Déformation photoinduite dans les films minces contenant des ...

Chapter 3. Microscopic mechanisms at the origin of the photo-induced deformation inazobenzene-containing thin films 106p-interferences-interferencetimeCalculateddeformationkinetics(a)pastel-00527388, version 1 - 19 Oct 2010Measureddeformationkinetics(PMMA)(b)Figure 3.35: PMMA-DR1: statistical model. (a) Simulations; (b) Experimentalresults (shear-force images of the photodeformation obtained on a 135 nm thick PMMA-DR1 sample, reproduced from ref. [15]). Sample thickness = 100 nm, laser wavelengthλ = 473 nm, laser power = 1 mW per beam.where θ and φ describe the molecule orientation in the space.So we obtain that:< p ‖ > Ω = 2 < p ⊥ > Ω (3.33)We recall that our experimental illumination configuration is characterized by the superimpositionof a E ‖ and E ⊥ interference patterns, spatially shifted one from the otheralong the x-axis by half an interference period (see section 3.3.2). The relative intensityof both the interference pattern depends on the value of ϕ. Since the statistical displacementrelies strictly on the spatial distribution of the light field intensity, we can definea displacement efficiency η I as:η I =< p ‖ > Ω(E 0 ‖ (ϕ) ) 2− < p⊥ > Ω(E0⊥ (ϕ) ) 2(3.34)where the first term describes matter migration away from the ‖ field component andthe second one matter migration away from the ⊥ field component. Therefore a positiveefficiency indicates matter migration towards the ⊥ field component.