[OPTICAL REVIEW Vol. 5, No. 1 (1998) 17-19]

Technique to Estimate the Reflectance of a High-Reflectance Dielectric Multilayer Coating Mirror Using Incident Beam Angular Dependence of Its Transmittance

Shinji MIYOKI, Shuichi SATO, Masatake OHASHI and Masa-Katsu FUJIMOTO

1Spacetime Astronomy Section, National Astronomical Observatory, 2-21-1, Osawa, Mitaka, Tokyo, 181 Japan

(Received September 18, 1997; Accepted November 19, 1997)

The reflectance of a high-reflectance dielectric multilayer coating mirror tuned to a monochromatic laser wavelength was estimated from its transmittance which was measured with 0.4 ppm accuracy. The transmittance was calculated from its theoretical formula including three parameters (refractive indexes of low and high refractive films (nL, nH) and a number of layer units composed of a pair of one low and one high refractive film (N)) which were estimated from the incident beam angular dependence curve of the transmittance. This calculated transmittance agreed with that measured as a ratio of the laser beam power before and after the mirror with 6 ppm difference.

Key words : high-reflectance, dielectric multilayer coating mirror, reflectance, transmittance, ultralow loss, complex refractive index, incident angle, absorption loss, scattering loss