Determination of fluorescence quantum efficiency and laser emission cross sections of neodymium crystals: Application to KNdP4O12

The stimulated emission cross sections σ
L
of neodymium crystals at the laser wavelengths (1.05 and 1.32 μm) are useful parameters to predict their laser performance. The determination of σ
L
has traditionally been a delicate experimental task. We describe here a method which relies upon the measurement of the branching ratios of the radiative transitions from the
⁴
F
3/2
doublet to the
⁴
I multiplets, and the calibration is provided by an absorption measurement concerning a
⁴
I
9/2
→
⁴
F
3/2
transition. The precise determination of the spectrometer system response over a broad spectral interval is not required. This method also leads to the value of the fluorescence quantum efficiency η of the
⁴
F
3/2
level. It is applied here to potassium-neodymium tetrametaphosphate, KNd P
4
O
12
.