Laser Action in a Flux-Grown Ruby

Abstract

A method of growing very perfect ruby crystals by slow cooling of a PbO (B₂O₃)_X flux doped with Al₂O₃ and Cr₂O₃ is described. A crystal grown by this method has been operated as a laser with its natural crystal faces used as feedback surfaces. Interferometry through these surfaces showed that the optical path length between the feedback faces varied only about λ/10 for red light over the entire face. The angles of laser emission high above threshold agreed accurately with those predicted for a Fabry‐Perot cavity. Near threshold the output consisted of a very regular damped oscillation of the Statz‐deMars type that was completely linearly polarized. A little farther above threshold a second train of oscillations was also present and was polarized at 90° to the first train. A formula for the laser threshold dependence on temperature was derived. A comparison of the model with measurements made between 90° and 305°K allowed a determination of the cavity loss under laser operation. With multilayer dielectric film reflectors a loss of less than 1% per pass was found, the bulk of which could be accounted for by known transmission and absorption losses in the end films.