Electric-field-induced optical second-harmonic generation in polydiacetylene solutions

Abstract

Electric-field-induced second-harmonic generation experiments on polydiacetylene solutions in dimethylformamide and in chloroform at 1.064 μm fundamental wavelength are presented. The technique allows for the measurements of both modulus and phase of the cubic susceptibility ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}$(-2ω;ω,ω,0). Influence of the phase on the measured harmonic intensities is discussed in detail as well as errors which can result when it is neglected. It is found that ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}$(-2ω;ω,ω,0) is complex with negative real part. This result is discussed in terms of a two-photon resonance. A small solvatochromic effect is also observed.