Multiphoton absorption in CsLiB6O10 with femtosecond infrared laser pulses.

Nonlinear absorption and refraction characteristics of cesium lithium borate (CsLiB₆O₁₀) crystal have been studied using Z-scan technique. Ti:sapphire laser with 110 fs pulse width operating at 800 nm wavelength and pulse repetition rate of 1 kHz is used as the source of photons. Intensity of the laser pulse is varied from 0.541 to 1.283 T W/cm² to estimate the intensity dependence of multiphoton absorption coefficients. Using the theory of multiphoton absorption proposed by Sutherland [Handbook of Nonlinear Optics, in 2nd ed., edited by D. G. McLean and S. Kirkpatrick, Dekker, New York (2003)], found that open aperture Z-scan data fit well for the five-photon absorption (5PA) process. 5PA coefficients are obtained by fitting the expressions into the open aperture experimental data for various peak intensities (I₀₀). The nonlinear refractive index n₂ estimated from closed aperture Z-scan experiment is 1.075×10^-4 cm²/T W at an input peak intensity of 0.723 T W/cm². The above experiment when repeated with a 532 nm, 6 ns pulsed laser led to an irreversible damage of the sample resulting in an asymmetric open aperture Z-scan profile. This indicates that it is not possible to observe multiphoton absorption in this regime of pulse width using 532 nm laser. [ABSTRACT FROM AUTHOR]