Maria Massaouti

Detection of harmful residues in honey using terahertz time-domain spectroscopy.

Terahertz time-domain spectroscopy (THz–TDS) has been applied for the detection and discrimination of harmful chemical residues in honey. Three antibiotics (sulfapyridine, sulfathiazole, and tetracycline) and two acaricides (coumaphos and amitraz) were characterized in the THz frequency regime between 0.5 THz and 6.0 THz. All chemical substances present distinct absorption peaks. THz transmission measurements of honey mixtures with antibiotics have been performed, revealing that antibiotic residues are traceable in highly absorptive food products, such as honey, at concentrations down to 1% weight percentage, thanks to their THz fingerprints. Moreover, multiple antibiotics were identified in their mixture with honey, pointing out the potential of the technique to be used in the near future as a fast, real-time technique for detecting and discriminating multi-residues strictly related to food safety issues.

Eutectic epsilon-near-zero metamaterial terahertz waveguides

We present and analyze the unique phenomena of enhanced THz transmission through a subwavelength LiF dielectric rod lattice embedded in an epsilon-near-zero KCl host. Our experimental results in combination with theoretical calculations show that subwavelength waveguiding of terahertz radiation is achieved within an alkali-halide eutectic metamaterial as result of the coupling of Mie-resonance modes arising in the dielectric lattice.

Strong terahertz emission enhancement via femtosecond laser filament concatenation in air.

We investigate the emission of terahertz (THz) radiation from two laser filaments in air. An increase by 1 order of magnitude of the overall THz power is found when the two filaments are coherently linked on-axis, leading to a single longer concatenated filament. The observed enhancement is found to be the same for the cases of single-color and two-color filamentation approaches.

Coherent control of THz pulses polarization from femtosecond laser filaments in gases

We demonstrate the possibility to rotate the polarization of linearly polarized THz pulses via the accurate control of the 2-color filament surrounding gas pressure. We also show ways to produce elliptically and circularly polarized THz pulses.

Optical emission spectroscopy and time-of-flight investigations of plasmas generated from AlN targets in cases of pulsed laser deposition with sub-ps and ns ultraviolet laser pulses

We performed a comparative study of the plasma generated from AlN targets under sub-ps vs ns UV (λ=248 nm) excimer laser pulses. Optical emission and time-of-flight spectra recorded in cases of samples irradiated with ns laser pulses showed the presence of Al lines, which became prevalent after the first laser pulse was incident on the target. These observations are congruent with the metallization of AlN targets inside each crater under multipulse ns laser action at laser fluences above the ablation threshold, observed by visual inspection and optical microscopy. Metallization was not observed when working with sub-ps laser pulses. Moreover, our studies confirmed the predominant presence of AlN positive molecular ions in the plasma generated in front of AlN targets submitted to sub-ps multipulse laser irradiation. The optical emission data are in good agreement with time-of-flight mass analysis. We emphasize that all investigations support the experimental evidence reported by Gyorgy et al. [E. Gyorgy et...

Vibrational constants and binding energies of Sr+Xe

Abstract The optical absorption spectrum of Sr+Xe, is measured in the 21 500–23 300 cm −1 energy region, using photofragmentation spectroscopy of mass-selected ions. The spectrum consists of two vibrational progressions that are due to dipole transitions from the X2Σ1/2 electronic ground state to vibrational levels of the excited A2Π1/2 and A2Π3/2 states. From isotope-resolved measurements and using the approximation of the anharmonic oscillator, we calculated the vibrational constants for the ground X2Σ1/2 and the excited A2Π1/2, A2Π3/2 states. Finally, we estimate the binding energies of the involved states with the aim of an electrostatic potential model.

Gas-phase Cu+– and Ag+–glycine complexes produced with a new source

Abstract A combination of the laser ablation of a metal target with an effusive amino acid oven and the free-jet expansion of helium is employed in order to produce gas-phase metal cation–amino acid complexes in a molecular beam. With this source, Cu + –glycine and Ag + –glycine complexes are formed through gas-phase reactions and are analyzed using a time-of-flight mass spectrometer. From the mass spectra we conclude that copper is dicoordinated while silver can attract up to four glycine molecules.

Controlling Laser Filamentation Induced Strong THz Fields

This article reviews recent advances on tuning intense THz pulses generated from 2-color femtosecond laser filaments in gases. In particular, extended tunability of the THz pulses is shown via filamentation molding and the use of cleverly engineered metamaterials and eutectics.