JPH0344982A - Solid state laser device - Google Patents

Abstract

PURPOSE:To maintain a constant divergent angle of a laser beam without dependence on the output of laser by installing a cooling means to one end face of a solid state element and a refracting mirror which is non-reflective to the light from an excitation light source and totally reflective to laser light so that it may serve as a resonance mirror. CONSTITUTION:The light transmitted from an excitation light source 3 lit up by a power source 4 is repeatedly reflected directly or on the inner surface of a cone-shaped light transmission passage 5 which is reduced in its mouth. It is integrated, passes through a reflecting mirror 2, and is applied to a solid state element 1, thereby generating a laser beam. The laser beams 9 and 11 generated inside an unstable type resonator which comprises an outlet mirror 6 and a reflecting mirror 2 are amplified by a laser medium 1 are emitted by way of a non-reflective film 8 of the outlet mirror 6, or a central part of the beams through a partial reflective film 7 on the inner surface of the outlet mirror 6. Both are synthesized and emitted as a laser beam 10. The generated heat is eliminated from the element 1 by way of a cooling medium 55.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a solid-state laser device, particularly to stabilizing the quality of a laser beam generated from a solid-state laser device.

[Prior art] Fig. 13 shows, for example, the laser handbook (Ohmsha,
1 is a cross-sectional configuration diagram showing a conventional solid-state laser device shown in 1982). In the figure, (1) is a solid-state element, for example, taking a YAG laser as an example, Y3-xNdx
A rod-shaped crystal made of AIso+2, (3) is an excitation light source, such as a flash lamp, and (4) is an excitation light R(
3) Q power supply for lighting, (5000) is a reflective mirror (6) is an exit mirror made of glass, for example (7)
For example, Tif is provided on the inner surface of the exit mirror (6).
(8) is a non-reflection film made of, for example, 5102, provided on the outer surface of the exit mirror (6) and both sides of the solid-state element (1), and (9) is a partially reflective film made of 5102 in the laser co-installation device. Laser beam, (10) is the laser beam taken out to the outside, (12) is the external workpiece, (20) is the total reflection mirror
(30) is a flow tube (
50) is the cooling water inlet, (51) is the cooling water outlet, (6
0) is an arrow indicating the flow of cooling water.

Next, the operation will be explained. The solid state element (1) is connected to the power source (4
) is excited by the direct light from the flash lamp (3) and the reflected light from the inner surface of the reflecting mirror (5000), and forms a laser medium. On the other hand, a laser beam (9) is confined within a so-called stable resonator consisting of an exit mirror (6) with partial reflectance and a total reflection mirror (20) due to a partial reflection film (7) provided on the inner surface. teeth,
Each time it travels back and forth between both mirrors, it is amplified by this laser medium, and when it reaches a certain size or more, a part of it is emitted to the outside as a laser beam (10) through an exit mirror (6).

In addition, the cooling water inlet (50
) is cooled from the side by the cooling medium flowing in.

[Problems to be Solved by the Invention] As described above, in conventional solid-state laser devices, the side surface of the rod, that is, the solid-state element, is cooled. Therefore, the temperature distribution within the rod cross section and the refractive index distribution caused by this temperature distribution As shown in Figure 14, a quadratic distribution was obtained, and due to the refractive index difference caused by the temperature distribution, the rod acted as a lens for the laser beam passing in the axial direction of the rod, changing the state of the resonator. . The degree of lens formation of the rod changes depending on the power input to the excitation light source that irradiates the rod, and therefore the laser output. Therefore, the divergence angle of the laser beam generated from the resonator varies depending on the laser output as shown in FIG. There was a problem that it changed due to

Incidentally, the size of the divergence angle of a laser beam can be said to be the focusing performance of the laser beam itself. This means that the condensing spot system φ5 by a condensing lens with focal length f is roughly expressed as φ, = f・θ with respect to the divergence angle θ, and therefore the condensing spot diameter changes in proportion to the divergence angle. This is because the size is determined.

Therefore, a change in the divergence angle depending on the laser output means a change in the light condensing characteristics, which has caused the problem that stable laser processing cannot be performed.

This invention was made to solve the above-mentioned problems, and its purpose is to obtain a stable solid-state laser device that can generate a laser beam with a constant divergence angle regardless of the laser output. do.

[Means for Solving the Problems] A solid-state laser device according to the present invention guides light from an excitation light source that excites a solid-state element to one end surface in the optical axis direction of the solid-state element through a cylindrical light guide path, and The end face was cooled, and a reflecting mirror that did not reflect the light from the excitation light source and totally reflected the laser light was provided on one of the above end faces as one of the resonator mirrors that constituted the laser resonator. It is something.

Note that it is preferable that at least a portion of the inner surface of the cylindrical light guide path be processed to diffusely reflect the light from the excitation light source.

[Function] The cylindrical light guide path in the present invention uniformizes the distribution of light from the excitation light source, guides it to one end surface in the optical axis direction of the cooled solid-state element, and guides the light from the excitation light source to one end surface in the optical axis direction of the solid-state element. The mirror completely transmits the light from the excitation light source, and the completely transmitted light uniformly excites the solid-state element in the cross-sectional direction (therefore, in the direction perpendicular to the laser beam traveling direction (optical axis direction)), and also excite the solid-state element from the excited solid-state element. The generated laser beam is reflected into the resonator to form a resonator state. In this configuration, no temperature distribution occurs in the direction perpendicular to the direction of travel of the laser beam, and therefore the laser beam is not focused or diverged by being incident on the solid-state element and reflected, resulting in an excitation light source. It is possible to reduce the change in the divergence angle of the laser output due to the change in human power and therefore the change in the laser output.

[Example code] An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, (1) is a solid-state element, for example '/A
Taking the G laser as an example, a rad-shaped crystal made of Y3-NdAl5O12, (2) is provided on one end surface of the rod (1) in the optical axis direction, and is a laser beam that undergoes total reflection. A reflecting mirror that completely transmits light from an excitation light source, for example, is made of a dielectric multilayer film made of a combination of TlO2 and 5102, and serves as a collimating mirror. (3) is an excitation light source, for example an arc lamp, and (4) is an excitation light source (
3) is a power source for lighting, (5) is a cylindrical light guide, (
6) is an exit mirror made of glass, for example, and serves as a magnifying mirror. (7) is a partial reflection film made of, for example, Ti(h) provided at the center of the inner surface of the exit mirror (6); (8)
is a non-reflective film made of S:02, for example, provided on the inner surface of the exit mirror, around the partially reflective film (7), on the outer surface of the exit mirror (6), and on the side surface of the solid-state element (1), (9)
(11) is a laser beam generated within a laser resonator consisting of an exit mirror (6) and a reflecting mirror (2), (10) is a laser beam taken out outside the laser resonator, (12)
) is the outer wall, (30) is a flow tube that forms a cooling medium passage around the excitation light source (3), for example, Pyrex glass with a coating that completely transmits the light from the light source, and (50) is a light guide path. inlet for cooling medium into (5
1) is a cooling medium outlet, (55) is a cooling medium,
For example, water, (60) is an arrow indicating the flow of the cooling medium (55), and (70) is a heat insulating material that insulates the periphery of the solid element (1).

Next, the operation will be explained. Part of the light emitted from the excitation light source (3) turned on by the power source (4) is directly transmitted, and most of the light is emitted from the excitation light source (3) to the solid state element (1).
It is repeatedly reflected on the inner surface of the cylindrical light guide (5), which has a cone shape that tapers toward the end, and as a result, the excitation light source (3
) is integrated and passes through the reflecting mirror (2),
The solid-state element (1) is uniformly irradiated from one end face in the optical axis direction, and the solid-state element (1) excited by the irradiation forms a laser medium. On the other hand, a laser beam (
9X11) is amplified by this laser medium every time it goes back and forth between both mirrors, and when it reaches a size larger than a certain chamber,
The entire peripheral part passes through the non-reflection film (8) on the inner surface of the exit mirror (6), and a part of the central part passes through the exit mirror (6).
The laser beam is emitted through a partially reflecting film (7) on the inner surface of the laser beam, and both are combined and emitted as a solid laser beam (10). Since an unstable resonator is used, the laser beam has almost the same phase, and therefore a laser beam with almost diffraction-limited focusing quality can be obtained.

Next, a description will be given of the end-face excitation configuration of the solid-state device, which is the center of this invention. After the light from the excitation light source (3) is integrated by the cylindrical light guide (5), it is converted into light with almost uniform intensity in the cross-sectional direction, and the solid-state element (1) is passed from the end face to the reflecting mirror (2). Uniform irradiation and excitation through. Solid-state device (
1) A part of the incident light is extracted to the outside as a laser beam (10), but the remaining light becomes heat and generates a temperature distribution and therefore a refractive index distribution within the solid-state element. However, due to the cooling medium (55), the solid state element (1)
Since it is cooled from the same end surface that is irradiated with light, and the surrounding surface is insulated by a heat insulating material (70), the refractive index distribution within the solid-state element occurs only in the optical axis direction of the laser beam.
Almost no distribution occurs in the cross-sectional direction. FIG. 2(a) shows the internal pressure refractive index distribution of the solid-state device (1) when the solid-state device is excited with a configuration according to an embodiment of the present invention, and FIG. 2(b) shows the same solid-state device (1). The refractive index distribution within a solid-state element when excited with a conventional configuration (FIG. 13) is shown. It can be seen that in the configuration according to the present invention, there is almost no change in the refractive index in the cross-sectional direction of the solid-state element. In addition, in the configuration according to the present invention, a refractive index distribution occurs in the laser beam optical axis direction, but this distribution is caused by the mirror (6), the mirror (
2) By only slightly changing the resonator length between the two, the divergence angle of the generated laser beam (10) is not affected. FIG. 3 shows changes in laser beam divergence angle with respect to changes in laser output. Here, the solid-state element (1) is excited by the arc lamp Y2. aNde, eAI5012, the diameter of its cross section is 12 mm, the length is 10 mm, the distance between the exit mirror (6) and the total reflection mirror (2) is 0,
44 m, and the reflectance of the partially reflective film (7) at the center of the inner surface of the exit mirror is 80 r.

As shown in Fig. 4, if a diffuse reflection surface (500) that diffusely reflects the light from the light source is formed on a part or the entire surface of the inner surface of the light guide, the effect of integrating the light will further increase, and the solid-state element can be integrated with higher accuracy. (1) can be uniformly irradiated from the end face.

In addition, in the above embodiment, a configuration using an unstable resonator with a negative branch configuration in which the laser beam is focused within the resonator was shown, but as shown in FIG. An unstable type resonator may be used, or a total reflection film (77) as shown in Fig. 6 may be used.
An unstable resonator that generates a ring-shaped laser beam (10) using Various resonators such as a resonator can be used.

In the above embodiment, the light from the excitation light source (3) is repeatedly reflected and integrated on the inner surface of the cylindrical light guide (5), which has a cone shape that tapers toward the solid-state element (1). Although the configuration in which the element (1) is uniformly irradiated from the end face is shown,
When the excitation light source (3) is sufficiently thin, a cylindrical light guide (5) with a cone-like opening that widens toward the solid-state element (1) is used, as shown in Figure 8. The more efficiently the light from the excitation light source (3) can be guided to the solid-state element (1).

In addition, a reflecting mirror (2) provided on one end surface of the solid-state element
may be used as a folding intermediate mirror in a resonator composed of an exit mirror (6) and a total reflection mirror (20), as shown in FIG.

Furthermore, the excitation light source is not limited to a lamp; for example, as shown in Figure 1O, an external light source such as a microwave excitation source (
If the light (310) generated by the device (300) is guided into the light guide path (5) through the window (80), the cooling medium (55) that cools the solid-state element only needs to cool the solid-state element; Increased efficiency.

Furthermore, as shown in FIG. 11, a semiconductor laser (301
) may be guided into the light guide path (5). In this case, by matching the wavelength of the semiconductor to the absorption wavelength of the laser oscillation of the solid-state element, only the light used for laser oscillation is transmitted to the solid-state element. Therefore, the heat generation within the solid-state device is reduced, and the effectiveness of the invention is enhanced.

Furthermore, as shown in FIG. 12, a semiconductor laser (301
) through an optical fiber (312) to a light guide path (5
), more light from the semiconductor laser can be guided into the solid-state element without being limited by the size of the semiconductor laser (301).

[Effects of the Invention] As described above, according to the present invention, the light from the excitation light source that excites the solid-state element is guided to one end face in the optical axis direction of the solid-state element through the cylindrical light guide path, and the above-mentioned end face is cooled. Furthermore, a reflecting mirror that does not reflect the light from the excitation light source and totally reflects the laser light is provided on one end face as one of the resonator mirrors that constitute the laser resonator, so that the solid-state element The refractive index in the cross-sectional direction within the solid-state element can be kept constant regardless of the degree of excitation, and therefore a laser beam with a stable divergence angle can be obtained regardless of the laser output.

Furthermore, on at least a part of the inner surface of the cylindrical light guide,
If the light from the excitation light source is processed to diffusely reflect it, the light from the excitation light source can be efficiently integrated, the solid-state element can be excited more uniformly in the cross-sectional direction, and a more stable laser beam can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional configuration diagram showing a solid-state laser device according to an embodiment of the present invention, and FIGS. 2(a) and 2(b) are refractive index distributions of solid-state elements in an embodiment of the present invention and a conventional solid-state laser device, respectively. FIG. 3 is a characteristic diagram showing the divergence angle characteristics of a solid-state laser device according to one embodiment of the present invention, and FIGS. 4 to 12 are distribution diagrams showing the divergence angle characteristics of a solid-state laser device according to another embodiment of the present invention. 13 is a cross-sectional diagram showing a conventional solid-state laser device, FIG. 14 is a distribution diagram showing the refractive index distribution of a solid-state element in a conventional solid-state laser device, and FIG. 15 is a diagram showing a conventional solid-state laser device. FIG. 2 is a characteristic diagram showing divergence angle characteristics in a laser device. (1)...Solid element, (2)...Reflection mirror (2
0)... Total reflection mirror (3)... Light source, (300
)...External light source, (30+)...Semiconductor laser, (
5)...Light guide path, (500)...Diffuse reflection surface, (6
)...Exit mirror (9X10) (11)...Laser beam, (50)...Cooling medium inlet, (51)...
・・Cooling medium outlet, (55) ・・Cooling medium,
In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] (1) a solid-state element, a light source that excites the solid-state element, a cylindrical light guide path that reflects and integrates the light from the light source on its inner surface and guides it to one end surface in the optical axis direction of the solid-state element; a cooling means for cooling the one end surface; a reflecting mirror provided on the one end surface of the solid-state element that does not reflect the light from the light source and totally reflects the laser beam; together with the reflecting mirror, a laser resonator; A solid-state laser device equipped with a resonator mirror. (2) The solid-state laser device according to claim 1, wherein at least a portion of the inner surface of the cylindrical light guide path is processed to diffusely reflect the light from the light source.