ICABU 2013, Nov. 11-13, 2013, Daejeon, Korea Time Resolved THz Spectroscopy and its Applications Jaehun Park Pohang Accelerator Laboratory Pohang University of Science and Technology fs-THz XFEL Your first slide must be the title slide. The suggested format is shown above. (You may adapt this slide to suit your tastes.) It is recommended that your company or university logo appear on the title slide only. This is followed by your outline slide and the other slides mentioned in this template. For additional details, please see the excellent article on giving a good presentation with quality slides. It is posted on the IMS2008 web site: Joseph F. White, “Your Paper Has Been Accepted!”, Applied Microwave & Wireless, Winter 1996, pp. 10-23.

Outline Introduction THz Light sources  By femtosecond laser pulses  Accelerator-based Femtosecond THz Program at PAL  Coherent Transition Radiation (CTR)  Electro-Optic Sampling , etc. THz Experiments THz Future Summary & Application Outline the high points of the presentation you are giving. Don’t include the title or conclusion in your outline. You should state the purpose of the work described in your paper. Describe the big picture of why you did the work, not the detailed technical objectives your work accomplished.

THz wave 0.1 THz 10 ps 3000 m 3.3 cm-1 0.41meV Let your slides highlight your talk, and not be a substitute for what you have to say. You, the speaker, deliver the message and let your slides augment your talk. Use fonts that do not have a blurred appearance or look like 70’s “computer characters”. Arial and Helvetica fonts are two fonts that project well. If you use other fonts, we suggest you project them electronically to get a feel for what your audience will see. 36 point titles with 28 point supportive text are visible from the rear of the session room. Smaller fonts may be visible at the front of the session room or on your monitor, but NOT from the rear half of the session room. USE NOTHING SMALLER THAN 28 POINT FONT! Larger font is even better. Make your text large enough so that your audience instantly reads your message. If they have to concentrate to read your slides they will be concentrating on the screen, and not on what you are saying, or they may just walk out on you... 0.1 THz 10 ps 3000 m 3.3 cm-1 0.41meV 1 THz 1 ps 300 m 33 cm-1 4.1meV 10 THz 0.1 ps 30 m 333 cm-1 41meV

Why is THz radiation important? Energy range overlaps with - band gaps of superconductors - excitation energy for protein folding - phonon energies - Resonant with many vibrational and rotational modes in molecules Imaging: complementary to X-ray imaging without the problems of ionizing radiation Security and short range communications Nonlinear optical experiments Accelerator diagnostics

THz Light sources Table Top THz pulses  Photoconductive antenna  Optical rectification: up to mJ  Plasma Accelerator based THz pulses : up to a few 100s of mJ/pulse or ~50 MV/cm-1  Coherent Transition Radiation(CTR), >100 mJ, < 5 THz  Synchrotron radiation  Free Electron Laser The fonts on the computer where you prepare your presentation will not necessarily all be present on the projection computers. Some authors were surprised to discover that bullet fonts and scientific character fonts displayed differently when loaded on the conference presentation computers. Problems were especially common with “Wingdings”, “MS Line Draw” and “Monotype Sorts” fonts. Also, some Asian language fonts were problem sources. If your presentation has special fonts, you can include the fonts in your upload by checking the “Embed TrueType Fonts” box that appears when the “File->Save As…” menu is selected. Caution: Use of this option increases the size of your presentation file by as much as 5X. Large presentation files take a long time to upload. Use embedded fonts only if necessary.

fs-THz Program at PAL  Purpose: Nonlinear and Ultrafast science using intense fs-THz radiation and laser beams.  Construction: 2005-2009  Commissioning and user service: 2010-  Radiation Specifications  Wavelength : 100 – 1000 m (0.3–3 THz)  Energy/pulse : up to 10 J (LINAC Based), ~200 pJ (fs-Laser Amplifier Based)  Pulse duration :< 200 fs  Type: 1. Electron Linac based Coherent THz Radiation Source  75 MeV / 100 fs electron beam  Coherent Transition Radiation (CTR) 2. fs-Laser Amplifier Based THz source: Optical rectification  Beamtime: 70% for Users, 30 % for Managers

Coherent Transition Radiation OTR Electron Beam q OTR Radiator 45o Transition radiation occurs when an electron crosses the boundary between two different media. For a relativistic electron (b º v/c @ 1) incident on a perfect conductor, the number of photons emitted per solid angle and wavelength range is: Intensity is 0 on axis, peaks at ~1/ . Coherent radiation emission: dWN /dw = N2 dW1 /dw | f (w)|2 We strongly suggest you minimize transition effects in your presentation when moving from a complete slide to the next slide. Make transition between slides be instantaneous. No exceptions! You will be able to control your presentation with a remote control that lets you move forward to the next visual or backward to a previous one. A laser pointer will let you point to areas on the projection screen. You should assume that no mouse or keyboard will be present on the podium, so your presentation must be designed to run in consecutive order from the first through the last slide. Hidden slides, graphic objects with action settings, PowerPoint menus, drawing on the screen and other effects that require the mouse or keyboard cannot be used. Final note: The Advance Setting “On mouse click” does not imply that there will be a mouse available during your presentation. The phrase “on mouse click” is the title of a Microsoft PowerPoint setting, and means only that pressing “enter” or clicking a mouse will begin animation. A mouse may not be available when you present. E= 50 MeV ->  = 100 ->  = 10 mrad Charge [nC] Radiation energy [μJ] 0.2 3.5 0.5 22 1 88 Intensity Distribution

fs THz Laboratory LINAC OPA Laser Room Laboratory Lead blocks RF gun QD1 AC2 QD2 QT1 Ti foil EO Sampling Tripler Chicane 1 Chicane 2 PSD OTR CTR THz radiation 266 nm, 1 kHz LINAC Stretcher QD ~1.4 mJ ~1 cm diameter Analog PID controller Analog PID controller OPA Pulse Compressor Spectrometer Regen. Amp. Oscillator Regen. Amplifier 3W, 120 fs, 1KHz Laser Room Laboratory

THz Energy Measurement Linac Lead blocks Accelerating Column Quadruple Magnet RF gun Al foil Chicane electron bunch compressor THz radiation PSD 266 nm, >250 uJ 1 kHz, > 2 ps Pyrocam III (THz beam imaging detector) 50 MeV ~0.3 nC 10 Hz ~5 μJ 9

Single-shot Electro-Optic Detection Shen et al. PRL 99, 043901, 2007

Bunch Length Measurement

THz TDS(Time domain spectroscopy) Not time resolved measurement The measurements are made in the time domain. Fourier transformed into the frequency domain. - The far-IR frequency-dependent absorption coefficient α(ω) and refractive index n(ω), permittivity , susceptibility (t), etc. (a) Real and (b) imaginary parts of the complex dielectric constants of liquid H2O, D2O, and H2 18O at 296 K. The absolute values of the dielectric constants of liquid D2O and H2 18O are shifted by 2 and 4, respectively. (Yada et al. Chemical Physics Letters 473, 279, 2009)

Wild type bacteriorhodopsin THz Spectra h all-trans-retinal 13-cis-retinal Wild type bacteriorhodopsin Reflectivity spectrum of strongly boron doped diamond film, PRL 97, 097002, 2006 Representative ε, n spectra of nucleobases via THz-TDS, Phys. Med. Biol. 47, 3807, 2002

fs-THz Time Domain Results Semi-clathrate hydrates Cluster Kang et al. CPL 587, 14, 2013 Ahn et. al. RSC Advances 3, 1055, 2013 Koh et. al. RSC Advances 3, 8857, 2013

Wound Response in Mouse Skin Kim et. al. submitted Top: A schematic of the procedures for in vivo exposure and analysis of the effects of fs-THz radiation. Bottom left: Experimental scheme. THz is generated via optical rectification method. Laser spec.: 150 fs pulse width, 1 kHz, 800 nm; THz spec: 0.26 nJ/pulse, 1 kHz, THz E field and spectrum is shown in the figure. Bottom right: Delayed wound healing associated with fs-THz radiation. Gross and microscopic time course photographs of skin wounds following treatment with sham or THz radiation. Upper panels: photographs are size-compensated and shown as binary images. Bottom panels: dotted lines indicate the margins between re-epithelialized skin and the original wound site. An arrow denotes strongly stained parts of scab spread in wounds. Kim et. al. Sci. Rep. 3, 2296, 2013

Phase Transition of Lipid bilayer Temperature dependence of absorption coefficient (α) of de-ionized water (solid square), lipid solution (empty square), and lipid film (solid circle) at 1 THz frequency. Choi et. al. JCP 137, 175101, 2012

Pump- Probe Experiment

TRTS(Time resolved THz Spectroscopy) Time resolved measurement Need pump and probe beam Probe the collective low-frequency solvent response in a liquid Determine the transient photoconductivity in materials The ultrafast relaxation and recombination dynamics of photogenerated electrons and holes in epitaxial graphene. The measured change in the real part of the complex amplitude transmission (gray) and the theoretical fit (black) for pump pulse energy of 14.8 nJ (George et al., Nano Lett., 8, 4248, 2008)

Pump dependent dynamics of nanowires Si1-xGex NWs Manuscript in preparation

Ultrafast Optical-Pump Terahertz-Probe Spectroscopy of the Carrier Relaxation and Recombination Dynamics in Epitaxial Graphene Figure 1. Measured terahertz pulses transmitted through the epitaxial graphene sample B without (gray) and with (black, scaled) an optical pump pulse preceding the peak of the terahertz pulse by 1 ps. Figure 2. (a) The measured change in the real part of the complex amplitude transmission (gray) and the theoretical fit (black) for pump pulse energy of 14.8 nJ (sample B). George et al., Nano Lett., 8, 4248, 2008

Influence of the Electron-Cation Interaction on Electron Mobility in Dye-Sensitized ZnO and TiO2 Nanocrystals: A Study Using Ultrafast Terahertz Spectroscopy Fig. (a) Evolution of transient THz conductivity (normalized to unity). The lines serve only to guide the eye. (b) Transient absorption of ZnTPP-Ipa/ZnO probed at 655 nm (symbols). Nemec et al., PRL, 104, 197401, 2010 Electron Mobility and Injection Dynamics in Mesoporous ZnO, SnO2, and TiO2 Films Used in Dye-Sensitized Solar Cells Fig. Early and later time photoconductivity dynamics in nanoporous ZnO, TiO2, and SnO2 films sensitized with Z907 dye. Tiwana et al., ACS Nano, 5, 5158, 2011

What can we do with intense fs-THz pulse? Resonant and nonresonant control over matter and light by intense terahertz Scheme for controlling matter using strong THz transients. Resonant THz control over ionic lattice dynamics and molecular rotation. Kampfrath et al., Nature Photon. 7, 680, 2013

What should we do with intense fs-THz pulse? Intense terahertz pulse induced exciton generation in carbon nanotubes Fig. Results for the near-IR-pump ( = 1.55 eV) ((a)–(c)) and THz-pump experiments ( ∼4 meV) ((d)–(f)). Watanabe et al., Opt. Exp., 19, 1533, 2011

Soft Modes in Ferroelectrics & Perovskites (PbTiO3) National Synchrotron Light Source

Future Plan-UV to THz Widely tunable UV, visible, IR output from Optical Parametric Amplifiers (OPAs) Mid-IR from high-energy OPA Terahertz (THz) - ZnTe - LiNbO3

Future Plan-Synchronization Fundamental Laser Laser based THz OPA Laser LINAC based THz

fs-THz Beamline LINAC OPA Laser Room Laboratory Lead blocks RF gun AC1 QD1 AC2 QD2 QT1 Ti foil EO Sampling Tripler Chicane 1 Chicane 2 PSD OTR CTR THz radiation 266 nm, 1 kHz LINAC Regen. Amp. QD ~1.4 mJ ~1 cm diameter Analog PID controller Analog PID controller OPA Pulse Compressor Spectrometer Regen. Amp. Oscillator Regen. Amplifier 3W, 120 fs, 1KHz Laser Room Laboratory

THz & X-ray synch. via Time of Flight J. Phys. B: At. Mol. Opt. Phys. 44 (2011) 243001

Undulator Terahertz Radiation E – field: ● Up to 10 THz - Study phonon modes of materials - Study intermolecular hydrogen bonding in solutions. BaFe1.85Co0.15As2 Avigo et al., J. Phys.: Condens. Matter 25, 094003, 2013 Khoury et al., Terahertz Science and Technology 3, 183, 2010

Summary & Applications ● Ultrafast dynamics - electronic excitations - THz driven magnetic dynamics ● Study Nonlinear properties of materials - vibrational modes (local phonon modes) - electronic modes ● Drive atoms in their local potential wells and probe motion as a function of time ● Medical applications Notice in the above slide that PowerPoint automatically places a small margin around the text. If you use a border, the effect will be a margin inside the border. You lose valuable space that would otherwise be useful for information. Remember, you’re projecting a dark background onto a darkened screen in the session room. The effect is better with no projected border.

Thank You for Your Attention! Acknowledgements Funding Support: ● Korean Ministry of Education, Science and Technology. ● National Research Foundation of Korea Grant funded by the Korean Government (grant code: 2011-0001291) ● WCI-KAERI Collaborators: Dr. Heung-Sik Kang(PAL) Mr. Junho Ko(Postech) Mr. Seonghoon Jung(PAL) Prof. Taiha Joo(Postech) Thank You for Your Attention! 31