The synthesis and optical properties of a series of amorphous polyesters with amino‐sulfone azobenzene chromophores in the main chain are presented. The condensation of alkyl diacid chlorides with 4‐[(2‐hydroxyethyl)ethylamino]‐4′‐(2‐hydroxyethylsulfonyl)azobenzene (7) gave polymers that showed low and unstable photoinduced birefringence because of their low glass‐transition temperature. The condensation of 7 with mixtures of adipoyl chloride and terephthaloyl chloride gave a polymer with a higher glass‐transition temperature and a stable reversible photoinduced birefringence. A photostationary birefringence of 0.07 was observed. Surface profile gratings were optically inscribed and produced diffraction efficiencies less than or equal to 19%. Photostationary, long‐term stable birefringence and surface‐grating efficiency increased with polymer rigidity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2245–2253, 2000

An all-optical control of light-angular-momentum transfer to nematic-liquid-crystal molecules is carried out by two copropagating noncoherent waves of orthogonal circular polarization. This allows the continuous variation of the total angular momentum of the light while conserving its circular symmetry. The molecular precession frequency is thus effectively and thoroughly controlled. The lightinduced molecular reorientation threshold is shown to depend significantly on the azimuthal symmetry of the excitation light, while remaining the same for different values of its total angular momentum. [S0031-9007(97)02929-3] PACS numbers: 42.70.Df The unique property of liquid crystals (LC) to spatially transfer the rotation momentum gives rise to fascinating intrinsic retroaction phenomena [1]. In addition, the collective character of the interaction of LC molecules with external electromagnetic fields provides extraordinary efficient light-matter coupling [1,2]. The above-mentioned conditions may lead to the light-induced first-[3,4] and second-[5] order phase transitions in the nematic LC (NLC) [6]. These are optical analogs of electric or magnetic field induced threshold reorientation of NLC molecules (so-called Fréedericksz transition), which is, in fact, a phase transition, when taking into account the character of LC orientational order parameter change. The theory of light-induced Fréedericksz transition via dielectric torque in LC materials was developed by Zel'dovich et al. [2].The transition threshold was predicted to depend on the polarization state of the excitation field, and the predicted doubling of this threshold value for circularly symmetric light with respect to the linear polarization case was experimentally proven in Ref. [5]. The delicate role of the light angular momentum in the system behavior above the phase transition threshold was established in Ref. [3]. The realization of the transfer of the light angular momentum to the quasimacroscopic collective of regularly precessing molecules [3] (this would be difficult for the case of macroscopic objects [7]) was rather surprising. The dependence of this precession frequency V upon the external control parameters, such as the excitation light intensity I and ellipticity g, is, however, strongly limited [8]. These limitations are determined, on the one hand, by the abrupt (first-order) phase transition induced by the circularly polarized light and, on the other hand, by the requirement of azimuthal symmetry in the light-matter system. Namely, the light intensity must be close to the light-induced phase transition value I th , and the circularity of the electromagnetic field must be high enough as to maintain the regular precession regime [8]. The precession frequency V was proven to exhibit a rather small variation versus I and g even in this regular precession regime, allowing, for example, a maximum of 7% of the V variation upon I [8].We propose and demonstrate, for the first time, to our best knowledge, an electromagnetic field configuration and ligh...

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Polarization holographic gratings were inscribed in azobenzene side chain polymer Films. The polarization »ratings were produced usine two orthogonally circularly polarized beams and the resulting stable transmission gratings were studied using a low power HcNe laser. The gratinss were observed to efficiently separate left and right circularly polarized light from the probe beam and two generate two elliptically polarized beams in the first order diffraction direction.

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