Second-harmonic generation from thick all-polymeric Langmuir–Blodgett films prepared using polyurethanes

Abstract

A polyurethane containing 4-dialkylamino-4′-nitroazobenzene (Disperse Red) chromophores has been used as the ‘active’ layers in alternating Y-type Langmuir-Blodgett films for second-harmonic generation from light of wavelength 1.06 µm. The choice of ‘passive’ polymer greatly affects the intensity of the second-harmonic light, I_2ω, obtained. With the best ‘passive’ polymer investigated, the square root of I_2ω increases in proportion to the number of bilayers in the film up to a thickness of ca. 75 bilayers. The value of I_2ω decreases significantly over a period of months when the films are stored at 20 °C.