JPH0595144A - Semiconductor laser-excited solid state laser - Google Patents

Abstract

PURPOSE:To obtain a stable laser in which a variation in an output of an inner resonator type second harmonic wave generator is suppressed by so disposing two solid state laser crystals to be polarizably oscillated that c-axes are perpendicularly crossed within the same resonator, and providing a nonlinear optical crystal second type-phase-matched between both the crystals. CONSTITUTION:A first solid state laser crystal 1a and a second solid state laser crystal 1b (e.g. Nd:YVO4 crystal) to be polarizably oscillated without using a polarizer are so disposed in one laser resonator that c-axes of the crystals 1a and 1b are crossed perpendicularly to the optical axis of the resonator and to each other. And, a secondary nonlinear optical crystal 2 second type-phase-matched for a frequency sum mixture and an optical element 3 for selectively outputting a frequency sum light generated by the crystal 2 out of the resonator are provided on the optical axis of the resonator between the crystals 1a and 1b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser using a semiconductor laser as an excitation light source, and more particularly to a solid-state laser for obtaining a second harmonic thereof.

[0002]

2. Description of the Related Art A second internal-cavity-type optical resonator in which a second-order non-warfare optical crystal is arranged in a laser cavity to generate a second harmonic wave
Harmonic generation is particularly effective for LD-pumped solid-state lasers having low pumping light output as a method of obtaining the second harmonic at a high rate.

However, in a general Nd: YAG laser as a solid-state laser, the internal resonator type second harmonic generation using the second-type phase-matching non-warfare optical crystal produces a very poor output. The phenomenon of becoming stable occurs. This phenomenon is called "green problem",
"Journal of Optical Society
ty of America B, Vol. 3, p. 1
175 (1986) ”.

As a method of solving this problem, there is a method of providing a quarter-wave plate in the resonator and controlling the polarization in the resonator. For this, see "Optics Lett
ers, Vol. 13, No. 10, pp. 805-8
07 (1988) ". Further, the problem has been solved by increasing the concentration of active ions in the solid-state laser and further reducing the crystal thickness to cause single-mode oscillation. For this, see "IEEE
Journal of Quantum Electr
onics, Vol. 26, No. 9, pp. 1457
-1459 ”has a detailed description.

[0005]

However, these methods have a problem that the control accuracy of the quarter-wave plate is strict, or that multimode oscillation occurs and the output fluctuates when the intensity of the excitation light is increased. Is left. In the present invention, the fluctuation of the output in the generation of the internal resonator type second harmonic is suppressed,
A stable laser device is provided.

[0006]

According to the present invention, in a semiconductor laser pumped solid-state laser, a first solid-state laser crystal and a second solid-state laser crystal that oscillate polarized light without using a polarizing element are included in one laser resonator. Is arranged such that the c-axes of the first solid-state laser crystal and the second solid-state laser crystal are perpendicular to the optical axis of the laser resonator, and are orthogonal to each other,
A second-order nonlinear optical crystal that performs a second-type phase matching for sum frequency mixing on the optical axis of the laser resonator between the first solid-state laser crystal and the second solid-state laser crystal; It is characterized in that an optical element for selectively extracting the sum frequency light generated by the nonlinear optical crystal to the outside of the laser resonator is provided.

[0007]

By providing a nonlinear optical crystal having birefringence in the laser resonator, the laser oscillates with two polarized lights orthogonal to each other inside the resonator. When the nonlinear optical crystal adopts the second type phase matching, sum frequency light between longitudinal modes of orthogonal polarizations is generated. The competition between the longitudinal modes due to the exchange of energy between the longitudinal modes through the generation of the sum frequency light becomes the output fluctuation, that is, the green problem. If these orthogonal polarizations oscillate independently of each other, there will be no competition between longitudinal modes and no green problem will occur.

Using two solid-state laser crystals that oscillate with polarization,
It is possible to oscillate independently by arranging the polarized lights so that they are orthogonal to each other in the same resonator. When the nonlinear optical crystal that achieves the second kind of phase matching in this resonator is made to coincide with one of the two independently polarized light beams oscillating independently of each other, the oscillation independence is To be kept. By doing so, the sum frequency light is generated from the two polarizations while maintaining the oscillations orthogonal to each other and independent of each other.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of a first embodiment of the present invention. Each of the Nd: YVO ₄ crystals 1a and 1b has one end face polished on a convex spherical surface, and these faces are coated with high reflection at an oscillation wavelength of 1064 nm to form a laser resonator. N is a uniaxial crystal
The d: YVO ₄ crystals 1a and 1b are both a-axis cut, and their c-axes are perpendicular to the axis of the laser resonator and are also orthogonal to each other.

The two Nd: YVO ₄ crystals oscillate independently by exciting the respective Nd: YVO ₄ crystals by the semiconductor lasers 5a, 5b through the lenses 4a, 4b. Nd: YVO ₄ oscillates polarized light without using a polarizing element. At this time, the electric field of the oscillated light is parallel to the c-axis of the crystals by the Nd: YVO ₄ crystals 1a and 1b. Strictly speaking, since Nd: YVO ₄ has a gain in the direction perpendicular to the c-axis, it cannot be said that the two Nd: YVO ₄ crystals oscillate completely independently. However, the gain in the direction parallel to the c-axis is 10 times or more larger than the gain in the direction perpendicular to the c-axis, and the maximum wavelength of the gain is slightly different. Therefore, it can be said that the oscillations of the two Nd: YVO ₄ crystals are substantially independent.

A KTP (KTiOPO ₄ ) crystal 2 having a second kind of phase matching is provided in the laser resonator.
The slicing direction of the KTP crystal 2 is an angle (θ = 90 °, φ = 24 °) at which the second harmonic of 1064 nm can be generated. The c-axis of KTP crystal 2 is Nd: YVO ₄ crystal 1a
It is parallel to the c-axis of. By doing so, the oscillation by the two Nd: YVO ₄ crystals 1a and 1b is kept independent. Then, the two oscillated lights are converted by the KTP crystal 2 into sum frequency light with a wavelength of 532 nm.

The dichroic mirror 3 is completely transmissive for the wavelength 1064 at 45 ° incidence and is 532n.
It is highly reflective for m. By providing this between the KTP crystal 2 and the Nd: YVO ₄ crystal 1b, the sum frequency light having a wavelength of 532 nm generated by the KTP crystal 2 is taken out of the resonator.

FIG. 2 is a perspective view of the second embodiment of the present invention. In the first embodiment, the optical axes of the semiconductor lasers 5a and 5b and the solid-state laser are straight, whereas in the second embodiment, the optical axes of the dichroic mirror 6 are bent in an L shape. Here, the dichroic mirror 6 is completely reflected at a wavelength of 1064 nm at 45 ° incidence, and has a wavelength of 5
It has a high transmittance for 32 nm.

In the first and second embodiments, two Nd: YVO ₄ crystals are independently excited by two semiconductor lasers. However, the excitation light emitted from the semiconductor laser is divided into two by a beam splitter, and the divided excitation light is divided into two Nd: YV by a reflecting mirror or the like.
One semiconductor laser may excite two solid-state laser crystals by guiding them to the O ₄ crystal. At this time as well, the independence of oscillation of the solid-state laser is maintained, so that the output fluctuation is not suppressed.

In the first and second embodiments, the a-axis cut Nd: YVO ₄ crystal is used as the solid-state laser crystal, but any solid-state laser crystal that oscillates polarized light without using a polarizing element may be used. For example, other materials such as Nd: YLF may be used.

Further, in the first and second embodiments, the KTP crystal is used as the nonlinear optical crystal, but the second kind of angular phase matching is taken for the oscillation wavelength of the solid-state laser crystal used. If

[0018]

As described above in detail, according to the present invention,
In a semiconductor laser-pumped solid-state laser using internal resonator type second harmonic generation, when a second-order nonlinear optical crystal that achieves the second type of phase matching is used, it is possible to eliminate significant output fluctuations and stabilize the output. it can.

[Brief description of drawings]

FIG. 1 is a perspective view for explaining a first embodiment of the present invention.

FIG. 2 is a perspective view for explaining a second embodiment of the present invention.

[Explanation of symbols]

1a, 1b Nd: YVO ₄ crystal 2 KTP crystal 3 dichroic mirror 4a, 4b lens 5a, 5b semiconductor laser 6 dichroic mirror

[Procedure amendment]

[Submission date] December 28, 1992

[Procedure Amendment 1]

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[Name of item to be corrected] Claim 1

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[0002]

BACKGROUND ART les - Internal generating a second harmonic of the second-order nonlinear optical crystal disposed in a resonator. The resonator type second
Harmonic generation, as a method for obtaining a second harmonic with high efficiency, it is particularly effective at the output low LD pumped solid-state laser excitation light.

[Procedure 3]

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[Name of item to be corrected] 0003

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However, as solid-state lasers general at the Nd: YAG laser, the internal resonator type second harmonic generation using nonlinear optical crystal taking the second type of phase matching, highly non outputs The phenomenon of becoming stable occurs. This phenomenon is called "green problem",
"Journal of Optical Societ
y of America B, Vol. 3, p. 11
75 (1986) ".

[Procedure correction 4]

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[Correction target item name] 0013

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[0013] In the dichroic mirror 3 is incident at 45 °, and completely transparent for the wavelength 1064 nm, 5
It is highly reflective for 32 nm. This is K
By providing it between the TP crystal 2 and the Nd: YVO ₄ crystal 1b, the sum frequency light with a wavelength of 532 nm generated by the KTP crystal 2 is taken out of the resonator.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

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[0018]

As described in detail above , according to the present invention,
In a semiconductor laser pumped solid-state laser utilizing internal cavity type second harmonic generation, when a second-order nonlinear optical crystal that achieves the second type of phase matching is used, significant output fluctuation can be removed and the output can be stabilized. it can.

Claims (1)

[Claims] 1. A semiconductor laser pumped solid-state laser,
A first fixed laser crystal and a second solid-state laser crystal that oscillate polarized light without using a polarizing element are provided in one laser resonator, and the first fixed laser crystal and the second fixed laser crystal with respect to the optical axis of the laser resonator. The second solid-state laser crystal is arranged so that the c-axis thereof is vertical and orthogonal to each other, and on the optical axis of the laser resonator between the first fixed laser crystal and the second solid-state laser crystal, A second-order nonlinear optical crystal for phase-matching the second type for sum frequency mixing and an optical element for selectively extracting the sum frequency light generated by the nonlinear optical crystal to the outside of the laser resonator are provided. Characteristic semiconductor laser pumped solid-state laser.