DÃ©formation photoinduite dans les films minces contenant des ...

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Chapter 3. Microscopic mechanisms at the origin of the photo-induced deformation inazobenzene-containing thin films 102pastel-00527388, version 1 - 19 Oct 2010(a)timeI/I 0 ! I/I 0 !0(c)optical fiber tipfilmsubstrate84assistingbeam(p-polar.)00 1 2 3 4 58400 1 2 3 4 5X (!m)!zyxT (a. u.)A (nm)(b)A (nm)P-assist.S-interf.ON(d)A (nm)840100-1080-80 1 2 3 4 520-20 1 2 3 4 5-2 0 2P-assist. S-interf. ON2000 300 600SS0 100 200TIME (s)0 1 2 3 4 5X (!m)SS+P20090211_8!""#"!$$%&'OPTICSTOPOGRAPHYFigure 3.33: PMMA-DR1 photodeformation under simultaneous p-assisted s-interfering beams. (a) Experimental setup; (b) transmitted light intensity T in arbitraryunits (top) and the corresponding photoinduced deformation amplitude A expressedin nm (solid curve), the dotted curve indicates the deformation obtained in thesame conditions without the assisting beam; (c)-(d) optical and topography images,scanning over the same line, scan-range = 4.5 µm. Laser power density: 2 mW/mm 2per beam (blue - non assisted experiment), 1 mW/mm 2 per beam (blue), 2.1 mW/mm 2per beam (green); sample = PMMA-DR1, ≃ 180 nm thick.
Chapter 3. Microscopic mechanisms at the origin of the photo-induced deformation inazobenzene-containing thin films 103pastel-00527388, version 1 - 19 Oct 2010power density of 1 mW/mm 2 while the green (λ = 523 nm) assisting beam, in normalincidence, has a power density of 2.1 mW/mm 2 . In (b) we report the first 200 s of the averagetransmitted light profile T (top) in arbitrary units, and (bottom) the deformationamplitude A of the assisted (solid curve) and non-assisted (dotted curve) photodeformations.In (c) and (d) we show the optical and topography images relative to (a), withthe detail of the profiles at some instants of interest 27 . Turning on simultaneously thethree beams at t = 0, we observe instantly a very weak deformation (0.8 nm), in phasewith the s interference pattern, which can be attributed to the matrix photoexpansion,which here yields a low magnitude photodeformation, since the intensity contrast acrossthe interference pattern is reduced by the uniform assisting beam (see 3.4.1).The photoexpansion is followed by a π-phase deformation which reaches a maximumamplitude of 5 nm after 25 s of exposure time. Subsequently, we observe an inversionof the photodeformation process, which leads to the growth of a SRG in phase with thes interference pattern, i. e. shifted by half an interference period with respect to thepreceding deformation. This SRG amplitude finally saturates at a value of 26 nm afterabout 500 s.The first stage of the mass transport, which gives a π-phase deformation, clearly correspondsto the intensity-dependent mechanism, which is observed also under non-assisteds-polarized light (dotted curve). On the other hand, the subsequent in-phase deformationis consistent with the polarization-dependent mass migration. These observationsshow that the two deformation processes produce matter transport in opposite directions,with different kinetics. In the conditions of the current experiment, the intensitydependentmatter transport appears to dominate at low time scales, while it is fullyovercome by the polarization-driven process at longer time.3.5.3 Intensity versus polarization matter migration mechanisms inPMMA-DR1In order to fully describe the relative weight of the intensity-dependent mechanism versusthe polarization-dependent mechanism, we perform an analysis of the photoinducedmatter migration obtained by varying the polarization angle ϕ of the interfering beams.This allows to control the relative amplitude of the intensity and polarization patterns.Figure 3.34(a) shows the matter migration deformation amplitude for ϕ values of0 ◦ , 45 ◦ , 90 ◦ . Since these configurations present different mass migration directions, wechoose the same convention adopted in 3.3.1 (see Figure 3.6). So, the sign of the deformationamplitude A and of its growth rate is given by the direction of the mass transport:27 On the optical image, we plot the transmitted light profile averaged over 200 s, since the measuredcontrast is very weak.
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Thèse de doctorat de l’Ecole Pol
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AcknowledgementsAt the beginning it
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vpastel-00527388, version 1 - 19 Oc
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ContentsAbstractiAcknowledgementsii
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List of Figures1.1 The trans/cis ph
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List of Figuresxiipastel-00527388,
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Introduction 2In this work, we stud
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Bibliography[1] A. Natansohn, P. Ro
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Introduction 6azobenzene-containing
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"##$%&'()')*#'+(%,-.(/#'011'2'"(%)(
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Chapter 1. The azobenzene molecules
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Chapter 2. Experimental setup and s
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pmma-dr1Chapter 2. Experimental set
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Conclusionspastel-00527388, version
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Bibliography[1] Chi-Ming Che et Al.
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Appendix A 156⎛ ⎞ ⎛n g sinθ
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Appendix A 158hence for each compon
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Appendix BPhotoisomerization dynami
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Appendix B 162( 1Since λ 2 = −(
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Appendix C 164L = 5000 nmu = 1 nmL!
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Appendix D 166n. light power densit
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Bibliography[1] A. Natansohn, P. Ro
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Bibliography 170azobenzene-containi
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Bibliography 172as estimated from a
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Bibliography 174[53] C. Barrett, A.
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