Optical Storage and Surface Relief Gratings in Azo-Compounds Cleber R. Mendonça University of São Paulo Instituto de Física de São Carlos Brazil
Azoaromatic compounds photo-isomerization polymers guest host functionalized
Motivation Optical Devices Second Harmonic Generation Electro-Optic Effect Optical Storage Holographic Relief Gratings Slow Optical Modulators Study of the physical and chemical properties
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
Absorbance Absorption spectra HPDR13 0.25 0.20 0.15 0.10 a b Absorption around 500nm (a) CHCl 3 Solution (b) LB film 0.05 0.00 Red Shift: J-type aggregation anti-parallel aggregation. 350 400 450 500 550 600 650 Wavelength (nm)
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 0.0 400 600 (nm)
Studied properties Trans-Cis-Trans Photisomerization Optical Storage Holographic Relief Gratings
Photo-isomerization Trans hu Cis Heat hu Abs. Abs. trans trans cis
Birefringence and Dichroism Isotropic Sample Anisotropic Sample n y E Linearly Elipticaly n x
Experimental Setup Ar ion laser at 514nm /4 mirror beam stop attenuator detector sample beam splitter detection system mirror
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 0.15 0.0 0.5 1.0 1.5 2.0 Time (seconds)
Transmission (arb. units) HPDR13 Results 0.008 0.007 0.006 LB film: HPDR13 and Cd St (75:25 w/w, 41 layers) 0.005 0.004 0.003 0.002 P=60mW trans-cis: 30ms 0.001 0.0 0.2 0.4 0.6 0.8 1.0 Time (sec.) cis-trans: slower
Transmission Transmission DR13 copolymer results 0.05 0.04 (trans-cis) Photoisomerization 0.03 0.02 0.01 0.00 0.04 0.03 0.00 0.05 0.10 0.15 biexponential behavior t fast 20ms (cis-trans) Thermal relaxation 0.02 0.01 0.00 biexponential behavior -0.01 0.00 0.05 0.10 0.15 0.20 Time (s)
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
Experimental setup Reading laser Hee ( =632.8 nm) polarizer mirror beam stop sample Writing laser d:yag ( =532 nm) detector polarizer
Transmitted Signal (a.u.) HPDR13 results writing/erasing sequence 1.0 0.8 0.6 B LB film: HPDR13 and Cd St (50:50 w/w, 100 layers) 0.4 C A: writing beam switched O 0.2 0.0 A B: writing beam switched OFF -50 0 50 100 150 200 250 300 350 Time (seconds) C: erasing beam switched O
Amplitude of Birefringence Time to achieve 50% birefringence (seconds) HPDR13 results Dependence of Optical Storage Characteristics on the laser Power 0.135 0.130 0.125 a 50 40 LB film: HPDR13 and Cd St (50:50 w/w, 100 layers) 0.120 0.115 0.110 30 20 a: Amplitude of Optical Storage Saturation Behavior (2mW) 0.105 0.100 0.095 10 b 0 0 2 4 6 8 10 Power (mw) b: Time to write 50% decrease dramatically (2mW)
Amplitude of Birrefringence HPDR13 results Dependence of the amplitude on the weight percentage of HPDR13 0.24 0.20 0.16 LB film: HPDR13 and Cd St (41 layers) 0.12 0.08 0.04 a: Amplitude of birefringence increases linearly with the weight percentage of HPDR13 0.00 0 10 20 30 40 50 60 70 80 90 Polymer Concentration (%)
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
Amplitude of Birrefringence HPDR13 Results Dependence of the amplitude on the number of layers 0.18 0.16 0.14 0.12 LB film: HPDR13 and Cd St (50:50 w/w) The maximum birefringence decreases with the number of layers 0.10 0.08 0 20 40 60 80 100 120 umber of Layers Related to the decrease in the ordering in the LB film
Transmitted Signal (arb. units) DR13 copolymer results writing/erasing sequence 14 12 10 (e) (d) B Copolymer LB films (15 layers) with different dye contents. (weight percentage) 8 6 4 2 0-2 (c) (b) (a) A 0 10 20 30 40 50 60 Time (s) C (a) CoDR6 : 6% DR13 (b) CoDR29 : 29% DR13 (c) CoDR37 : 37% DR13 (d) CoDR57 : 57% DR13 (e) CoDR77 : 77% DR13
Amplitude of Birrefringence DR13 copolymer results Time 50% (s) Dependence of the amplitude on the DR13 weight percentage 0.10 0.08 0.06 a 0.8 0.6 a: Amplitude of Optical Storage : nonlinear behavior - thermal effect 0.04 0.02 0.00 0 20 40 60 80 Weight Percentage of Dye (%) b 0.4 0.2 b: Time to write 50% decrease almost exponentially - cooperative effect Thermal Effect Cooperative Effect
Fraction of Remaining Birrefringence (%) DR13 copolymer results Remaining birefringence as a function of DR13 weight percentage 90 80 Exponential decay with the dye content: - cooperative motion 70 40 60 80 Weight Percentage of Dye (%)
Optical storage in LBL Layer-by-layer (LBL) 40 bilayers films
Optical storage in LBL slower process electrostatic interaction hampers molecular movement
Optical storage in LBL water effect a: as deposited b: blowing water vapor few seconds Entrapped water decrease the interaction between the sample components
Biocompatible samples a: chitosan b: Ponceau-S Film prepared in a LBL approach
Optical storage : solvent effect Samples immersed in solvent for 20 s and then dried with 2 increase in birefringence amplitude decrease in writing time
Optical storage: solvent effect Optical storage features change can be used as a sensor
Optical storage: solvent effect Influence of the polymer rigidity on the optical storage
Transmission (%) 2D Optical storage 0.16 B We selected MDI (cast film) 0.12 C 0.08 Residual fraction 80 % 0.04 0.00 A 0 100 200 300 400 500 600 700 800 Time (s) n = 0.03 ot the best n, but an interesting residual rate
2D Optical storage bi-dimensional optical storage 1 2 3 5 MDI 4
ormalized Transmittance (arb. units) 2D Optical storage long-term memory 1.0 0.9 0.8 0.7 0.6 0 5 10 15 20 25 30 35 40 45 Time (h)
3D optical storage P = ( 1 ).E ( 2 ) : EE ( 3 ) EEE... Two-photon absorption Im ( 3 ) = 0 I : two-photon absorption coefficient
Absorbance two-photon induced birefringence: 3D optical storage 1-photon Photoisomerization rate Luz Calor - 2 R cos f Calor 1.4 1.2 1.0 2-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 0.8 0.6 0.4 0.2 0.0 DR1 200 400 600 800 1000 1200 (nm) DR1 O 2 CH 2 CH 3 CH 2 CH 2 OH
Two-photon absorption onlinear interaction provides spatial confinement of the excitation = 0 = 0 I
Signal (arb. units) 3D optical storage reading beam Hee ( =632.8nm) mirror 1.0 B 0.8 1-fóton 2-fótons writting beam 0.6 detector polarizer sample polarizer 0.4 0.2 0.0 A C 0 200 400 600 Time (s) = 532 nm I= 0.1 W/cm 2 = 775 nm I= 25 GW/cm 2
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
Optical storage and surface relief gratings Study of optically induced birefringence (molecular orientation) in azopolymers Trans hu Cis Orientation heat, hu Movement
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
Experimental setup d:yag ( =532 nm) mirror sample beam splitter mirror AFM
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
AFM phase image HPDR13 results The CdSt domains have moved along with HPDR13 molecules Two types of material with different viscoelasticity.
Experimental setup Surface relief gratings
Surface relief gratings p - polarized s - polarized Polarization in the direction of the intensity gradient
Surface relief gratings Surface relief grating in LBL films both polymers move together
Signal Surface relief gratings 0.4 0.3 x =3.5 m y =3.5 m 0.2 0.1 0.0 0 5 10 15 20 Time (min.) Diffraction of a probe beam to monitor the grating formation We are able to microstructure the polymer surface using only cw lasers
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