Second Harmonic Generation By Langmuir-Blodgett Multilayers Of An Organic Azo Dye

Multilayers of the compound 4-[4-(N-n-dodecyl-N-methylamino)phenylazo]-3-nitrobenzoic acid (DPNA) have been deposited onto glass slides using the Langmuir-Blodgett technique. Both Y-type and Z-type multilayers have been obtained. All these multilayers doubled the frequency of Nd3+:YAG laser radiation (1.064μm). Frequency doubling from the "centrosymmetric" Y-type layers can possibly be ascribed to the effect of the interface between the multilayers and the glass slide. By comparison of the second harippic intensity obtained from Z-type monolayers with that from quartz standards a x / value of 2.2 x 10-20 C3 J-2 was calculated for films of pure acid and a value of 2.5 x 10-20 C3 J-2 was obtained for films containing Cd2+ ions. These correspond to molecular a values of 4.5 x 10- 48 C3J-2m 3 and 3.3 x 10-48C3J-2m3 respectively. These high nonlinearities are due to resonant enhancement resulting from the proximity of the second harmonic wavelength to the absorption maxima of the films.