Abstract

The interaction of single femtosecond laser pulses tightly focused in the bulk of LiNbO₃ doped with Fe (400 ppm doping) and LiTaO₃ crystals was recently studied [1,2]. Single shots of 150 fs, 800 nm laser pulses, 3–50 nJ per pulse, were focused inside a crystal to the depth of 50 microns to the focal spot with diameter of 1.8 μm; the intensity in the interaction region varied from 1.0 TW/cm² to 16.7 TW/cm². The threshold for optically detectable change of refractive index has been found to be 3.8±0.5 nJ in Fe: LiNbO₃ and 5.2±0.5 nJ in pure LiNbO₃ crystal (intensity TW/cm² and 1.37 TW/cm² respectively). The permanent modification of LiTaO₃ was observed at 32±5 nJ (~10 TW/cm²) that might be considered as a result of breakdown. It has been found that the laser-induced material transformation is fully reversible at the energy per pulse of 14.5 nJ (3.8 TW/cm²).

© 2009 IEEE