Transcript Electronic Presentation Guidelines

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
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
THz wave
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 J
 Plasma
Accelerator based THz pulses : up to a few 100s
of J/pulse or ~50 MV/cm-1
 Coherent Transition Radiation(CTR), >100 J, <
5 THz
 Synchrotron radiation
 Free Electron Laser
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
Transition radiation occurs when an
electron crosses the boundary between
two different media. For a relativistic
electron (  v/c @ 1) incident on a
perfect conductor, the number of
photons emitted per solid angle and
wavelength range is:
Electron Beam
OTR
dN
  sin  cos 
 2
d  d    1   2 cos 2  
2
2
OTR Radiator
45o
OTR
2

Intensity is 0 on axis, peaks at ~1/ .
Coherent radiation emission:
E= 50 MeV ->  = 100 ->  = 10 mrad
Charge
[nC]
Radiation energy
[μJ]
0.2
3.5
0.5
22
1
88
0.8
Intensity, d2W/ddw
dWN /dw = N2 dW1 /dw | f (w)|2
1.0
0.6
0.4
0.2
0.0
-4
-2
0
2
4

Intensity Distribution
fs THz Laboratory
Lead blocks
RF gun
AC1
QD1
QD2
Ti foil
QT1
EO Sampling
Tripler
PSD
AC2
Chicane 2
OTR CTR
THz radiation
Chicane 1
266 nm, 1 kHz
LINAC
Stretcher
Spectrometer
Regen. Amp.
Oscillator
Laser Room
Regen. Amplifier
3W, 120 fs, 1KHz
Laboratory
Pulse
Compressor
QD
OPA
~1.4 mJ
~1 cm diameter
Analog PID
controller
Analog PID
controller
THz Energy Measurement
RF gun
Accelerating
Column
Quadruple
Magnet
Lead blocks
Linac
Al foil
PSD
266 nm, >250 uJ
1 kHz, > 2 ps
Chicane
electron bunch
compressor
THz radiation
Pyrocam III
(THz beam imaging
detector)
50 MeV
~0.3 nC
10 Hz
~5 μJ
Single-shot Electro-Optic Detection
Shen et al. PRL 99,
043901, 2007
6
1x10
Close
Open
6
1x10
4
6.0x10
6
5
9x10
Iopen - Iclose
Counts (AB)
1x10
5
8x10
5
7x10
5
4
3.0x10
0.0
6x10
5
5x10
5
4x10
4
-3.0x10
5
3x10
790
795
800
805
810
Wavelength (nm)
815
820
790
795
800
805
810
Wavelength (nm)
815
820
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  (w ) , 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)
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
Kang et al. CPL 587, 14, 2013
Cluster
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
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
Nanowire
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
( w pump = 1.55 eV) ((a)–(c)) and THzpump experiments ( w pump ∼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
• Mid-IR from high-energy OPA
1000
Signal
Idler
SHI
SHS
SFI
SFS
FHI
FHS
SHSFI
SHSFS
NDFG1
NDFG2
100
Power (mW)
• Widely tunable UV, visible, IR
output from Optical Parametric
Amplifiers (OPAs)
10
1
100
1000
10000
Wavelength (nm)
• Terahertz (THz)
- ZnTe
- LiNbO3
100000
Future Plan-Synchronization
Fundamental
Laser
Laser based
THz
OPA Laser
LINAC based
THz
fs-THz Beamline
Lead blocks
RF gun
AC1
QD1
QD2
QT1
Chicane 2
OTR CTR
THz radiation
266 nm, 1 kHz
~1.4 mJ
~1 cm diameter
Spectrometer
Regen. Amp.
Regen. Amp.
Oscillator
Regen. Amplifier
3W, 120 fs, 1KHz
Laboratory
Pulse
Compressor
QD
OPA
Chicane 1
Analog PID
controller
Laser Room
Ti foil
EO Sampling
Tripler
PSD
AC2
LINAC
Analog PID
controller
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
Acknowledgements
Collaborators:
Dr. Heung-Sik Kang(PAL)
Mr. Junho Ko(Postech)
Mr. Seonghoon Jung(PAL)
Prof. Taiha Joo(Postech)
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
●
Thank You for Your Attention!