JPS60189703A - Damage preventing mechanism for reflecting mirror for laser resonance - Google Patents

Abstract

PURPOSE:To trap plasma or an electron which travels to a reflection mirror and to prevent the reflection mirror from damaging by interposing a conductive sleeve which is connected electrically between an electrode or a power source between the reflection mirror and the nearby electrode. CONSTITUTION:A carbon dioxide gas laser oscillator which has an output mirror at the left half and a total reflection mirror at the right half is provided with a conductive sleeve 17 inserted into the electrode-side opening part of a holder 11 on the side of the output mirror 8 and also with a conductive sleeve 17' inserted into the center hole of the holder 11 nearly to its overall length on the side of the total reflection mirror 8'. Further, the conductive sleeves are connected electrically to the electrode 5 through a conductive auxiliary sleeve 18 and a compression spring 19 and held at the same potential with the electrode 15 during discharging operation. Consequently, coat layers on surfaces of the mirrors 8 and 8' are held at the same potential with the electrode 15, so the acceleration of plasma and an electron is prevented between the electrode 15 and mirrors 8 and 8' and damage to the mirrors due to overheating is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a damage prevention mechanism for a reflecting mirror with a discharge tube, particularly for a resonant reflecting mirror in a discharge excitation type gas laser oscillator.

(b) Prior art and its problems For example, as shown in FIG. 1, a general carbon dioxide laser oscillator includes a base plate 1, a plurality of stabilizing rods 2 made of quartz glass, invar, etc., a discharge tube 3, etc. The resonator base 4 includes an output mirror part 5 and a total reflection mirror part 6 connected in opposite directions on both sides of the resonator base part 4.

This type of gas laser oscillator obtains laser oscillation by applying a voltage to the gas, which is the laser medium, filled inside the discharge tube and causing it to discharge, and the discharge excites the gas molecules to generate stimulated emission. At this time, electrons and high-temperature plasma whose temperature exceeds 1040 K collide with the opposing reflecting mirrors, that is, the output mirror and the total reflection mirror, raising the temperature of the reflecting mirrors.

The puller, zuma, and electron flow will be explained based on the conventional example shown in FIG. It is accelerated by the voltage applied between the cathode (cathode) 9 and 10 close to the output mirror 8 in FIG. 2, and most of it flows into the cathode as shown by the solid arrow, or The part continues to accelerate as shown by the dotted arrow and travels straight ahead, colliding with the mirror. This phenomenon also occurs on the total reflection mirror side because there is a cathode near the mirror, and as a result, the surface layer of the mirror is heated to an extremely high temperature, damaging its thermal coating layer and impairing the optical performance of the mirror. This results in a significant decrease.

Conventionally, as a countermeasure to this problem, a method has been adopted in which the gap 2 shown in FIG.

However, this method (1) increases the total length of the resonator, which hinders plans for downsizing the laser oscillator.

■ The spacing is a useless part from the point of view of the laser's amplification and oscillation functions, and the larger it becomes, the more loss due to diffraction spreading of the beam and absorption by the laser gas increases.
Even with the spacing shown in the figure, the output decreases, albeit slightly. For this reason, it is difficult to obtain a large blemish, but if the blemish is small, the amount of plasma etc. trapped will be reduced and the protective effect of the mirror will be weakened. As described above, in the conventional method, either the laser output or the mirror protection effect is necessarily sacrificed.

The above situation is the same even in a resonator in which the anode and cathode are reversed.

(c) Means for solving the problem This invention was made with the purpose of eliminating the above-mentioned problem, and the damage prevention mechanism for the reflector of the present invention that achieves this purpose is based on the reflector and the damage prevention mechanism for the reflector. A conductive sleeve electrically connected to the electrode or another power source is inserted between adjacent electrodes, and the sleeve traps plasma or electrons that pass through the electrodes and head toward the mirror.

Note that a conductive sleeve can be considered an extension of an electrode if it is made to have the same potential as a nearby electrode, so even if it has an axially symmetrical shape, some linear plasma that has passed through the original electrode will still be generated. flows into the sleeve, making the mirror more effective at preventing damage than before. However, if the sleeve has a non-axisymmetric shape, the trapping efficiency will be improved and the above effects will be fully realized. The reason for this will be explained in detail in the Examples section below.

(→Embodiment FIG. 3 is a cross-sectional view of a mirror coupling part that employs the damage prevention mechanism of the present invention, with the left half showing the output mirror side and the right half showing the total reflection mirror side.

In the figure, 3 is a discharge tube, 8 is an output mirror, 8' is a total reflection mirror, 11 is a ceramic main body 11a1 and a presser 11b.
1 a mirror holder consisting of a fastener 11c; 12 a mirror mounting plate supporting the mirror holder; 13 an end plate of the resonator; 14 an electrode cover; 15 an anode or cathode electrode; and 16 a holder cooling unit. On the output mirror 8 side, a conductive sleeve 17 is placed in the electrode-side opening of the holder 11, while on the total reflection mirror 8' side, a conductive sleeve 17 is placed in the center hole of the holder 11, and the conductive sleeve 17 extends over the entire length of the hole.
′ is inserted in each case.

As shown in FIG. 4, the conductive sleeve 17 has a flange 17a at one end that engages with the opening step of the holder, and a cylindrical portion 17b extending from the flange is cut in half by a notch 17c. It has a symmetrical shape, as shown in Figure 3.
The holder is brought into pressure contact with the adjacent electrode 15 via a conductive auxiliary sleeve 18 and a compression spring 19, and at the same time it is electrically connected to the electrode 15 to maintain the same potential as the electrode during discharge.

Here, the reason why the compression spring is inserted between the electrode 15 is that it is necessary to slightly move the mirror in order to adjust the optical axis of the resonator, and the amount of displacement caused by the relative misalignment between the holder and the electrode at this time is This is to absorb it by the expansion and contraction of the spring and maintain the electrical connection to the electrode.

Although the auxiliary sleeve 18 has the effect of lengthening the trap space 4, it may be omitted and one end of the spring 19 may be brought into direct contact with the sleeve 17.

Further, voltage can be applied to the sleeve 17 from a power source other than the electrodes, and in that case, the spring 17 can also be omitted.

Of course, with this spring, there is no need for a separate power supply, and the structure of the resonator does not become unnecessarily complicated.

The sleeve 17' on the side of the total reflection mirror 8' is similarly electrically connected to the electrode 15, but this sleeve has a cylindrical portion 17b extending from the collar 17a' as shown in FIG.
A notch 17c' is provided in the middle of the cylindrical part 17b', and a conductive coating layer on the surface of the total reflection mirror 8' made of gold, silver, etc. is pressed against the end face of the cylindrical part 17b'. In this way, the coating layer on the surface of the mirror has the same potential as the electrode, so that acceleration of plasma and electrons between the electrode and the mirror can be prevented. However, this point is not an essential requirement of the present application, and the purpose of the invention can be achieved even if the sleeve 17' is separated from the mirror 8'.

Next, the reason why the trapping efficiency is improved by making the sleeves 17, 17' non-axisymmetric is as follows.

That is, if the sleeve has an axially symmetrical shape, the electric field inside the sleeve will also be axially symmetrical, and the force that changes the direction of straight-advancing plasma or the like will be weak. Therefore, there are many plasmas and electrons that slip through the gap and collide with the mirror.

On the other hand, if the sleeve has a non-axisymmetric shape, the electric field inside will also be non-axisymmetric. That is, a component perpendicular to the axis is generated, so that the linear plasma or electrons that have passed through the electrode change their flow direction as a whole and flow into the semi-cylindrical portion of the sleeve. Therefore, collisions of plasma or electrons against the mirror are reduced, and damage to the mirror due to heating is prevented.

(e) Effects As explained above, according to the present invention, a conductive sleeve is inserted between the mirror and the nearby electrode, and the sleeve traps plasma or electrons that have passed through the electrode. , it is possible to enhance the trap effect without increasing the length of the resonator or reducing the laser output, and various conventional problems are solved at once.

It should be noted that the present invention has experimentally obtained the effects shown in the table below regarding the prevention of mirror damage.

The table above shows a comparative experiment in which the distances between the electrodes and mirrors were all 25 mm, and the numerical values in the table represent the time until small defects appear in the coating layer on the surface of the surface.

[Brief explanation of drawings]

Figure 1 is an external view of a general gas laser generator, and Figure 2 is an external view of a typical gas laser generator.
The figure is a sectional view showing a mirror coupling part of a conventional resonator, FIG. 3 is a sectional view of a mirror coupling part showing an embodiment of the reflector damage prevention mechanism of the present invention, and FIGS. 4 and 5 are sectional views of the mirror coupling part of the present invention. FIG. 3... Discharge tube, 8... Output mirror, 8'... Total reflection mirror, 11... Mirror holder, 12... Mirror mounting plate, 13... Resonator end plate, 14...
...Electrode cover, 15...Electrode, 17.17'...
Conductive sleeve, 17c, 17c'... cutout, 19
... Compression spring patent applicant: Sumi Electric Industry Co., Ltd. Agent: Kama 1) Text 2 Figure 4 Figure 5 17'170' 7a 7b'

Claims (4)

[Claims] (1) A conductive sleeve electrically connected to the electrodes or to a separate power supply is inserted between the reflecting mirrors that are placed facing each other with the discharge tube in between and the electrodes close to each reflecting mirror. Features a damage prevention mechanism for laser resonant reflectors. (2) A damage prevention mechanism for a laser resonant reflector as set forth in claim (1), wherein the conductive sleeve is at the same potential as the electrode. (3) A damage prevention mechanism for a laser resonant reflecting mirror according to claim (1) or (2), characterized in that the conductive sleeve has a non-axisymmetric shape. (4) The conductive sleeve is inserted into a reflector holder movably connected to the discharge tube, and a spring is compressed and interposed between the sleeve and the electrode. A damage prevention mechanism for a laser resonant reflecting mirror according to any one of the ranges (1) to (3).