Electronic changes of refractive index in intensively pumped Nd:YAG laser crystals

Refractive index changes accompanying changes in population of electron levels of Nd3+ ions in a Nd:YAG laser crystal tinder intensive diode and laser pumping have been studied using a highly sensitive polarization interferometer. An electronic. change of the index due to population of the F-4(3/2) level is measured to be high (comparable with the thermal component) in the crystal under QCW diode-stack pumping (at 808 nm). The electronic component increased dramatically under pumping by an additional laser (at 266 nm) due to population of a higher-lying level F-2(2)(5/2). Analytical estimation reveals a predominating contribution of the well-allowed 4f-5d inter-shell transitions in polarizability of the excited levels F-4(3/2) and F-2(2)(5/2) both at a testing wavelength of 633, nm and at a Wavelength of the strongest laser transition 1044.2 nm.