Sobolewska Anna, Miniewicz Andrzej
Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
J Phys Chem B. 2007 Feb 22;111(7):1536-44. doi: 10.1021/jp067021l. Epub 2007 Jan 31.
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.
通常通过观察随时间发展的衍射光栅上的光散射效率,来研究偶氮苯功能化聚合物薄膜中的激光辅助全息光栅记录过程。导致光栅形成的各种可能机制,以及光散射的体相或表面起源(体相折射率和/或浮雕光栅),使得仅从光散射数据来分析光栅记录的动力学变得困难且具有不确定性。为了全面解释实验观察到的一阶光衍射强度的各种复杂(通常为非指数形式)动力学,我们考虑了同一聚合物薄膜中两相光栅的简单单指数增长。在建模过程中,我们假设体相折射率光栅Δn(t)和表面浮雕光栅Δd(t)的生长速率有很大差异,并考虑了它们之间在记录过程中实验观察到的非平稳相移Δφ(t)。非平稳相移的起源是由于照明条件下微妙的对称性破坏(例如,光束强度差异和样品上精确对称光束入射角的偏差)导致干涉图案缓慢移动的结果。仅改变诸如折射率和浮雕光栅的平稳振幅以及它们之间的相移范围(0 - π)等参数,我们得到了一系列动力学响应并进行了讨论和解释。在我们的工作中模拟的相同光栅形成动力学的衍射效率随时间演变的各种示例,提供了证据表明在正确解释实验结果时必须格外小心。