Déformation photoinduite dans les films minces contenant des ...

Chapter 3. Microscopic mechanisms at the origin of the photo-induced deformation inazobenzene-containing thin films 74where:⎧⎨if E‖ 0 ≤ E0 ⊥ (ϕ) ⇐⇒ tgϕ ≤ 1/√ cos2θ g then ψ = π/2, ˆv = û ⊥(3.26)⎩if E‖ 0 > E0 ⊥ (ϕ) ⇐⇒ tgϕ > 1/√ cos2θ g then ψ = 0, ˆv = û ‖and the field amplitudes are:E int = |E‖ 0 (ϕ) − E0 ⊥ (ϕ)| (3.27)E pol = min{E‖ 0 (ϕ), E0 ⊥ (ϕ)} (3.28)pastel-00527388, version 1 - 19 Oct 2010= E0 ‖ (ϕ) + E0 ⊥ (ϕ) − |E0 ‖ (ϕ) − E0 ⊥ (ϕ)|2= 1 ) (E ⎡ ⎤‖ 0 2(ϕ) + E0 ⊥ (ϕ) ⎣1 − |E0 ‖ (ϕ) − E0 ⊥(E (ϕ)|) ⎦‖ 0 (ϕ) + E0 ⊥ (ϕ)We note that in our geometry the condition stated in 3.26 reads: 0 ◦ ≤ ϕ ≤ 47.5 ◦ and47.5 < ϕ ≤ 90 ◦ respectively.This decomposition is shown in Figure 3.12(b-c) where, respectively, ⃗ E int and ⃗ E pol aredepicted. The first component is linearly polarized along the ˆv direction and its intensityis spatially modulated. The second component has a spatially modulated polarization,while its intensity is constant. In this case, the polarization ellipse is:⎛E‖ pol⎞⎝⎠E pol sin(φ x )2()Epol⊥ 2+= 1 (3.29)E pol cos(φ x )where E ‖ pol and E⊥ polare defined in eq. 3.25.In Figure 3.13 we report the calculated 10 values of E int and E pol (eq. 3.27, 3.28) as afunction of ϕ, together with the normalized saturation amplitude (✕), the normalizedgrowth rate (□) and the average normalized efficiency (), previously estimated (seeFigure 3.9). The good agreement between experimental values and E pol shows a directcorrelation between the polarization spatial modulation and the matter migration processes.When the light field is s-polarized, E pol = 0 and the interference field is a pureintensity grating, which does not give rise to matter migration. Increasing the spatialmodulation of the polarization leads to a more efficient matter migration, which reaches10 Unitary interfering beams: E 0 = 1.