Déformation photoinduite dans les films minces contenant des ...

Chapter 3. Microscopic mechanisms at the origin of the photo-induced deformation inazobenzene-containing thin films 88Polarizergreen laserS-polarizedblue lasertipbeamsplittersample!pastel-00527388, version 1 - 19 Oct 2010half-waveplatemotorizedrotatinghalf-waveplateFigure 3.24: Reversible directional matter transport: ss-p and pp-p configurations.In order to switch the interfering beams’ polarization between the s and the p states,a rotation of 90 ◦ is imposed to the motorized rotating halfwave plate, which has thetwo axis oriented long the s and the p directions. Another halfwave plate is usedto compensate the phase of the reflected beam from the beam splitter. Blue laser:(λ = 473 nm). Green laser: (λ = 532 nm).of the matrix in the bright fringes (deformation amplitude ≃ 4 nm), followed by a slightelastic relaxation. As we turn on the p-polarized assisting beam (t = 40 s), we observea quick increase of the deformation in phase with the bright fringes. By changing theinterfering beam polarization to p ( t = 100 s), the brighter zones are quickly depleted,as matter migrates in the opposite direction, i. e. towards the darker zones. Switchingback to s reverses the matter migration orientation, which again conveys matter towardsthe bright areas. It is important to underline that no spatial shift of the intensity profilealong the x-axis appears during all the experiment 17 , so we observe a true effect ofthe light polarization. Switching back and forth between both polarizations allows toobtain six oscillations in ≃ 10 min, before the sample photoresponse starts weakening(probably because of a photo-bleaching effect). In figure Figure 3.26(a) we show a 3Dplot relative to the first 400 s of Figure 3.25. In (b), for the same time range, we plot17 In Figure 3.25 we see a little drift towards the right, due to small piezoelectric non-linearities.