JPS61154187A - Electron beam excited laser oscillator - Google Patents

Abstract

PURPOSE:To prevent occurrence of plasma potential disturbance such as anode spots, by forcibly equalizing the plasma potential in the vicinity of the surface of an external accelerating electrode by a plasma-potential-distribution shaping electrode, which is further arranged around the external accelerating electrode. CONSTITUTION:A cylindrical inner accelerating electrode 2 serves the role of a laser tube 1 and has a plurality of slit shaped openings 3. A cylindrical external accelerating electrode 4 is coaxially arranged at the outside of the inner accelerating electrode 2 with a specified interval being provided. Openings 5 are provided in the external accelerating electrode 4 in correspondence with the openings 3 of the inner accelerating electrode 2. A plasma-potential- distribution shaping electrode 15 is provided at the outside of the external accelerating electrode 4 with a specified space being provided. A cylindrical cathode electrode 8 forming a part of a plasma container 7 is further formed at the outside thereof. The plasma-potential-distribution shaping electrode 15 and the cylindrical cathode electrode 8 are insulated from the external accelerating electrode 4 by spacer 6' and 9 and fixed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an electron beam excitation laser oscillation device, in particular, which uses plasma as a cathode and accelerates electrons in the plasma to generate an electron beam. The present invention relates to an electron beam excitation laser oscillation device that excites a laser medium by entering the electron beam at right angles to the electron beam.

(Prior Art) As a laser oscillation device that generates a high-output laser with high efficiency, an electron beam excitation laser oscillation device that excites a laser medium filled in a laser tube with an externally incident electron beam is known.

This electron beam excitation laser oscillation device excites the laser medium by entering an electron beam formed outside the laser tube, so it can perform high-output laser oscillation. In order to perform oscillation with a larger output, it is preferable that an electron beam having the optimum energy for exciting the laser medium and a larger current be incident on the laser medium. To this end, as an electron beam generating means for generating an electron beam that excites the laser medium, it is recommended to use the following method that uses plasma as a cathode, since energy and current can be controlled independently. This is preferable since it is possible to obtain a high-current electron beam with energy.

That is, a plasma is used as a cathode, electrons are extracted from the plasma by a positive electrode, and ions formed by the extracted electrons are drawn toward the plasma side by a negative electrode, and a space is formed at the electron beam emission port of the plasma. It is preferable to use one that emits an electron beam without being limited by charge. As an electron beam excitation laser oscillation device using this electron beam generating means, an outer accelerating electrode made entirely of metal mesh is placed coaxially on the outside of an inner accelerating electrode made entirely of metal mesh, which corresponds to a conventional laser tube. An electron beam that excites the laser medium by arranging electrodes and applying a voltage between these inner and outer accelerating electrodes to enter the electron beam from a direction transverse to the axis of the laser tube. The applicant proposed an excitation laser oscillation device. In this electron beam excitation laser oscillation device, two mesh electrodes are used to connect the plasma region, the acceleration region, and the
An ion generation region is formed, and electrons are injected into the laser medium without being subject to space charge limitations. In addition, since this electron beam excitation laser oscillation device injects the electron beam from the lateral direction, compared to the case where the electron beam is injected in the same direction as the axis of the laser oscillation device, the Even when the gas pressure is high, the laser medium can be excited with a low-energy electron beam with good excitation efficiency. Furthermore, it is possible to increase the cross-sectional area of the Rede tube, which has the advantage of increasing laser output.

(Problems to be Solved by the Invention) The above-described electron beam excitation laser oscillation device that injects an electron beam perpendicularly to the axis of the laser tube has the potential to:
It has extremely good advantages. However, when trying to operate this electron beam excited laser oscillation device steadily, the current concentrates on a part of the inner or outer mesh electrodes, causing a discharge between the electrodes and eventually causing the electrodes to melt or break out inside the mesh electrodes. A problem arises in that the inner and outer mesh electrodes are short-circuited due to melting and deformation, making it impossible to operate the device continuously for a long period of time.

The cause of this melting of the mesh electrode is thought to be as follows.

One of the causes of this is the occurrence of anode spots on the outer electrode surface. When the outer accelerating electrode is used as one electrode (anode electrode) of a pair of discharge electrodes, as the discharge current density for plasma generation increases, the plasma density distribution on the outer accelerating electrode surface becomes uneven and An anode point occurs. When an anode spot is generated, current is concentrated at the anode spot, partially heating the electrode and leading to melting.

In this way, even a part of the surface of the outer electrode has a high plasma density (if it becomes too high, it will no longer be able to fulfill its role as an outer electrode, and the plasma will reach the inner electrode, causing a gap between the cathode and the inner electrode). This is a serious problem because it leads to a transition to direct discharge, which causes the laser oscillation to become unstable and to lower the upper limits of the electron beam current and electron beam energy.

Another reason for this difference is the shape of the accelerating electrode. The outer and inner accelerating electrodes are formed of metal mesh based on the natural idea of injecting a large amount of electrons into the laser tube and uniformly exciting the laser medium. The positions of the openings (mesh) of the two electrodes do not match in the direction perpendicular to the axis of the device, and ions generated in the inner electrode by electron beam irradiation collide with the outer electrode. Since the electrode is a metal mesh formed by weaving thin metal wires,
It has poor thermal conductivity and is easily heated by ion collisions. When the metal is heated to a high temperature, it begins to emit thermoelectrons, causing a discharge between the outer electrode and the inner electrode.

Further, since the electrodes are formed from metal mesh and the distance between the two electrodes is uneven, it is difficult for this discharge to occur uniformly, and the inner and outer electrodes are locally heated. A large number of thermoelectrons are emitted from a portion of the mesh where the temperature is high, and the electrode is partially heated at an accelerated rate, resulting in melting of the mesh or shorting of the electrode.

(Means for Solving the Problems) The above objects include: a laser tube whose interior is filled with a laser medium; an inner accelerating electrode provided on the circumferential surface of the laser tube and having an opening; an outer accelerating electrode disposed outside the laser tube, the outer accelerating electrode having an aperture aligned with the aperture of the inner accelerating electrode in the direction of the plasma potential; The electron of the present invention comprises a distribution shaping electrode, a plasma container that holds plasma around the outer accelerating electrode, and a power source that applies an accelerating voltage between the outer accelerating electrode and the inner accelerating electrode. This is achieved by a beam-pumped laser oscillation device.

Various modifications are possible to the present invention.

A metal tube with a mesh-like or slit-like opening can be used as the plasma potential distribution shaping electrode provided outside the opening of the outer accelerating electrode, but only near the opening of the outer accelerating electrode. electrodes placed in the area can be used. The distance between the plasma potential distribution shaping electrode and the outer acceleration electrode is preferably about 2 mm from l+r+m. If a metal tube with an opening is used as the laser tube, the inner accelerating electrode and the laser tube can be integrated. The inner accelerating electrode can also be formed by attaching a plate-shaped electrode with curvature to the outer peripheral surface of the laser tube. In addition to using a single metal cylinder that encloses the laser tube as the outer accelerating electrode, if there is an insulating part on the circumferential surface of the laser tube, multiple metal cylinders separated at this part and arranged in series can be used. It is also possible to use one consisting of Furthermore, this outer acceleration electrode can be used as one electrode (anode electrode) of a pair of discharge electrodes for generating plasma. When the outer accelerating electrode is heated, a discharge occurs between it and the inner accelerating electrode, so it is necessary to expand the surface area of the outer accelerating electrode as much as possible so that the cooling means can cool it efficiently. is preferred. As for the electrode material, it is preferable to use metals with good thermal conductivity such as copper or stainless steel to avoid local heating and from the viewpoint of cooling. However, it is preferable to use conductive materials such as metal compounds. You can also use Although the effect of heating on the inner accelerating electrode is smaller than that on the outer accelerating electrode, it is necessary to cool the laser tube in order to prevent the material of the inner accelerating electrode from turning into vapor and mixing with the laser medium as much as possible. be. For this purpose, the laser tube and the outer accelerating electrode are electrically insulatively and thermally conductively connected so that by cooling the outer accelerating electrode, the laser tube, that is, the inner accelerating electrode is also cooled. It's good to do that.

In addition, the distance between the inner accelerating electrode and the outer accelerating electrode is determined so that the product of the gas pressure between the electrodes and the distance between the electrodes is a sufficiently small value so that no discharge occurs between these electrodes. However, for example, it is about 1 mm to 0°5+n+++. Further, the apertures provided in the inner accelerating electrode and the outer accelerating electrode can take various shapes such as rectangular, elliptical, circular, etc., but there are many apertures so that the laser medium is uniformly irradiated with the electron beam. It is desirable to provide one. If the width of this opening is wide, even if the distance between the electrodes is short, the discharge will shift to a blocked discharge at a low voltage. On the other hand, if the width is too narrow, the discharge starting voltage will increase and electrons can be accelerated to high energy, but this will lead to a decrease in electron beam acceleration efficiency and partial heating of the accelerating electrode due to an increase in current density. It is necessary to choose. For example, it is preferably about 1 mm to 0.3 mm. In the present invention, by attaching a metal mesh to the opening of at least one of the outer accelerating electrode and the inner accelerating electrode,
The width of the opening can be adjusted to substantially 1/3 or 1/3, and this is considered to be possible because the generation of anode spots is prevented by the plasma potential distribution shaping electrode. That is, the present invention described in the claims also includes an embodiment in which a metal mesh is attached to the openings of the inner accelerating electrode and the outer accelerating electrode, and even in this case, similar or better It is possible to obtain the effect.

Note that a hollow cathode discharge type laser oscillation device is conventionally known in which a cylindrical anode is arranged coaxially inside a cylindrical hollow cathode, but in this device, a discharge occurs between the hollow cathode and the anode. This is different from the present invention because it causes laser oscillation by causing . In addition, in this hollow cathode discharge type laser oscillator, it is possible to control the discharge voltage by appropriately selecting the distance between the anode and cathode and the anode spacing, but there are important factors such as discharge current, discharge voltage, and gas pressure. The parameters are not independent of each other, and it is not possible to obtain a high-current electron beam with energy compatible with the excitation of the laser medium.

(Function) The plasma potential distribution shaping electrode further placed around the outer accelerating electrode forcibly equalizes the plasma potential near the surface of the outer accelerating electrode, thereby preventing the occurrence of disturbances in the plasma potential such as those at the anode point. prevent.

In the present invention, cylindrical or plate-shaped electrodes with openings are used instead of metal mesh as the inner accelerating electrode and the outer accelerating electrode, so the openings of both the inner and outer electrodes can be easily aligned. It can be carried out. Therefore, the ions generated by electron beam implantation are emitted from the laser tube without much collision with the outer accelerating electrode, so that the outer accelerating electrode is not heated to a high temperature. In addition, since the accelerating electrode is formed from a cylindrical or plate-shaped metal, heat conduction efficiency is high, the accelerating electrode is not locally heated, and there is no opening for the outer accelerating electrode. Since the cooling pipe can be placed in close contact with the side wall, the external accelerating electrode can be efficiently cooled. Moreover, when the internal accelerating electrode and the external accelerating electrode are formed from a highly rigid cylindrical body, the interval between the internal accelerating electrode and the external accelerating electrode can be made uniform and accurate.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view of the electron beam excitation laser oscillation device of the present invention, and FIG. 2 is a sectional view taken along the line 1--2 of FIG.

A cylindrical inner accelerating electrode 2, which also serves as a laser tube 1, has a plurality of slit-shaped openings 3, and a cylindrical outer accelerating electrode 4 is arranged at a predetermined interval on the outside of this inner accelerating electrode 2. They are arranged coaxially. This outer accelerating electrode 4 is provided with an opening 5 that is aligned with the opening 3 of the inner accelerating electrode 2 .

An insulating spacer 6 is interposed between the end of the outer accelerating electrode 4 and the outer circumference of the inner accelerating electrode 2, thereby fixing the outer accelerating electrode 4 to the inner accelerating electrode 2. . A plasma potential distribution shaping electrode 15 is provided outside the outer acceleration electrode 4 at a predetermined interval, and a cylindrical cathode electrode 8 forming a part of the plasma container 7 is provided further outside the electrode 15 for shaping the plasma potential distribution. The plasma potential distribution shaping electrode 15 and the cylindrical cathode electrode 8 are fixed and insulated from the outer acceleration electrode 4 by spacers 6' and 9, respectively.

The end of the laser tube 1 is provided with a blini star window 10, 10' like a normal gas laser, and a pair of external windows 10, 10' of a fully reflective type and a partially transmissive type are provided on the axis of the laser tube 1. Mirrors 11, 11' are provided so that laser oscillation is performed and laser light is emitted from the external mirror 11. A voltage is applied between the inner accelerating electrode 2 and the outer accelerating electrode 4 by an accelerating power source 12 with a variable voltage. A voltage is applied between the outer accelerating electrode 4 and the cathode electrode 8 by a discharge power source 13, and plasma is generated in the plasma container 7. The inner particles of this plasma are attracted by the inner accelerating electrode 2, pass through the openings 5 and 3, and are injected into the inner accelerating electrode 2. When the laser medium is irradiated with electrons, the laser medium is decomposed into ions and electrons. Of these, the ions are attracted to the outer accelerating electrode 4, but the ions are formed at the opening of the outer accelerating electrode 4. Therefore, even if the accelerating voltage provided by the power source 12 is low, by increasing the current of the power source 13 and increasing the electron density in the plasma vessel 7, the high current electron beam can be directed inward. It can be injected into the inside of the accelerating electrode 2 (Lade tube 1). Although the plasma potential distribution shaping electrode 15 has a floating potential, the plasma potential is constant in the portion where this electrode is located, and no anode point is generated. Further, when the opening 3 of the inner accelerating electrode 2 and the opening 5 of the outer accelerating electrode 40 match, ions do not collide with the outer accelerating electrode 4, so that the outer accelerating electrode 4 is less likely to be heated. moreover,
Since the distance between the inner accelerating electrode 2 and the outer accelerating electrode 4 can be made equal and small in all parts, no local discharge occurs. Furthermore, if a cooling pipe 14 is provided on the outer circumferential surface of the outer accelerating electrode 4 as shown in the figure, it is possible to completely prevent the temperature of the outer accelerating electrode 4 from rising.

Note that the plasma potential distribution shaping electrode 15 does not surround the entire circumference of the outer acceleration electrode 4, but is provided only on the outer part of the opening 5 of the outer acceleration electrode 4 as shown in FIG. The portion may be covered with an insulating material.

The plasma potential distribution shaping electrode 15 may have a floating potential, or may have an appropriate potential applied from the outside.

In the configuration shown in FIGS. 1 and 2, He is used as the medium, the accelerating voltage is 200 μm, and the gas pressure is 2.0 μm.
QTorr, and the electrode opening size is 3cm x 0.5
cm, and furthermore, the opening of the outer accelerating electrode is set to 0.
FIG. 4 shows the relationship between the discharge current Id and the acceleration current Ib when an MO metal mesh dividing into 25 cm x 0.5c+r+ is provided. As shown in FIG. 4, when the discharge current Id increases, that is, when the plasma density increases, the current 1b flowing between the accelerating electrodes, that is, the current of the electron beam flowing into the laser tube increases linearly. It is shown. That is, even if the accelerating voltage is constant, the laser medium can be excited by a large current electron beam because it is not limited by space charge.

Further, the accelerating electrode was not deformed by heating.

FIG. 5 is a side sectional view showing another embodiment of the invention. In this embodiment, the cathode electrode 8 that forms plasma is
is separate from the plasma container 7, and the plasma container 7
attached to the outside of the If the cathode electrode 8 is formed into a pipe or disk shape made of tantalum (Ta), LaB5, etc. as shown in the figure, the discharge will be concentrated at the tip of the cathode electrode 8, so that discharge can be caused at a low voltage.

As shown in FIG. 6, the cathode electrode 8 can also be a small-diameter pipe having a slit in its side wall, the axis of which is different from and parallel to the accelerating electrode 2.4.

FIG. 7 is a side sectional view showing still another embodiment of the present invention.

In this embodiment, the inner accelerating electrode 2 is formed separately from the laser tube 1, and the tubular inner accelerating electrode 2 is formed separately from the laser tube 1.
is mated to. The inner accelerating electrode 2 and the outer accelerating electrode 4 do not need to be tubular, and may be divided into a plurality of pieces and attached to the circumferential surface of the laser tube l. At this time,
In order to ensure uniform irradiation of the electron beam over the entire length of the laser tube, it is also important to balance the operation by coupling a resistor to each outer acceleration electrode piece. Further, in this embodiment, the cathode electrode 8 that forms plasma is separated from the plasma container 7.

FIG. 8 is a side sectional view showing still another embodiment of the present invention.

In this embodiment, an inner accelerating electrode 2, an outer accelerating electrode 4
and plasma container 7 all have rectangular cross sections, and the plasma region is divided into two.

FIG. 9 is a further modification of FIG. 8, and has a configuration that is extremely easy to assemble.

(Effects of the Invention) In the electron beam excitation laser oscillation device of the present invention, since the plasma potential shaping electrode is provided outside the opening of the outer accelerating electrode, disturbances in the plasma potential similar to those at the anode point occur. This prevents the current density from increasing locally. Furthermore, since the openings provided in the inner and outer accelerating electrodes can be easily aligned in the direction perpendicular to the axis of the laser tube, ions are less likely to collide with and heat the outer accelerating electrodes. Therefore, since the accelerating electrode is not locally heated, there is no possibility that the electrode will melt or that the inner and outer accelerating electrodes will be short-circuited due to melting and deformation. Also,
By arranging the plasma potential distribution shaping electrode, the plasma density distribution on the surface of the outer accelerating electrode is kept uniform even in the region where the discharge current is high, so that the upper limits of the electron beam current and beam energy can be greatly improved.

As described in detail above, according to the present invention, it is possible to continuously oscillate a high-output laser with high efficiency over a long period of time.

[Brief explanation of the drawing]

1 is a side sectional view of one embodiment of the electron beam excitation laser oscillation device of the present invention, FIG. 2 is a sectional view taken along line II-II in FIG. 1, and FIG. 3 is a sectional view of FIG. 1 in another embodiment. -■ sectional view; FIG. 4 is a graph showing the relationship between discharge current and accelerating current in the embodiment shown in FIGS. 1 and 3; FIG. 5 is a side sectional view of another embodiment of the present invention. , FIG. 6 is a cross-sectional view of still another embodiment of the present invention. FIG. 7 is a side sectional view of still another embodiment of the present invention. FIGS. 8 and 9 are cross-sectional views of a case where the cross-sectional shape is rectangular. It is a perspective view of an example. 1191, laser tube, 2. ,,inward acceleration electrode,3,
,,,Aperture, 4. ,,,Outer accelerating electrode, 5,,,Aperture, 6.6',,,Spacer,? , , , plasma container 8. , , Cathode electrode, 9, , Spacer, 10.10', , Brewster's window, 11.1
1', , External mirror, 12. ,,,acceleration power supply, 13
,,,discharge power supply, 14. ,,,cooling pipe, 15
,,, Electrode for plasma potential distribution shaping. Figure 1 Figure 2 (WLLI) l) I Figure 7

Claims (4)

[Claims] (1) A laser tube whose inside is filled with a laser medium, an inner accelerating electrode provided on the circumferential surface of the laser tube and having an opening, and an opening of the inner accelerating electrode in a direction perpendicular to the axis of the laser tube. an outer acceleration electrode having apertures that coincide with each other and arranged outside the laser tube; a plasma potential distribution shaping electrode provided outside the opening of the outer acceleration electrode; An electron beam excitation laser oscillation device comprising: a plasma container surrounding which plasma is held; and a power source applying an accelerating voltage between the outer accelerating electrode and the inner accelerating electrode. (2) The electron beam excitation laser oscillation device according to claim (1), wherein the laser tube is made of metal and also serves as the inner accelerating electrode. (3) The electron beam excitation laser oscillation device according to claim (1), wherein the power source is a variable voltage power source. (4) The electron beam excitation laser oscillation device according to claim (1), wherein the outer acceleration electrode also serves as one electrode of a discharge electrode that forms plasma.