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

Femtosecond laser excitation (800 nm, ∼150 fs, 80 MHz) induced 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 nonlinear refraction. Intensity dependent nonlinear absorption studies portray the 2PA coefficient 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. In addition, using molecular electrostatic potential (MEP) analyses polarizability (5.30×10−24 esu) and dipole moment (7.317 Debye) were calculated using the density functional theory. A variation in the NLO coefficients with respect to orientation of excitation arises due to the anisotropy of the crystal. EDAPA crystal along (1 1 1) orientation has high laser damage threshold (9.1 GW/cm2) and low optical limiting threshold (24.36 μJ/cm2) and thus the wide dynamic range make it a preferred candidate towards laser safety devices for high repetition rate ultrashort laser pulse excitation. [ABSTRACT FROM AUTHOR]