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 the
⁴
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}
cm
²
for 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}
cm
²
for the effective emission cross section of LNP, which is in good agreement with the value obtained from the spectroscopic data.