High Reflectance Measurements Using the Cavity Phase Shift Method

Abstract

The cavity phase shift (CAPS) method shows promise for direct measurements of high reflectances on various spherical surfaces at reasonable spatial resolution (1mm). The unknown reflectance is placed in an high Q optical interferometer, through which an intensity modulated laser beam is passed. A phase shift in the sine wave modulation yields the direct measurement. The multi-pass nature of an interferometer causes increased sensitivity and precision as the reflectances improve. Previous work with this approach has been done in the visible region. 1,2 This work has included the abilities to detect high transmittances or low absorbance-scattering in optical mirrors.