Stimulated Emission Cross-Section Measurement for Laser Crystals of High-Power Solid-State Lasers Using Relaxation Oscillation Frequency

We demonstrate a new method for measuring the stimulated emission cross-section (
$\sigma _{s}$
) of laser crystals for high-power solid-state lasers at working state using the relaxation oscillation frequency (ROF). The method is implemented by measuring the ROF of the laser together with making the relation curve between the ROF and
$\sigma _{s}$
of the laser. The stimulated emission cross-section of the laser crystal can be obtained when the ROF in the relation curve equals to that of the measured value. Employing the method, the actual
$\sigma _{s}$
of the Nd:YVO4 crystals with doping concentrations and pumping powers of 0.2 at.% and 51.5 W at 808 nm, 0.8 at.% and 80 W at 888 nm, and 0.8 at.% and 113 W at 888 nm are measured upon considering the influence of concentration quenching and energy transfer upconversion of the lasers. The measured results are
$23.34\times 10^{-19}$
,
$23.77\times 10^{-19}$
, and
$23.42\times 10^{-19}$
cm2, respectively. The results are further compared and analysed with considering the temperature gradient of the laser crystals. It is found that the anomalous temperature gradient of the laser crystal at working state can induce an inhomogeneous gain spectral broadening, which can severely impact
$\sigma _{s}$
of the laser crystal.