Spectroscopy and laser oscillation properties of lithium neodymium tetraphosphate

Optical absorption, fluorescence, and laser characteristics of lithium neodymium tetraphosphate (LiNdP4O12, abbreviated as LNP) were examined. The crystal belongs to the monoclinic system (pseudoorthorhombic system) and the Nd content is4.37 × 10²¹cm-3. The lifetime of the4F3/2level is 120 μs, which is one-half of 230μs observed in Nd:YAG. The largest effective emission cross section at the line peak (1.047₇ ) was spectroscopically determined as3.2 × 10⁻¹⁹cm2for the electric vector parallel to the pseudoorthorhombiccaxis and quantum efficiency was estimated as 0.48. Quasi-continuous laser oscillation pumped by a chopped Ar-ion laser was achieved with a 1.85-mm-long crystal. The output light was linearly polarized along the pseudoorthorhombiccaxis of the crystal, which does not depend on the polarization direction of the pump light. The measured threshold and round-trip loss yield the value of3.1 × 10⁻¹⁹cm2for the effective emission cross section of LNP, which is in good agreement with the value obtained from the spectroscopic data.