TERASPARC Characterization of the THz source Stefano Lupi

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

The Terahertz gap 0. 1 THz – 10 THz No electronics, few microwaves generators Vanishing thermal power, few tunable and pulsed lasers.

THz Science Condensed Matter Physics Life Sciences Macromolecules conformation Secondary and tertiary structure Coherent dynamic development Superconductivity Energy gap Symmetry of the order parameter Direct determination of the superfluid density Dynamics of Cooper pairs Imaging 3 D tomography of dry tissues Near-field sub-wavelenght spatial resolution Low-dimensional materials Dimensionality crossover Non-Fermi liquid normal states Broken symmetry ground states Coherent Phase Transitions Polarons Structural Phase Transitions New Technologies Magnetic sub-ps Dynamics Physical and Analytical Chemistry Polar liquids Hydrogen bond Van der Waals interactions Acoustic-Optic phonon mixing in water Solutions Static and dynamic interactions between solvated ions and solvent 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 F(w) Gaussian pulse st = 10 ps st = 0. 2 ps st = 1 ps 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 SPARX QCL SPARC A. Perucchi et al, 2007

SPARC Overview Undulators u = 2. 8 cm Diagnostic and Matching 150 Me. V S-band linac Velocity Bunching Kmax = 2. 2 r = 500 nm 15 m Long Solenoids Seeding THz Source S-band Gun Beam energy 155– 200 Me. V Bunch charge 1 n. C 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

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/Hz 0. 5 Fast time (microsecond) response

Optical Components Detector x, y 90° off-axis parabolic mirrors: Øz 50. 8 mm EFL 152. 4 mm y-Dy Filters/ polarizer 70 mm electrons z In collaboration with CNR-IFN y CTR (30 x 30 mm, 300 mm Si. O 2, 80 nm Al) 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 N 2 f(w) -Detector mapping

Two SPARC working points have been investigated On crest operation Compression Factor 4 Q = 500 p. C Energy= 167 Me. V 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 Q = 500 p. C Energy= 94 Me. V 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 m. J s. E = 0. 73 m. J No filter Emean = 9. 5 m. J s. E = 1. 0 m. J Filter 0. 3 THz Emean = 0. 80 m. J s. E = 0. 1 m. J Filter 1. 5 THz Emean = 1. 60 m. J s. E = 0. 23 m. J

→ 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 N 2 Dependency Charge (p. C) Bunch Length (ps) 125 1. 81+/-0. 019 225 1. 96+/-0. 018 335 2. 22+/-0. 021 490 2. 49+/-0. 034 V=V 0 Qa 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 Custom. THz 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 highbrightness 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: 1. Measurements of the life-time of Si-Ge Quantum Wells for Quantum Cascade Laser applications; 2. Inducing resonant depinning in Charge-Density Wave materials and measuring the resulting dc current;

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