JPH0563264A - Semiconductor laser end pumped solid-state laser device - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser end pumped solid-state laser device capable of ensuring higher power keeping beam quality satisfactory by a relatively simplified construction. CONSTITUTION:There is employed as an output mirror 2 a reflectivity distributed mirror which has reflectivity to oscillation laser beam becoming progressively reduced as it goes in the direction of an outer periphery from the center. Hereby, there is effectually increased a lasing mode volume such that a higher order transversal mode is prevented from being produced to derive satisfactory beam quality laser beam L1. Hereby, a mode volume of pumping laser light L0 coincident with the foregoing lasing mode volume is increased, and the amount of the incident pumping laser beam is increased by increasing the incident area of the pumping laser beam. Thus, higher output power is ensured, keeping beam quality satisfactory.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output laser by exciting laser light emitted from a semiconductor laser device from the end faces of the solid-state laser medium, which are the entrance and exit faces of the resonant laser light, to excite the solid-state laser medium. The present invention relates to a semiconductor laser edge-pumped solid-state laser device for obtaining light.

[0002]

2. Description of the Related Art An output laser beam is obtained by exciting a laser beam emitted from a semiconductor laser device from an end surface of a solid-state laser medium which is an entrance / exit surface of a resonant laser beam to excite the solid-state laser medium. Semiconductor laser edge-pumped solid-state laser devices are described, for example, in the literature [J. Berger et a
L., Appl. Phys. Lett., vol. 51, pp1212-1214 1987] are known.

FIG. 5 is a view showing the arrangement of the apparatus disclosed in the above-mentioned document, which is an Nd: YAG laser rod (diameter: 2 m).
m, length 10 mm) of the solid-state laser medium 1 having one end face (= resonance laser beam entrance
Excitation laser light L ₀ (wavelength: 0.81 μm) emitted from the excitation semiconductor laser device 2 from the emission surface) enters through the condensing optical system 3 to excite the solid-state laser medium 1 and output laser light L ₁ (wavelength: 1.06 μm). The left end face of the solid-state laser medium 1, that is,
The excitation laser light L _{0 is on} the incident surface of the excitation laser light L _0.
A selective reflection film 4 which transmits 93% of the laser light but totally reflects the oscillated laser light L _1, and the output mirror 5 arranged on the right outer side of the solid-state laser medium 1 with the same optical axis. It is designed to form a resonator.

This output mirror 5 has a concave surface with a radius of curvature of 10 cm as a reflecting surface and reflects the output laser beam L ₁ by 95%. The resonator length is 5.5 cm with the selective reflection film 4 described above.
The laser resonator of TEM ₀₀ oscillation mode of the laser oscillation mode in this laser resonator has a beam spot diameter of 130 μm. In addition,
The reflectance of the output mirror 5 is uniform over the entire reflecting surface.

Here, in order to maintain a high conversion efficiency of the pumping laser light into the output laser light and obtain a Gaussian beam output laser light with good mode quality, the pumping laser light is used in the solid laser medium. It is necessary to match the mode volumes of the two so that the region where the laser light propagates and the region where the oscillating (resonant) laser light travels exactly overlap. In the above-mentioned conventional example, the condensing degree of the condensing optical system 3 is set so as to satisfy this condition. Therefore, when the output of the pumping semiconductor laser device 2 is 1.41 W, the output power is 415 mW. The conversion efficiency is 36.6%, and the output laser beam L ₁ is a Gaussian beam with a good mode quality in the TEM ₀₀ mode.

[0006]

By the way, in the conventional semiconductor laser edge-pumped solid-state laser device as described above, there are many cases in which a device having a larger output power is desired. To increase the output power, the output of the excitation semiconductor laser device may be increased to increase the excitation energy. In order to increase the excitation energy, the energy density of the excitation laser light may be increased, or the incident area of the excitation laser light on the solid-state laser medium may be increased to increase the incident light amount.

However, in order to increase the energy density of the exciting laser light, it is necessary to increase the output per unit light emitting area of the exciting semiconductor laser device, but this is limited. On the other hand, it is possible to increase the incident light amount by increasing the incident area of the excitation laser light on the solid-state laser medium, but even if the incident area is increased unnecessarily, the mode volume of the oscillation laser light and the excitation laser light are increased. Since it becomes impossible to match the mode volume, the conversion efficiency is deteriorated and the mode quality of the oscillated laser light is deteriorated. That is, for example, in the above-mentioned conventional example, since the beam spot diameter that determines the mode volume of the oscillation laser light in the TEM ₀₀ oscillation mode that can maintain good beam quality is 130 μm, the excitation laser light having an area exceeding this diameter is obtained. Is caused, a mode volume mismatch occurs, which not only deteriorates the conversion efficiency but also deteriorates the beam quality of the output laser light.

The present invention has been made under the background described above, and a semiconductor laser end-pumped solid-state laser capable of obtaining high output power while maintaining good beam quality with a relatively simple structure. It is intended to provide a device.

[0009]

In order to solve the above problems, the present invention provides (1) a solid-state laser in which a laser beam for pumping emitted from a semiconductor laser device for pumping is arranged in a laser resonator. In a semiconductor laser end-pumped solid-state laser device in which a resonant laser beam of the solid-state laser medium is incident on the medium from an end face which is an input / output face to excite the solid-state laser medium to obtain an output laser beam, the laser resonance A reflectance distribution type mirror is used as an output mirror that configures the container and transmits the oscillated laser light to the outside as output laser light to gradually reduce the reflectance of the oscillated laser light from the center toward the outer circumference. In addition, as a mode of the configuration 1,
(2) In the semiconductor laser edge-pumped solid-state laser device of configuration 1, the output mirror is a Gaussian mirror whose reflectance distribution is represented by a Gaussian function or a super Gaussian function. Is.

[0010]

According to the above-mentioned structure 1, by using the reflectance distribution type mirror whose reflectance with respect to the oscillated laser light gradually decreases from the center toward the outer circumference, the high-order transverse mode is generated. It is possible to effectively increase the oscillation mode volume that can suppress the laser light and extract the oscillated laser light with good beam quality. As a result, the mode volume of the excitation laser light that matches the oscillation mode volume can be increased, and the incident area of the excitation laser light can be increased to increase the amount of incident excitation laser light. It is possible to obtain high output power while maintaining good beam quality.

Further, according to the configuration 2, the operation obtained by the configuration 1 can be performed in a state close to the best.

[0012]

FIG. 1 is a diagram showing the structure of a semiconductor laser edge-pumped solid-state laser device according to an embodiment of the present invention, and FIG. 2 is a diagram showing the reflectance distribution of an output mirror. An embodiment of the present invention will be described in detail below with reference to these drawings. Since this embodiment has many parts in common with the configuration of the above-mentioned conventional example, the same parts are designated by the same reference numerals in the following description.

In FIG. 1, reference numeral 1 is a solid-state laser medium,
Reference numeral 2 is a pumping semiconductor laser device, reference numeral 3 is a converging optical system, reference numeral 4 is a selective reflection film attached to one end face of the solid-state laser medium, and reference numeral 5 is an output mirror. The selective reflection film 4 and the output mirror 5 form a laser resonator.

The solid-state laser medium 1 is an Nd: YAG laser rod having a diameter of 2 mm and a length of 10 mm, and its oscillation wavelength is 1.06 μm, as in the above-mentioned conventional example.

The central axis of the rod of this solid-state laser medium 1 (=
The excitation semiconductor laser device 2, the focusing optical system 3, and the output mirror 5 are arranged on both sides in the (optical axis) direction with the optical axis being common.

The pumping semiconductor laser device 2 has a wavelength of 0.8.
Fifteen semiconductor lasers capable of oscillating a laser beam of 1 μm with an output of 1 W were used, and the laser beam emitted from each semiconductor laser was guided to a fiber bundle so that the laser beam could be emitted so as to be substantially equivalent to an output of 8 W. It is a device.

The condensing optical system 3 condenses the excitation laser light L ₀ emitted from the excitation semiconductor laser device 2 into a predetermined beam spot diameter and intersects with the optical axis of the solid-state laser medium 1 at one end surface. Is incident on the solid-state laser medium 1.

The selective reflection film 4 is attached to the left end surface of the solid-state laser medium 1, that is, the incident surface of the excitation laser light L ₀ , and is composed of a dielectric multilayer film. Although it transmits 93% of L ₀ , the oscillated laser beam L ₁ has a property of being totally reflected (reflectance: 99.9% or more). The selective reflection film 4 and the output mirror 5 constitute a laser resonator having a resonator length of 5 cm.

The output mirror 5 constitutes the characteristic point of the present invention, and a reflectance distribution type mirror (VRM; Variable Reflectivity) in which a concave surface having a radius of curvature of 1 m is directed toward the solid-state laser medium 1 side and is used as a reflecting surface. Mirror). FIG. 2 shows the oscillation laser light L ₁ (wavelength; 1.
It is a figure which shows the reflectance distribution curve with respect to (06 μm). In FIG. 2, the vertical axis R (x) is the reflectance and the horizontal axis x is the distance from the center of the output mirror 5. As shown in FIG. 2, the reflectance R (x) is represented by a Gaussian function or a super Gaussian function represented by the following equation.

R (x) = R ₀ exp [−2 (x / ω) ⁿ ] where R ₀ is the peak reflectance, ω is the beam spot diameter,
n is a super Gaussian factor. Therefore, this output mirror 5 is a Gaussian mirror (GRM).
eflectivity Mirror or Graded Reflectivity Mi
rror) is also called. A mirror having such a reflectance distribution may be formed, for example, by forming a dielectric multilayer film on the surface of a glass substrate having a concave lens shape, and selecting one or more of the thin films constituting the multilayer film. It can be obtained by gradually changing the thickness from the center toward the outer periphery (for details, see, for example, Japanese Patent Application No. 2-2
9476). In this example, R ₀ = 95
%, Ω = 0.35 mm, and n = 2,
Beam spot diameter in TEM ₀₀ oscillation mode is 500
could be set to μm. Therefore, when the pumping laser light L ₀ is focused by the focusing optical system 3 so as to match the beam spot diameter and the mode volumes of both are matched, the incident area can be made larger than in the conventional case. Therefore, it becomes possible to increase the light amount of the excitation laser light. That is, in the above-mentioned conventional example using the same solid-state laser medium as this example, the beam spot diameter of the oscillated laser beam was 130 μm.

When a laser oscillation experiment was conducted with the device of this example, when the output of the pumping semiconductor laser device 2 was 8 W, the output power was 3 W and its conversion efficiency was 37.
%, It was possible to obtain the output laser light L ₁ which was a Gaussian beam having a good mode quality in the TEM ₀₀ mode.

As shown in FIG. 3, the selective reflection film 4 in the above-described embodiment is removed, and instead, a flat plate-shaped external selective reflection mirror 42 having the same function is provided on the left side of the solid laser medium 1. In addition to being provided outside, instead of using the output mirror 5, the right end surface in the figure of the solid-state laser medium 1 is formed as a convex spherical surface on the outside, and an internal output reflection film 52 having the same function as the output mirror 5 is attached. It may be configured. In this case, the characteristics of each mirror, the laser cavity length, and the like are the same as in the above-described embodiment.

Further, as shown in FIG. 4, instead of the selective reflection mirror 42 in FIG. 3, an external convex surface selective reflection mirror 43 having a convex spherical curved surface shape on the solid laser medium 1 side is used, and an output reflection film 52. Instead of using, the output mirror 53 having a concave spherical curved surface shape on the solid-state laser medium 1 side may be used. In this case, the external convex surface selective reflection mirror 43
Has a radius of curvature of 5 m and the output mirror 53 has a radius of curvature of 4.1.
7 m to form a laser resonator having a cavity length of 45 cm, and in the function expressing the reflectance distribution of the output mirror, R ₀ = 60%, ω = 0.7 mm, and n = 2. The characteristics substantially equivalent to those of the first embodiment can be obtained.

In the above-described embodiment, an example in which the Nd: YAG rod is used as the solid-state laser medium is given. However, as the solid-state laser medium, Nd: YLF and Nd: gl are used.
ass, Nd: YVO ₄ , Nd: GGG, Nd: YSG
G, NYAB, NAB, Er: YAG, Er: YLF,
Er: glass or the like may be used. In that case, it is needless to say that conditions such as a laser resonator should be selected according to each laser medium.

As the pumping semiconductor laser device, a broad area semiconductor laser, a semiconductor laser array, a two-dimensionally stacked semiconductor laser array, or the like can be used in addition to a general single-stripe semiconductor laser device.

Further, the condensing optical system may be an optical system using an optical fiber in addition to the condensing optical system using a general lens.

[0027]

As described in detail above, in the semiconductor laser end-pumped solid-state laser device according to the present invention, as an output mirror, the reflectance distribution is such that the reflectance for the oscillated laser light gradually decreases from the center toward the outer circumference. It is possible to suppress the generation of higher-order transverse modes and effectively increase the oscillation mode volume that can extract the oscillation laser beam with good beam quality by using the type mirror. It is possible to increase the mode volume of the pumping laser light to increase the incident area of the pumping laser light and increase the amount of the pumping laser light to be incident, thereby maintaining good beam quality. This makes it possible to obtain high output power.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a semiconductor laser edge-pumped solid-state laser device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a reflectance distribution curve of an output mirror.

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

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

FIG. 5 is a diagram showing a configuration of a conventional example.

[Explanation of symbols]

1 ... Solid-state laser medium, 2 ... Excitation semiconductor laser device, 3
... Condensing optical system, 4 ... Selective reflection film, 5 ... Output mirror.

Claims (2)

[Claims] 1. A pumping laser beam emitted from a pumping semiconductor laser device is supplied to a solid-state laser medium arranged in a laser resonator from an end face which is an entrance / exit face of the resonant laser beam of the solid-state laser medium. In a semiconductor laser end-face pumped solid-state laser device that is incident and excites the solid-state laser medium to obtain output laser light, the laser resonator is configured and the oscillation laser light is transmitted and taken out as output laser light to the outside. A semiconductor laser edge-pumped solid-state laser device characterized in that a reflectance distribution type mirror whose reflectance with respect to an oscillating laser light gradually decreases from the center toward the outer periphery is used as an output mirror. 2. The semiconductor laser edge-pumped solid-state laser device according to claim 1, wherein the output mirror is a Gaussian mirror whose reflectance distribution is represented by a Gauss function or a super Gauss function. Edge-pumped solid-state laser device.