A laser output coupler using frustrated total internal reflection

A unique component has been developed, constructed, and incorporated into an optically pumped ruby laser system. Without using thin film optical coatings, this component allows a known fraction of the radiation to be coupled from a laser system while simultaneously serving as the partial reflector at the output end of the laser. The output coupler, herein described, utilizes a frustrated total internal reflection configuration and is fabricated of fused silica with an air gap 0.483 micro in thickness as the critically controlled element. Techniques have been developed for establishing and maintaining the spacing of the silica members to a predetermined fraction of the ruby emission wavelength of 6943 A. The measured transmission, reflection, and scattering loss characteristics of the coupler are discussed. In addition, schematic diagrams and photographs of the operating coupler are shown. This coupler has withstood repeated Q-spoiled bursts of laser radiation without damage. However, equivalent radiation pulses have consistently destroyed dielectric reflectors. Thus, more reproducible laser experiments can be performed with this coupler than with conventional optically coated reflectors.