Spectrally resolved measurement of small optical losses by cavity enhanced spectroscopy techniques

Abstract

In general losses of optical of less than 1 % cannot be measured precisely with the best-established techniques (e.q. two-beam spectroscopy). However, it is possible to measure losses in the 0.0001 -0.5 % range with high accuracy using cavity enhanced spectroscopy (CES) methods. Such low losses can be measured with CES, due to an increased interaction path way with the object. The Cavity Ring-Down (CRD) technique takes advantage of the CES method and transforms the optical loss information into the time domain.Two types of CRD setups for spectrally resolved loss measurement of laser mirrors will be presented. The first setup uses a tunable laser system for serial detection of the reflectivity spectra. The second method determines the spectral losses using a super continuum source. Here, simultaneous excitation and a spectrometer based camera system for separate detection of several wavelengths is used. Results will be shown and compared with direct absorption measurements of the same sample.