Déformation photoinduite dans les films minces contenant des ...

Chapter 3. Microscopic mechanisms at the origin of the photo-induced deformation inazobenzene-containing thin films 98Bessel beam (e-f) the distribution is inverted. In the particular case of an azimuthallypolarized Bessel beam (i-j), the ⃗ E ⊥ component is zero.In Figure 3.31(c,g,k) we report the results that have been obtained on a PMMA-DR1 thin film having a thickness of 100 nm, using a 200 mJ/mm 2 light dose, in thethree polarization configurations, respectively. Under radial and circular polarizations,a relief growth is observed always in correspondence of the ⃗ E ⊥ component, while matteris driven away from the ⃗ E ‖ component. This is the same behavior that we have observedin our experiments, confirming that the orientation of the matter migration is strictlydependent on the spatial distribution of the field polarization.pastel-00527388, version 1 - 19 Oct 2010Only in the case of an azimuthally polarized Bessel beam (i-l), the observed matteraccumulation is associated to the E ⃗ ‖ component. In this case an extremely weak deformationis produced (≃ 2 nm). We note that in this polarization configuration onlythe E ⃗ ‖ component is present, since the E ⃗ ⊥ = 0, so the amplitude of the spatial modulationof the polarization E pol = 0. This is the symmetric configuration with respectto the s-polarized interference that we have used in our experiments, where E ⃗ ‖ = 0 andE pol = 0. In this case, we observe also a weak relief growth in phase with the lightintensity, which is due to the matrix photoexpansion. This suggests that the matteraccumulation observed in the bright zones using an azimuthally polarized Bessel beamcould be due to the matrix photoexpansion as well.Local probe illumination and apertureless SNOMIn the experiments involving near-field illumination through the aperture of a metallizedoptical fiber (≃ 40 nm aperture [21]), matter accumulation is observed in the enlightenedzones ([4, 22]). The irradiating light field is transversally polarized ( E ⃗ ‖ ) and farfrom the tip apex (in the bulk and in the periphery) the light polarization is essentiallytransversal. However, a longitudinal component along the z axis ( E ⃗ ⊥ ) is present in thevicinity of the tip apex [18]. So, matter accumulates towards the area where the E ⃗ ⊥ ismaximum and away from the transversally polarized light, which is the same behaviorthat we observe in our experiments.Similar results have been obtained in the experiments using irradiation by aperturelessSNOM [23, 24]. When p-polarized light is concentrated, in near field, using a laser beamincident on a metal coated tip brought close to the sample’s surface, the growth of arelief is observed in the vicinity of the tip. When s-polarized light illuminates the tip,the effect is qualitatively similar, but much weaker then using p-polarized light. This isalso coherent with our observations, since in this case the light field has almost only one