Analysis of the Kinetics of Diffraction Efficiency during the Holographic Grating Recording in Azobenzene Functionalized Polymers

Abstract

The laser-assisted holographic grating recording process in films of azobenzene functionalized polymers is usually studied by observation of the efficiency of light scattering on a developing in time diffraction grating. Various possible mechanisms contributing to grating formation as well as the bulk or surface origin (bulk refractive index and/or relief grating) of light scattering make the analysis of kinetics of grating recording, from the light scattering data only, difficult and ambiguous. To fully explain experimentally observed various and complex (frequently nonexponential) kinetics of the first-order light diffraction intensity, we considered a simple single-exponential growth of the two phase gratings in the same polymer film. In modeling we assumed that the bulk refractive index grating Deltan(t) and the surface relief grating Deltad(t) differ considerably in their growth rates and we allowed for a nonstationary phase shift Deltaphi(t) between them which was experimentally observed during the recording process. The origin of the nonstationary phase shift is a result of a slow shift of interference pattern due to delicate symmetry breaking in illumination conditions (e.g., difference in beam intensities and deviation of exact symmetrical beam incidence angles on the sample). Changing only such parameters as stationary amplitudes of refractive index and relief gratings for a span of phase shifts (0-pi) between them, we obtained a series of kinetic responses which we discuss and interpret. The various examples of temporal evolution of diffraction efficiency for the same grating formation kinetics, modeled in our work, supply evidence that great care must be taken to properly interpret the experimental results.

Graphene Functionalized with Azo Polymer Brushes: Surface‐Initiated Polymerization and Photoresponsive Properties

“…[30][31][32][33] The effect of the phase shift is not a dominant factor for SRGs with large surface modulation. [ 32 ] In order to understand the cause of the signifi cant DE enhancement, the modulated amplitudes of the SRGs were analyzed by AFM.…”

Thermal, optical and photoinduced properties of a series of homo and co-polyimides with two kinds of covalently bonded azo-dyes and their supramolecular counterparts

“…Upon irradiation by linearly polarized light of appropriate wavelength, they undergo reversible cycles between a thermodynamically stable trans-form and a meta stable cis-form [4,5]. Perpendicular alignment of the azobenzene molecules to the electric field vector generates a photoinduced optical anisotropy, which is observed as changes in the absorption coefficient (DA) and the refractive index (Dn) [5][6][7]. Moreover, the cyclic photoisomerisation of azobenzene-based groups can lead to large-scale mass transport of the polymer chain, which is observed as a sinusoidal modulation of the polymer film referred to a surface relief grating (SRG) [8][9][10][11].…”

Rigid and flexible azopolymers modified with donor/acceptor groups. Synthesis and photochromic behavior

“…The precise identification of the parameters influencing the surface structure is not an easy task and will need further experiments involving azo-polymers with different donor/acceptor groups and substitution degrees, in order to selectively modify each feature of the materials. Additionally, the investigation of the relative contributions of the birefringence grating, resulting from the photoinduced azobenzene molecules angular redistribution, and the surface grating can be an efficient tool in understanding the influence of the material chemical structure on the nano-structuration mechanisms [33][34][35]. Preliminary tests to determine the ability of the azopolysiloxanic films to support cell growth were also performed using the HepG2 and HeLa cell lines, of human hepatic and epithelial origin.…”