Optically induced nonresonant changes in the refractive index of Ti:Al_2O_3

Changes in the refractive index of Ti:Al(2)O(3) induced by 10-nsec, 532-nm pump pulses from a frequency-doubled Nd:YAG laser have been measured interferometrically at 632.8 nm for signal polarizations parallel (pi) and perpendicular (sigma) to the c axis. The nonthermal portion of these changes decays on a 3-microsec time scale characteristic of the fluorescence lifetime of Ti(3+). For the sigma polarization, the nonthermal index change is equal to the concentration of excited Ti(3) ions times (4 +/- 2) x 10(-24) cm(3). The change for the pi polarization is lower by a factor of 3.7 +/- 0.6. The average change is consistent with the value estimated from a harmonic oscillator model that considers virtual transitions to a charge-transfer band.