Interferometric study of electronic changes in the refractive index of a Nd:YAG laser crystal caused by intense pumping

Changes in the refractive index of a Nd:YAG laser crystal caused by intense pumping are measured using a polarisation interferometer. A significant electronic component in the refractive-index changes associated with the excitation of the ⁴F_3/2 electronic level of Nd³⁺ ions is revealed in the crystal pumped by 808-nm radiation of a pulsed diode array. An appreciable increase in the electronic component of the refractive index, which is caused by the population of the ²F(2)_5/2 high-energy level, is observed in a Nd:YAG crystal additionally pumped by a 266-nm laser beam. Analytic calculations show that the short-wavelength 4f–5d transitions provide a predominant contribution to the polarisability of excited Nd³⁺ ions at the 1064.2-nm lasing transition.