Ricerc@Sapienza

The point-spread function of an optical system imaged by a camera carries, in its geometrical details, key information on the optical components that are part of the system. In this work we explore the possibility of detecting anomalous structures buried under the skin surface by studying the deformations of the ideal Airy-disk point-spread function of a terahertz microscope, which are observed when the skin becomes one of the reflecting surfaces of the optical system. A custom terahertz microscope working in reflection mode at an angle of incidence of 45 degree has been built.

Terahertz (THz) radiation is of great interest for a variety of applications, e.g., particle accelerations, spectroscopy investigations of quantum systems, and high-field study of materials. One of the most common laser-based processes to produce THz pulses is optical rectification, which transduces an infrared pump laser to the THz domain (0.1–20 THz). In this work, we propose and theoretically describe a method to characterize the amplitude and phase of the electric field of the pump laser pulse relying on THz generation and detection.

HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) is a recently discovered anisotropic organic crystal that can be exploited for the production of broadband high-intensity terahertz (THz) radiation through the optical rectification (OR) technique. HMQ-TMS plays a central role in THz technology due to its broad transparency range, large electro-optic coefficient and coherence length, and excellent crystal properties. However, its anisotropic optical properties have not been deeply researched yet.

We study radiative relaxation at terahertz frequencies in n-type Ge/SiGe quantum wells, optically pumped with a terahertz free electron laser. Two wells coupled through a tunneling barrier are designed to operate as a three-level laser system with non-equilibrium population generated by optical pumping around the 1→3 intersubband transition at 10 THz. The non-equilibrium subband population dynamics are studied by absorption-saturation measurements and compared to a numerical model.

The waveguide losses from a range of surface plasmon and double metal waveguides for Ge/Si1−xGex THz quantum cascade laser gain media are investigated at 4.79 THz (62.6 µm wavelength). Double metal waveguides demonstrate lower losses than surface plasmonic guiding with minimum losses for a 10 µm thick active gain region with silver metal of 21 cm−1 at 300 K reducing to 14.5 cm−1 at 10 K.

Modelling the dynamics of a solution requires a
deep comprehension of the aqueous medium. In this work we
investigate different aqueous solutions through terahertz time domain
spectroscopy in order to gain a better understanding of
the water’s structure and it’s relation with the system of ions
solved in it. The results suggest a biphasic model of water; we
expect the two phases and their equilibrium at a given
temperature to be a determinant factor in the dynamics of the
molecules solved in it.

Tunable THz antennas based on a single unpatterned graphene sheet placed inside a grounded dielectric multilayer are studied with the aim of characterizing their performance in terms of pattern reconfigurability, directivity, and radiation efficiency. The considered structures belong to the class of Fabry-Perot cavity (FPC) antennas, whose radiation mechanism relies on the excitation of cylindrical leaky waves with an ordinary (i.e., non-plasmonic) sinusoidal transverse modal profile.

High frequency detection based on MOS-FET technology was long justified using a mechanism described by the plasma wave detection theory. In this paper we propose a new model based on the self-mixing process, taking place not in the channel, but in the depleted portion of the transistor body. Hydrodynamic semiconductor equations are solved in the small signal approximation. As a result, we present the dependence of the rectified voltage on the bias gate voltage, which fits carefully several experimental literature results.

This paper reports the design, the microfabrication and the experimental characterization of an ultra-thin narrow-band metamaterial absorber at terahertz frequencies. The metamaterial device is composed of a highly flexible polyimide spacer included between a top electric ring resonator with a four-fold rotational symmetry and a bottom ground plane that avoids misalignment problems.

It has recently been shown that the relaxation time of a graphene sheet is the crucial parameter that governs the radiation performance in graphene THz antennas based on either plasmonic or nonplasmonic leaky waves. Moreover, the radiating properties of these devices have always been derived assuming an ideal dipole-like source, and no full-wave and experimental results on realistic feeders have been reported, yet. To this purpose, in this work we aim at bringing the designs of graphene-based Fabry-Perot cavity leaky-wave antennas (FPC-LWAs) towards an experimental stage.