NONLINEAR COLORATION EFFECTS IN TRANSITION-METAL-DOPED SRTIO3 CRYSTALS

Nonlinear coloration effects were discovered in doped crystals of SrTiO3 and were attributed to twophoton excited electron-hole pairs that subsequently become trapped by color centers. An induced absorption coefficient of 2.6 cm-1 was measured at 6328 A in samples doped with Ni and Mo when exposed to ruby laser pulses with peak intensities of 160 MW / cm2 and about 15-nsec duration. Calculated and previously reported experimental values of the two-photon absorption coefficient for SrTiO3 are in good agreement with these results. A model which assumes a coloration rate proportional to the square of the intensity and a simultaneous first-order bleaching process was found to give a good fit to the experimental data on coloration versus intensity. © 1969 The American Physical Society.