The standard electric-field-induced second-harmonic (EFISH) technique for measurement of the first hyperpolarizability (β) of nonlinear optical molecules is limited by the fact that the second hyperpolarizability (γ) also contributes to the second-harmonic signal from which β is deduced. We present a modified time-resolved EFISH in which the first and the second hyperpolarizabilities can be determined separately and accurately in the same experiment. We studied para-nitro aniline dissolved in a highly viscous solvent, glycerol, under conditions whereby the electric field was applied faster than the characteristic time for molecular rotation. This technique enabled the γ contribution to the signal to be resolved separately from the β contribution. The results confirm that for this molecule γ contributes only ~10% of the total EFISH hyperpolarizability.
© 2002 Optical Society of America
G. Meshulam, Z. Kotler, and G. Berkovic, "Time-resolved electric-field-induced second harmonic: simultaneous measurement of first and second molecular hyperpolarizabilities," Opt. Lett. 27, 1132-1134 (2002)