JPS59134886A - Laser oscillator - Google Patents

Abstract

PURPOSE:To prevent the production of an unstable output phenomenon by providing a shielding plate outside the transparent section of a Brewster's window as seen from a laser beam direction in a laser discharge tube which is resonated and amplifies by an outer mirror by providing the window on the end face of the tube, and preventing the temperature rise of the window. CONSTITUTION:Brewster's windows 3, 4 made of ZnSe or the like are provided on both end faces of a laser tube 1 surrounded by a coolant jacket 2, an output coupling mirror 5 and a fully reflecting mirror 6 are arranged outside the windows, and a resonance and amplification are taken place in the tube. In this structure, a shielding plate 12 which has high reflectivity made of aluminum, copper, gold or silver is bonded with an adhesive layer 7 on the outside of the transparent section of the window 4 as seen from the laser beam direction on the window 4, as shown, and an elliptical hole 13 is formed at the part surrounded by the plate. In this manner, it prevents the beam from being emitted by diffraction to the plate 12, thereby preventing the temperature rise thereat and maintaining the output constant for a long period.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a laser oscillator with an external mirror 11'l having a Brewster window which produces a stable output.

Conventional configuration and its problems External mirror resonator lasers are characterized by the separation of the laser tube and the optical resonator, which requires precise optical adjustment. It can be said that this is an extremely useful technique in the case of a one-stop tube gas laser that requires pretreatment at the bottom.

In this case, it is essential to ensure airtightness for the gas laser tube, and both a vertical incidence window with an anti-reflection 11-film and a Brewster window with Brewster angle incidence are used for this purpose. C
Since it is currently not possible to obtain a reflection number IJ-film with sufficient durability for a laser that oscillates at high output in the far infrared region of 10.6μ, such as an O2 laser, the inventor developed a Brewster window made of Zn5e. It has been used conventionally. CO2
In the case of lasers, 114 diagrams of conventional laser oscillators are shown in the first section.
As shown in the figure. Since the C02 laser technology is well known, the figure shows the minimum parts necessary for explaining the present invention, such as a laser tube 1, a cooling water jacket 2, and a Brewster window 3 such as Zn5e.
4, output coupling mirror 5, and total reflection mirror 6 are shown, and the others are omitted. The present technology, which is a prior art, showed extremely satisfactory operation in the output range of 15 W or less, but presented the following difficulties in the output range of 16 W' or more. That is, the output coupling mirror 5
When the total reflection mirror 6 is fully adjusted and laser oscillation is performed, the laser output reaches its maximum value, but immediately begins to decrease, and after about 1 minute, the output drops to 20% of the initial value. Resulting in.

When one of the output coupling mirror 5 and the total reflection mirror 6 is adjusted in a direction in which the axis of rotation is perpendicular to the plane of incidence, the output again reaches its maximum value, but then decreases again.

If you keep making these optical adjustments and pursue the maximum output, the result will be as shown in Figure 2. During this time, no deviation in the -J adjustment occurred in the direction in which the rotation axis was included in the plane of incidence. In Fig. 2, the target of the above-mentioned curve of the mirror around the axis of rotation measured using an autocollimator is marked (, l). 1.11 It can be seen that it is repeatedly going back and forth.

With this, unless an automatic tracking device is attached to the mirror surface, it will not be possible to print the maximum output.

The present inventor investigated the mechanism of occurrence of the above-mentioned J instability phenomenon, and as a result, it was revealed that the phenomenon is a two-stage complex phenomenon as follows.

For the purpose of explanation, FIG. 3 shows an enlarged view of the vicinity of the prufter window E 1 located 1° at the end of a conventional laser tube.

(1) 41i in Figure 3! A Brewster window such as Zn5e, a cutting agent layer such as 7il-j:l・-Lucille, 8 a laser ablation material such as glass or quartz, 9 a laser beam, 10 a laser tube center axis, and 11 a laser beam center. It is determined by the resonator at the axis.

In order to maximize the output of the CO2 laser, a resonator 2rik type resonator similar to a plane Fapley-Bello is used, so the laser beam spreads out in a tube-like manner as shown in the figure. Since the two axes 10 and 11 do not exactly align, a portion of the laser beam is cut by the glue 11 and the glass 8 shown in the figure.

The Brewster window 4 is a transparent material with an absorption coefficient of 10-3 cm-', but since the Currane 8 and the adhesive 7 are almost perfect absorbers at 10.6 μm, they are heated by absorption of the laser beam 9, and the Brewster window 4 is heated by absorption of the laser beam 9. The window 4 is also heated by thermal conduction. It has been determined that the Zn5e Brewster window 4 is often heated to over 100°C.

(1) It has been confirmed that when the Brewster window 4 is heated, the alignment around the rotation axis described above is quickly affected. It is determined that this phenomenon is caused by a refraction phenomenon within the Brewster window 4.

The above-mentioned instability is a combination of the two types (i) and (b) mentioned above, and the cut of a part of the laser beam shown in Figure 3 is due to the distance from the laser tube end to the mirror surface, T5j, or It is inferred that this is noticeable in multistage folded resonators.

OBJECTS OF THE INVENTION The purpose of the present invention is to detect the occurrence of the output instability phenomenon described in l'l'lJ in a laser oscillator equipped with a Brewster window, and to eliminate it by hitting f1 once in the optical adjustment. The objective is to stabilize the period output) J at a constant n11 and improve the operability of the laser oscillator.

The present invention has been made to achieve the above-mentioned object. Laser emission: A Brewster window is provided at the end of the tube, and both are amplified by an external FF15 mirror. (11) to prevent the laser beam from being irradiated by diffraction on the opaque part located at the transparent l side of the window viewed from the laser beam direction. , t due to the laser beam absorption in the opaque part, the accuracy of the Brewster window caused by /7+i'+
The present invention provides a laser oscillator designed to prevent Uf1 in one ship.

DESCRIPTION OF THE EMBODIMENTS A first embodiment of the present invention uses a VCa shielding plate to shield the cross section of the laser beam so that it does not exceed the effective transparent cross section of the Brewster window. I'M of the Brewster window itself, which prevents laser beam absorption and causes heat generation near the Brewster window.
It has a structure that prevents duplication. Separately, narrowing down the laser beam cross section can also be achieved by reducing the reflector curvature and employing a spherical mirror resonator, such as a confocal resonator, but this reduces the mode volume compared to the active region inside the laser tube. This is not the intention of the present invention since this would lead to a decrease in both laser output and efficiency.

FIG. 4 shows the main part of a laser oscillator according to a first embodiment of the present invention. Although a description of the parts common to FIG. 3 will be omitted, in this embodiment, a shielding plate 12 (shaded area) made of a reflector is installed above the Brewster window 4. Shown in Figure 4 including 1g plate 12 refraction! 714 <Laser tube 8
The opening has the same inner diameter and the same cross-sectional shape when viewed from the laser beam direction. That is, it has an opening 13 having a circular shape.

This apertured shielding plate 12 does not act on the beam coming from the left direction, but reflects the laser beam entering the tangent M layer A for the beam coming from the right direction.
Prevents humidity 1 and 1 due to laser beam absorption in the surrounding area II
It's about doing. The shielding plate 12 is made of aluminum, copper, gold, silver, or other material having high reflectivity. It may be formed by installing a thin plate produced by mechanical work, or it may be formed by vapor deposition on the surface of the Brewster window 4. Alternatively, a dielectric multilayer film having high reflectivity at the wavelength of the laser beam may be used.

In this case, it is especially safe because it prevents dangers of high voltage.

Moreover, the reflectance can also be made higher.

When this shielding plate 12 is installed, the Brewster window 4 does not generate geothermal heat that directly absorbs the laser beam, so if a material with a sufficiently high transmittance is selected, p emission can be sufficiently suppressed.

A second embodiment of the invention is shown in FIG. The explanation of the parts common to those in FIG.
4 is intervening. This is because in the method shown in Figure 4, even though the shielding plate is made of a highly reflective metal, when it comes into contact with the laser beam, it absorbs a portion of the laser beam, heating it up by about 20°C/JIl from room temperature, and this amount of heat is transferred to the Brewster window 4. However, in the case of this embodiment, such a situation can be prevented.

A third embodiment of the invention is shown in FIG.

In this embodiment, the Brewster window 4 has a metal window holder 18.
It is installed in the laser tube 15 with a . 17 and 7 are adhesive layers between the laser tube 15 and the boulder 18, and between the holder 18 and the window 4, respectively. The laser tube 15 has a double tube structure and is cooled by cooling water 16. Therefore, the window 4 is indirectly cooled by the cooling water 16, making it possible to ensure stability even against a high-power laser beam compared to the first and second embodiments.

In this embodiment, the opening is provided in the bottom surface of a cap 19 provided on the outer periphery of the window boulder, and is designated by 20 in FIG. In this case as well, as in the embodiment described above, the cross-sectional shape of the laser tube 15 is made equal to the internal cross-sectional shape of the laser tube 15, taking into account the refraction at the Brewster window 4. In this embodiment, the cap 19 that performs the shielding function is not in contact with the Brewster window 4, so it may generate heat, and therefore it can be made of a nonmetal that absorbs laser light well. Unlike the above-mentioned embodiments, in this case there is no reflection of the laser beam, so it can be said that this method is safer in handling the laser oscillator.

The present invention can also be realized by making the diameter of the end of the laser tube including the Brewster window sufficiently larger than the inner diameter of the laser tube. At this time, the laser beam is limited by the diameter of the laser discharge tube, so even if the beam spreads to some extent, the opaque area is located far enough away from the beam that heating will not occur.

FIG. 7 shows a fourth embodiment of the present invention.

In this embodiment, the diameter of the portion of the laser tube 8 to which the Brewster window 4 is attached is increased, and a shielding plate on the Brewster window 4 is not used. Laser beam 1'f=tdv-
Since it is limited by the inner diameter of the laser tube 8, even if there is some expansion as described in 611, as long as the end of the laser tube 8 has a sufficient bulge, the laser beam will not be irradiated onto opaque parts such as the adhesive layer 7. do not have. The constriction of the laser tube 8 shown in FIG. 7 is an opaque portion that touches the laser beam, but even if the altitude of this portion increases, it will not cause instability. Although this embodiment makes the laser tube structure a little more complicated, when the laser tube is made with this structure, there is an advantage that there is no need to pay attention to the accuracy of mounting the shield plate, and there is no risk of high voltage.

FIG. 8 shows a fifth embodiment of the present invention.

In this embodiment, neither the shielding plate of the Brewster window 4 nor the bulge at the end of the laser tube 8 is necessary; however, a diaphragm 21 made of a resin opaque to the laser beam is provided in the laser tube 8 to restrict the diameter of the laser beam. ing.

At this time, the diameter of the laser beam is made sufficiently smaller than the inner diameter of the laser 'f8, so that even if the above-mentioned expansion occurs, the adhesive layer 7 is not irradiated with the laser beam. At this time, the simplicity of the laser tube structure can be maintained, and the risk of high voltage due to the presence of the shielding plate can be avoided, which is advantageous. However, there is a drawback in that the mode volume is reduced due to the aperture effect compared to the volume of the discharge region, resulting in a slight decrease in output and efficiency.

Although specific examples of 54Φ have been shown above, the present invention is not limited to these examples. l#/f rj that prevents laser beam absorption
';j, other configurations may be used.

Effects of the Invention As described in 2., the present invention is configured such that a Brewster window is provided on the end face of the laser discharge tube so that it is resonated and amplified by an external source, and the reflected beam from the external source is reflected from the laser discharge tube. This prevents the opaque area facing the end face and Brewster window from being irradiated, and prevents the humidity from being absorbed by the laser beam in the opaque area and the resulting rise in the Brewster window. , it is possible to oscillate a laser oscillator while maintaining a high degree of stability, which has a great effect. Further, according to the present invention, it is convenient without incurring a large drop in cost L and without sacrificing monthly output or efficiency.

Moreover, it can be said that some embodiments of the present invention have remarkable industrial effects, such as guaranteeing high safety.

[Brief explanation of the drawing]

Figure 1 is a diagram of the configuration of a conventional external source type laser oscillator using a Brewster window laser tube, Figure 2 is a characteristic diagram of the output instability phenomenon that occurs in the laser with the configuration shown in Figure 1, and Figure 3 is 4, 5, 6, 7, and 8 are enlarged views of the laser tube end for explaining the mechanism of the instability phenomenon described above. FIG. 1...Laser tube, 2...Cooling water jacket, 3.4...Brewster window, 6,6.
...Reflecting mirror constituting the optical system, 7...Adhesive layer for Brewster window, 8...Inside the glass tube at the end of the laser tube, 9...Laser Beam, 10...
...Resonator center axis, 11...Laser beam center axis, 12...Apertured shielding plate, 13...
- A circular opening provided in the same plate, 14... A thermally poor conductor layer interposed between the shielding plate and the Brewster window, 15.
...Laser tube end, 16...Cooling water, 1
Completed... Adhesive layer for Brewster window holder, 1
8... Briny Nuku window holder, 19...
・Cap and shield plate for the same purpose, 20...Circular opening provided in the cap, 21...Aperture provided in the laser tube. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure Lego 6 10 minutes Figure 3 δ 74 Figure 5/4 Figure 8? /

Claims (10)

[Claims] (1) A Brewster window is provided on the end face of the laser detonator, and 1) the beam passing through the Brewster window 11 is reflected by a total reflection mirror and an output coupling mirror (17+), and A laser oscillator, characterized in that a beam reflected by a coupling mirror is sandwiched between an end face of a laser discharge tube and a Brewster window, and is provided with means for preventing the beam from being irradiated to an opaque area. . (2) A shielding means is provided on the surface of the flumeta window on the side of the total reflection mirror and the partial reflection mirror to prevent the reflected beam from irradiating the opaque area. laser oscillator. (3) The laser oscillator according to paragraph 2 of subsection 11 of the patent claim, characterized in that the eclipse i4+& means is made of a highly reflective material. (4), 1.1. ! 8. The laser oscillator according to item 2, characterized in that the shielding means is a deposited film. (5) The laser oscillator according to claim 4, wherein the deposited film is one of gold, silver, copper, and aluminum. (6) The laser oscillator according to claim 4, wherein the deposited film is a dielectric film. (7) Claim 2, characterized in that the shielding means has a composite structure in which a highly reflective material is provided on a poor thermal conductor layer.
Laser oscillator described in section. (8) The laser oscillator according to claim 2, wherein the shielding means is an opaque body having an opening and provided isolated from the Brewster window. (9) The first aspect of the present invention is characterized in that the inner diameter of the Brunuta window on the end face of the laser discharge tube is made larger than the inner diameter of the laser discharge tube to prevent the reflected beam from irradiating the opaque area. Laser oscillator described in section. (10) The laser discharge tube is characterized in that irradiation of the reflected beam to the opaque area is prevented by providing a diaphragm means for controlling the beam diameter inside the laser discharge tube. 'l'
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