STIMULATED EMISSION FROM Ho3+ AT 2 μm IN HoF3

Abstract
Efficient laser emission of Ho3+ at 2μ has been obtained from a single crystal of HoF3 at liquid‐nitrogen temperatures. This is the first pure, undiluted rare‐earth compound laser. Fluorescence and absorption spectra indicated a spontaneous linewidth of 1.5 cm−1 for the laser transition. The fluorescence lifetime at 77°K was 2.6 msec, or 29% of the radiative lifetime as measured in dilution in an isomorphic host. The laser threshold for a 15‐mm rod was about 1 J.