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

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

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

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

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)

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

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

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

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 155–200 MeV Bunch charge 1 nC Rep. rate 10 Hz Peak current 100 A en 2 mm-mrad en(slice) 1 mm-mrad sg 0.2% Bunch length (FWHM) 10 ps THz Source

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: NEP@20 Hz ~ 10-8 W/Hz0.5 Fast time (microsecond) response

Optical Components 90° off-axis parabolic mirrors: Ø 50.8 mm EFL 152.4 mm Detector y-Dy z Filters/ polarizer x, y 70 mm electrons z CTR (30x30 mm, 300 mm SiO2, 80 nm Al) y In collaboration with CNR-IFN z-cut quartz window: Ø 60 mm, 4.8 mm thick Metamaterials THz band pass filters

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

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 = 17.73 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 = -2.774 ey = 3.3 mm mrad by = 33.83 m ay = -2.539 st = 0.5 ps

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)

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)

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)

Investigating the Spectral Stability No filter Emean = 12.20 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

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.

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

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

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,

Ultra Short CTR Pulses D. Nicoletti et al 2010

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;

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