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Single-crystal thin films of 4-aminobenzophenone have been prepared by a modification of the shear method, and the significant elements of the second-order optical polarizability tensor have been measured by the transverse second-harmonic generation (SHG) technique. Films with thickness less than the coherence length allowed measurements without significant effects due to phase-mismatch. Detailed SHG experiments with different polarization conditions were performed to determine the d coefficients. The magnitudes of the d coefficients at the fundamental wavelength of 1064 nm were found to be d23=7.3±0.4 pm/V and d22=0.73±0.04 pm/V. Directions for both type-I and type-II phase-matched propagation parallel to the film were identified. The results showed that guided-wave phase-matched SHG (type I and type II) should be possible using the films.

We have performed a detailed measurement of the sign of the nonlinear refractive index of PTS-polydiacetylene using Michelson interferometry and z-scan at 1.06 μm wavelength. The measurement was performed using 60 ps laser pulses at 10 Hz repetition rate that avoided any significant thermal contribution. The sign of n2 was found to be negative. The negative sign was explained considering saturation of the exciton absorption for off-resonant pumping. The saturation far outweighs two photon resonances in determining sign and magnitude of n2 in the off-resonant domain within the wavelength range 700–1064 nm.