Modified theory of photoinduced molecular polar alignment in azo polymers

Abstract

An improvement on the simplified theory of all-optical poling [Chem. Phys. Lett. 286, 415 (1998)] is proposed. In this improvement the influence of the cis isomer is taken into account in the process of photoinduced molecular polar alignment. An analytical expression for the induced polar order in the steady-state regime is derived. This expression shows that, although the contribution to the photoinduced second-order susceptibility from the cis state itself can be neglected, the population of the cis state plays an important role. This result suggests the possibility that one can improve the induced polar order by increasing the poling temperature, so that thermal-assisted optical poling can be explained.

Photoinduced molecular polar alignment in E-O polymers by all-optical poling holographic methods

“…Our study of all-optical poling kinetics of E-O polymers is based on the theoretical model developed in [6,7]. The physical origin of all-optical poling is attributed to the orientational hole burning and molecular reorientation of azo-dye chromophores in the polymer host matrix.…”

“…As a consequence, the angular distributions ( ) t n Ω and ( ) c n Ω depend only on the polar angle and can be projected on the Legendre polynomials (cos ) j P θ by introducing expansion coefficients called the Order Parameters for trans and cis isomers [6,7].…”

“…In the case of an assembly of non-interacting molecules, the macroscopic polarizabilities (2) and (3) can be theoretically obtained from the corresponding microscopic polarizability and after averaging over all possible orientations [6][7][8][9], that is,…”

“…The local effects are considered in the second and third order hyperpolarizabilities and . In the present rod-like azo-dye polymeric systems, the induced (2) and (3) obviously dominate by contribution of trans isomer and are expressed in terms of the order parameter [6][7][8][9].…”

All optical switching in azo-polymer planar waveguide

“…In photoinduced and photoassisted poling [31], isomerization is used to help the alignment and to obtain nonlinear effects. Upon isomerization, there can be significant changes to the optical, geometric, mechanical and chemical properties of azobenzene molecules [5].…”