JPH0464475B2 - - Google Patents

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, 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 to the plasma side by a negative electrode, causing the plasma to emit an electron beam. Preferably, one is used which emits an electron beam without being restricted by space charges formed at the exit. 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. By arranging electrodes and applying a voltage between these inner and outer accelerating electrodes,
The present applicant has proposed an electron beam excitation laser oscillation device in which a laser medium is excited by an electron beam incident from a direction transverse to the axis of a laser tube. In this electron beam excitation laser oscillation device, 2
A plasma region, an acceleration region, and an ion generation region are formed from the outside by the two mesh electrodes, 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 laser tube, which has the advantage of increasing the laser output.

(Problems to be Solved by the Invention) The above-described electron beam excitation laser oscillation device that injects an electron beam at right angles to the axis of the laser tube potentially has extremely excellent advantages. However, when attempting to operate this electron beam excited laser oscillator in a steady state, 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. 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 over 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 is created. When an anode spot is generated, current is concentrated at the anode spot, partially heating the electrode and leading to melting.

In this way, if the plasma density becomes too high even on a part of the surface of the outer electrode, it will no longer be able to fulfill its role as an outer electrode, and the plasma will reach the inner electrode, causing direct contact between the cathode and the inner electrode. If the laser oscillation becomes unstable due to the transition to electric discharge,
This is a big problem because it leads to lowering the upper limits of 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 laser oscillation 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, this discharge is difficult to occur uniformly, and the inner and outer electrodes are locally heated. The higher the temperature of the mesh, the more thermoelectrons are emitted, and the electrode is partially heated at an accelerated rate, causing the mesh to melt or short-circuit the electrode.

(Means for Solving the Problems) The above objects are: 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; perpendicular to the axis of the laser tube; an outer acceleration electrode arranged outside the laser tube, the outer acceleration electrode having an opening aligned with the opening of the inner acceleration electrode in the direction of the plasma potential; a distribution shaping electrode; a plasma container that holds plasma around the outer accelerating electrode; and applying an accelerating voltage between the outer accelerating electrode and the inner accelerating electrode to accelerate electrons in the plasma. This is achieved by the electron beam excitation laser oscillation device of the present invention, which includes a power source that forms an electron beam that is incident perpendicularly to the laser tube and excites the laser medium.

Various modifications are possible to the present invention. A metal tube with a mesh-shaped or slit-shaped 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 1 mm to 2 mm. 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 having curvature to the outer peripheral surface of the laser tube. In addition to using a single metal cylinder containing the laser tube as the external acceleration electrode,
If there is an insulating part on the circumferential surface of the laser tube, it is also possible to use a plurality of metal cylinders separated in this part and arranged in series. 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 preferable to expand the surface area of the outer accelerating electrode as much as possible so that cooling can be efficiently performed by the cooling means. Note that it is preferable to use metals with good thermal conductivity, such as copper or stainless steel, as the material for the electrodes, in order to avoid local heating and from the standpoint of cooling. However, other conductive materials such as metal compounds may be used. 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. be. For this purpose, the laser tube and the outer accelerating electrode are electrically insulatively and thermally conductively connected, and by cooling the outer accelerating electrode, the laser tube, that is, the inner accelerating electrode is also cooled. It is better to do this. 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. For example, 1
It is about 0.5 mm from mm. 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 it is narrow, the discharge starting voltage will increase,
It becomes possible to accelerate electrons to high energies,
It is necessary to select an appropriate width because this leads to a decrease in electron beam acceleration efficiency and an increase in current density, which leads to partial heating of the accelerating electrode. For example 1mm
0.3 mm is preferable. 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 1/2 or 1/3, but this depends on the plasma potential distribution. This is thought to be possible because the shaping electrode prevents the occurrence of anode spots. 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, the same or more 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 the cathode and the anode spacing, but the discharge voltage, discharge voltage, gas pressure, etc. The important parameters of are not independent of each other and it is not possible to obtain a high current electron beam of energy compatible with the excitation of the laser medium.

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

In the present invention, cylindrical or plate-shaped electrodes having openings are used instead of metal meshes as the inner accelerating electrode and the outer accelerating electrode, so that 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 injection are emitted from the laser tube without colliding with the outer accelerating electrode much, so that the outer accelerating electrode is not heated to a high temperature. In addition, since the heating electrode is formed from a cylindrical or plate-shaped metal, the 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 -
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 has an opening 5 and an opening 3 of the inner accelerating electrode 2.
It is located in the same position as the 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, whereby the outer accelerating electrode 4 is fixed to the inner accelerating electrode 2. ing. 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. Plasma potential distribution shaping electrode 15 and cylindrical cathode electrode 8
are fixed and insulated from the outer accelerating electrode 4 by spacers 6' and 9, respectively. The end of the laser tube 1 is provided with Brewster windows 10 and 10', similar to a normal gas laser, and a pair of completely reflective and partially transmissive types are provided on the axis of the laser tube 1. External mirrors 11 and 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 discharge power source 1 is provided between the outer accelerating electrode 4 and the cathode electrode 8.
3 applies a voltage, and plasma is generated in the plasma container 7. Electrons in 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, and the ions are attracted to the outer accelerating electrode 4. The space charge that forms is removed. 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 container 7, a large current electron beam is transferred to the inner accelerating electrode 2 (laser). It can be injected inside the 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 4 are aligned, ions do not collide with the outer accelerating electrode 4, so that the outer accelerating electrode 4 is hardly heated. Furthermore, the inner accelerating electrode 2 and the outer accelerating electrode 4
Since the distance between the two parts 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;
As shown in the figure, it may be provided only in the outer portion of the opening 5 of the outer acceleration electrode 4, and the other portions may be covered with an insulator.

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 was used as the medium, the acceleration voltage was 200 V, the gas pressure was 2.0 Torr, and the electrode opening size was 3 cm.
× 0.5 cm, and the opening of the outer acceleration electrode is further provided with a Mo metal mesh that divides this opening into 0.25 cm × 0.5 cm. Discharge current Id and acceleration current
The relationship with Ib is shown in Figure 4. As shown in Fig. 4, as the discharge current Id increases, that is, as the plasma density increases, the current Ib flowing between the accelerating electrodes, that is, the current of the electron beam flowing into the laser tube increases linearly. It has been shown that
That is, even if the accelerating voltage was constant, the laser medium could be excited by a large current electron beam because it was 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 for forming plasma is separate from the plasma container 7 and is attached to the outside of the plasma container 7. If this cathode electrode 8 is made into a pipe or disk shape made of tantalum (Ta), _LaB6 , etc. as shown in the figure, the discharge will be caused by the cathode electrode 8.
Since it is concentrated at the tip of the electrode, it is possible to generate a discharge at a low voltage.

As shown in FIG. 6, the cathode electrode 8 may also be a small-diameter pipe having a slit in its side wall and disposed parallel to and on a different axis from the accelerating electrodes 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 fitted into the laser tube 1. 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 1. 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 connecting 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, the inner accelerating electrode 2, the outer accelerating electrode 4, and the 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, the accelerating electrode is not locally heated, so there is no chance of the electrode melting or blowing out.
The inner and outer accelerating electrodes will not be short-circuited due to melting and deformation. Further, 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 limit values 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 at a high interest rate over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a side cross-sectional view of one embodiment of the electron beam excitation laser oscillation device of the present invention, and FIG. 2 is a -
3 is a cross-sectional view of FIG. 1 in another embodiment, and 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 invention, FIG. 6 is a cross-sectional view of yet another embodiment of the invention, and FIG. 7 is a side sectional view of still another embodiment of the invention. FIGS. 8 and 9 are perspective views of an embodiment in which the cross-sectional shape is rectangular. 1... Laser tube, 2... Inner acceleration electrode, 3...
Opening, 4... Outer accelerating electrode, 5... Opening, 6,
6'...Spacer, 7...Plasma container, 8...
Cathode electrode, 9... Spacer, 10, 10'...
...Brewster's window, 11,11'...External mirror,
12...Acceleration power supply, 13...Discharge power supply, 14...
Cooling pipe, 15... Electrode for shaping plasma potential distribution.

Claims (1)

[Scope of Claims] 1. A laser tube whose inside is filled with a laser medium; an inner acceleration electrode provided on the circumferential surface of the laser tube and having an opening; an outer acceleration electrode having an opening aligned with the opening of the electrode and disposed outside the laser tube; an electrode for plasma potential distribution shaping provided outside the opening of the outer acceleration electrode; a plasma container that holds plasma around the outer acceleration electrode; and an acceleration voltage is applied between the outer acceleration electrode and the inner acceleration electrode to accelerate electrons in the plasma and cause the electrons to move toward the axis of the laser tube. An electron beam excitation laser oscillation device comprising a power source that forms an electron beam that is incident at right angles to excite the laser medium. 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 accelerating electrode also serves as one electrode of a discharge electrode that forms plasma.