Abstract

A method to measure the reflectivity of laser mirrors and to determine optical losses of laser elements Such as windows, capillaries and especially waveguides including slab waveguides has been developed. Measurements have been carried out using a Scanning-Fabry-Perot-Interferometer wind, forms a stable optical resonator and creates thereby laser-like conditions. One mirror is movable by a circular arrangement of piezo elements to tune resonator length by several laser wavelengths. Laser power is coupled into the interferometer and power transmitted through or reflected by the interferometer can be described by Airy-functions. Both values are functions of interferometer length and depend on optical losses within the interferometer. Evaluating measured Airy-curves enables the determination of losses in stable resonators, in waveguide resonators, and also in hybrid slab-waveguide resonators, the latter using cylindrical mirrors. The reflec- tivity of different laser mirrors, the optical losses of alumina ceramic and copper waveguides and coup bug losses were determined for different wavelengths between 9.2 µm 10.8 µm The standard deviation is about 1% of resonator losses. Losses of ceramic-waveguide resonators have been measured for different mirror-waveguide gaps, varying mirror tilt-angles and with apertures placed close to the mirror. Measured optical losses show some minima and maxima at different mirror-waveguide distances. Moreover, it was observed that an aperture placed between the waveguide and the mirror can reduce measured losses.

© 1996 IEEE