JPH0135509B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser oscillation device.

In many cases, discharge excitation was used to generate ion lasers. However, in the discharge excitation method, most of the electrons generated are in the low energy region,
Only a small number of high-energy electrons can excite ions. In order to increase the number of high-energy electrons, it is necessary to use a large current discharge, but this also increases the number of unnecessary low-energy electrons that cannot excite ions, and the efficiency of using the discharge to excite ions becomes extremely low. . Also, narrow laser tubes must be used to increase the current density and the proportion of high-energy electrons. However, it is not possible to increase the output of the laser. Electron beam excitation, which involves externally injecting high-energy electrons that can excite a laser medium, is considered to be a promising method for increasing laser output and generating it efficiently. However, in conventional electron beam excitation laser devices, a negative potential barrier is created in front of the cathode, and electrons that are extracted from the cathode surface and cross this barrier are accelerated (space charge control). The beam current can be increased by increasing the accelerating voltage, but this increases both the beam current and the kinetic energy of the electrons at the same time, and these cannot be controlled independently. Beam current is also 2~
Even at an accelerating voltage of 3KV, it was only about 1A, and it was difficult to increase it much more than this.

Research on electron beam pumped lasers has mainly focused on metal vapor lasers. Based on these research results, we can expect to increase the laser output by increasing the input power of the electron beam.
However, if the accelerating voltage of the electron beam is made too high, the laser medium will be transmitted through the laser medium without being sufficiently excited, so instead of increasing the accelerating voltage and increasing the beam current, The most advantageous solution to the problem of increasing laser power is to generate a high current electron beam that can be controlled independently and thereby has sufficient energy to excite the laser medium.

An object of the present invention is to provide a laser device with high laser oscillation efficiency and large laser output.

This objective is achieved by eliminating the space charge limitation and accelerating the electron flow extracted from the plasma (plasma cathode) created by the discharge and impinging on the laser medium to excite it.

A plasma cathode can draw an electron current in proportion to the discharge current, but a large beam current cannot be obtained as it is because it is subject to space-time charge limitations that accelerate the electron beam from the plasma cathode and draw it into the vacuum.
In order to eliminate the space charge limitation, a neutral gas was introduced into the acceleration region, and the positive ions generated by the ionization were moved toward the cathode under the accelerating electric field to neutralize and eliminate the space charge. However, discharge easily occurs in the acceleration region, making it impossible to obtain a stable electron beam.

In the present invention, a neutral gas is introduced into another region downstream of the acceleration region, the neutral gas is ionized in that region by an accelerated electron beam, and the generated positive ions flow back through the acceleration region to create a space charge. Neutralize and reduce this. As a result, the electron flow flowing from the plasma cathode can be freely accelerated, and the electron beam current can be controlled by controlling the discharge current.

Therefore, the acceleration voltage is adjusted to give the electrons kinetic energy that excites them when they collide with the laser medium, and the discharge current is adjusted independently of this to adjust the beam current size over a wide range. However, it is possible to obtain a beam output of the required size. Since the diameter of the extracted electron beam is not subject to severe conditions as in the discharge excitation method, the cross-sectional area of the laser tube can also be increased, which is advantageous in increasing the output of the laser.

Embodiments of the invention will be described in detail below with reference to the accompanying drawings.

Reference is made to FIG. 1, which shows the principle of the structure of the electron beam excitation laser device of the present invention.

1 is a plasma region, 2 is an electron beam acceleration region,
Reference numeral 3 denotes a region that generates ions for neutralizing space charges generated in the acceleration region, and these regions constitute an electron beam source. 4 is a laser tube connected to the ion generation region 3, 5 and 6 are a pair of laser mirrors that repeatedly reflect the laser light generated in the laser tube, and 7 is an accelerating voltage applied to accelerate the electron beam. It is a variable power supply for

FIG. 2 shows a more detailed structure of the electron beam excitation laser device.

Argon gas is introduced from the inlet 14, the space between the hollow cathode 8 and the anode 9 is maintained at 0.8 Torr, and the space between the hollow cathode 8 and the anodes 9, 10, 11 is
Perform a steady discharge of −15 amperes. 19 is the power supply,
20 indicates an ammeter. The acceleration region (between electrodes 11 and 12) with a length of about 40 cm was fixed at 0.1 mTorr, and the region for generating ions for neutralizing space charges (between electrodes 12 and 13) was fixed at 0.7 mTorr. When an acceleration voltage is applied to the acceleration region, an electron beam is generated, passes through the ion generation region, and enters the laser tube 4. Apply an external magnetic field in the direction of the arrow to guide the electron beam along the laser tube.
The neutral gas is exhausted from the exhaust ports 16, 17, 18 by a vacuum pump.

The electron beam current incident on the laser tube (measured with ammeter 21) could be controlled up to 3-11A, regardless of the accelerating voltage. Further, argon gas is introduced from the inlet 15 so that the average pressure inside the laser tube becomes around 15 mTorr. When the electron beam current is 3A or more, a high-density plasma is generated by the electron beam in an optical resonator arranged so that the axis of the laser tube and the optical axis coincide, and a laser beam of monovalent ions of argon at 488CÅ is generated. Oscillation was observed.

FIG. 3 shows, as an example, how the laser output changes with respect to the accelerating voltage when the electron beam current is 8.5 A. It is clear from this figure that there is an optimum value of the accelerating voltage for laser oscillation. Furthermore, when the accelerating voltage is fixed at 120 V and the electron beam current is increased to 11 A, the laser output continues to increase monotonically, and there is no tendency to saturate yet.

As is clear from the above description, in the electron beam excitation laser oscillation device of the present invention, the basic operating conditions such as the energy of the electron beam, the current of the electron beam, and the density of the laser medium of the laser tube can all be controlled independently. It becomes possible to operate a laser device close to the ideal.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the principle of the configuration of a large current electron beam excitation laser oscillation device according to the present invention. FIG. 2 shows an embodiment of the invention. FIG. 3 is a graph showing the relationship between laser output and acceleration voltage. In the figure: 1: plasma region, 2: electron beam acceleration region, 3: ion generation region, 4: laser tube,
5; 6: Laser mirror, 7: Variable accelerating voltage source.

Claims (1)

[Claims] 1. An electron beam source including a plasma region, an electron beam acceleration region, and a region that generates ions for neutralizing space charges generated in the acceleration region; a laser tube connected to the electron beam output end of the electron beam source; It is characterized by comprising a pair of mirrors set at a position to repeatedly reflect the laser light generated within the laser tube, and means for adjusting an accelerating voltage applied to accelerate the electron beam incident on the laser tube. Laser oscillation device.