Impact of shock layer radiation on laser photography of ultrafast metal jets

Charles L. Goldey; J. F. Cronin; Edmond Y. Lo; Hart H. Legner; Peter E. Nebolsine

doi:10.1117/12.218298

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1 September 1995 Impact of shock layer radiation on laser photography of ultrafast metal jets

Charles L. Goldey, J. F. Cronin, Edmond Y. Lo, Hart H. Legner, Peter E. Nebolsine

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Proceedings Volume 2549, Ultrahigh- and High-Speed Photography, Videography, and Photonics '95; (1995) https://doi.org/10.1117/12.218298
Event: SPIE's 1995 International Symposium on Optical Science, Engineering, and Instrumentation, 1995, San Diego, CA, United States

Abstract

The light emission from the bow shock around the tip of a metal jet formed by the collapse of a shaped-charge linear was computed for tip speeds up to 15 km/s and the laser energy needed to overwhelm this emission for a front-lit photographic application has been determined. Upon approximating the nose of the jet as a hemisphere with a 2 cm radius, a 3D inviscid flow field code was used in conjunction with a nonequilibrium air radiation code to compute the shocked air properties including the temperature, pressure and emission. For comparison, an analytical calculation of the shocked air properties and visible radiation at the flow stagnation point was made. Both calculation methods yield results which indicate that at a tip velocity exceeding 10 km/s the emission from the bow shock is equivalent to blackbody radiation. Additional values for the emission at tip velocities below 10 km/s are also contained in the paper. These results specify that a laser pulse energy of 10 mJ would be required to match this background luminosity for the 10 km/s case assuming a 1000 cm² illuminated object area, a 1.5 nm spectral bandpass and 50 ns exposure time for a camera.

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Charles L. Goldey, J. F. Cronin, Edmond Y. Lo, Hart H. Legner, and Peter E. Nebolsine "Impact of shock layer radiation on laser photography of ultrafast metal jets", Proc. SPIE 2549, Ultrahigh- and High-Speed Photography, Videography, and Photonics '95, (1 September 1995); https://doi.org/10.1117/12.218298

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