JPH02109382A - Laser apparatus - Google Patents

Abstract

PURPOSE:To take out a high quality laser beam stably by using an unstable type optical resonator on a ring shaped light path as a specified output mirror. CONSTITUTION:A laser beam 18 is reflected from a second reflecting mirror 15 in an unstable type optical resonator 16 and amplified in a laser medium 1. Thus a laser beam 17 is obtained. The laser beam 17 is condensed and magnified with a first reflecting mirror 13. Most of the peripheral part of the beam is emitted to the outside as a laser beam 19 through a non-reflecting film 8 at the peripheral part of the inner surface of an output mirror 14. A part of the central part of the beam remains at the outside as a part of the laser beam 19 through a partial reflecting film 7 at the central part of the inner surface of the mirror 14. The remaining part of the beam is guided into the medium 1 again as the beam 18 and circulated in a ring pattern in the oscillator 16. Since the difference between losses of the lower-order mode and the higher-order mode having the aligned phase is large, the mode of the laser beam which is generated after the circulation is only the lowest-order mode. The beam is expanded at every circulation. Therefore, the high quality beam having the large cross sectional area can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an optical path of an optical resonator composed of a plurality of mirrors.
This invention relates to a laser device that generates a laser beam by irradiating excitation light onto a laser medium placed in -.

[Prior Art] FIG. 6 is a cross-sectional view showing a schematic configuration of a conventional laser device shown in, for example, the Laser Handbook (Ohmsha, 1982). In the figure, (1,) indicates the solid-state element 1. For example, a laser medium consisting of a rod-shaped crystal made of Y, -UNdxAQ, O Reflection mirror (5) is a total reflection mirror, (6) is an exit mirror made of glass, for example 2 (7) is an exit mirror (6)
) A partial reflection film made of, for example, TiO2 provided on the inner surface, (8) is the outer surface of the exit mirror (6) and the laser medium (1
) A non-reflective film made of, for example, SLO□ provided on both sides, (9) is an optical resonator consisting of mirrors (5) and (6), (10) is a laser beam in the optical resonator (9), ( 1
1) is a laser beam taken out to the outside, and (1, 2) is an outer frame.

Next, the operation will be explained. The laser medium (1) is powered by a power source (
3) is excited by the direct light from the arc lamp (2) turned on and the reflected light from the condensing and reflecting mirror (4). On the other hand, there is an exit mirror (6) which has a partial reflectance due to a partial reflection film (7) provided on the inner surface, and a total reflection mirror (
5) So-called stable optical resonance consisting of! The laser beam (10) confined in the chamber (9) is amplified by the laser medium (1) each time it goes back and forth between the two mirrors, and when the size of the chamber exceeds a certain level, a part of it is amplified by the exit mirror (6).
) is emitted to the outside as a laser beam (11).

FIG. 7 shows an example of the oscillation output characteristics. In 22, the laser medium (1) is Y2,4N d , &A Q , 01
□, the diameter of the cross section is 8 m, the length is 150 ++v, the curvature of the inner surface of the mirror (6) and the total reflection mirror (5) are both 0 and 4 rn, and the distance between both mirrors is 0.45 m.
, the reflectance of the mirror is 70%. Further, the input power is the power consumed for lighting the arc lamp (2), and a laser output of approximately 00 W is obtained with input power of 6 kW.

[Problems to be Solved by the Invention] Conventional laser devices use a stable resonator as described below, so the laser beam generated is a so-called higher-order molar beam with a large divergence angle. − becomes. An index of the degree of this higher-order mode is the ratio of the cross-sectional diameter of the lowest-order mode with the same phase that can occur in the resonator to the cross-sectional diameter of the laser medium. In this example, the lowest-order mode has a normal distribution and is a so-called Gaussian beam, so its intensity is centered at 1
The cross-sectional diameter φ defined at the point where /e2. is calculated as the distance between both mirrors and the wavelength λ of the laser beam. On the other hand, since the cross-sectional diameter of the laser medium is 8H, the ratio between the two is very large, about 15, and from this value it is empirically predicted that higher-order modes of the 100th order or higher are generated. The order of the higher mode is determined experimentally by measuring the divergence angle of the generated laser beam. For example, an example of actual measurement is shown in FIG. From this figure, the divergence angle is 1
It is grasped to be about 0 mrad, and the order of the corresponding higher-order mode is calculated to be about 100th order. The size of this divergence angle can be said to be the focusing performance of the laser beam itself. This is the condensed spot diameter φ by the condensing lens of the focal hole El f.
S is approximately φ3−? for a divergence angle of 0? This is because the diameter of the focused spot is determined in proportion to the divergence angle.

If we compare the value of lomrad here to that of a commercially available CO2 laser, it is approximately 10 times larger, and therefore the condensing characteristics of such a conventional solid-state laser device are 1/1 of that of a CO2 laser device.
It can be said that lo. In addition, in the conventional configuration, two laser beams with different propagation directions pass through the laser medium at the same time, resulting in interference between the laser beams, and this interference wave also causes disturbances in the amplification factor distribution within the laser medium. As a result, the width of the oscillation spectrum widened and the laser output became unstable for an hour.

This invention was made in order to solve the above-mentioned problems, and provides a stable laser device that uses a laser beam with a large area and a small divergence angle without being adversely affected by beam interference within the laser medium. The laser device according to the present invention includes, as an optical resonator, an unstable optical resonator having a ring-shaped optical path that returns from a laser medium to the laser medium via a first reflecting mirror, an exit mirror, and a second reflecting mirror. The exit mirror used to extract a portion of the laser beam from the optical resonator is constructed so that the central portion is partially reflective and the surrounding portion is non-reflective.

Further, the laser device according to the second aspect of the present invention has a ring-shaped optical path that returns from the laser medium to the laser medium via a first reflection mirror, an exit mirror, and a second reflection mirror as an optical resonator. Have.

This uses a negative branch optical resonator with a focal point in its optical path, and also provides a spatial filter in the optical path to adjust the outline of the focused laser beam.

[Function] In the ring-shaped unstable optical resonator according to the present invention, an optical path of the laser beam that passes through the laser medium in only one direction is formed, and the central part is formed by an exit mirror having a partially reflective property. A hollow laser beam is extracted from this optical path.

Furthermore, by using a negative branch type optical resonator formed in a ring shape and having a focal point in the optical path in combination with a spatial filter in the second aspect of the present invention, disturbance of the laser beam within the optical resonator can be prevented. A corrected and high quality laser beam is stably extracted.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a cross-sectional view showing a schematic atli configuration of an embodiment of the present invention, and Figure 2 is a characteristic diagram showing its output characteristics. In Figure 0, (1) is a laser medium, (2) is an arc lamp, (
3) is the power supply for lighting the arc lamp (2).

(7) is, for example, partial reflection +1L (8
) is a non-reflection film made of, for example, Sin, (12) is an outer frame, and (+3) is a first reflection mirror.A concave total reflection mirror (14) is an exit mirror that constitutes a collimating mirror made of glass, for example. , a partially reflective film (7
), a non-reflective IFJ (8) is provided on the outer periphery and outer surface of the partially reflective film (7). (15) is a total reflection mirror which is a second reflection mirror, (1,6) is an exit mirror (14) and the first and second reflection mirrors (+3).

(17) and (18) are the laser beams generated within the optical resonator (16), and (19) is the laser beam taken out to the outside of the optical resonator (16). be.

Next, the operation will be explained. The laser medium (1) is powered by a power source (
3) is excited by the arc lamp (2) turned on by the arc lamp (2). On the other hand, the laser beams (17) and (18) generated in the optical resonator (16) are amplified by this laser medium (1), and when they reach a certain size or more, a part of them becomes the laser beam (19). It is taken out to the outside as. To explain the operation of this optical resonator (16) in more detail,
An unstable optical resonator (technique 6) is formed by the first reflecting mirror (13), the exit mirror (14) and the second reflecting mirror (15).
, and the laser beam (18) passes through the second reflecting mirror (
15), is reflected by the laser medium (1) and amplified, and is then focused and expanded by the first reflecting mirror (13) as a laser beam (17), and its periphery is reflected by the inner surface of the exit mirror (14). Most of it is emitted to the outside as a laser beam (19) due to the action of the non-reflection film (8), and a part of it is partially reflected at the center of the inner surface of the exit mirror (14) II! Due to the action of (7), a part is extracted to the outside as part of the laser beam (19), and the remaining part is reflected as a laser beam (18) and guided to the laser medium (1) again into the optical resonator (16). ) circulates in a ring shape. Therefore, the external laser beam (19) becomes stuck. In such an unstable resonator, the difference in loss between the phase-aligned lowest-order mode and higher-order mode is much larger than that in a stable AI resonator, so the laser beam generated after circulating several times is the lowest-order mode. Since it is only a mode and is expanded with each circulation, a high-quality beam with a large cross-sectional area can be obtained. Further, the radius of curvature of the outer surface of the exit mirror is smaller than the radius of curvature of the inner surface, and is shaped like a meniscus, so that the output beams are made almost parallel. From these facts, the most ideal laser beam, which is a parallel beam with a large cross-sectional area in the form of a quintic phase, can be obtained. In one or more configurations, at the beginning of laser oscillation, a right-rotating laser beam exists in the optical resonator (16) in addition to the above-mentioned left-turning laser beam.

However, this clockwise laser beam is gradually attenuated because it is reduced in size with each cycle, and eventually only a counterclockwise laser beam remains. Therefore, the laser beam passes through the laser medium (1) in only one direction.

In the above configuration, as the laser medium (1).

Made of Y2, Nd, 6AQ50□2, cross-sectional diameter 8m
.

A lot-shaped crystal with a length of 150 ll1 m was used, the curvature of the inner surface of the exit mirror (14) and the first reflecting mirror (13) was 0.48 m and 0.8rn, respectively, and the distance between both mirrors was 0.44 m. FIG. 2 shows an example of the oscillation output characteristics when the reflectance of the partially reflective film (7) at the center of the inner surface of the exit mirror (14) is set to 80%. Here, the input power is the power consumed to turn on the arc lamp, and approximately 100 W of laser output is obtained with 8 kW of input power.

FIGS. 3(a) and 3(b) are characteristic diagrams showing the condensing patterns of this embodiment and the conventional laser device. The laser beam from the laser device of this embodiment with a laser emission month of 00 W is focused by a lens. The light pattern is shown in Figure 3(a), and the pattern of the laser beam from a conventional solid-state laser device is shown in Figure 3(a).
As is clear from Figure 0 shown in comparison with Figure (b), the width of this embodiment is not only reduced to about 1740 compared to the conventional one, but also the solid axial strength is 1. 0
00 times or more”2. In addition, the beam pattern was stable with respect to time, but this is because the laser beam passes through the laser medium (1) in only one direction. This is probably because the influence of interference caused by the beam passing in two directions has been removed.

In addition, in the above embodiment, the phase difference between the laser beam passing through the central part and the peripheral part of the inner surface of the exit mirror was small and did not pose a problem, but this may become a problem depending on the configuration of the partially reflective film (7). Conceivable. In that case, a means for canceling the phase difference between both laser beams may be provided. FIG. 4 is a sectional view showing a schematic configuration of an embodiment provided with this phase difference canceling means.

In the figure, (20) is an exit mirror with a step (21) provided on the outer surface, and this step (21) makes the exit mirror (20)
) The phase difference between the laser beams passing through the center and periphery of the inner surface is canceled out.

Further, in the above embodiment, a condensed laser beam (17) is reflected from the first reflecting mirror (13).

Although an example of a so-called negative branch type optical resonator has been shown, a parallel laser beam may be reflected.In short, the unstable type optical resonator (16) may be configured in a ring shape.

FIG. 5 is a sectional view showing a schematic configuration of another embodiment of the present invention. In this embodiment, the laser beam (17) reflected from the first reflecting mirror (13) in a negative branch type optical resonator. A so-called spatial filter (23) with a small diameter aperture is provided near the actual light point (22). This spatial filter (23) removes noise components generated on the outer periphery of the laser beam (17), further improving the quality of the laser beam (19) taken out to the outside, and eliminating noise caused by instability of the laser medium (1). Since the component can also be cut, the extracted laser beam (
17) The quality is stabilized.

[Effects of the Invention] As described in "2" below, according to the present invention, as an optical resonator, a ring-shaped optical resonator returns from the laser medium to the laser medium via the first reflecting mirror, the exit mirror, and the second reflecting mirror. In addition to using an unstable optical resonator with an optical path of This has the effect of providing a laser device that can stably extract a high-quality laser beam with a large cross-sectional area.

In addition, a negative branch optical resonator with a real light spot in the ring-shaped optical path is used, and a spatial filter is installed in the optical path to adjust the outer shape of the focused laser beam, resulting in even higher quality. This has the effect of providing a laser device that can extract a stable laser beam.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an embodiment of the present invention;
Figure 2 is a characteristic diagram showing its output characteristics, Figure 3 (a)
, (b) is a characteristic diagram showing condensing patterns in this embodiment and a conventional laser device, FIG. FIG. 5 is a sectional view showing a schematic configuration of another embodiment of the present invention, FIG. 6 is a sectional view showing a schematic configuration of a conventional laser device, and FIGS. 7 and 8 are a sectional view of a conventional solid-state laser device. FIG. 3 is a characteristic diagram showing laser output and divergence angle in the device. In the figure, (1) is the laser medium, and (2) is the light source (arc).
Clamp), (7) is a partially reflective film, (8) is a non-reflective film, (12) is an outer frame, (13) is a first reflective mirror, (
14), (20) are output mirrors, (15) are second reflection mirrors, (16) are optical resonators, (17), (L,
S), (19) is a laser beam, (21) is a step,
(22) is a focal point, and (23) is a spatial filter. The same reference numerals in the figures indicate the same or corresponding parts.

Claims (2)

[Claims] (1) In a laser device comprising an optical resonator configured with a plurality of mirrors, a laser medium disposed on the optical path of the optical resonator, and a light source that irradiates the laser medium with excitation light, the optical resonator is an unstable optical resonator having a ring-shaped optical path returning from the laser medium to the laser medium via a first reflecting mirror, an exit mirror, and a second reflecting mirror, and from this optical resonator, a laser beam is emitted from the optical resonator. A laser device characterized in that the exit mirror for extracting a portion of the beam is configured such that a central portion thereof is partially reflective and a peripheral portion thereof is non-reflective. (2) In a laser device comprising an optical resonator configured with a plurality of mirrors, a laser medium disposed on the optical path of the optical resonator, and a light source that irradiates the laser medium with excitation light, the optical resonator is a negative branch type optical resonance having a ring-shaped optical path from the laser medium, returning to the laser medium via a first reflecting mirror, an exit mirror, and a second reflecting mirror, and having a focal point in the optical path. What is claimed is: 1. A laser device characterized in that a spatial filter is provided in the optical path of the laser beam to adjust the outer shape of the focused laser beam.