Gas laser in particular CO.sub.2 laser

Details Gas laser in particular CO.sub.2 laser Gas laser in particular CO.sub.2 laser

1994-01-12

1995-03-21

Scott, Jr., Leon

Coherent light generators

Particular pumping means

Electrical

372 64, 372 92, 372 76, 372 97, 372 34, H01S 3097

Patent

active

054003571

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION



Gas laser, in particular CO.sub.2 laser

The invention relates to a gas laser, in particular CO.sub.2 laser, having as laser medium a gas which is excited to form a plasma by the supply of RF power, in particular in the form of microwave energy, the RF waves being coupled into the laser medium from a rectangular waveguide.
In principle, the excitation of the laser medium to form a photon-emitting plasma can be performed by applying an electric field, which can be a direct or alternating field. In the course of the development of gas lasers, the advantages due to excitation by means of radio-frequency power have become ever clearer. The exciting frequency can reach in this case as far as into the microwave region.
Various techniques are known for coupling the radio-frequency power into the gas plasma. In the case of a so-called ribbon conductor laser, the laser medium is located between opposite surfaces of two wall parts which are simultaneously constructed as electrodes and for the coupling in of the energy. Since there forms along the two plasma-bounding surfaces of the ribbon conductor electrodes a boundary layer which contributes only a little or not at all to the generation of the laser radiation, the achievable laser output power is limited.
It would be conceivable to increase the exciting frequency, since the thickness of the boundary layers in the plasma decreases with increasing exciting frequency.
The satisfactory attainment of an exciting frequency in the MHz region has not been possible using the previous ribbon conductor lasers.
A gas laser of the type mentioned at the beginning has been disclosed in EP 0,280,044 A2. This reference describes a gas laser in which microwave energy is laterally coupled into the laser medium from a rectangular waveguide with a gradual transition. Not only does this technique require a relatively large amount of space, but it also does not permit a high efficiency for the coupling in of the microwave energy.
It is therefore the object of the invention to permit a compact structure and a high efficiency for the coupling in of the RF power in a gas laser of the type mentioned at the beginning.
This object is achieved according to the invention by means of a gas laser of the type mentioned at the beginning by coupling in with the aid of a ribbon-shaped waveguide which projects into the rectangular waveguide.
The ribbon-shaped waveguide in this case ensures lateral coupling of the RF power into the plasma discharge chamber, it being the case that it can itself form the end electrodes of the discharge chamber. In a preferred embodiment, the coupling of the RF waves into the laser medium is therefore performed over the entire length of the plasma.
The design according to the invention permits a compact structure of the laser, correct coupling also of high exciting frequencies into the plasma, and coupling out on all sides of the rectangular waveguide.
In order to be able to introduce the RF energy, preferably microwave energy, easily into the discharge chamber from the rectangular waveguide, and as few reflections as possible at the joint which is produced by the discontinuity in the rectangular waveguide, the waveguide projects with an asymmetrical shape into the rectangular waveguide, the maximum depth of immersion of the waveguide into the rectangular waveguide being displaced on the length of the waveguide, starting from the middle thereof, towards the end averted from an RF generator.
In a preferred embodiment of such a waveguide, the waveguide has a constant camber which extends from the end nearer the RF generator with a lesser curvature to the maximum point of immersion of the waveguide into the rectangular waveguide than from the maximum point of immersion to the other end. In this case, the waveguide can approximately have the shape of an e.sup.-x function.
In an alternative, asymmetrical embodiment, the waveguide extends approximately rectilinearly from the end nearer the RF generator up to the maximum depth of immersion and returns approximatel

REFERENCES:
patent: 4987577 (1991-01-01), Seunk et al.

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