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USA As Represented by Secretary of the Navy

Joel M Avidor

Evan R Pugh

Charles C Stewart

Charles J Knight

John W Lothrop

The aerodynamic window is formed of a contiguous pair of gas jet streams driven at subsonic velocity across the entire cross-sectional area of an annular laser beam. One of the jet streams has a shear interface with the interior gas of the laser and has its index of refraction matched to it. The other interfaces with the outside air into which the beam passes and it too has a refraction index matched to the air. Matching of the indices minimizes optical distortion of the beam at the shear interfaces. Distortion produced at the boundary layer of the contiguous jet streams is minimized by equalizing their velocities. To maintain a desired laser cavity pressure, the jet streams are permitted to bend responsively to the pressure differential. The degree of the bending is controlled to reduce window gas consumption.

Gas laser aerodynamic window

Laser gas injected into a multiple-pulsed electric discharge laser (EDL) must be removed as quickly as possible following each laser pulse. This `clearing time` can limit the average laser output power. Fast, efficient mass transport is needed and it, in turn, requires the establishment of a uniform velocity flowfield. Such a uniform flowfield can be established by injecting the laser gas through arrays of porous tubes formed with eccentric walls tailored in wall thickness to introduce a non-uniform injection velocity around the circumference of each tube. Preferably, the tubes have a cross-sectional shape formed of displaced circular inner and outer contours to provide a progressively thickening wall. Tailoring is designed to establish an optimum, non-uniform injection velocity distribution capable of producing a nearly irrotational flow that rapidly develops into a uniform flowfield downstream of the tube array. Because of the enhanced heat transfer characteristics of the porous tubes, a beneficially uniform gas temperature also is maintained to assure good optical medium homogeneity.

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Rehovot, Israel

Joel M Avidor