Déformation photoinduite dans les films minces contenant des ...

Chapter 3. Microscopic mechanisms at the origin of the photo-induced deformation inazobenzene-containing thin films 94S+S (mW/mm 2 ) P (mW/mm 2 ) photoexp (nm/s) matter migr. (nm/s)2 0 0.4 02 0.4 0.4 0.042 0.75 0.4 0.132 1.1 0 0.142 1.7 0 0.172 2.1 0 0.21Table 3.3: Dependence of the matter-migration-induced SRG growth rate on theirradiation power density under s-polarized interfering blue beams assisted by a p-polarized green beam. The incident power density of the interfering (S+S) and thespeedassisting (P) beams are a*sqrt(Ip) given in mW/mm 2 ; the SRG growth rate is given in nm/s.Sample: sol-gel Si-DR1, 450 nm thick.0,3ss+p_powers_speed_corr2pastel-00527388, version 1 - 19 Oct 2010SRG growth speed rate (nm/s)0,20,100 1 2 3 4 5I g (mW/mm Ip2 )(assisting beam power density)SRG growth rateFigure 3.28: Correlation between the SRG growth rate and the spatial modulation ofthe polarization under p-assisted s-polarized interference. Data relative to the experimentsreported in Figure 3.27. Best fit of E pol (in arbitrary units) for a scaling factorof 0.1445. Assisted beam power density = 2.1 mW/mm 2 , interfering beams’ powerdensity = 1 mW/mm 2 , sample: sol-gel-DR1, thickness ≃ 200 nm.E poldata and the calculated values of the spatial modulation of the polarization indicatesthat also in the experiments with an assisting beam this parameter governs the massmigration efficiency. Moreover, it suggests that the deformation efficiency is dependentmainly on the less intense field. This seems to be in agreement also with the saturatingbehavior of the growth rate when the assisting field intensity I assist increases. Therefore,the maximum growth rate would be obtained for I assist = I interf and further raising ofthe assisting beam intensity (I assist > I interf ) should not lead to a growth rate increase.Experiments in these two cases may confirm our hypothesis.From a quantitative point of view, the matter migration rate observed in the assisted