiconductor laser;
A second harmonic generation crystal and a third harmonic generation crystal disposed in an optical resonator including the solid-state laser medium and outputting a third harmonic of a fundamental wave generated in the optical resonator; ,
A temperature adjustment unit for controlling the temperature of each of the second harmonic generation crystal and the third harmonic generation crystal;
Each length of the second harmonic generation crystal and the third harmonic generation crystal is such that a plurality of peaks of the third harmonic generation crystal output with respect to the temperature of the second harmonic generation crystal are obtained. A solid-state laser device characterized by setting the thickness.   2. The solid according to claim 1, wherein the temperature adjusting unit sets the temperature of the second harmonic generation crystal to a temperature intermediate between a plurality of peak temperatures of the third harmonic generation crystal output. Laser device.

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