Optical Storage and Surface Relief Gratings in Azo-Compounds

Transcription

1 Optical Storage and Surface Relief Gratings in Azo-Compounds Cleber R. Mendonça University of São Paulo Instituto de Física de São Carlos Brazil

2 Azoaromatic compounds photo-isomerization polymers guest host functionalized

3 Motivation Optical Devices Second Harmonic Generation Electro-Optic Effect Optical Storage Holographic Relief Gratings Slow Optical Modulators Study of the physical and chemical properties

4 Studied materials HPDR13 DR13 Copolymers H 2 C CH 3 C C O O H 2 C CH 3 C C O O H 2 C CH 3 C C O O CH 2 CH 3 CH 2 CH 2 n LB CH 2 CH 2 OH 1-n CH 2 CH 3 CH 2 CH 2 n Cl films Cl O 2 O 2

5 Absorbance Absorption spectra HPDR a b Absorption around 500nm (a) CHCl 3 Solution (b) LB film Red Shift: J-type aggregation anti-parallel aggregation Wavelength (nm)

6 ABS Absorption spectra DR13 copolymer 0.3 B C Absorption around 500nm 0.2 J-type aggregation 0.1 (B) CHCl 3 Solution (C) LB film (nm)

7 Studied properties Trans-Cis-Trans Photisomerization Optical Storage Holographic Relief Gratings

8 Photo-isomerization Trans hu Cis Heat hu Abs. Abs. trans trans cis

9 Birefringence and Dichroism Isotropic Sample Anisotropic Sample n y E Linearly Elipticaly n x

10 Experimental Setup Ar ion laser at 514nm /4 mirror beam stop attenuator detector sample beam splitter detection system mirror

11 Transmission (a.u.) HPDR13 Results 0.35 HPDR13 in CHCl 3 Solution 0.30 P=80mW 0.25 trans-cis: 30ms 0.20 cis-trans: 18ms Time (seconds)

12 Transmission (arb. units) HPDR13 Results LB film: HPDR13 and Cd St (75:25 w/w, 41 layers) P=60mW trans-cis: 30ms Time (sec.) cis-trans: slower

13 Transmission Transmission DR13 copolymer results (trans-cis) Photoisomerization biexponential behavior t fast 20ms (cis-trans) Thermal relaxation biexponential behavior Time (s)

14 Orientation mechanism Photochemical trans-cis rate: R= I cos 2 (f) Light Heat Heat E Light P dye R=I P dye f=0 0 f=90 0 E Light R=0 Induces mobility Mobility not induced

15 Experimental setup Reading laser Hee ( =632.8 nm) polarizer mirror beam stop sample Writing laser d:yag ( =532 nm) detector polarizer

16 Transmitted Signal (a.u.) HPDR13 results writing/erasing sequence B LB film: HPDR13 and Cd St (50:50 w/w, 100 layers) 0.4 C A: writing beam switched O A B: writing beam switched OFF Time (seconds) C: erasing beam switched O

17 Amplitude of Birefringence Time to achieve 50% birefringence (seconds) HPDR13 results Dependence of Optical Storage Characteristics on the laser Power a LB film: HPDR13 and Cd St (50:50 w/w, 100 layers) a: Amplitude of Optical Storage Saturation Behavior (2mW) b Power (mw) b: Time to write 50% decrease dramatically (2mW)

18 Amplitude of Birrefringence HPDR13 results Dependence of the amplitude on the weight percentage of HPDR LB film: HPDR13 and Cd St (41 layers) a: Amplitude of birefringence increases linearly with the weight percentage of HPDR Polymer Concentration (%)

19 HPDR13 results Comparison with casting/spin coating films LB film HPDR13 and Cd St 41 layers 75% of HPDR13 Spin coating PDR13a (similar to ourpolymer) n=0.19 n=0.08 Ordering in the packing contributes to the optical induced birefringence

20 Amplitude of Birrefringence HPDR13 Results Dependence of the amplitude on the number of layers LB film: HPDR13 and Cd St (50:50 w/w) The maximum birefringence decreases with the number of layers umber of Layers Related to the decrease in the ordering in the LB film

21 Transmitted Signal (arb. units) DR13 copolymer results writing/erasing sequence (e) (d) B Copolymer LB films (15 layers) with different dye contents. (weight percentage) (c) (b) (a) A Time (s) C (a) CoDR6 : 6% DR13 (b) CoDR29 : 29% DR13 (c) CoDR37 : 37% DR13 (d) CoDR57 : 57% DR13 (e) CoDR77 : 77% DR13

22 Amplitude of Birrefringence DR13 copolymer results Time 50% (s) Dependence of the amplitude on the DR13 weight percentage a a: Amplitude of Optical Storage : nonlinear behavior - thermal effect Weight Percentage of Dye (%) b b: Time to write 50% decrease almost exponentially - cooperative effect Thermal Effect Cooperative Effect

23 Fraction of Remaining Birrefringence (%) DR13 copolymer results Remaining birefringence as a function of DR13 weight percentage Exponential decay with the dye content: - cooperative motion Weight Percentage of Dye (%)

24 Optical storage in LBL Layer-by-layer (LBL) 40 bilayers films

25 Optical storage in LBL slower process electrostatic interaction hampers molecular movement

26 Optical storage in LBL water effect a: as deposited b: blowing water vapor few seconds Entrapped water decrease the interaction between the sample components

27 Biocompatible samples a: chitosan b: Ponceau-S Film prepared in a LBL approach

28 Optical storage : solvent effect Samples immersed in solvent for 20 s and then dried with 2 increase in birefringence amplitude decrease in writing time

29 Optical storage: solvent effect Optical storage features change can be used as a sensor

30 Optical storage: solvent effect Influence of the polymer rigidity on the optical storage

31 Transmission (%) 2D Optical storage 0.16 B We selected MDI (cast film) 0.12 C 0.08 Residual fraction 80 % A Time (s) n = 0.03 ot the best n, but an interesting residual rate

32 2D Optical storage bi-dimensional optical storage MDI 4

33 ormalized Transmittance (arb. units) 2D Optical storage long-term memory Time (h)

34 3D optical storage P = ( 1 ).E ( 2 ) : EE ( 3 ) EEE... Two-photon absorption Im ( 3 ) = 0 I : two-photon absorption coefficient

35 Absorbance two-photon induced birefringence: 3D optical storage 1-photon Photoisomerization rate Luz Calor - 2 R cos f Calor photons f=0 0 f=90 E 0 Luz P dye P dye E Luz R=I R=0 induces mobility Does not induce mobility DR (nm) DR1 O 2 CH 2 CH 3 CH 2 CH 2 OH

36 Two-photon absorption onlinear interaction provides spatial confinement of the excitation = 0 = 0 I

37 Signal (arb. units) 3D optical storage reading beam Hee ( =632.8nm) mirror 1.0 B fóton 2-fótons writting beam 0.6 detector polarizer sample polarizer A C Time (s) = 532 nm I= 0.1 W/cm 2 = 775 nm I= 25 GW/cm 2

38 3D optical storage Thick samples PMMA/DR13 (1x2x0.5 cm 3 ) Use two-photon excitation to induce molecular orientation (a) (b) Taking advantage of the spatial localization of excitation

39 Optical storage and surface relief gratings Study of optically induced birefringence (molecular orientation) in azopolymers Trans hu Cis Orientation heat, hu Movement

40 Grating formation mechanism The force density exerted on the dipole molecule is: f= (P(r,t). )E(r,t) I(x) Facilitated by the photoisomerization E(x) Worm like movement f(x) S(x) x

41 Experimental setup d:yag ( =532 nm) mirror sample beam splitter mirror AFM

42 HPDR13 results AFM 3D- topography image LB film: HPDR13 and Cd St (100 layers 50:50 w/w) P=180mW/cm 2 p-polarized grating spacing: 2.6 m peak-valey height: 50-60nm

43 AFM phase image HPDR13 results The CdSt domains have moved along with HPDR13 molecules Two types of material with different viscoelasticity.

44 Experimental setup Surface relief gratings

45 Surface relief gratings p - polarized s - polarized Polarization in the direction of the intensity gradient

46 Surface relief gratings Surface relief grating in LBL films both polymers move together

47 Signal Surface relief gratings x =3.5 m y =3.5 m Time (min.) Diffraction of a probe beam to monitor the grating formation We are able to microstructure the polymer surface using only cw lasers

48 Conclusion Possible to control the optical storage using different polymeric matrix using different azodyes using distinct fabrication methods application in sensors 2D optical storage with long-term 3D optical storage using two-photon absorption Surface relief gratings using low-power cw laser