Beam Quality Of Continuous And Pulsed Axial Aerodynamic Windows

H. W. Behrens; J. Shwartz; V. A. Kulkarny

doi:10.1117/12.933733

19 November 1982 Beam Quality Of Continuous And Pulsed Axial Aerodynamic Windows

H. W. Behrens, J. Shwartz, V. A. Kulkarny

Proceedings Volume 0343, Laser Diagnostics; (1982) https://doi.org/10.1117/12.933733
Event: 1982 Technical Symposium East, 1982, Arlington, United States

Abstract

Aerodynamic windows utilize gas flows to provide pressure and gas species isolation interfaces which are transparent to laser radiation. For CW chemical and gasdynamic lasers, a continuously operating window is required. An axial type window is described which is capable of sustaining a large pressure ratio (of at least up to 100) and is characterized by excellent optical quality. In this window the laser beam is extracted from the low pressure environment through an optical duct and enters into the supersonic uniform flow region of a Laval nozzle via an oblique opening in the duct. The beam crosses the oblique shock formed by the wedge surface of the opening and passes along the nozzle centerline through the nozzle throat, its subsonic section and into the atmosphere. Dry nitrogen flows through the supersonic nozzle opposite to the laser beam direction past the oblique duct opening into the aerowindow diffuser. Two windows of this type have been designed, built and operated over the past 9 and 7 years, respectively. The feasibility of using a shock tube generated pulsed flow field as a single-shot window for short, high-energy laser pulses was also investigated. Experiments were performed to define operating conditions which cause a minimal degradation in the quality of a laser beam transmitted through the window. In the experiments a scribed diaphragm shock tube with glass endwalls was used to simulate the window, and a laser pulse was transmitted along the tube axis after the diaphragm burst. The optical quality of the nearly one-dimensional pressure wave field and the turbulent contact interface was determined using both direct beam quality ("power in the bucket") and interferometric techniques. It was shown that with proper choice of design variables the beam quality degradation caused by this pulsed aerodynamic window is less than 10%.

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H. W. Behrens, J. Shwartz, and V. A. Kulkarny "Beam Quality Of Continuous And Pulsed Axial Aerodynamic Windows", Proc. SPIE 0343, Laser Diagnostics, (19 November 1982); https://doi.org/10.1117/12.933733

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