Diode laser based continuous-wave cavity ring-down technique for high reflectivity measurement

Abstract

A continuous-wave cavity ring-down (CRD) technique, in which a diode laser is employed as light source, is developed to determine the high reflectivity of optical dielectric mirrors. Based on on-axis alignment, large resonant peaks are obtained for CRD signal. When the amplitude of signal exceeds the predefined threshold, laser beam is switched off and a single exponential decay signal is obtained to fit the cavity decay time. The reflectivity of the cavity mirror, measured at several cavity lengths, is statistically determined to be 0.99737 at 1064 nm, with an uncertainty of 6×10^-5. On the other hand, with off-axis geometry, a steady signal is obtained to make a sensitive lock-in measurement and the steady signal itself fitted with appropriate theories to determine the cavity decay time. The reflection of the cavity mirror obtained by three methods and at different cavity lengths are in excellent agreement.