18 research outputs found
Intense terahertz pulses from SPARC-LAB coherent radiation source
The linac-based Terahertz source at the SPARC_LAB test facility is able to gene
rate highly intense Terahertz broadband
pulses
via
coherent transition radiation (CTR) from high brightness electron beams. The THz pulse duration is typically
down to 100 fs RMS and can be tuned through the electron bunch duration and shaping. The measured stored energy in a
single THz pulse has reached 40
μ
J, which corresponds to a peak
electric field of 1.6 MV/cm at the THz focus. Here we
present the main features, in particular spatial and sp
ectral distributions and energy
characterizations of the
SPARC_LAB THz source, which is very competitive for investigations in Condensed Matter, as well as a valid tool for
electron beam longitudinal diagnostics
Nonlinear quantum magnetophononics in SrCu(BO)
Harnessing the most advanced capabilities of quantum technologies will
require the ability to control macroscopic quantum states of matter. Quantum
magnetic materials provide a valuable platform for realizing highly entangled
many-body quantum systems, and have been used to investigate phenomena ranging
from quantum phase transitions (QPTs) to fractionalization, topological order
and the entanglement structure of the quantum wavefunction. Although multiple
studies have controlled their properties by static applied pressures or
magnetic fields, dynamical control at the fundamental timescales of their
magnetic interactions remains completely unexplored. However, major progress in
the technology of ultrafast laser pulses has enabled the dynamical modification
of electronic properties, and now we demonstrate the ultrafast control of
quantum magnetism. This we achieve by a magnetophononic mechanism, the driving
of coherent lattice displacements to produce a resonant excitation of the
quantum spin dynamics. Specifically, we apply intense terahertz laser pulses to
excite a collective spin state of the quantum antiferromagnet
SrCu(BO) by resonance with the nonlinear mixing frequency of the
driven phonons that modulate the magnetic interactions. Our observations
indicate a universal mechanism for controlling nonequilibrium quantum many-body
physics on timescales many orders of magnitude faster than those achieved to
date.Comment: 24 pages, 9 figure
Terahertz displacive excitation of a coherent Raman-active phonon in V2O3
Nonlinear processes involving frequency-mixing of light fields set the basis for ultrafast coherent spectroscopy of collective modes in solids. In certain semimetals and semiconductors, generation of coherent phonon modes can occur by a displacive force on the lattice at the difference-frequency mixing of a laser pulse excitation on the electronic system. Here, as a low-frequency counterpart of this process, we demonstrate that coherent phonon excitations can be induced by the sum-frequency components of an intense terahertz light field, coupled to intraband electronic transitions. This nonlinear process leads to charge-coupled coherent dynamics of Raman-active phonon modes in the strongly correlated metal VO. Our results show an alternative up-conversion pathway for the optical control of Raman-active modes in solids mediated by terahertz-driven electronic excitation
Tailoring of Highly Intense THz Radiation Through High Brightness Electron Beams Longitudinal Manipulation
The ultra-short electron beams, produced through the velocity bunching compression technique at the SPARC_LAB test Facility (Frascati, Italy), are used to produce Coherent Transition Radiation in the terahertz (THz) range. This paper reports on the main features of this THz source, which have a spectral coverage up to 5 THz, a pulse duration down to 100 fs, and an energy per pulse on the order of tens of μJ. These figures of merits open the possibility to apply this source for nonlinear and THz pump-probe experiments in Solid-State Physics and material science
Overcoming the thermal regime for the electric-field driven Mott transition in vanadium sesquioxide
Thermal effects limit the speed of the electrically driven insulator-metal transition in V2O3 to tens of picoseconds. Here the authors show that under an intense THz-electric-field excitation the thermal regime can be overcome, achieving a purely electronic transition on ultrafast timescales
Leggett mode controlled by light pulses
The discovery of symmetry-broken phases that host multiple order parameters, such as multiband superconductors(1,2), has triggered an enormous interest in condensed matter physics. However, many challenges continue to hinder the fundamental understanding of how to control the collective modes corresponding to these multiple order parameters(3,4). Here we demonstrate that, in full analogy with phonons, Raman-active electronic collective modes can be manipulated by intense light pulses. By tuning a sum-frequency excitation process, we selectively trigger collective excitations that can be ascribed to the relative phase fluctuations between two superconducting order parameters-the so-called Leggett mode-in the multiband superconductor MgB2. The excellent comparison between experiments and theory establishes a general protocol for the advanced control of Raman-active electronic modes in symmetry-broken quantum phases of matter
Supercontinuum generation in OHQ-N2S organic crystal driven by intense terahertz fields
A laser supercontinuum is generated by cross-phase modulation (XPM) driven by an intense terahertz (THz) field in organic crystal OHQ-N2S. In this highly nonlinear medium, the THz electric field induces a time-varying optical phase modulation, which causes a spectacular spectral broadening and shifting of a co-propagating near-infrared laser pulse. The effect is enabled by the large electro-optic coefficient, the low absorption, and the good velocity matching between the laser and the THz pulse over the OHQ-N2S crystal thickness. The XPM occurs when the THz field is aligned along the polar axis of the OHQ-N2S. The results display a promising pathway for ultrafast control of the spectral and temporal properties of laser pulses using THz stimuli
Terahertz plasmonic excitations in Bi2Se3 topological insulator
After the discovery of Dirac electrons in condensed matter physics, more specifically in graphene and its derivatives, their potentialities in the fields of plasmonics and photonics have been readily recognized, leading to a plethora of applications in active and tunable optical devices. Massless Dirac carriers have been further found in three-dimensional topological insulators. These exotic quantum systems have an insulating gap in the bulk and intrinsic Dirac metallic states at any surface, sustaining not only single-particle excitations but also plasmonic collective modes. In this paper we will review the plasmon excitations in different microstructures patterned on Bi2Se3 topological insulator thin films as measured by terahertz spectroscopy. We discuss the dependence of the plasmon absorption versus the microstructure shape, wavevector, and magnetic field. Finally we will discuss the topological protection of both the Dirac single-particle and plasmon excitations