Second Harmonic Generation by Langmuir-Blodgett Multilayers of an Organic Azo Dye

Abstract

Second harmonic generation (SHG) was observed from Z-type Langmuir-Blodgett multilayers of 4-[4-(N-n-dodecyl-N-methylamino)phenylazo]-3-nitrobenzoic acid (DPNA) on irradiation at 1.06 μm (Nd3+:YAG laser). Even a single LB layer gave a SH signal significantly above background; further layers increased the intensity although the increase did not obey the expected square law. As the incidence angle was varied, all the signals showed a pattern of fringes due to dispersion of the glass substrate. The χ(2) of film deposited in the presence of Cd2+ ions was calculated to be (2.5 ± 0.5) · 10-20 C3 J-2, a value significantly higher than the best known crystalline materials and comparable with other LB materials.