Circularly polarized light-induced rearrangement of optical axis in photoanisotropic recording media

Cyclic Azobenzene-Containing Side-Chain Liquid Crystalline Polymers: Synthesis and Topological Effect on Mesophase Transition, Order, and Photoinduced Birefringence

“…The kinetics of photoinduced birefringence at room temperature for linear and cyclic polymers of two different sizes, PAzoMA 35 and PAzoMA 18 , are compared in Figure . A typical experiment consisted in first applying a linearly polarized 488 nm light to induce the birefringence, then turning off the excitation to examine the stability of the birefringence, and finally applying a circularly polarized light to “erase” the “in-plane” anisotropy . For all films, the small birefringence existing prior to the linearly polarized excitation was normalized to zero to better show the part of the photoinduced birefringence.…”

“…Thin films were prepared on quartz plates to exhibit an absorbance at 360 nm suitable for measuring the orientation of trans azo mesogens. They were preirradiated at room temperature with unpolarized UV light to reach the photostationary cis-rich state (this should also create an anisotropy axis perpendicular to the film plane since the light was normally incident) and then exposed to linearly polarized visible light to induce an “in-plane” orientation of trans azo mesogens in the direction perpendicular to the polarization of the excitation visible light. This photoinduced molecular orientation in thin films could be measured by recording polarized UV−vis spectra with the polarization of the spectrophotometer’s beam set to be parallel ( A ∥ ) and perpendicular ( A ⊥ ) to the polarization of the excitation visible light; from the dichroic ratio of the 360 nm band ( R = A ⊥ / A ∥ ) the order parameter S , characterizing the average orientation of trans azo mesogens, could be calculated according to S = ( R − 1)/( R + 2).…”

“…A typical experiment consisted in first applying a linearly polarized 488 nm light to induce the birefringence, then turning off the excitation to examine the stability of the birefringence, and finally applying a circularly polarized light to "erase" the "in-plane" anisotropy. 29 For all films, the small birefringence existing prior to the linearly polarized excitation was normalized to zero to better show the part of the photoinduced birefringence. From the results, it becomes immediately clear that the cyclic polymers behave differently from their linear precursors.…”

Photoinduced absorption and refraction in azo dye doped PMMA films: the aging effect

“…Azo dye doped polymers have been shown to be promising candidates for reversible optical storage applications [1][2][3][4][5][6][7][8][9]. Five new azo dye derivatives doped in PMMA matrices were characterized for these purposes [5].…”