Anisotropic Nonlinear Optical and Optical Limiting Studies of an Ethylenediamminium Picrate Crystal with Femtosecond Excitation

摘要

Femtosecond laser excitation (800 nm, ～150 fs, 80 MHz) in- duced anisotropic nonlinear optical behaviour and optical limiting action of ethylenediamminium picrate (EDAPA) crystal along two prominent orientations (2 0 0) and (1 1 1) was studied using the Z-scan technique. EDAPA exhibited reverse saturable type nonlinear absorption ascribed to two-photon absorption (2PA) process and self-defocusing based on non- linear refraction. Intensity dependent nonlinear absorption studies portray the 2PA caefficient is independent of the peak intensity of excitation. Frontier molecular orbitals studies revealed the non-availability of real states at laser excitation (1.55 eV) and the measured energy gap of 3.18 eV avails the energy states for simultaneous absorption of two photons involving virtual states leading to the occurrence of genuine 2PA.