Experiments with THz radiation at
SPARC_LAB
S. Lupi
Dipartimento di Fisica and INFN, Sapienza University of Rome, Italy
on behalf of the THz collaboration at SPARC_LAB
OUTLINE
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THz production at SPARC_LAB;
Pump-Probe Spectroscopy;
Figures of Merit of the SPARC THz Source;
THz Experiments at SPARC_LAB;
Conclusions;
THz Radiation at SPARC_LAB
1 THz=33 cm-1=300 microns=50 K=1 ps
d 2I
dd

d 2 I sp
dd
N  N (N 1)F()
Transition and Diffraction Radiation

Electron Bunch
THz Radiation
1) Longitudinal diagnostic of the electronic beam;
2) Use of radiation for Pump-Probe experiments;
OUTLINE
•
•
•
•
•
THz production at SPARC_LAB;
Pump-Probe Time resolved Spectroscopy;
Figures of Merit of the SPARC THz Source;
THz Experiments at SPARC_LAB;
Conclusions;
Pump-Probe Spectroscopy
Temporal evolution of excitations
THz Pump-THz Probe Spectroscopy
T=0
Optical Pump-Optical Probe Spectroscopy
Pump and Probe
Accordable THz PumpT=Δt
pulses;
pulses (often at a single frequency) fall in the visible/near-IR
•Possibility to resonate and/or selectionate several
• High energy pumping;
?
fundamental excitations;
• Strong scattering effects;
Pump
•Intrinsic dynamics
Probe
Extrinsic dynamics
When a light Pulse is a Pump Pulse
Figures of merit of a pump source:
1)Energy per pulse ≈1 mJ-1 mJ (Peak Power W≈100 kW-10 GW);
2)Pulse durationsub-ps scale;
3)Rep rate tens of Hz to KHz (to reduce thermal loading);
4)Frequency tunability (to be in resonance);
5)Associate electric field 100 KV/cm (1 mV/Å) to 100 MV/cm
(1V/Å)Atomic field;
6)Associate magnetic field ≈ 1 T
THz Radiation measured at
SPARC
SPARC
Electron
beam
energy
Charge
t
&
bandwidth
THz pulse
energy
E-field
120 MeV
300 pC
120 (50) fs
5 (10) THz
≈50 mJ
MV/cm
Constraints for a THz Pump source well satisfied
E. Chiadroni et al, APL 2013
OUTLINE
•
•
•
•
•
THz production at SPARC_LAB;
Pump-Probe Time resolved Spectroscopy;
Figures of Merit of the SPARC THz Source;
THz Experiments at SPARC_LAB;
Conclusions;
Insulator to Metal Transitions
Many materials are insulating although band theory suggests a
metallic ground state: V2O3, VO2, NiO, NiSe2, La2CuO4, Cs3C60
Strong Electronic Correlations
(Basic Ingredient for High-Tc Superconductivity)
Filling-Controlled MIT:
U Coulomb repulsion
t Bandwidth
Bandwidth-Controlled MIT:
• static (pressure)
• static (doping)
MIT in V2O3
Crossover
PI
PM
AFI
D.B. McWhan et al, PRB 7, 1920 (1973)
V2O3
THz controlled Mott-Hubbard MIT
Filling-Controlled MIT:
U Coulomb repulsion
t Bandwidth
• static (Doping)
•Dynamic (Phoexcitation)
Bandwidth-Controlled MIT:
• static (Pressure)
•dynamic (Radiation)
THz pulses in the MV/cm range
can drive lattice displacements
in the pm range
A. Perucchi et al
Dynamical modulation of U
through intramolecular pumping
THz Controlled MIT in V2O3
(in collaboration with University of Pavia and IIT)
Study of transmittance vs THz intensity of V2O3 resonators
Tunable THz Device
Low THz Field Transmittance
T<TMIT
T>TMIT
LC Resonance
THz Controlled MIT in V2O3
THz Electric field varied of many orders of magnitude
Localized Charge Carriers
at low THz FieldInsulator
Mobile Charge Carriers
at high THz FieldMetal
THz Control of Superconductivity
Bosonic Glue
Superconductivity
Forming Cooper pairs and establishing a
macroscopic phase coherence
The formation energy is 2THz
Breaking Cooper Pairs and studying their temporal reformation
may provide important information about the bosonic glue in
particular in High-Tc Cuprates
Electrodynamics of Superconductors
s1()
d()Supercurrent=Jc
2
Photoionization
For hω>2Δ light breaks
Cooper pairs
1) Optical Pump - Optical Probe
(THz Probe) hω>>2Δ
Recombination Dynamics
affected by excess phonons
2) THz Pump – THz Probe hωTHz≥2Δ
Intrinsic dynamics

Alternative processes if hω<2Δ
Δ=Δ(J, B) at fixed T<Tc
The high E (~MV) THz field may induce
currents exceeding the critical current
(breaking the Superconducting State with an
Electric Field)
The high B (~1 T) THz field may be larger
that Bc
(breaking the Superconducting State with a
magnetic Field)
Conclusions
The High-Power Sub-ps pulses of THz radiation
currently produced at SPARC_LAB is strongly
competitive for spectroscopic applications in
non-linear physics and Pump-Probe
experiments