Laser oscillations have been produced in large crystals of Nd3+-doped Ca5(PO4)3F (the mineral fluorapatite, whence the coined name FAP) at room temperature under both tungsten lamp and flash lamp excitation. The laser tests show that FAP:Nd crystals have four times greater gain per incident pump energy and over one and a half times greater differential (slope) energy efficiency than equal size YAG: Nd crystals. The fluorescence, excitation, and absorption spectra of FAP:Nd are partially polarized, as expected for Nd3+ substituting Ca II sites of C1h symmetry. The fluorescence lifetime is 0.24 msec at 300°K. Laser oscillations occur at 1.0629 µ in π polarization (E‖c), which has 2.6 times the gain of σ polarization (E⊥c).
R. C. Ohlmann, K. B. Steinbruegge, and R. Mazelsky, "Spectroscopic and Laser Characteristics of Neodymium-doped Calcium Fluorophosphate," Appl. Opt. 7, 905-914 (1968)