Characteristics of co-existence of third-order and transient thermally induced optical nonlinearities in nanosecond regime

We report the experimental results on characteristics of co-existence of third-order and transient thermally induced optical nonlinearities using a nanosecond pulse laser and CS2 solutions of nigrosine. Results show that thermally induced optical nonlinearity is very sensitive to linear absorption, beam waist size and pulsewidth. Numerical simulations obtained by solving simultaneously acoustic and electromagnetic wave equations, agrees basically with experimental results. Meanwhile, the transition of optical nonlinearity from self-focusing pattern to self-defocusing pattern was observed when the contribution from thermally induced optical nonlinearity exceeds that from third-order optical nonlinearity.