Mechanisms of a change in the refractive index of an intensely pumped Yb:YAG crystal

Mechanisms of a change in the refractive index appearing in an intensely diode-pumped Yb:YAG-laser disk element are studied with the help of polarisation interferometry and dynamic grating testing. It is found that changes in the electronic component of the refractive index arising upon changing the populations of electronic levels of Yb3+ ions (the ground 2F7/2 state and the upper 2F5/2 level of the laser transition) and caused by the difference in the polarisability of these levels are an order of magnitude greater than thermal changes in the refractive index. It is shown that the difference ?p in the polarisability at the probe wavelength of 633 nm is 1.9 × 10 -26 cm3 and at the laser transition wavelength of 1029 nm is 1.6 × 10-26 cm3.