LANGMUIR-BLODGETT-FILMS FOR NONLINEAR-OPTICAL APPLICATIONS

Azo-benzene chromophores with an oxygen donor and five different end-g roups have been attached to octadecyl chains or to polysiloxane backbo nes via hexadecyl spacer groups. These were deposited by the Langmuir- Blodgett (LB) technique using our own design of diamond-barrier trough . The LB deposition properties of the polymers were superior to those of the low molecular mass materials, which did not show second harmoni c generation (SHG) as deposited monolayers. The strength of SHG from t he polymers correlated with acceptor strength, but the maximum signal was only about 10% of that of hemicyanine. Only one of the polymers ga ve thick films of very high quality; this had a hydroxyl end-group and showed no SHG except when deposited from an acid subphase. This was p resumed to result from protonation of the azo group to create an accep tor. The quality of the deposited films may correlate with their phase behaviour; the best material showed only a presumed soft crystalline phase. The film-forming properties of that film were remarkable; loss figures of around 2.5 dB cm-1 have been recorded at 633 nm in films of 1.3 mum thickness. Future work will seek to isolate and independently control the factors involved in good film formation and in high SHG.