3RD-ORDER NONLINEAR-OPTICAL PROPERTIES OF SIDE-CHAIN LIQUID-CRYSTALLINE POLYMERS STUDIED BY 3RD-HARMONIC GENERATION FROM THIN-FILMS

Highly-conjugated main chain polymers have been studied extensively in recent years as third order non-linear optical materials. However, in a non-centrosymmetric system such as a polyene which has been substit uted with an electron donor and acceptor group, the relaxation of cert ain selection rules results in an increase in the static third order h yperpolarisibility. Consequently, there has been recent interest in th e third order non-linear optical properties of materials more typicall y studied for their quardratic non-linear response. One of the driving forces for this work has been the possibility of producing single dev ice substrates possessing significant second and third order non-linea rities which could lead to highly integrated optical devices. We prese nt the third order non-linear susceptibilities of some asymmetrically- substituted, side-chain liquid crystalline polymers, measured in amorp hous thin films by third harmonic generation at 1064 nm and 1579 nm. T he highest chi((3)) value of 1.02 x 10-(18) m(2)/V-2 from a polymer wi th an azo side group is expected to have some resonance contribution a nd is comparable with the non-resonant susceptibility of main chain po lymers such as poly(phenylacetylene) and poly(p-phenylenebenzobislhiaz ole).