JP2580703B2 - Laser device - Google Patents

Description

The present invention relates to a laser device having a wavelength conversion function.

[Prior Art] FIG. 5 is a cross-sectional view showing a conventional solid-state laser device disclosed in, for example, a laser handbook (Ohm Co., Ltd., 1982). In the figure, (1) is a solid element, e.g. Taking YAG laser _{Y 3-X Nd x Al 5} O 12 rods shaped crystals composed of, (2) total reflection mirrors, (3) is in a light source For example, the flash lamp (4) is a power supply for lighting the flash lamp (3), (5) is a condensing reflection mirror, (6) is an exit mirror made of, for example, glass,
(7) is a partially reflective film made of, for example, TiO _{2 provided} on the inner surface of the exit mirror (6); (8) is a non-reflective film made of, for example, SiO _{2 provided} on the outer surface of the exit mirror and on both side surfaces of the solid state element; 9) is a laser beam in a laser resonator,
(10) is a laser beam extracted outside, and (12) is an outside work.

Next, the operation will be described. The solid state element (1) is excited by direct light from a flash lamp (3) turned on by a power supply (4) and reflected light from a converging / reflecting mirror (5) to form a laser medium. On the other hand, the laser beam (9) confined in a so-called stable resonator consisting of an exit mirror (6) having a partial reflectance and a total reflection mirror (2) by a partial reflection film (7) provided on the inner surface. Each time the laser medium reciprocates between the two mirrors, it is amplified by the laser medium, and when it becomes a certain size or more, a part thereof is emitted outside as a laser beam (10) through the exit mirror (6).

[Problems to be Solved by the Invention] Since the conventional laser device uses the stable resonator as described above, the generated laser beam is a so-called higher-order mode having a large divergence angle. As an index of the degree of the higher-order mode, there is a ratio between the cross-sectional diameter of the lowest-order mode having a uniform phase that can be generated in the resonator and the diameter of the laser medium. In this example, the lowest-order mode is a so-called Gaussian beam having a normal distribution. Therefore, the sectional diameter φ ₀ defined at a point where the intensity is 1 / e ^{2 of the} center is the distance L between the two mirrors, the wavelength of the laser beam. as λ Is calculated. On the other hand, since the cross-sectional diameter of the laser medium is 8 mm, the ratio between the two is very large, about 15, and from this value, empirically, higher-order modes of 100th or higher are usually generated. Therefore, the divergence angle of the laser beam is 10 mrad. The magnitude of the divergence angle can be said to be the laser beam focusing performance itself. This is because the converging spot stage Φs by the converging lens having the focal length f is roughly represented by φsf · θ with respect to the divergence angle θ, so that the size of the converging spot diameter is proportional to the divergence angle. Because it is decided. Compared to commercially available CO ₂ laser a value of 10mrad herein, is about 10 times, thus focusing characteristics of the conventional solid-state laser apparatus CO ₂
It can be said that it is 1/10 of the laser device.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to obtain a laser device which has a small divergence angle and can obtain a laser beam having good light-collecting performance.

[Means for Solving the Problems] A laser device according to the present invention uses an unstable type laser resonator having a negative branch and converts a laser beam into a laser beam having a shorter wavelength than a laser beam generated in the resonator. The wavelength conversion element is provided near a focal point formed in a resonator.

[Action] The negative branch unstable laser resonator according to the present invention generates a high-quality laser beam with a large cross-sectional area and generates a very narrow spot at a focal point formed in the resonator. The laser beam is efficiently converted into a harmonic by the wavelength conversion element installed near the spot, and a laser beam with a small divergence angle is obtained.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, (1) is a solid element, e.g. Taking YAG laser in Example _{Y 3-X Nd x Al 5} O 12 rods shaped crystals composed of, (2) total reflection mirrors, (3) A flash lamp, (4) a power supply for lighting the flash lamp (3), (5) a condenser mirror, (6) an exit mirror made of glass, for example, and (7) an exit mirror (6). A partial reflection film made of, for example, TiO _{2 provided} at the center of the inner surface, (8) is on the outer periphery of the partial reflection film (7) on the inner surface of the exit mirror, and the outer surface of the exit mirror (6), and furthermore, the solid state device (1).
An anti-reflection film made of, for example, SiO ₂
(9) and (11) are laser beams generated in a laser resonator comprising an exit mirror (6) and a total reflection mirror (2), (10) is a laser beam extracted outside the laser resonator, and (12) ) Is an external device, (13) is a focus formed in the resonator, and (30) is a wavelength conversion element made of, for example, a KTP crystal.

Next, the operation will be described. The solid-state element (1) is excited by the direct light from the flash lamp (3) turned off by the power supply (4) and the reflected light from the condenser mirror (5) to form a laser medium. On the other hand, the laser beams (9) and (11) generated in the laser resonator composed of the exit mirror (6) and the total reflection mirror (2) are amplified by the laser medium and have a certain size or more. A part thereof is taken out as a laser beam (10).

The laser resonator will be described in more detail. The exit mirror (6) and the total reflection mirror (2) constitute a so-called negative branch unstable resonator. The laser beam (11) is amplified by the solid-state element (1), then condensed by the total reflection mirror (2) and amplified by the solid-state element (1) to become a laser beam (9). Most of the peripheral part of the outer mirror is emitted to the outside by the action of the anti-reflection film on the inner peripheral part of the exit mirror (6), and a part of the central part is a part of the partial reflective film on the central part of the inner surface of the exit mirror (6). Taken out by the action,
The remaining portion reciprocates inside the laser resonator as a laser beam (11). Therefore, the external laser beam (10) is jammed. Also, in such an unstable type resonator, the difference in loss between the lowest-order mode and the higher-order mode with the same phase is much larger than that of the stable type resonator, and the laser beam is expanded every round-trip. ,
After several round trips, the generated laser beam is only the one in the lowest mode with a large cross-sectional area. The exit mirror (6) has a meniscus shape smaller than the radius of curvature of the outer surface and the radius of curvature of the inner surface, and makes the exit beam substantially parallel. From these facts, an in-phase parallel laser beam (10) having the same phase is obtained. This laser beam is converted into a second high frequency by a wavelength conversion element (30) provided near a focal point (13) formed in the resonator. The efficiency of the wavelength conversion is substantially proportional to the intensity of the laser beam incident on the wavelength conversion element (30). In the present invention, the wavelength conversion element ( Most of the emitted laser beam (10) is the wavelength-converted second high frequency wave because of the installation of (30). The divergence angle θ of the output laser beam is expressed as wavelength λ and the outer diameter D of the output beam. However, in the present invention, a laser beam having the same diameter as that of a laser medium having a diameter of 8 mm is obtained from a laser medium having the same size as that described in the conventional example, and the divergence is obtained because the wavelength is half in the present invention. Angle (θ _{1 of the} present invention, θ _{1 of} the conventional
₀ )) Therefore, a laser beam having a very good condensing property can be obtained. Although the exit mirror has a partial reflectivity at the center of the inner surface of the exit mirror, the exit mirror may exhibit a total reflection. In this case, a ring-shaped laser beam is generated, and the shape of the laser beam depends on the ring shape. Although the light-gathering performance is deteriorated due to the diffraction effect, a sufficiently high-quality laser beam can be generated as compared with the conventional example.

In the above embodiment, the central part (7) of the inner surface of the exit mirror is used.
The phase difference between the laser beams passing through the laser beam and the surrounding portion (8) was small and did not cause a problem. However, this may be a problem depending on the configuration of the partial reflection film (7). Means for canceling the phase difference between them may be provided. For example, as shown in FIG. 2, it can be realized by providing a step (70) on the outer surface of the exit mirror.

In the above embodiment, the laser mirror is provided separately from the solid-state element. However, as shown in FIG. 3, the end face of the solid-state element (1) is processed to form a total reflection film (20), which is integrated. Is also good.

Further, in the above embodiment, an example is shown in which a converging laser beam is reflected from the total reflection mirror, but a parallel laser beam may be reflected as shown in FIG.

Any solid laser device may be used as long as it uses a laser medium, and the wavelength conversion element is not limited to a solid.A laser beam having a shorter wavelength than the laser beam generated in the resonator is used. It is needless to say that a liquid or a gas may be used as long as the laser beam is converted into a laser beam.

[Effects of the Invention] As described above, according to the present invention, an unstable resonator having a negative branch is used, and a laser beam having a shorter wavelength than a laser beam generated in the resonator is provided near a focal point in the resonator. Since the wavelength conversion element for converting the laser beam into the laser beam is provided, a high-quality laser beam having a low divergence angle can be obtained very efficiently.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a laser device according to an embodiment of the present invention, and FIGS. 2, 3, and 4 are sectional views showing a laser device according to another embodiment of the present invention. FIG. 5 is a sectional view showing a conventional laser device. (1) Solid state device (2) Total reflection mirror (3) Light source (6) Exit mirror (7) Partially reflective film (9) (10) (11) Laser beam (13) Focus, (30) Wavelength conversion element In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] An unstable resonator configured to be a negative branch by a plurality of mirrors, and a laser installed near a focal point formed in the resonator and configured to generate a laser beam in the resonator A laser device provided with a wavelength conversion element for converting a laser beam having a shorter wavelength than the beam.