The Pockels' effect in Langmuir-Blodgett films
Simple, compact and inexpensive automated apparatus for recording surface plasmon resonance and the Pockels (or linear electro-optic) effect in Langmuir-Blodgett films has been used to estimate the thickness, permittivity and second order non linear susceptibility X(^(2))(_xxx)(-w;w,0) of several novel Langmuir-Blodgett film-forming materials. The results agree with estimates of nonlinear susceptibility obtained by second-harmonic generation. The materials synthesised at Durham were all functionalised diaryl alkynes of the general formula CH(_3)(CH(_2))(_n)(Py(^+))C=C(Ph-R), wherein n =17 or 21 and R=H or OCH(_3). Of these, that with n =21 and R=OCH(_3) showed particularly promising Langmuir-Blodgett film-forming properties; its nonlinear susceptibility per mono layer, however, was approximately one hundredth that of a hemicyanine monolayer. The nonlinear susceptibility per monolayer, as measured by the Pockels effect and second harmonic generation, was inversely proportional to the square root of the film thickness. This indicated rapid deterioration of in-plane order with increasing film thickness. Several novel polymeric materials synthesised at Hull and examined at Durham consisted of a siloxane spine of approximately 16 Si atoms, with randomly substituted bipolar chromophoric sidegroups. All were highly stable in floating film form. Of them, one known as AMCR23 showed promising optical nonlinearity when deposited on silver: a nonlinear susceptibility of-15+9.6i pm V(^-1) was recorded for a monolayer (cf. 94.5+49.9i pm V(^-1) for a hemicyanine monolayer).