Narrow-band stimulated emission from neodymium-doped phosphate glass in a selective resonator

Narrowing of the stimulated emission spectrum was studied using a neodymium-doped niobium-phosphate glass element. Under free-oscillation conditions the linewidth could be reduced to 1.7 cm^–1 when the threshold was exceeded sixfold; this could be done without a significant reduction in the efficiency. The narrowest emission line obtained was 0.15–0.2 cm^–1 wide. This result was achieved by the use of new niobium-phosphate laser glass elements in selective resonators.