Third-order optical nonlinearities of naphthalocyanine derivatives measured by resonant femtosecond degenerate four-wave mixing technique

The third-order optical nonlinearities of several naphthalocyanine derivatives were measured under resonant conditions by the femtosecond degenerate four-wave mixing (DFWM) technique. Temporal profiles of the DFWM signal were measured with a time resolution of 0.3 ps, and were found to consist of at least two components, the coherent instantaneous nonlinear response and the slow response with a decay time constant longer than several hundred picoseconds. The latter can be attributed to the long-lived excited state and molecular rotational relaxation. The electronic molecular hyperpolarizability, γe, was evaluated to be in the range (2.1–7.5) × 10−29 esu for these macrocycles, two orders of magnitude greater than the nonresonant values.