Anomalous large nonlinearity of thin SnCl2 phthalocyanine films observed upon pulsed laser excitation

The nonlinear susceptibility of thin stannum dichloride phthalocyanine (SnCl₂Pc) films was studied by the method of degenerate four-wave mixing (DFWM) using the second-harmonic 532-nm, 10-ns pulses from a single-mode, TEM₀₀, 1.5-mJ Nd³⁺:YAG laser and by the method of nonlinear lens (the Z-scan method). The intensity of the first-order self-diffraction upon the DFWM on dynamic gratings induced in SnCl₂Pc films has a cubic dependence on the recording-beam intensity, indicating to the third-order nonlinear response of the films. The value of the nonlinear susceptibility χ⁽³⁾(ω;ω,-ω,ω) = (4.4 ± 0.5) × 10^-7 esu noticeably exceeds this value for phthalocyanines known in the literature. The mechanisms that can be responsible for the nonlinear response of the new synthesised material are discussed.