Spectroscopy and laser oscillation properties of lithium neodymium tetraphosphate

Optical absorption, fluorescence, and laser characteristics of lithium neodymium tetraphosphate (LiNdP 4 O 12 , abbreviated as LNP) were examined. The crystal belongs to the monoclinic system (pseudoorthorhombic system) and the Nd content is 4.37 \times 10^{21} cm-3. The lifetime of the4 F_{3/2} level is 120 μs, which is one-half of 230μs observed in Nd:YAG. The largest effective emission cross section at the line peak ( 1.047_{7} \mu m) was spectroscopically determined as 3.2 \times 10^{-19} cm2for the electric vector parallel to the pseudoorthorhombic c axis 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 pseudoorthorhombic c axis 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 of 3.1 \times 10^{-19} cm2for the effective emission cross section of LNP, which is in good agreement with the value obtained from the spectroscopic data.

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