OPTICAL NONLINEARITIES AND TRANSIENT DYNAMICS OF 2-(2'-HYDROXYPHENYL)BENZOXAZOLE STUDIED BY SINGLE-BEAM AND TIME-RESOLVED 2-COLOR Z-SCAN TECHNIQUES

Optical nonlinearities (including nonlinear absorption and nonlinear r efraction) and the temporal properties of the nonlinear refraction of 2-(2'-hydroxyphenyl)benzoxazole (HBO) based on excited-state intramole cular proton transfer in its two-photon absorption (TPA) range have be en investigated, for the first time to our knowledge, by single-beam a nd time-resolved two-color Z-scan techniques. By establishing the kine tic model of HBO that is due to the TPA, we obtained the TPA coefficie nt, the molecular hyperpolarizability of the ground state of the enol tautomer of HBO, and the nonlinear. refraction, represented by a,, of the excited state of the keto tautomer of HBO. The theoretical results are in good agreement with the experimental ones, which shows that, o n the one hand, the excited-state intramolecular proton transfer of HB O can be achieved through the excitation in its TPA range and that, on the other hand, the optical nonlinearities of HBO are closely related to the dynamics of HBO that are involved in the excited-state intramo lecular proton transfer. (C) 1998 Optical Society of America.