RESEARCH

THz Time Domain spectroscopy (THz-TDS)

Terahertz time-domain (THz-TDS) spectroscopy is a spectroscopic technique in which the properties of matter are probed with short pulses of terahertz radiation.  The THz-gap represents yet one of the most difficult spectral regions to generate and detect, thus hindering some of the most important transport properties of materials that fall into this gap.  At the Terahertz Sapienza laboratory (1), linear and nonlinear THz-TDS experiments are developed through the use of multiple photoantennas generation systems (Hamamatsu and Batop) and the use of optical rectified radiation, respectively. The transmitted/reflected THz pulses are detected using gating processes with an external time coherent optical probe. Lock-in amplifiers and boxcar integrators are also used to filter the relatively small signal from the background noise.

THz generation through two-color plasma mixing

The optical appartus developed at the Terahertz Sapienza laboratory (1) permits the generation of THz radiation through a four-wave rectification process, taking place in a plasma filament generated in air by a high power femtosecond optical pulse. The source is a Coherent Legend Ti:Sa laser amplifier (7 mJ, 1 KHz, 35 fs, 780 nm).

THz generation through optical rectification in organic crystals

Some crystals show nonlinear properties that, when combined with a low THz transparency and structural robustness, permits an optical rectification process that generates strong THz pulses. At the Terahertz Sapienza laboratory (1), we use a Coherent Legend Ti:Sa source (7 mJ, 1 KHz, 35 fs, 780 nm) as an input for an optical parametric amplificator (TOPAS-prime from Light Conversion) in order to obtain femtosecond pulses in the IR range and up to 4 mJ in energy. The output beam is then impinged on a nonlinear crystal (organic crystals like HMQ-TMS) to produce strong THz pulses covering a broad range of the THz spectrum, up to 6 THz.

THz pulsed imaging (TPI)

Many efforts were done in THz technology, improving THz sources and detectors’ responses and ensuring devices’ flexibility and portability, in recent decades. This has stimulated a wide diffusion of THz systems for spectroscopic and imaging purposes, applicable in various science fields like biology and medicine, gas sensing, chemical analysis, new materials characterization in low-frequency range and non-destructive evaluation of composite materials and constructions, astronomy, microelectronics and security, agri-food industry, art conservation , etc. 

Despite a vast variety of applications, THz imaging is a challenging research field. THz imaging  is considered  an emerging and significant nondestructive evaluation (NDE) technique. It has the ability to look into and through transparent objects such as many material packages like PET, for food inspection; or can be used for tumor margins delineation both on in-vivo and ex-vivo biological tissues, for dielectric materials analysis and quality control in the pharmaceutical, biomedical, security, materials characterization, and aerospace industries.

3D Graphene Networks

The development of three-dimensional (3D) graphene structures holds the promise to extend the unique electrical, thermal and optical properties of 2D graphene into a full 3D network. Current technologies allow the production of sponge like materials, composed by stacking high-quality monolayer graphene sheets into a wide variety of three dimensional structures. A variety of growth techniques are possible, and the produced 3D porous systems have demonstrated performances beyond 2D graphene devices. Applications of graphene-based structures range from supercapacitors, lithium batteries and electrocatalysts , to photodetectors, biochemical applications, transistors and plasmonics. However, these networks often suffer from undesirable phenomena, mainly due to their 3D morphology. A complete characterization of their behaviour is thus required, especially in the AC transport regime, where the network composed of holes and branches is supposed to interact collectively with the entire broadband spectrum.

Spectroscopy of Topological and Novel Quantum Materials

Most of the materials in condensed matter physics are characterized by low-energy electronic excitations showing a quadratic energy/momentum dispersion (Schrodinger electrons). Only recently, electrons with a linear energy/momentum (relativistic) dispersion (massless Dirac carriers), have been discovered first in graphene, and after in Topological Insulators and Weyl systems, and their potentialities in the fields of plasmonics and photonics have been readily recognized, leading to different applications in active and tunable optical devices. My recent research concerns the applications of Dirac/Weyl electronic systems in terahertz optics and plasmonics.