THz Spectroscopy
withCoherent Synchrotron Radiation
Ulrich SchadeBESSYUVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Why Terahertz?

Condensed Matter Physics
Life Sciences
Superconductivity
Energy gap
Symmetry of the order parameter
Strength of coupling

Protein dynamic
Secondary and tertiary structure
Metabolism
Influence of nutrition, waterIon channels in cell membranes

Low-dimensional effects
Dimensionality crossover
Non-Fermi liquid normal states
Broken symmetry ground states

Imaging
3D tomography of dry tissues
Near-field

Strongly correlated electrons
Kondo problem
Heavy electrons

Physical and Analytical Chemistry

New Technologies

Polar liquids
Hydrogen bondVan der Waals interactions
Acoustic-Optic phonon mixing in water

Medical diagnostic
Early cancer detection

SolutionsInteractions between solvated ions and solvent

Defense industry/Homeland security
Detection of explosives and biohazards

Industrial production
Material inspection

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Outline

Instrumentation• Infrared Beamline at BESSY, THz Performance

THz Radiation from the Storage Ring BESSY• Radiation Properties

Spectroscopic Application of the CSR• Superconductors• THz Near-field Spectroscopy

Conclusions

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Instrumentation• Infrared Beamline at BESSY, THz Performance

THz Radiation from the Storage Ring BESSY• Radiation Properties

Spectroscopic Application of the CSR• Superconductors• THz Near-field Spectroscopy

Conclusions

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

IRIS - Infrared Beamline at BESSY• Dipole radiation from dipole 2.2• NIR to FIR• 60(h) x 40(v) mrad2 acceptance

Schade et al., Rev. Sci. Instr. 73 1568 (2002).

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

THz Transmission of IRIS Beamline

Schematic of the optical beam path tothe experiments.

F3 @ 1 THz

Calculated transmittance for different positions along the beam path (SRW code).
UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Outline

Instrumentation• Infrared Beamline at BESSY, THz Performance

THz Radiation from the Storage Ring BESSY• Radiation Properties

Spectroscopic Application of the CSR• Superconductors• THz Near-field Spectroscopy

Conclusions

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Steady-state vs. Bursting CRS

CSR at higher frequencies observed than for Gaussian bunches expectedWith increasing current of the bunch:• the CSR spectrum extends to higher photon energies.
• the low-frequency noise in the THz beam drastically increases.

Present understanding:Interaction of bunch with CSR-wakefield leadsto:•a static non-Gaussian deformation ofthe bunch (Bane, Krinsky and Murphy,1996)→ steady-state CSR•bursting CSR emission above a current
threshold (micro-bunching, Stupakow andHeifets, 2002)→ high power bursting CSRUVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Coherent Amplification Factor

I coh
Af == Nfν ,I incohf v = ∫ n( z ) eiπ cos(θ ) z2dz

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

min. bunch length: 1.3 ps (0.5 mm)
max. charge:
10 pC

Coherent Amplification Factor

Total power of the coherent
synchrotron radiation
measured at F3.

IA f = coh = Nfν ,I incohf v = ∫ n( z ) eiπ cos(θ ) z2dz

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Pulse energy: max 100 pJoule
Peak E-field: max 50 V/cm

CSR as a sub-THz Spectroscopic Source

Integrated Spectral Intensity (a.u.)

Noise (% rms from 100 % line)(5 -25 cm-1)(7 -20 cm-1)

400 bunches stored, Bruker 66/v, 64 scans, ∆ω = 0.5 cm-1, 4.2 K Bolometer, 50-µm BS, 1.3 cm/s scanning velocity
UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Coherent Synchrotron Radiation in the low-α mode

“100%-line” for CSR

Source Comparison• long life time of the beam (>20 h)

256 scans, ∆ω = 0.5 cm-1, 1.4 K Bolometer, 5 mm aperture diameter• gain of 103 below 10 cm-1 (0.3 THz)
• highly reproducible

M. Ortolani et al., Phys. Rev. B 73, 184508 (2006).
UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Polarization Characteristics of CSR
Intensity distribution on M1

Polarization properties of IR synchrotron
radiation from a bending magnet at 500 cm-1.

Calculated s1 for the entrance and for theend focus of the beamline (SRW code).

Normalized CSR intensity at F3 as a functionof the azimuth angle of the analyzer.

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Application of the CSR:
- Superconductors- THz Near-field Spectroscopy

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Boron–doped Diamond•

Recently discovered superconductor: E.A. Ekimov, Nature 428, 542 (Nov. 2004).

•Superconductivity appears at high B-doping beyond the Metal-to-Insulator transition.

•Tc increases to 8 K with increasing Boron concentration.

Size: 3 mm x 3 mm
Y. Takano et al., Diamond & Related Mat. 14, 1936 (2005) and Nature 438, 647 (2005).

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Boron–doped Diamond

Increase of the normal-incidence reflectivity belowTc for ω < 2∆ (total screening) observed.
The peak in the RS/RN ratio indicates the energy ofthe optical gap.

As a result of the BCS theory for weak electron-phonon
coupling:→Our sample:→M. Ortolani et al., Phys. Rev. Lett. 97, 097002 (2006).
UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

2∆0 = 3.53 Tc
ω = 2∆ = 12 cm-1 = 17 K
Tc = 5 K

High–TC “Cuprate” Superconductor

c-axisc-axis
BiOc-axis reflectance of optimally doped BSCCO 2212
• structural anisotropy• high Tc (90 K) but low “gap energy”

SrO
CuO2
CaCuO2SrO
BiOBiOT>TC• Charge transport is blocked by insulating layers.
• Behaves like an insulator with R <1.

SrO
CuO2
CaCuO2SrO

T<TC• Cooper pairs tunnel through insulating layers, R ~ 1.
• Josephson Plasma Resonance (JPR) below 10 cm-1

BiO

4
2=JPR

ω

πne2
m*

Bi2Sr2CaCu2O8: - extreme structural anisotropy- highly insulating
UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

High–TC “Cuprate” Superconductor
Optimally doped Bi2Sr2CaCu2O8012345 mm• First scientific experiment using coherent synchrotron radiation as a spectroscopic source.
• Absolute measurements of reflectivity with high photometric accuracy on small samples at low temperatures.
• Direct measurement of JPR in optimally doped Bi2Sr2CaCu2O8.
• Bridge between microwave magneto-absorption and conventional far-IR spectroscopy.
E. J. Singley et al., Phys. Rev. B. 69, 092512 (2004).
UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

THz Problems Near-field Approaches Could Solve

THz ellipsometer formagneto-optic investigations(M. Schubert, U. of Leipzig)

Small-Throughput Experiments- complicated optical path (cryostat, magnets, etc.)- large F#

Small Sample Geometry- new and rare materials- spatial resolution

Bi2Sr2CaCu2O8012345 mm

Large THz Focal Spot
- Frauenhofer diffraction (1. disk: 84 % intensity)

D = 10 mm(F/4, ν = 10 cm-1)
D = 25 mm(F/4, ν = 4 cm-1)

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

THz Near-field Imaging with CSR

Aperture Cone

Coaxial Aperture cone

Spectra of the empty spectrometer (tobe multiplied by 100), of the aperturecone and of the coaxial aperture cone.
200 µm diameter aperture

200 µm diameter aperture,
80 µm wire diameterprobe design according to: F. Keilmann, Infrared Phys. & Technol. 36 217 (1995).
UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

THz Near-field Imaging with CSR

U. Schade et al., APL 84 1422 (2004)
UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

THz Near-field Imaging with CSR• “knife edge test” on Al-film on Si-substrate• spatial resolution @ 1 mm wavelength (0.33 THz):
100 µm aperture:

70 µm ≈ 1/14 λ

200 µm aperture:
130 µm ≈ 1/8 λ(@ 5 mm wavelength (0,066 THz):≈ 1/38 λ)UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

THz Near-field Imaging with CSR

Tooth decay diagnostics:
lesion

X-ray: little material contrast due to demineralization
THz imaging taken fromthis side

NIR:

good for enamel but dentin almost opaque

THz:

?

Simulated caries lesion (tooth decay)
composed of hydroxyapatite powder.

• shadow image• x-ray• far-field @ 1 mm (0.3 THz)
• con-focal geometry• bursting mode

• near-field @ 1 mm
• 200 µm aperture• bursting mode

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

• near-field @ 1 mm
• 200 µm wire cone
• low alpha modeTHz Near-field Imaging with CSR

Spectral near-field images ofthe lesion region between 3 and20 cm-1 (between 0.5 and 3 mmwavelength).

enamelThe corresponding wavenumber
is indicated on top of eachframe. Note that the simulatedcaries lesion is indicated by alower absorption between 5 and7 wavenumbers.

dentinIntegral THz Image

35678

1011121415

16171920U. Schade et al., Proc. SPIE Vol. 5725 46 (2005).

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Conclusions

Coherent Synchrotron Radiation from low α operation at BESSY

FIR, low-noise, broadband, steady-state, high power, diffraction limited, polarized, pulsed

New science opportunities by employing FIR diffraction-limited spectromicroscopy• superconducting gap (B-doped diamond, optimally doped BISCOO 2212)

Development of analytical methods• near-field spectral imaging of biological and biomedical samples• waveguide structures• Martin-Puplett ellipsometer

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007

Acknowledgments

Michele Ortolani
Jonseok LeeTino Noll
Jörg Feikes
Karsten Holldack
Peter Kuske
Gode Wüstefeld

BESSY

Arnulf Röseler
Ernst-Heiner Korte
Karsten Hinrichs
Michael Gensch (DESY)
Gert Hinte

ISAS

Heinz-Wilhelm Hübers
Paul Dumas
Bernhard Lendl
Michael C. Martin
E. Jason Singley
Dimitri N. Basov
Dan Fried
Paolo Calvani
Stefano Lupi

DLR
SOLEILTU Vienna
ALSALSUC SD
UC SF
U La Sapienza

UVSOR Workshop on THz Coherent Synchrotron Radiation, Okazaki, September 24th, 2007