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Optical rectification and electro-optic sampling in the THz regime using electro-optic polymers

Optical rectification and electro-optic sampling in the THz regime using electro-optic polymers. Michael Hayden Physics Department University of Maryland, Baltimore County hayden@umbc.edu. Physics and Chemistry Intertwined. Nobel prizes in Chemistry (but really physics)

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Optical rectification and electro-optic sampling in the THz regime using electro-optic polymers

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  1. Optical rectification and electro-optic sampling in the THz regime using electro-optic polymers Michael Hayden Physics Department University of Maryland, Baltimore County hayden@umbc.edu

  2. Physics and Chemistry Intertwined • Nobel prizes in Chemistry (but really physics) • 2000 Heeger et. al., (conductive polymers) • 1999 Zewail (control of chemical reactions with femtosecond lasers) • 1998 Kohn, et. al., (density functional theory) • Rational drug design • Molecular electronics (nano, nano, nano) • Consumer products (liquid crystal devices, displays) • Catalysis • Sensors • Optical data storage • Solid state lighting

  3. Physics and Chemistry Intertwined • Rational drug design Anthrax lethal factor (LF) studies byT. Glennon, Accelrys, Inc., http://www.accelrys.com/cases/anthraxlf.html

  4. Physics and Chemistry Intertwined Molecular electronics (nano, nano, nano) Molecular computing http://www.molecularelectronics.com

  5. Physics and Chemistry Intertwined Consumer products (liquid crystal devices, displays) http://www.uniax.com http://www.emagin.com

  6. Physics and Chemistry Intertwined Optical data storage http://www.inphase-technologies.com/

  7. Physics and Chemistry Intertwined Catalysis Sensors (mechanical) bonding effects from different types of deformations in carbon nanotubes(NASA Ames) diffusion of NO2 through zeolite automotive exhaust catalyst http://www.accelrys.com/cases/appindex.html#catalysis

  8. Nonlinear optics and organics at UMBC • Polymer physics of dopant-host interactions (Shane Brower, Shane Strutz) • Molecular modeling of electric field orientation of dipoles in polymers (Won-Kook Kim) • Photochromic/Photorefractive polymers (Shane Strutz) • Terahertz generation and detection using electro-optic polymers (Alex Sinyukov) • Sub-picosecond studies of photoconduction and photogeneration in photorefractive polymers (Megan Leahy) • Holographic, speckle-corrected extra-solar telescope using photopolymer (Tim Bole)

  9. Nonlinear optics in molecular materials p-bond

  10. Chromophore orientation + E-field GRND

  11. Electro-optic polymer types Guest-Host system variables: chromophore size polymer molecular weight repeat unit size and shape (a) Side-Chain system variables: chromophore size molecular weight spacer group length/type (b) repeat unit size and shape repeat unit size and shape Main-Chain system variables: Head-Head vs Head-Tail (c) chromophore size molecular weight (d) spacer group length/type repeat unit size and shape

  12. Photorefractive effect E E sc sc - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + Charge Interference z Generation Pattern - - - - - - - - - - - - - - - - - - - - E Charge sc Mobility z Charge and Density Trapping + + + + + + + + + + + + + + + + f + + + + D Linear n z Index Electro-optic Effect p /2

  13. Two beam coupling Read Diffracted Beam Beam Write Beam Write Beam Large gain coefficient even forsmall chromophore doping level

  14. Photorefractive diffraction efficiency Sample Composition EHDNPB 55% PVK 43% TNFDM 2% 830 nm 1 W/cm2

  15. Current materials PVK C BBP 60 (photoconductor) (charge generator) (plasticizer) Lemke-e (electrooptic/birefringent/photochromic)

  16. Photochromiceffect = + hn photochemical 2+2 cycloaddition S1 intersystem crossing triplet-triplet energy exchange S1 T1 hn T1 S0 S0 C60 energy levels Lemke energy levels

  17. Four wave mixing diffraction efficiency (photorefractive) • Diffraction efficiency increaseswith shorter wavelength • > 50% external diffraction efficiency with only 7% Lemke-e • Diffraction efficiency increases with lower Tg

  18. Co-located holographic images photochromically Images stored in the 7% Lemke-e composite. The vertical lines in the “H” are 4 pixels wide, each pixel is 15x15 m m. (a) original image transmitted through sample, (b) recovered holographic image. (a) (b) Images stored photorefractively in the same location as the previously stored images above. (a) original image transmitted through sample, (b) recovered holographic image. (b) (a)

  19. THz spectrum Frequency (Hz) microwave optical X-ray gamma ray 1012 1018 106 109 1015 1021 Wavelength (µm) intermolecular vibrations electronic transitions 102 108 105 10-1 10-4 10-7 Wavenumber (cm-1) bend stretch collective modes 1011 10-4 105 108 10-1 102 1THz ~ 1 ps ~ 300 µm ~ 33 cm-1

  20. Sources and sensors of far IR radiation • Sources • Free electron lasers • Blackbodies • Photoconductive dipole antennas (PDA) • Electro-optic materials • Detectors • Bolometers • Photoconductive antennas • Electro-optics materials

  21. Probe pulse Si lens Pump pulse THz field V Data acquisition system ETHz(t)dIphoto/dt BIAS Data acquisition system Parabolic mirrors Pump pulse EO emitter EO sensor Balanceddetector /4 W Probe pulse THz emitters Photoconductive dipole antennas Optical rectification ETHz(t)d2P(t)/dt2 P()=(2)(;+,-)E(+)E*() CLEO’2003

  22. Probe pulse THz Si lens Pump pulse THz field V Data acquisition system BIAS probe beam Pellicle Beam Splitter THz Data acquisition system  Parabolic mirrors E Pump pulse W  EO emitter probe beam EO sensor Balanceddetector /4 W Probe pulse THz detectors Photoconductive dipole antennas Electro-optic sampling CLEO’2003

  23. Probe pulse Si lens Pump pulse THz field V BIAS S.Ralph and D.Grischkowsky, Appl.Phys.Lett, 60, 1070 (1992) Data acquisition system Parabolic mirrors Pump pulse EO emitter EO sensor Balanceddetector /4 W Probe pulse X.-C.Zhang et al. Appl.Phys.Lett.,73, 3049 (1998). THz emitters and detectors Photoconductive dipole antennas Data acquisition system Electro-optic CLEO’2003

  24. S.Ralph and D.Grischkowsky, Appl.Phys.Lett, 60, 1070 (1992) S.Ralph and D.Grischkowsky, Appl.Phys.Lett, 60, 1070 (1992) Frequency response limitations Photoconductive dipole antennas • Rise time of the photocurrent, • RC time constant of antenna. 100 fs pulses, 10 µm wide electrodes 80 µm gap Electro-optic sampling • Phonon absorption in crystals, • Dispersion, • Velocity mismatching. 12 fs pulses X.-C.Zhang et al. Appl.Phys.Lett.,73, 3049 (1998). CLEO’2003

  25. Applications • Scattering studies • Coherent spectroscopy • semiconductors • polymers • multiple quantum well devices • biological materials • Imaging • industrial • quality control of plastic parts • flame emissions • trace gas analysis • food inspection • medical • skin cancer • burn depth assessment • dental • caries • periodontal disease Toshiba Research Europe Kincade, Laser Focus World May 2000 (Qinetiq) Technology Review, June 2003

  26. Imaging • package inspection • chemical content mapping B. B. Hu and M. C. Nuss, Optics Lett. 20, 1716 (1995)

  27. Biological imaging Jiang and Zhang, IEEE Trans. Micro. Th. and Tech. 47, 2644 (1999) Han, Cho, Zhang, Opt. Lett.25, 242 (2000) • onion cells, ~ 100 x 400 µm • for tissue, THz scattering in Rayleigh • regime, ~1/l4 • mammographic phantom • resolution on par or better than x-ray, • ~ 250 µm speck

  28. Impulse ranging Cheville and Grischkowsky, App. Phys. Lett. 67, 1960 (1995) • realistic target to wavelength ratios • scattering from arbitrary shapes

  29. Impulse ranging Cheville and Grischkowsky, App. Phys. Lett. 67, 1960 (1995) • realistic target to wavelength ratios • scattering from arbitrary shapes

  30. THz spectroscopy - gases • collision broaded rotational lineshapes determined • atmospheric remote sensing • astronomical spectroscopy; interstellar gas Harde, Cheville, Grischowsky, J. Phys. Chem. A101, 3646 (1997)

  31. THz THz Terahertz spectroscopy (pump-probe) optical pump THz probe optical pump • photorefractive polymer • conducting polymer • GaAs MQW

  32. Optical rectification

  33. polymer layer z x glass substrate pump beam y k E Polymer frame z’ x’ Laboratory frame y’ THz emission from poled polymers Nonlinear susceptibility tensor of polymer (in the polymer frame) In the laboratory frame : Pump field

  34. Nonlinear polarization

  35. ETHz K  z x Pump beam E y k Polymer frame z’ x’ Laboratory frame y’ THz emission from poled polymers ETHz 2PNL In the laboratory frame :

  36. THz amplitude ETHz K  z x Pump beam E y k Polymer frame z’ x’ Laboratory frame y’ THz emission from poled polymers

  37. ETHz K  z x Pump beam E y k Polymer frame z’ x’ Laboratory frame y’ THz emission from poled polymers THz polarization

  38. EO detection THz beam pellicle [110] [1-10] polarizer c(2) material ZnTe polymer compensator polarizer

  39. z (001) ETHz K  Eprobe  ETHz  z x y (010) Pump beam x (100) E y k z’ x’ y’ EO detection with ZnTe crystal P.C.M.Planken et al JOSA B,18(3), 313, 1996

  40. Experimental setup

  41.  is the probe beam polarization angle   = 450  = 00 Block <110> ZnTe Polymer  EO polymer emitter/ ZnTe sensor

  42. ZnTe properties • r41 = 4 pm/V @ 633 nm • n = 2.85 @ 800 nm • static dielectric constant, e = 10.1 • phonon absorption at 1.6, 3.7, and 5.3 THz • phase matched for 800 nm pump & 150 µm (2 THz) beam Gallot, Zhang, McGowan, Jeon, Grischowsky, Appl. Phys. Lett.74, 3450 (1999)

  43. 1mm ZnTe 2 mm ZnTe 2 ITO slides 100 mm polymer on ITO slide 100 mm polymer free standing Image quality Transmission through crossed polarizers

  44. ZnTe response • optical/THz velocity mismatch • thickness dependent frequency response • flat response negated by phonons • extremely thin crystals needed for wide bandwidth Han and Zhang, Appl. Phys. Lett.73, 3049 (1998)

  45. Optical wave THz wave Coherence length tuning possible! Nahata et. al., Appl.Phys.Lett.,69(16),1996

  46. Coherence length Experimental results : nopt =1.71, nTHz =1.9 for 0-3 THz dispersion 0.54 µm-1 at 800 nm

  47. Frequency response • resonance gaps in ZnTe, GaP response • no resonances in polymer composites • coherence length tuning possible in polymers • polymers have larger response (rpolymer>rcrystal) 13 µm thick scaling • very thin crystals required • EO polymer response much larger velocity mismatch scaling

  48. 1 2 0.1 Amplitude (a.u.) Amplitude (a.u.) 1 0.01 EO GaAs emitter polymer detector 0.001 0 10 20 30 40 0 10 20 30 40 THz THz EO sampling: crystals and polymers EO GaAs emitter Polymer detector P.Y.Han and X.-C.Zhang, Appl.Phys.Lett.,73, 3049 (1998). H.Cao, T.Heinz and A.Nahata, Optics Letters, 27, 775 (2002). • Phonon absorption • Dispersion • Phase mismatch • Amorphous : no phonons • Good phase matching

  49. EO polymer properties • r33 = 50 pm/V @ 785 nm • n = 1.70 @ 800 nm • static dielectric constant, e ~ 3 • no phonon absorption !! • phase matching ?? Lemke-e

  50. Fabrication and characterization film • cast films baked ~ Tg • plates pressed ~ Tg + 80° • 50-300 µm thick • poled at 130-140 V/µm ITO 1 cm glass

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