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

Changes in the refractive index of a Nd:YAG laser crystal caused by intense pump are measured using a polarisation interferometer. A significant electronic component in the refractive-index changes associated with the excitation of the F-4(3/2) electronic level of N3+ 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 F-2(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.