Winter College on Optics and Energy February Optical nonlinearities in organic materials

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1 Winter College on Optics and Energy 8-19 February 2010 Optical nonlinearities in organic materials C.R. Mendonca University of Sao Paulo Brazil

2 Optical nonlinearities in organic materials Prof. Cleber R. Mendonca

3 University of Sao Paulo - Brazil students undergrad grad. employers professors Sao Carlos Sao Paulo Sao Carlos (9.000) Ribeirao Preto

4 University of Sao Paulo in Sao Carlos

5 University of Sao Paulo in Sao Carlos

6 Instituto de Física de São Carlos Professors: 80 Employers: 180 (technical and administration) Students: 450 (undergrad) 100 (master) 140 (phd) Several research areas in Physics and Material Sciences

7 Grupo de Fotonica Photonics Groups The purpose of the Photonics Group is to develop fundamental science and applied technology in Optics and Photonics Some of the research areas Nonlinear optics Coherent control of light matter interaction fs-laser microfabrication and micromachining Optical spectroscopy Optical storage

8 Optical nonlinearities in organic materials Prof. Cleber R. Mendonca

9 Outline introduction to nonlinear optics nonlinear optics in organic materials experimental methods examples of some results

10 Nonlinear optics Nonlinear Optics Nonlinear Optics The branch of optics that describes optical phenomena that occur when very intense light is used

11 Linear optics E rad. << E inter. harmonic oscillator linear response P = χe

12 Nonlinear optics high light intensity E rad. ~ E inter. anharmonic oscillator nonlinear polarization response P = χ ( 1 ) E + χ ( 2 ) E 2 + χ ( 3 ) E

13 Nonlinear optics nonlinear expansion of the polarization r P r r r ( 1) ( 2 ) ( 3 ) = χ.e + χ : EE + χ M r r r EEE +... linear processes SHG THG Kerr effect

14 Nonlinear Optics Second order processes ( 2 ) χ Second Harmonic Generation ω 2ω

15 Nonlinear Optics χ ( 2 ) = 0 (3) χ Third order processes Nonlinear polarization

16 Nonlinear Optics Third order processes (3) χ ω 3ω ω Nonlinear media

17 Nonlinear Optics Third order processes ( 3 ) χ Kerr media: n = n0 + n2i n ( 3 ) 2 χ Index of refraction depends on the light intensity

18 Kerr media: n Self phase modulation centre symmetric: = ( ) 3 n n I P NL = χ 3 E χ () 2 = 0 n 2 >0 2 Material behaves as a convergent lens xd f y z Sample

19 Nonlinear optics 2ω ω Nonlinear material ω? 3ω Intense light induced nonlinear response in the material Material change the light in a nonlinear way Self action effect

20 χ (3) is a complex quantity Nonlinear Optics

21 Third order processes: χ (3) Refractive process: Absorptive process: = n n I α α + β I n + = β self-phase modulation lens-like effect nonlinear absorption two-photon absorption

22 Two-photon absorption (2PA) process Phenomenon does not described for the Classical Physics and does not observed until the development of the Laser. 2ω ω ω Theoretical model: Maria Göppert-Mayer, 1931 Two photons from an intense laser light beam are simultaneously absorbed p g y in the same quantum act, leading the molecule to some excited state with energy equivalent to the absorbed two photons.

23 applications of 2PA - optical limiting low intensity high intensity To protect eye and sensors from intense laser pulses

24 applications of 2PA - two-photon fluorescence α = α 0 + βi ω ω light emission fluorescence

25 localization of the excitation with 2PA dilute solution of fluorescent dye 2PA 1PA spatial confinement of excitation

26 two-photon fluorescence microscopy microscopy by two-photon fluorescence 3D image of a cell Human chromosome Laboratory for Optics and Biosciences Ecole polytechnique Fluorescent marker fluorophores

27 applications of 2PA - microfabrication two-photon polymerization Nature 412, (2001) oscillator Venus statue Two-photon polymerization Opt. Exp. 12, (2004) Bull

28 Real applications in nonlinear optics Very intense light: femtosecond pulses Ti:Sapphire lasers 100 fs 50 fs 20 fs 1fs= s Laser intensities ~ 100 GW/cm 2 1 x W/cm 2 Laser pointer: 1 mw/cm 2 (1 x10-3 W/ cm 2 )

29 Organic materials Flexibility to tune the nonlinear optical response by manipulating the molecular structure π-conjugated structures σ C C Conjugation: alternation of single and doubles bonds π between carbon atoms

30 Conjugation π-conjugation σ bond: forms a strong chemical bond; localized π bond: weaker bond; out of the C atoms axis π bond in conjugated system: delocalized electrons high optical nonlinearities χ (3)

31 Research study of optical nonlinearities in organic materials fs-laser microfabrication optical storage and surface relief gratings in azopolymers coherent control of light matter interaction

32 Optical nonlinearities in organic materials Understanding the physical principles behind two-photon absorption Understanding the relationship between molecular structure and two-photon absorption Developing molecules with high optical nonlinearities that can be used for application

33 Z-scan (nonlinear absorption) open aperture Z-scan z<0 α ( I ) = α0 + βi rmalized transm mittance alized Trans mittace nor Norm z> Z T ( z) = ΔTT βi [ q0 ( z,0) ] 3 / 2 ( m 1) = + m q m 2 2 ( z / ) 0( z,t ) = βi0l / 1 z0

34 150 fs laser system Ti:Sapphire amplifier 775 nm 150 fs 800 μj

35 Nonlinear spectrum nonlinear absorption intense laser (ultra short pulses) α = α + β 0 I discrete λ s δ(λ) n 2 2( (λ) nonlinear refraction n = n + 0 n2i nonlinear spectrum???

36 Nonlinear absorption spectrum Optical parametric amplifier nm 120 fs μj

37 Azoaromatic samples N N AZO H 2 N N N NH 2 DIAMINO H 2 N N N p-amino H 2 N N N NO 2 DO3 Cl HO H 2 C HO H 2 C H 2 C H 2 C N N N NO 2 DR19Cl HO H 2 C HO H 2 C H 2 C H 2 C N N N NO 2 Cl DR19 HO H 2 C H 2 C H 3 C H 2 C N N N NO 2 DR13 HO H 2 C H 2 C H 3 CH 2 C N N N NO 2 DR1

38 Linear absorption of azoaromatic compounds 0.9 nce absorba AZOB PAMINO DO3 DR13 DR1 DR19 DR19Cl DIAMINO wavelength (nm)

39 Two-photon absorption 1.00 DR13 Normaliz zed Transmit ttance nm 750 nm 860 nm 930 nm 1010 nm O 2 N Cl N N N CH 2 CH 3 CH 2 CH 2 OH 0.85 [ ( )] q0 z,0 T ( z) = 3 / 2 Z / cm m= 0 ( m + 1 ) m α α + βiβ I = 0 β: two-photon absorption coefficient

40 0.9 Pseudostilbenes DO3 600 Aminoazobenzenes PAMINO DR1 DR Absorb bance DIAMINO δ (GM M) DR λ (nm) 0 Absorbance DR19-Cl δ (GM) δ 2 ν A ( ) + 1 A2 ν ( ) ( ) ( ) ν i0 ν + Γi0 ν f 0 2ν + Γ f 0 ν f 0 2ν + Γ f λ (nm)

41 Planarity of the π-bridge Thermally induced torsion in the molecular structure

42 Molecular design strategy Increasing the molecular conjugation Adding charged groups to the molecule Keep molecular planarity

43 White light continuum Z-scan a 4 b inten nsity (arb. unit) wavelength (nm)

44 White light continuum Z-scan Transm mitância No ormalizada a RB (d) ΔT 0.04 Espectro de Luz branca Potência Total = 5 mw (a) z (cm) 0.03 P (mw) λ (nm)

45 White light continuum Z-scan Non resonant effects MeH-PPV Perylenes derivatives α (cm -1 ) δ(10 3 GM) δ (10 3 GM M) Wavelength (nm) Wavelength (nm) each measurement takes only a few minutes

46 fs-laser microfabrication Novel concept: build a microstructure using fs-laser and nonlinear optical processes

47 two-photon polymerization applications micromechanics waveguides microfluidics biology optical devices

48 Two-photon absorption Nonlinear interaction provides spatial confinement of the excitation fs-microfabrication α = α 0 α = α 0 + βi

49 Two-photon polymerization Monomer + Photoinitiator Polymer light Photoinitiator is excited by two-photon absorption R2 PA I The polymerization is confined to the focal volume. 2 High spatial resolution

50 Two-photon polymerization bellow the diffraction limit

51 Two-photon polymerization even higher spatial resolution

52 Two-photon polymerization setup Beam Expansion y x Laser Scanning Mirror Ti:sapphire laser oscillator 130 fs 800 nm 76 MHz 20 mw CCD camera glass (150 micron) Objective Objective z spacer resin glass (150 micron) 40 x 0.65 NA Illumination

53 Two-photon polymerization After the fabrication, the sample is immersed in ethanol to wash away any unsolidified resin and then dried

54 Microstructures containing MEH-PPV MEH-PPV Fluorescence Electro Luminescent Conductive

55 Microstructures containing MEH-PPV waveguiding of the microstructure fabricated on porous silica substrate (n= 1.185) 185) Applications: micro-laser; fluorescent microstructures; conductive microstructures

56 Other studies microstructures for optical storage birefringence p r dye p r dye φ N N E r Light Relax trans cis trans N N N N φ E r J. Appl. Phys., 102, (2007)

57 Other studies microstructures for optical storage birefringence Ar + ion laser irradiation nm one minute intensity of 600 mw/cm 2

58 Other studies microstructures for optical storage birefringence The sample was placed under an optical microscope between crossed polarizers and its angle was varied with respect to the polarizer angle

59 Other studies microstructures for optical storage birefringence J. Appl. Phys., 102, (2007)

60 Other studies 3D cell migration studies in micro-scaffolds SEM of the scaffolds 110 µm pore size 52 µm pore size Top view 110, 52, 25, 12 µm pore size Side view 25, 52 µm pore size

61 Other studies 3D cell migration studies in micro-scaffolds Advanced Materials, 20, (2008)

62 Thank you!

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