Déformation photoinduite dans les films minces contenant des ...

Chapter 3. Microscopic mechanisms at the origin of the photo-induced deformation inazobenzene-containing thin films 96E z E zE xzzyx(a)yx(b)(c)pastel-00527388, version 1 - 19 Oct 2010Figure 3.30: Far-field photodeformation under a p-polarized gaussian beam (a) wereport the experiment performed in [17] and a scheme of the intensity profile relativeto the E x and E z field components; (b-c) theoretical field distribution ([18], pag. 52)for a gaussian beam (in the calculation λ = 800nm) (b): total field distribution; (c) E zfield distribution.of these experiments have been raised, since in the far field matter was observed to migrateaway from the enlightened zones, while in the near-field matter migrated towardsthe bright areas.By considering the dependence of the matter migration efficiency,direction and orientation on the spatial distribution of the polarization, we obtain acoherent interpretation of these phenomena. As an example, we will report experimentsperformed in the far field using a single focused gaussian beam or a Bessel beam, as wellas in the near field, such as local probe illumination and apertureless SNOM.Gaussian beamIn the experiments reported in ref. [17], a gaussian laser beam is focused on the sampleusing spherical and cylindrical lenses and a 10 × microscope objective. Photoinducedmatter migration has been observed using p-polarized light, while approximately nomass transport has been reported for the s polarization. Matter migrates along the⃗E ‖ polarization direction, from the centre towards the periphery. In this configuration,the amplitude of the E ⃗ ⊥ component decreases going from the periphery towards thecentre of the spot, where its amplitude is zero and, instead, the amplitude of the E ⃗ ‖ ismaximum [18] as depicted in Figure 3.30. So, matter accumulates in the zones wherethe intensity of the E ⃗ ⊥ component is maximum, while the zones corresponding to themaximum intensity of the E ⃗ ‖ component are depleted, which is in line with our results.Similar observations have also been reported in [19], using highly focused HG 00 andHG 10 beams.