USA As Represented by Secretary of the Navy

John P Rahn

Richard Swart Hughes

Marion L Scott

Stray scattering in a scatterometer is removed by use of a lens and aperture system in conjunction with a beamsplitter. Backscattered light from a mirror being tested is deflected by a beamsplitter and focused by a lens through an aperture onto a detector. The distance from the beamsplitter to the lens is much smaller than the distance from the mirror to the beamsplitter in order to increase the detected signal as compared with detected noise caused by light scattered by the beamsplitter. The scatterometer system disclosed is further refined by use of a cavity dumper which absorbs stray light left after reflection from the mirror being tested. The cavity dumper is a silicon semiconductor on a metal backing which absorbs the light with minimum reflection back along the original incident light path.

Stray light eliminator in a scatterometer

A tunable laser using surface acoustic waves in the sides of a piezoelect prism to provide two reflective diffraction gratings for tuning the resonant cavity.

Surface acoustic wave tuning for lasers

A pulsed laser having a laser gain medium of broadband output is tuned to essentially monochromatic output. An acousto-optic cell is driven with an acoustic wave which varies linearly in frequency, causing the laser beam to be resolved into a number of essentially monochromatic focal points. The focused beam of the desired wavelength is reflected to the output through one or more apertures which block out the unwanted wavelengths.

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Ridgecrest, CA, United States of America

John P Rahn