Closed Aperture Cw Z-Scan Of L-Tryptophan For Determination Of Optical Nonlinearity In The Thermal Regime

The closed aperture continuous wave Z-scan of L-tryptophan at 661 nm was performed to investigate the variat ion of on-axis nonlinear phase shift (Delta Phi(0)) with the change of optical field strength. Delta Phi(0) was found to vary nonlinearly with irradiance (4) in the range from 150 to 290 MW/m(2). This nonlinear variation is explained by considering the effect of linear and nonlinear absorption of radiation on the thermo-optical refractive index. Using the quadratic fitting of Delta Phi(0) with I-0 , we have found the thermo-optic coefficient of refractive index dn/dT, thermal coefficient of nonlinear refractive index n(2)(T), and the nonlinear absorption coefficient beta in the observed power regime. (C) 2021 Optical Society of America