1. TERASPARC Characterization of the THz source
Stefano Lupi on behalf of TERASPARC team

2. The Terahertz gap 0.1 THz – 10 THz
Vanishing thermal power, few tunable and pulsed lasers.
No electronics, few microwaves generators

3. THz Science Life Sciences Condensed Matter Physics New Technologies
Superconductivity Energy gap Symmetry of the order parameter Direct determination of the superfluid density Dynamics of Cooper pairs
Low-dimensional materials
Dimensionality crossover Non-Fermi liquid normal states Broken symmetry ground states
Coherent Phase Transitions Polarons Structural Phase Transitions
Magnetic sub-ps Dynamics
Condensed Matter Physics
Life Sciences
Macromolecules conformation
Secondary and tertiary structure
Coherent dynamic development
Imaging
3D tomography of dry tissues
Near-field sub-wavelenght spatial resolution
Polar liquids
Hydrogen bond
Van der Waals interactions
Acoustic-Optic phonon mixing in water
Solutions
Static and dynamic interactions between solvated
ions and solvent
Physical and Analytical Chemistry
New Technologies
THz technologies
Array THz detectors
Metamaterials
Medical diagnostic
Skin cancer detection
Industrial production
Material inspection
Production line monitoring
Defense industry/Homeland security
Detection of explosives and biohazards

4. Coherent THz Radiation (CDR/CTR)
Transition Radiation occurs when an electron
crosses the boundary between two different media
Intensity is 0 on axis and peaked at Q~1/g
Polarization is radial

5. Longitudinal Diagnostics
Measuring the coherent spectrum it is possible to reconstruct the bunch length and even its longitudinal structure.
By inverse Fourier transforming
Gaussian pulse
st = 0.2 ps
st = 10 ps
st = 1 ps
F(w)
Frequency (Hz)

6. Figures of Merit of THz sources: energy/pulse
SPARX
SPARC
A. Perucchi et al, 2007

7. Figures of Merit of THz sources: peak power
SPARX
SPARC
A. Perucchi et al, 2007

8. Figures of Merit of THz sources: average power
QCL
SPARX
SPARC
A. Perucchi et al, 2007

9. Diagnostic and Matching
SPARC Overview
150 MeV S-band linac
Velocity Bunching
Diagnostic and Matching
Undulators
u = 2.8 cm
Kmax = 2.2
r = 500 nm
S-band Gun
15 m
Long Solenoids
Seeding
Beam energy –200 MeV
Bunch charge nC
Rep. rate Hz
Peak current A
en mm-mrad
en(slice) mm-mrad
sg %
Bunch length (FWHM) ps
THz Source

10. Characterization of the SPARC CTR THz Source
Pyro-electric detector
Actual operating spectral range: 0.1 – 3 THz
Active element: 2 mm x 3 mm
Sensitivity: Hz ~ 10-8 W/Hz0.5
Fast time (microsecond) response

11. Optical Components 90° off-axis parabolic mirrors: Ø 50.8 mm
EFL mm
Detector
y-Dy z
Filters/
polarizer
x, y
70 mm
electrons z
CTR (30x30 mm, 300 mm SiO2, nm Al) y
In collaboration with CNR-IFN
z-cut quartz window:
Ø 60 mm, 4.8 mm thick
Metamaterials THz band pass filters

12. Measurements and Results
-Detector signal analysis -Statistical analysis to evaluate fluctuations -Dependence of CTR intensity on N2f(w) -Detector mapping

13. Two SPARC working points have been
investigated
On crest operation
Q = 500 pC
Energy= 167 MeV
energy spread = 0.1%
ex= 3.5 mm mrad
bx = m
ax = -1.17
ey = 4.1 mm mrad
by = 25 m
ay = -2.78
st = 2.0 ps
Compression Factor 4
Q = 500 pC
Energy= 94 MeV
energy spread = 1%
ex= 6.4 mm mrad
bx = 28.4 m
ax =
ey = 3.3 mm mrad
by = m
ay =
st = 0.5 ps

14. Effect of Bunch Compression
A gain of a factor 25 in intensity with respect to the on crest operation has been detected in the RF compression mode
--- Compressed bunch
(st = 0.5 ps)
--- Non Compressed bunch
(st = 2.0 ps)

15. Investigating the Spectral Emission
red curve: CTR energy at 350 GHz with a BW of nearly 50 GHz
green curve: broad band CTR energy (up to 3 THz)

16. Investigating the Spectral Emission
red curve: CTR energy at 1.5 THz with a BW of nearly 0.3 THz
blue curve: broad band CTR energy (up to 3 THz)

17. Investigating the Spectral Stability
No filter
Emean = mJ
sE = 0.73 mJ
No filter
Emean = 9.5 mJ
sE = 1.0 mJ
Filter 1.5 THz
Emean = 1.60 mJ
sE = 0.23 mJ
Filter 0.3 THz
Emean = 0.80 mJ
sE = 0.1 mJ

18. Shot-to-Shot e-beam fluctuations affect the THz pulse stability;
Typical fluctuations of THz around 10 % due mostly to charge (particle number) instability
Charge fluctuations
5% fluctuations
TO DO:
increasing statistics;
For e-beam diagnostics purposes: installing a two channels interferometer with custom wire grids;
For spectroscopic purposes: single-shot capability EOS.

19. Investigating the N2 Dependency
Charge (pC)
Bunch Length (ps)
125
1.81+/-0.019
225
1.96+/-0.018
335
2.22+/-0.021
490
2.49+/-0.034
V=V0Qa a=1.9

20. Figures of Merit of THz sources: energy/pulse
SPARX
SPARC
A. Perucchi et al, 2007

21. Developments -The charge should be measured at the end of the dogleg
-Air absorption
Purging optics
-Substitution of the Quartz window
Diamond window for a larger spectral range
-Characterization of CTR for different wavelengths
CustomTHz filters: 350 GHz, 1 THz, 1.5 THz, 2.5, 3.8, THz
Martin-Puplett and Michelson interferometer for frequency domain measurements
-More sensitive detectors
Golay cells, bolometers, etc,

22. Ultra Short CTR Pulses
D. Nicoletti et al 2010

23. Laser Comb THz Source
BROAD BAND with ultra-short high-brightness electron bunches
MONOCHROMATIC THz source with a comb beam
TUNABLE THz source with velocity bunching and comb beam
A possible application of a comb bunch is the generation of two narrow THz micropulses perfectly synchronized each other but with a variable time delay, to
perform pump-and-probe measurements:
Measurements of the life-time of Si-Ge Quantum Wells for Quantum Cascade Laser applications;
Inducing resonant depinning in Charge-Density Wave materials and measuring the resulting dc current;

24. TERASPARC collaboration:
Acknowledgments
TERASPARC collaboration:
M. Bellaveglia, E. Chiadroni, M. Boscolo, P. Calvani, M. Castellano, A.Cianchi, L. Cultrera, G. Di Pirro, M. Ferrario, L. Ficcadenti, D.Filippetto, G. Gatti, O.Limaj, B. Marchetti, A. Mostacci, D.Nicoletti, E. Pace, A. R. Rossi, C. Vaccarezza;
and the techincal staff: F. Anelli, S. Fioravanti, R. Sorchetti