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

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Abstract
Changes in the refractive index of Ti:Al2O3 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 (π) and perpendicular (σ) to the c axis. The nonthermal portion of these changes decays on a 3-μsec time scale characteristic of the fluorescence lifetime of Ti3+. For the σ polarization, the nonthermal index change is equal to the concentration of excited Ti3+ ions times (4 ± 2) × 10−24 cm3. The change for the π 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.