JPH0786668A - Semiconductor laser pumped solid state laser device - Google Patents

Abstract

(57) [Abstract] [Objective] In a semiconductor laser pumped Q-switched solid-state laser device, means for preventing high-power solid-state laser beam from returning to the semiconductor laser by Q-switch operation is provided to protect the semiconductor laser from deterioration and destruction. [Structure] Resonator structure including laser crystal and Q in cavity
A solid-state laser device in which a switch and a semiconductor laser that excites the laser crystal are arranged on the optical axis of the oscillation beam of the solid-state laser formed by the resonator, and the solid-state laser oscillation beam does not return to the excitation semiconductor laser. It has an isolated structure for

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the field of optoelectronics, in particular to the fields of optical information processing and laser processing.

[0002]

2. Description of the Related Art Since the wavelength conversion technology was first experimentally confirmed in 1961, many experiments have been attempted with a combination of various solid-state laser crystals, resonator configurations and nonlinear optical crystals. With the recent achievement of higher output of semiconductor lasers, tubeless solid-state laser devices using semiconductor lasers as pumping light sources and solid-state laser devices having wavelength conversion elements have attracted attention in place of conventional lamp pumping. became. Semiconductor laser pumped solid-state laser device has (1) longer life than lamp pumping, (2) high conversion efficiency of optical output against input power, and pumping wavelength can be matched efficiently with absorption wavelength of laser crystal Therefore, it has a feature of low power consumption. In addition, a method has been proposed in which the optical axis of the pumping optical system is aligned with the optical axis of the resonator to excite the laser crystal from the end face so that the overlap with the mode volume of the solid-state laser oscillation can be made large to enhance the pumping efficiency ( D. L. Sipes, "Highly efficient Nd: YAG laser by edge-pumping a semiconductor laser array" Applied Physics Letter; DLSipes, "Highly efficient neodymium:
yttrium alminum garnet laser end pumped by asemico
nductor laser array ", Appl.Phys.Lett., vol.47,74 (198
Five)). Further, by inserting a Q switch such as an AO (acousto-optic) modulator or an EO (electro-optic) modulator, which is a loss modulation means, inside the resonator of the semiconductor laser pumped solid-state laser device, a Q switch having a large peak value is inserted. A proposal for a laser device was made (Japanese Patent Laid-Open No. 63-168063). FIG. 4 is a diagram for explaining the basic configuration of a semiconductor laser pumped Q-switch solid-state laser device. The semiconductor laser output 24 is focused on the laser crystal 32 by the focusing optical system 23. At this time, in order to increase the excitation efficiency, the oscillation beam 3 of the solid-state laser
6 is designed to maximize the spatial overlap of 6 and the excitation beam 24. That is, the excitation beam 24 and the solid-state laser oscillation beam 36 are on the same straight line. Figure 4
In the above configuration, the resonator configuration in which the one surface 31 of the laser crystal 32 and the concave mirror 33 are used as the reflecting mirror is shown, but any configuration may be used as long as the laser crystal 32 is included in the resonator. The mirror 31 on the excitation input side, that is, the incident side end face of the laser crystal is coated with a total reflection coating having a reflectance of about 99.5%, and the concave mirror 33 is coated with a reflectance of 95%, and the concave mirror 34 is used as an output mirror. An AO modulator 35 is arranged in the resonator and performs a Q switch operation. Next, the operating principle of the Q switch will be described. While the laser crystal is being pumped, the Q value of the resonator (energy stored in the resonator machine / power dissipated from the resonator) is kept low, and when the population inversion by pumping is maximized Return the Q value to the normal value. At this time, the oscillation sharply rises, and the population inversion is remarkably reduced by the excessive progress of stimulated emission, so that the pulse is attenuated with a certain time constant. The high-power solid-state laser oscillation that sharply rises is output from the reflecting mirror according to the reflectance.

[0003]

As described above, in the semiconductor laser pumped solid-state laser, the output corresponding to the reflectance of the reflecting mirror forming the resonator is emitted in both directions. At this time, since the solid-state laser beam 36 and the excitation beam 24 are arranged on the same straight line as shown in FIG. 4, the solid-state laser beam 36 is irradiated on the semiconductor laser 21. When a semiconductor laser pumped solid-state laser is Q-switched, the peak value is about 1000 times that in continuous operation, and the fundamental wave output applied to the pumping semiconductor laser cannot be ignored. For example, when the peak value of the output emitted from the output mirror 34 is 1 kW, the output of about 100 W is emitted to the semiconductor laser side when calculated from the reflectance described above. When half of the power is returned to the semiconductor laser, the semiconductor laser is always exposed to the power having a peak value of 50 W, which poses a risk of deterioration or destruction of the semiconductor laser.

[0004]

In the present application, the feedback of the solid-state laser beam to the semiconductor laser is reduced or blocked,
A means to protect the pumping semiconductor laser was proposed. Also,
The present invention embodies the following new distinctive features in a semiconductor laser pumped solid state laser device. (1) Oscillation of solid-state laser in which a resonator structure including a laser crystal such as Nd: YAG, a Q switch arranged inside the resonator, and a semiconductor laser for exciting the laser crystal are formed by the resonator. In a solid-state laser device arranged on the optical axis of the beam, the solid-state laser oscillation beam has an isolation structure such as a wavelength selection filter or a polarization separation element for reducing the power returned to the pumping semiconductor laser to at least 10% or less. A semiconductor laser pumped solid state laser device was proposed. That is, the present invention provides a resonator structure including a laser crystal, a Q switch disposed inside the resonator, and a semiconductor laser for exciting the laser crystal, which is a solid-state laser formed by the resonator. In the solid-state laser device arranged on the axis, a solid-state laser pumped solid-state laser device having an isolated structure for preventing the solid-state laser oscillation beam from returning to the pumping semiconductor laser. In the present invention, the laser crystal is Nd: YAG,
It is characterized by containing neodymium (Nd) such as Nd: YVO ₄ and Nd: YLF. Further, the isolated structure is a wavelength selection filter. The wavelength selection filter has a transmittance of 90% or more for an excitation wavelength and a transmittance of 10% or less for a solid-state laser oscillation wavelength. The isolated structure is a polarization separation element. Further, the present invention has a non-linear optical crystal inside the resonator structure, and has an isolated structure for preventing the second harmonic generated by the solid-state laser oscillation beam and the non-linear optical crystal from returning to the pumping semiconductor laser. In the present invention, the nonlinear optical crystal is potassium titanate phosphate (KTP; KTiOP).
O ₄ ).

[0005]

In the present invention, the wavelength selection filter and the polarization separation element have the function of separating the output emitted from the resonator mirror on the excitation light incident side from the excitation light optical axis and guiding the light along a predetermined optical axis.

[0006]

(Embodiment 1) FIG. 1 is a diagram for explaining an embodiment of the present invention. The semiconductor laser 21 is a broad area type semiconductor laser with an output of 1 W, and has a structure in which the oscillation wavelength is controlled by using the temperature control element 22 so that the absorption of Nd: YAG which is a laser crystal becomes maximum. The semiconductor laser output 24 is focused on the laser crystal 32 by the focusing optical system 23. The diameter of the oscillation beam 36 of the solid-state laser is 50 μm, the excitation beam 24 is included in the solid-state laser oscillation beam 36 when the crystal length of the laser crystal 32 is 5 mm, and the diameter of the excitation beam 24 is set so that the excitation efficiency is near the peak value. 10 μm
And Further, for the same reason, the excitation beam 24 and the solid-state laser oscillation beam 36 are made to exist on the same straight line. The solid-state laser was formed so that the resonator structure using the one surface 31 of the Nd: YAG crystal, which is the laser crystal 32, and the concave mirror 33 as a reflecting mirror contains the Nd: YAG crystal. At this time, the resonator structure may be any structure as long as the laser crystal 32 is included in the resonator. The mirror 31 on the excitation input side, that is, the incident side end surface of the laser crystal is coated with a reflectance of 99.5%, and the concave mirror 33 is coated with a reflectance of 95%, and the concave mirror is used as an output mirror 34. An AO modulator 35 is arranged in the resonator and performs a Q switch operation. The pulse width is 20 to 50 nsec and the repetition frequency is 1 to 1 kH.
It is variable up to z. The peak output was 1 kW when the pulse width was 20 nsec and the repetition frequency was 10 Hz. Further, the wavelength selection filter 40 is arranged between the excitation light incident side mirror 31 and the semiconductor laser 21 so that the solid-state laser output 36 does not return to the semiconductor laser 21. The wavelength selection filter 40 has a transmittance of 98% at an excitation wavelength of 0.8 μm and a solid-state laser wavelength.
The reflectance was 99.9% at 1.06 μm. This wavelength selection filter 4
The solid-state laser beam 36 is separated at a right angle from the excitation beam 24 by 0, and the solid-state laser beam 36 is irradiated to the laser-machined housing 10 which has been blackened. At this time, the solid-state laser beam 36 is partially absorbed, converted into heat, and partially scattered. Most of the scattered solid-state laser beam 36 is similarly absorbed by the laser head housing 10 and converted into heat by repeating scattering,
It is emitted from the laser head housing. As a result, the solid-state laser beam passing through the wavelength selection filter 40 has a peak value.
It was 0.1 W, and even if half the power was returned to the semiconductor laser 21, it could be reduced to 0.05 W, which is a safe feedback amount.

(Embodiment 2) FIG. 2 is a diagram for explaining an embodiment of the present invention. In the present invention, the semiconductor laser 2
1 is a broad-area type semiconductor laser with an output of 1 W, and its oscillation wavelength is 0.8 μ at which the absorption of Nd: YVO ₄ , which is a laser crystal, becomes maximum.
The structure is such that the temperature is controlled to be m. The semiconductor laser output 24 is focused on the laser crystal 32 by the focusing optical system 23. Excitation beam 24 and solid-state laser oscillation beam 36
The beam diameter of was set to be the same as in Example 1 so that the excitation efficiency could be large. The basic structure of the resonator is the same as that of the first embodiment. Further, an angle formed by the C axis of the Nd: YVO ₄ crystal 32 with respect to the polarization direction of the excitation light 24 is set to 90 °, and the polarization direction of the excitation beam 24 and the solid-state laser beam 36 which coincides with the c axis of the Nd: YVO ₄ crystal. The polarization directions of are set to be orthogonal to each other. The Q switch operation similar to that in Example 1 was performed, and the peak output was 1 kW. At this time, the polarization beam splitter 41 is arranged between the excitation light incident side mirror 31 and the semiconductor laser 21, and the excitation light 24
Was adjusted to maximize the transmission of As described above, since the solid-state laser beam 36 is orthogonal to the excitation beam, it is separated orthogonally to the optical axis by the polarization beam splitter 41 and the transmittance is 0.1%. The solid-state laser beam 36 separated from the optical axis of the excitation beam 24 was converted into heat and emitted by the same means as in Example 1. Therefore, the peak value of the solid-state laser beam 36 passing through the polarization beam splitter 41 is 0.1 W, and even if half the power is returned to the semiconductor laser 21, it is 0.05.
It was possible to reduce to W and a safe return amount. In addition, the present invention is Nd: YVO
A uniaxial laser crystal such as ₄ can be applied with the same configuration.

(Embodiment 3) FIG. 3 is a diagram for explaining one embodiment of the present invention. The laser crystal 32 and the pumping semiconductor laser 21 are the same as in the first embodiment. In the present invention, a KTP, which is a nonlinear optical crystal 37, is arranged inside the resonator, and the second harmonic (SH; Second Har) of the solid-state laser oscillation wave is arranged.
monic) The structure to get the wave. In order to obtain a high-power SH wave, it is necessary to increase the power of the solid-state laser oscillation wave inside the resonator, and the reflectivity of the resonator mirrors 31 and 33 should be 9
It was set to 9.5%. Further, with respect to the SH wave wavelength, the excitation light incident side mirror 31 has a reflectance of 90%, and the output mirror 33 has a transmittance of 90%. When the Q switch operation similar to that of the first embodiment is performed, the solid-state laser beam radiated to the semiconductor laser side has a peak value of 300 W and the SH wave has a peak value of 10 W, and the mixed wave 38 of the solid-state laser beam and the SH wave has a total of 310 W. Met. In addition, the excitation light incident side mirror 31 and the semiconductor laser 2
A wavelength selection filter 40 is arranged between the two to prevent the solid-state laser beam and the SH wave 38 from returning to the semiconductor laser 21. The wavelength selection filter 40 has a transmittance of 98% at an excitation wavelength of 0.8 μm, a reflectance of 99.9% at a solid-state laser wavelength of 1.06 μm, and an SH.
The wavelength is set to 99%. Therefore, the mixed wave 38 passing through the wavelength selection filter has a peak value of 0.4 W, and even if half the power is returned to the semiconductor laser, it can be reduced to 0.2 W, which is a safe feedback amount.

[0009]

In the present invention, the wavelength selection filter and the polarization separation element have a resonator mirror on the pumping light incident side inserted between the resonator and the semiconductor laser, so that the pumping semiconductor laser is not deteriorated by the solid-state laser beam. Protect from destruction,
The reliability of the entire device has been improved. Further, it is possible to eliminate the danger to the operator due to scattered light when the semiconductor module is irradiated with the returning light to the exciting semiconductor laser.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram for explaining an example of the present invention.

FIG. 3 is a diagram for explaining an example of the present invention.

FIG. 4 is a diagram for explaining the basic configuration of a semiconductor laser pumped Q-switch solid-state laser device.

[Explanation of symbols]

10 laser head housing, 21 semiconductor laser, 22
Temperature control element, 23 Condensing lens, 24 Excitation beam (light), 31 Excitation light incident side resonator mirror, 32 Laser crystal, 33 Laser output resonator mirror, 34 Output mirror, 35 AO modulator, 36 Solid-state laser beam Three
7 Nonlinear Optical Crystal, 38 Solid State Laser Beam and S
H wave, 40 wavelength selection filter, 41 polarization separation element

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kimio Tateno 1-280, Higashi Koigakubo, Kokubunji, Tokyo Metropolitan company Central Research Laboratory, Hitachi Ltd.

Claims (7)

[Claims] 1. A resonator structure including a laser crystal, a Q switch disposed inside the resonator, and a semiconductor laser for exciting the laser crystal, which is a solid-state laser formed by the resonator. In the solid-state laser device arranged on the axis, a solid-state laser pumped solid-state laser device having an isolated structure for preventing the solid-state laser oscillation beam from returning to the pumping semiconductor laser. 2. The laser crystal is Nd: YAG, Nd: YVO ₄ , Nd:
The semiconductor laser pumped solid-state laser device according to claim 1, which contains neodymium (Nd) such as YLF. 3. The semiconductor laser pumped solid state laser device according to claim 1, wherein the isolation structure is a wavelength selection filter. 4. The semiconductor laser pumping according to claim 3, wherein the wavelength selection filter has a transmittance of 90% or more for an excitation wavelength and a transmittance of 10% or less for a solid-state laser oscillation wavelength. Solid-state laser device. 5. The semiconductor laser pumped solid-state laser device according to claim 1, wherein the isolation structure is a polarization separation element. 6. The resonator structure has a non-linear optical crystal, and has an isolation structure for preventing the second harmonic generated by the solid-state laser oscillation beam and the non-linear optical crystal from returning to the pumping semiconductor laser. Item 6. A semiconductor laser pumped solid-state laser device according to any one of Items 1 to 3. 7. A semiconductor laser pumped solid-state laser device, wherein the nonlinear optical crystal according to claim 6 is potassium titanate phosphate (KTP; KTiOPO ₄ ).