JPH07183605A - Solid-state laser device - Google Patents

Abstract

(57) [Summary] [Purpose] Longitudinal single-mode oscillation and laser noise reduction of solid-state laser and internal cavity SHG laser. [Structure] In an internal cavity type SHG laser pumped by a semiconductor laser, an etalon 12 is oscillated in the cavity 1
5 is used in a vertical direction, and the output light is monitored to feed back the change in the cavity length. [Effect] By moving the resonator mode in accordance with the mode selected by the etalon, the solid-state laser can be oscillated in the longitudinal single mode. By achieving the longitudinal single mode, it is possible to obtain a solid-state laser device that outputs SHG stably without mode competition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to single mode oscillation of a solid-state laser device or stable oscillation of a laser device in which the solid-state laser generates optical harmonics of a fundamental oscillation wavelength, and more particularly to reduction of laser noise.

[0002]

2. Description of the Related Art As shown in FIG. 1, an edge-pumped solid-state laser device that is pumped by a semiconductor laser 1 from an end face of a laser medium 3 is expected to have various applications due to its small size and high efficiency oscillation. In particular, the SHG laser device that is used together with the nonlinear optical crystal 4 to generate the second harmonic (SHG) is highly expected as a computer peripheral device such as an optical disk and a laser printer. Reference numeral 2 for converging the laser is a converging lens, and 5 is an output mirror.

By the way, a standing wave type solid-state laser generally oscillates in a longitudinal multimode unless special means is provided. However, there are many cases where it is desired to apply laser light in the longitudinal single mode. Furthermore, in the internal cavity type SHG laser, the SHG output can be stabilized when the fundamental wave is single mode, and the application range of this device is widened.

As shown in FIG. 2, there is a wavelength selection method for making a laser into a single mode by using an etalon 5 (parallel plate) provided with reflective coatings 5a on both sides and utilizing the multiple reflection thereof. This is because an etalon (parallel plate made of a transparent material such as quartz) is inserted inside the resonator and the optical path length is changed by inclining the etalon to select the etalon wavelength and a large number of resonator modes (resonance). This is a method of causing single mode oscillation by matching one of the discrete wavelengths that satisfy the condition). A stable SHG can be obtained by inserting a nonlinear optical crystal 4 inside the resonator that oscillates in single mode.
Output is obtained. Examples of this are William Kruschau, Jay Kanelaud, I Triple E Journal of Quantum Electronics (Will
iam Clushaw, J. Kannelaud, IEEE Journal of Quantum
Electronics), vol. QE-10, No.2, p253 (1974), Minoru Kakutani and 5 others, Proceedings of the 40th Joint Lecture Meeting on Applied Physics in Spring 1993 No3, p996, 31p-Z-4 etc. Is mentioned.

[0005]

According to the conventional method of tilting the etalon with respect to the traveling direction of the laser (8 in FIGS. 1 and 2), when the etalon is placed in an environment different from the environment at the time of adjustment, the etalon is selected. There is a shift between the wavelength and the resonator mode. Therefore, it is necessary to readjust the tilt angle. Also, when SHG occurs, the multiple reflection spots of SHG do not match due to the inclination of the etalon, which causes a reduction in output.

The present invention has been made in consideration of this point, and an object of the present invention is to provide a solid-state laser device using an etalon, which does not require readjustment of the inclination of the etalon even when environmental changes occur. Another object of the present invention is to provide a laser device which does not have unstable output due to mode competition by utilizing this solid-state laser device for generation of optical harmonics.

[0007]

According to the present invention, as shown in FIG. 2, the etalon 5 is fixed perpendicularly to the laser traveling direction, and the resonator mode is controlled by controlling the resonator length 7 to match the selected wavelength of the etalon. Achieve single mode oscillation. Further, this resonator length control is automatically performed by monitoring the output laser and feedback. Etalon and oscillation laser 8
Since the traveling directions of are orthogonal, it is possible to increase the output by overlapping multiple reflection spots when SHG occurs.

[0008]

The wavelength of light that can exist inside the resonator length L (resonator mode) can be expressed by equation (1), where N is an integer.

[0009]

[Equation 1]

(1) Further, the transmittance of the etalon can be expressed by the following equation (2).

[0011]

[Equation 2]

(2) Here, R is the coating reflectance of the etalon, and φ can be expressed by equation (3).

[0013]

[Equation 3]

(3) λ is the wavelength, and n, l, and θ are the refractive index, thickness, and inclination angle of the etalon (θ = 0 ° in the direction perpendicular to the etalon surface). Therefore, when one resonator mode is desired to be transmitted, θ may be changed, or L may be slightly changed from Expression (1) to create λ that matches θ. In the present invention, the latter is performed by fixing θ = 0 ° (the etalon is perpendicular to the traveling direction of light) and changing the resonator length. In addition, since the etalon and laser travel directions are orthogonal to each other, multiple reflected spots can overlap when SHG occurs and the output can be increased.

When slightly changing L, it is necessary to tune so that one resonator mode is exactly T = 1. Therefore, a part of the output light is monitored and fed back to the resonator length control. As a result, the vertical single mode is automatically achieved. Also, since there is no fundamental wave competition, the SHG output is stable.

[0016]

【Example】

Example 1 As shown in FIG. 3, a solid-state laser resonator is formed on a copper plate 15 bonded to a Peltier element 16. Nd: YVO ₄ 9 whose left surface 9a is non-reflective for wavelength 808 nm and highly reflective for 1064 nm is mounted on the holder 9b, and the holder is fixed to 15. Output mirror 1 mounted in holder 13b
The left curved surface 13a of 3 is coated with high reflection for 1064 nm and non-reflection for 532 nm, which is fixed to 15.
The resonator is composed of 9a and 13a. The KTP 11 and the etalon 12 mounted on the holder 11b are arranged inside the resonator.
The c-axis of 11 should be 45 ° with the c-axis of 9. A laser beam (wavelength of about 808 nm) of the semiconductor laser 7 is condensed and excited by a condenser lens 8 on 9 to oscillate a laser (fundamental wave, SHG). 12
Is fixed so that its surface is perpendicular to the traveling direction of the fundamental wave or SHG. Only the SHG of the output laser is transmitted by the fundamental wave cut filter 19 and part of it is beam splitter 1
It is taken out by 7 and made incident on the detector 20. 20 SHG light 24
Is converted into an electrical signal 25, which is passed through an electrical low frequency transmission filter 21 and a high frequency transmission filter 22. The outputs of 21 and 22 are input to the feedback circuit 26. At 26, first feedback is applied to the temperature controller 23 to maximize the input from 21. Then, so that the output of 22 is the minimum
Give feedback to 23. 23 changes the current applied to the Peltier element 16 according to 26, and minutely changes the resonator length by the temperature change of 15.

Example 2 In the device as shown in FIG. 4, the resonator and excitation are the same as in Example 1.
A part of the output laser light is taken out as a monitor light 28 by a polarization separation splitter (S-polarized light 100% transmitted, P-polarized light 100% reflected) 27. 27 is arranged so that the direction of 28 is perpendicular to the c-axis of 11 as shown in FIG. In addition, the take-out surface 27a of 28 is 532
It is highly reflective for nm and non-reflective for 1064 nm. Therefore, only the fundamental wave is received by 20 and the electrical signal is received.
After converting to 25, 25 is input to the feedback circuit 29. 29 controls the resonator temperature through 23.
When the cavity length is appropriate, the fundamental wave polarization direction is 11 c-axis and 45
Only the polarized component 30, which forms an angle of ° but is parallel to 32, is taken out by 27. If the voltage of 25 at this time is obtained in advance, 29 controls 23 so that it becomes that value. SH
The G polarization direction is parallel to the plane of incidence of 27, which is 31. A fundamental wave cut filter 33 is placed after 27 to pass only SHG.

[0018]

As described above, according to the present invention,
A solid-state laser using an etalon can oscillate in a single longitudinal mode. In addition, the internal cavity type SHG laser to which this solid-state laser is applied can obtain stable laser output with low noise. Since the output of this laser light is stable, it can be effectively used in the fields of optical disk systems, optical communications, laser beam printers, and the like.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a conventional edge-pumped internal cavity SHG laser.

FIG. 2 is a configuration diagram showing a structure of an edge-pumped solid-state laser and a method of using an etalon.

FIG. 3 is a configuration diagram showing a first embodiment of the present invention.

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

FIG. 5 is a perspective view showing a direction of a polarization beam splitter and a direction of monitor light in Example 2 of the present invention.

[Explanation of symbols]

1 ... Semiconductor laser, 2 ... Focusing lens, 3 ... Laser medium, 4 ...
Nonlinear optical crystal, 5 ... Etalon, 5a, 9a, 13a, 27a ... Coating, 6 ... Output mirror, 7 ... Resonator length, 8 ... Oscillation laser light, 9 ... Nd: YVO4, 9b, 11b, 13b ... Holder, 11 … KTP, 12…
Etalon, 13 ... Output mirror, 15 ... Copper plate, 16 ... Peltier element, 17 ... Beam splitter, 18 ... Output SHG, 19 ... Fundamental wave cut filter, 20 ... Detector, 21 ... Low frequency transmission filter, 22 ... High frequency transmission filter , 23 ... Temperature controller, 24, 28 ... Monitor light, 25 ... Electric signal, 26, 29 ... Feedback circuit, 27 ... Polarization beam splitter, 28 ... Monitor fundamental wave, 30 ... Fundamental wave polarization direction, 31 ... SHG polarization direction , 32 ... KTP c-axis direction, 33 ... Basic wave cut filter.

Claims (9)

[Claims] 1. A resonance source having an excitation light source, a laser medium excited by the excitation light source, a laser resonator for oscillating light from the laser medium, and an etalon arranged in the laser resonator. A solid-state laser device comprising means for controlling the length. 2. The laser device according to claim 1, wherein a nonlinear optical crystal is provided inside the laser resonator, and the second harmonic (SH
Solid-state laser device characterized by generating G). 3. The solid-state laser device according to claim 2, wherein the etalon surface is coated with a fundamental wave reflection coating. 4. The solid-state laser device according to claim 3, wherein the laser traveling direction and the etalon surface are arranged perpendicular to each other. 5. The solid-state laser device according to claim 3, wherein the etalon surface is coated with a low reflection coating for the wavelength of SHG. 6. The solid-state laser device according to claim 2, wherein the output laser light is monitored and fed back to the cavity length control. 7. A solid-state laser device according to claim 6, wherein the SHG light is monitored in particular. 8. A solid-state laser device according to claim 7, wherein the monitor output is taken out as an electric signal and is fed back to the cavity length control using a low-pass filter and a wide-pass filter. . 9. A solid-state laser device according to claim 6, wherein the component of the polarization direction of the fundamental wave is monitored to perform feedback control of the cavity length.