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 under 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 4F3/2 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 2F(2)5 /2. Analytical estimation reveals a predominating contribution of the well-allowed 4f-5d inter-shell transitions in polarizability of the excited levels 4F3/2 and 2F(2)5/2 both at a testing wavelength of 633 nm and at a wavelength of the strongest laser transition 1064.2 nm.