JPH04287988A - Semiconductor excited solid-state laser - Google Patents

Abstract

PURPOSE:To improve energy efficiency of a laser oscillation by absorbing an exciting light while the light is enclosed in a narrow region by an inner reflection of a solid laser medium having thinner thickness, width, etc., than spreading width of the light. CONSTITUTION:A solid laser medium 3 to be used has a thinner thickness than a spreading width in a solid laser medium 3 of an exciting light 2. Or, it has thinner thickness and width than the spreading width in the medium 3 of the light 2. Or, it has smaller diameter than the spreading width in the medium 3 of the light 2. A nonreflecting coating 32 is provided on the exciting light incident end face of the medium 3. The end face of the medium 3 is so disposed near a semiconductor laser 1 as to reduce a distance between the laser 1 and the end face to a degree not to vary the oscillation wavelength of the laser 1 by a reflected light from the incident end face. Thus, a beam of high quality having a high energy efficiency of a laser oscillation and a stable output can be emitted.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a semiconductor-excited solid-state laser using a semiconductor laser as an excitation source, and in particular to stabilizing the output of a semiconductor-laser proximity type solid-state laser for the purpose of improving oscillation efficiency and beam mode. .

0002

2. Description of the Related Art FIG. 3 shows a schematic configuration of a conventional semiconductor-excited solid-state laser, which is disclosed, for example, in Mitsubishi Electric Technical Report Vol. 63, No. 4, (1989) P287-290. In the figure, 1 is a semiconductor laser, and 2 is a laser beam emitted from the semiconductor laser 1, which is hereinafter referred to as excitation light. 8 and 9 are lenses, 3 is a solid laser medium, 6 is a laser beam output from the solid laser medium, and 7 is a partially reflecting mirror. A total reflection coating 32 and a non-reflection coating 33 are applied to the end face of the solid-state laser medium 3 for the laser beam 6, and a laser resonator is formed between the total reflection coating 32 and the partial reflection mirror 7. has been done.

Next, the operation will be explained. Excitation light 2 emitted by semiconductor laser 1 is collimated by lens 8 and condensed into solid-state laser medium 3 by lens 9 . The excitation light 2 is absorbed while spreading in the solid-state laser medium 3, and excites the solid-state laser medium 3. A part of the absorbed energy of the excitation light 2 is outputted to the outside as a laser beam 6.

0004

[Problem to be Solved by the Invention] The conventional solid-state laser is constructed as described above, and the excitation light 2 spreads widely in the solid-state laser medium 3, so that the cross-sectional area of excitation is substantially reduced. was difficult. As a result, the threshold for laser oscillation becomes large, resulting in low energy efficiency of laser oscillation, and the laser beam 6 has high-order modes, making it difficult to obtain a fundamental mode beam with good focusing. .

The present invention has been made to solve the above-mentioned problems, and provides a semiconductor-excited solid-state laser that emits a high-quality beam with high laser oscillation energy efficiency and stable output. The purpose is to obtain.

[0006]

[Means for Solving the Problems] The semiconductor pumped solid-state laser according to the present invention has a plate-like structure having a thickness thinner than the spread width of the excitation light in the solid-state laser medium, or This method uses a solid-state laser medium whose cross-sectional shape is thinner than the spread width of the excitation light, or whose cross-sectional shape is approximately circular and has a diameter smaller than the spread width of the excitation light in the solid-state laser medium. An anti-reflection coating is applied to the excitation light input facet (hereinafter referred to as the input facet) of the solid-state laser medium, and the distance between the semiconductor laser and the input facet is adjusted such that the reflected light from the input facet matches the oscillation wavelength of the semiconductor laser. The semiconductor laser is
It should be placed close to the area.

The reflectance of the anti-reflection coating applied to the excitation light incident end face for the excitation light is 2% or less, and the distance between the above incident end face and the semiconductor laser is between 100 μm and 500 μm.
It is preferable to set it between μm.

[0008] The semiconductor pumped solid-state laser according to another aspect of the present invention is a plate-shaped laser having a thickness thinner than the spread width of the pumping light in the solid-state laser medium, or A solid-state laser medium whose cross-sectional shape has a thickness and width thinner than the spread width of the solid-state laser medium, or a solid-state laser medium whose cross-sectional shape is approximately circular and has a diameter smaller than the spread width of the excitation light in the solid-state laser medium. It is arranged close to the laser, and the optical axis of the excitation light is inclined from the normal line of the excitation light incident end face.

[0009]

[Operation] In the present invention, the energy efficiency of laser oscillation can be improved because the excitation light can be absorbed while being confined in a narrow region by internal reflection of the solid laser medium, which has a thickness and width smaller than the spread of the excitation light. In addition, an anti-reflection coating is applied to the input facet, and the distance between the semiconductor laser and the input facet is set close to the semiconductor laser so that the distance between the semiconductor laser and the input facet is so small that the reflected light from the input facet does not change the oscillation wavelength of the semiconductor laser. Because the optical axis of the excitation light is tilted from the normal line of the input end facet, the excitation light reflected at the entrance end facet is incident on the semiconductor laser.
Since it is not affected by so-called return light, the output is stable,
It is possible to generate laser light with high efficiency and good beam quality.

0010

[Example] Example 1. Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an embodiment of a semiconductor-excited solid-state laser according to the present invention. In the figure, reference numeral 1 denotes a 1W class semiconductor laser having a stripe width of, for example, 150 .mu.m. 2 is the excitation light emitted from the semiconductor laser 1, and 3 is a solid laser medium, for example, 5 mm in length and 2 in width.
Nd:YAG (Y3
-x Ndx Al5 O12) crystal, and is installed so that the incident end face is at a distance of 100 to 500 μm from the semiconductor laser 1. 4 is an optical adhesive, and 5 is a metal block, for example, a rectangular parallelepiped gold-plated copper block with a length of 5 mm, a width of 4 mm, and a thickness of 3 mm. 32 is a coating formed on the end face of the solid-state laser medium 3, and the excitation light 2
There is no reflection for the laser beam 6, total reflection for the laser beam 6, and the reflectance for the excitation light 2 is set to be 2% or less. 33 is a coating formed on the end face of the solid laser medium 3, which does not reflect the laser beam 6. 7 is a partial reflection mirror, and 10 is a housing.

Next, the operation will be explained. The excitation light 2 enters from the coating 32 on the end face of the solid-state laser medium 3. The excitation light 2 emitted from the semiconductor laser 1 generally has a wide spread; for example, the divergence angle is 60° in the direction perpendicular to the active layer of the semiconductor laser 1 (hereinafter simply referred to as the vertical direction), and 60° in the parallel direction (hereinafter simply referred to as the parallel direction). Although it has a very large angle of 20° (both full-width) and is anisotropic, by arranging the semiconductor laser 1 and the solid-state laser medium 3 close to each other,
The excitation light 2 is effectively made incident on the laser medium 3. With this incident method, the excitation light 2 is repeatedly internally reflected on the upper and lower surfaces of the plate-shaped solid-state laser medium 3, which has a thickness thinner than the spread width of the excitation light in the solid-state laser medium 3, and is confined within the solid-state laser medium 3. It is absorbed as it is, effectively exciting it. By reflecting the light that spreads in the vertical direction of the semiconductor laser active layer on the upper and lower surfaces, the optical excitation region in the solid-state laser medium can be made approximately 0.5 mm in both the vertical and parallel directions. Heat generated in the solid-state laser medium 3 is efficiently radiated through the metal block 5 and the housing 10. A stable resonator is constructed between the coating 32 and the partially reflecting mirror 7. For example, when the coating 32 is flat, the radius of curvature of the partially reflecting mirror 7 is 2500 mm, and the resonator length is 10 mm, the beam diameter of the fundamental mode (Gaussian mode) is Approximately 0.3
It is 5mm. Therefore, the fundamental mode cross section of the laser is
The cross-sectional area in which the excitation light 2 is confined almost matches, and a high-quality Gaussian beam can be outputted with high efficiency.

The distance between the incident end facet and the semiconductor laser 1 must be set in consideration of efficiency and output stability. If it is too close, a small amount of reflected light from the incident end face of the excitation light 2 will enter the semiconductor laser 1, and the operation of the semiconductor laser 1 will become unstable due to the influence of so-called return light, that is, the output and the emitted excitation will be affected. The wavelength of light 2 changes. On the other hand, solid laser medium 3
When the semiconductor laser 1 moves away from the solid state laser medium 3, the amount of excitation light 2 incident on the solid laser medium 3 decreases, and the laser output decreases. In this embodiment, this problem is solved by reducing the reflectance at the incident end face to 2% or less using the anti-reflection coating 32 and setting the distance between the incident end face and the semiconductor laser 1 to 100 μm to 500 μm.

Example 2. In addition, in the above example, 150μ
For a 1W class semiconductor laser with a stripe width of about m, the reflectance of the anti-reflection coating was set to 2% or less, and the distance between the semiconductor laser and the incident end facet was set to 100 μm to 500 μm. By setting the reflectance of the anti-reflection coating and the distance between the semiconductor laser and the incident end facet to appropriate values depending on the type, the same effects as in the above embodiment can be obtained.

Example 3. In addition, in the above embodiment, the influence of the return light from the semiconductor laser 1 was avoided by setting the anti-reflection coating and the distance between the semiconductor laser and the incident end facet, but by changing the reflection angle of the excitation light 2, the return light could be reduced. You can avoid the effects. FIG. 2 shows an embodiment in which the installation angle of the semiconductor laser 1 is tilted so that the optical axis of the excitation light 2 is tilted from the normal line of the incident end face, and the same effect as the above embodiment is achieved. A numerical example is shown below. The stripe width of the semiconductor laser is 150 μm,
The vertical opening angle is 60°. Solid laser medium is Y
Assuming AG, the reflectance of the end face without anti-reflection coating is approximately 9%. Here, consider the effect when the vertical installation angle of the semiconductor laser is set to half the opening angle, that is, 30 degrees. The light returned to the semiconductor laser is approximately proportional to the intensity of the excitation light in the region where the light is incident perpendicularly to the solid-state laser medium. When the installation angle is not tilted, the peak portion of the Gaussian intensity distribution contributes to the returned light. On the other hand, while keeping the distance between the semiconductor laser and the incident end face the same, the installation angle was adjusted to 30°.
When tilted at an angle of .degree., the intensity of the excitation light contributing to the returned light is e-2 of the peak, or approximately 13.5%. As a result, by tilting the installation angle, the reflectance was approximately 1.2% (=9% x
The effect is almost the same as that obtained by applying an anti-reflection coating of 0.135). For example, if the input end face is coated with a 2% anti-reflection coating, tilting the installation angle will further reduce the effect of the returned light. Therefore, the distance between the semiconductor laser and the input end face can be reduced to improve oscillation efficiency. Improvements can be made. That is, when the installation angle is set to half the opening angle as described above, the returned light is about 13.5% compared to when the installation angle is vertical. Considering that the amount of returned light is approximately inversely proportional to the square of the distance between the semiconductor laser and the incident end face, by tilting the installation angle, the semiconductor laser
It becomes possible to reduce the distance between the incident end faces to approximately 1/3. Note that if the installation angle is 3/4 of the opening angle, the intensity of the excitation light contributing to the return light will be about 5%. If it is tilted too much, the excitation light will leak out from the incident end face, so the appropriate installation angle is about 1/2 to 3/4 of the opening angle.

Example 4. Further, in the above embodiment, the optical axis of the laser resonator and the excitation light almost coincide with each other, but a plurality of semiconductor lasers are arranged on the side of the laser medium, and the excitation light is made incident from the side of the laser medium. It can also be applied to structures where the optical axis and excitation light are orthogonal.

Example 5. In addition, in the above embodiment, the laser medium used was a plate-shaped one having a thickness thinner than the spread width of the excitation light in the solid-state laser medium. A solid-state laser medium having a cross-sectional shape with thickness and width, or a solid-state laser medium having a diameter smaller than the spread width of the excitation light in the solid-state laser medium and having a substantially circular cross-sectional shape may be used.

[0017]

As described above, according to the present invention, a plate-shaped plate having a thickness thinner than the spread width of the excitation light in the solid-state laser medium, or Using a solid-state laser medium with a cross-sectional shape that has a small thickness and width, or a diameter smaller than the spread width of the excitation light in the solid-state laser medium, and whose cross-sectional shape is approximately circular, this solid-state laser medium A non-reflective coating is applied to the excitation light incident end face of the semiconductor laser, and the distance between the semiconductor laser and the incident end face is made small to the extent that the reflected light from the incident end face does not change the oscillation wavelength of the semiconductor laser. Since it is placed close to the laser, it is possible to obtain a semiconductor-excited solid-state laser that is efficient and can generate laser light with stable output and good beam quality.

Specifically, the reflectance of the anti-reflection coating applied to the excitation light incident end face for the excitation light is 2% or less, and the distance between the above incident facet and the semiconductor laser is 100 μm.
If it is set between 500 μm and 500 μm, a highly efficient and stable laser can be obtained.

According to another aspect of the present invention, there is provided a plate-shaped plate having a thickness thinner than the spread width of the excitation light in the solid-state laser medium, or A solid-state laser medium with a cross-sectional shape that has a small thickness and width, or a diameter smaller than the spread width of the excitation light in the solid-state laser medium, and whose cross-sectional shape is approximately circular, is used as a semiconductor laser. Semiconductor-pumped solid-state lasers are arranged close to each other and the optical axis of the pumping light is tilted from the normal line of the pumping light input end face, making it possible to generate efficient, stable output, and high-quality laser light. There is an effect that can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional configuration diagram showing a semiconductor-excited solid-state laser according to an embodiment of the present invention.

FIG. 2 is a semiconductor-excited solid-state laser showing another embodiment of the present invention.
FIG.

FIG. 3 is a configuration diagram showing a conventional semiconductor-excited solid-state laser.

[Explanation of symbols]

1 Semiconductor laser 2 Excitation light 3 Solid laser medium 6 Laser light 7 Partial reflection mirror 32 Coating

Claims (3)

[Claims] 1. A semiconductor laser that emits excitation light, and an excitation light input end face coated with an anti-reflection coating, and a distance between the excitation light input end face and the semiconductor laser determined by reflection from the excitation light entrance end face. A plate-shaped plate disposed close to the semiconductor laser so that the light is small enough not to change the oscillation wavelength of the semiconductor laser, and having a thickness thinner than the spread width of the excitation light in the solid-state laser medium. or a cross-sectional shape having a thickness and width thinner than the spread width of the excitation light in the solid-state laser medium, or a diameter smaller than the spread width of the excitation light in the solid-state laser medium; A laser resonator comprising: a solid-state laser medium having a substantially circular cross-sectional shape; and a laser resonator configured to emit a laser beam from the solid-state laser medium and whose optical axis travels straight through the solid-state laser medium. Semiconductor-pumped solid-state laser. 2. The anti-reflection coating applied to the excitation light incident end face has a reflectance of 2% or less for the excitation light,
2. A semiconductor-excited solid-state laser according to claim 1, wherein the distance between said incident end face and the semiconductor laser is set between 100 .mu.m and 500 .mu.m. 3. A semiconductor laser that emits excitation light, and a plate-shaped plate disposed close to the semiconductor laser and having a thickness smaller than the spread width of the excitation light in the solid-state laser medium.
Alternatively, the cross-sectional shape has a thickness and width smaller than the spread width of the excitation light in the solid-state laser medium, or the cross-sectional shape has a diameter smaller than the spread width of the excitation light in the solid-state laser medium. a solid-state laser medium having a substantially circular shape, and a laser resonator configured to emit a laser beam from the solid-state laser medium and with its optical axis traveling straight through the solid-state laser medium; A semiconductor pumped solid-state laser configured such that the optical axis of the pumping light is inclined from the normal to the pumping light incident end face of the solid-state laser medium.