Aerodynamic window for a gas laser

Details Aerodynamic window for a gas laser Aerodynamic window for a gas laser

1991-02-28

1993-02-09

Scott, Jr., Leon

Coherent light generators

Particular resonant cavity

Specified cavity component

372103, 359894, H01S 308

Patent

active

051857600

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The invention relates to an aerodynamic window for a gas laser, whose active chamber emits a focussed laser beam and is flow connected by means of a beam passage opening with a window chamber connected to a vacuum pump and which has a beam exit opening in an outer area which is preferably under atmospheric pressure.
2. Prior Art
Laser radiation is emitted from the active chamber through a beam passage opening, which forms a so-called window, which in the case of gas lasers must prevent the exit of active material, i.e. the gas from the active chamber. This window is normally made from a radiation-transparent, solid material. In the case of high power lasers the materials absorb so much energy, that they can no longer be used. They are replaced by aerodynamic windows, in which moving gas is used for sealing purposes. Such a flow is e.g. obtained by a differential pump. The sealing action of said aerodynamic window is essentially based on the fact that a window chamber is present from which pumping takes place with a vacuum pump. Such a window with the aforementioned features is known from DE-OS 35 10 057. The window chamber is arranged under an angle to the laser beam axis and the beam passes through the window chamber undeflected by the beam passage opening and the beam exit opening. The two said openings are located in walls which are at right angles to one another, in order to have a minimum length radiation path in the area through which there is a turbulent flow located between the openings. This turbulent flow significantly disturbs the beam quality. In the case of the known aerodynamic window it is also disadvantageous that the said openings are inclined with respect to the laser beam, so that the cross-sectional surface thereof for passing through the laser beam in unimpeded form must be larger than if they were positioned at right angles to the laser beam. This leads to an increased pump delivery volume and consequently to an increased energy expenditure, together with increased disturbance to the beam quality.


DESCRIPTION OF THE INVENTION

The problem of the present invention is to so improve an aerodynamic window of the aforementioned type, that a comparable sealing action of the beam passage opening is obtained with reduced pumping power and with an improved beam quality.
This problem is solved in that the laser beam emitted by the active chamber has a first focus located in the vicinity of the beam passage opening and is deflected onto a focussing mirror positioned in the window chamber and the laser beam leaving the said chamber is given by the said mirror a second focus located in the vicinity of the beam exit opening.
It is important for the invention that the laser beam has in the vicinity of the two beam openings in each case a minimum possible cross-section and consequently the two beam openings can be minimized with respect to their cross-section. Due to the fact that the opening cross-sections are small, for specific pressure differences there is a smaller gas flow through the beam openings. Thus, less laser gas flows out of the active chamber and into the window chamber and less air has to be pumped out of the latter, because the air inflow through the beam exit opening is comparatively small. In connection therewith less air can diffuse into the laser chamber than in the case of conventional aerodynamic windows. On the basis of reduced gas or air quantities, it can be assumed that the flow rates are smaller and consequently so is the flow-caused, optical influencing of the laser beam, which therefore has a higher beam quality. In order to minimize laser gas losses, the window chamber pressure can be at a value which is only slightly smaller than that in the active chamber.
In an embodiment of the invention the beam passage openings and the beam exit openings are closely juxtaposed with a spacing corresponding to an acute reflection angle at the focussing mirror. As a result that area in which the laser beam is influenced by flowing gases in the sense

REFERENCES:
patent: 4013977 (1977-03-01), Behrens
patent: 4721370 (1988-01-01), Goede
patent: 4821283 (1989-04-01), Wildermuth et al.

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