Gas lasers, in particular CO.sub.2 lasers

Details Gas lasers, in particular CO.sub.2 lasers Gas lasers, in particular CO.sub.2 lasers

1991-10-17

1993-06-29

Scott, Jr., Leon

Coherent light generators

Particular pumping means

Electrical

372 66, 372 35, 372 37, 372 64, 372 59, 372 92, 372 55, H01S 3097

Patent

active

052241173

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to a gas laser, in particular a CO.sub.2 laser, in which the laser gas is excited by the supply of high-frequency energy. More particularly, the invention relates to the excitation of a slab laser by specifically coupling high-frequency energy.


BACKGROUND OF THE INVENTION

In gas lasers, the laser-active medium is a gas which is excited to a plasma. To maintain the plasma state, energy must be constantly supplied. This is usually done by applying an electric field, which is capable of accelerating the free electrons. In principle, the field can be a direct-current field or an alternating field, whereby an obvious solution is to inject high-frequency energy. The advantages of high-frequency excitation are that no losses occur at a series resistor and that there are no voltage drops across the cathodes region. The simple pulsing capability of the generators is advantageous for applications with gas lasers. However, so-called high-frequency boundary layers occur in the plasma which are laser-inactive. Moreover, a comparatively expensive generator is needed.
Theoretically, the frequency of the excitation energy can vary from the range of radio frequencies up to beyond the microwave range. However, at high frequencies, for example in the 2.45 GHz range usually used for microwave applications, it is difficult to inject the microwave energy uniformly and effectively in plasmas, whose expansion is great enough for a laser configuration.
The German Published Patent Application 37 43 358 discloses a so-called "fast-flow" laser, which is operated at a frequency of 2.45 GH.sub.z. The gas that flows axially through the laser at a high speed is ignited with microwave energy even before it enters the laser. These types of lasers can produce a comparatively high power output in the kilowatt range; however, the laser gas must have a high flow-through speed in order to eliminate the dissipated heat of the plasma out of the laser-active volume.
From the technical literature (W. Ranz "Untersuchungen zur CO2-Laseranregung mit MikrowellenGasentladungen in nichtresonanten Strukturen" [Analyses of CO.sub.2 Laser Excitation with Microwave Gas Discharges in Non-Resonant Structures], Thesis (1988), FAU Erlangen-Burnberg), an excitation structure for a laser is known, in which a ceramic tube, which is situated inside a microwave guide and whose axis is aligned in the direction of propagation of the microwave energy, contains the laser-active gas. As a result of this design, the microwave power is attenuated by the plasma contained in the ceramic tube, so that the energy is injected into the plasma irregularly with respect to the longitudinal axis of the tube. Consequently, here as well, only so-called "running discharges" could be generated in a pulsed operation, so that at a time only a part of the gas is excited to the plasma state.
Furthermore, so-called slab lasers are known, in which the laser-active gas is situated between opposite surfaces of two wall parts, which are equally designed as electrodes for injecting the energy. In the case of the German Published Patent Application 37 29 053, a high-frequency electric alternating field is injected into such a gas slab laser. It advantageously foresees injecting the high-frequency energy at several locations to provide for uniform activation over the entire length.
Finally, the EP-A-O 275 023 discloses a type of gas slab laser, in which the excitation is supposed to take place with high-frequency energy in the radio-frequency range, whereby the energy is supplied via lines to the upper wall part of the laser configured in a receptacle. In this case, the frequency has an upward limitation, since otherwise standing waves would form and lead to corresponding irregularities of the plasma.
Given a discharge volume of a slab laser, it is desirable to increase the laser's power output by increasing the injected electric power accordingly. This is possible then at a constant plasma gas temperature, when the clearance between the plasma-limiti

REFERENCES:
patent: 4646313 (1987-02-01), Seeling
patent: 4719639 (1988-01-01), Tulip
patent: 4890294 (1989-12-01), Nishimae et al.
patent: 4987577 (1991-01-01), Seunik et al.

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