1,720,981 research outputs found
THz Multi-Mode Q-Plate with a Fixed Rate of Change of the Optical Axis Using Form Birefringence
Full text linkWe report the design, fabrication and experimental validation of a THz all-dielectric multi-mode q-plate having a fixed rate of change of the optical axis. The device consists of space-variant birefringent slabs manufactured by 3D printing using melt-extruded Acrylonitrile Butadiene Styrene (ABS). The desired form birefringence is analytically evaluated and experimentally measured by the THz time domain spectroscopy technique. The manufactured q-plate design is characterized using a polarization-sensitive imaging setup. The full electric field spatial maps are acquired from the beam propagating through the q-plate. The device enables the realization of both radial and azimuthal vector beams at discrete frequency intervals by controlling the space-dependent orientation of the ordinary and extraordinary axes in the transverse plane with a multi-mode sequence
THz Multi-Mode Q-Plate with a Fixed Rate of Change of the Optical Axis Using Form Birefringence
No full textWe report the design, fabrication and experimental validation of a THz all-dielectric multi-mode q-plate having a fixed rate of change of the optical axis. The device consists of space-variant birefringent slabs manufactured by 3D printing using melt-extruded Acrylonitrile Butadiene Styrene (ABS). The desired form birefringence is analytically evaluated and experimentally measured by the THz time domain spectroscopy technique. The manufactured q-plate design is characterized using a polarization-sensitive imaging setup. The full electric field spatial maps are acquired from the beam propagating through the q-plate. The device enables the realization of both radial and azimuthal vector beams at discrete frequency intervals by controlling the space-dependent orientation of the ordinary and extraordinary axes in the transverse plane with a multi-mode sequence
Terahertz time-domain ellipsometry: tutorial
No full textEllipsometry is extensively used in the optical regime to investigate the properties of many materials as well as to evaluate with high precision the surface roughness and thickness of thin films and multilayered systems. Due to the inherent non-coherent detection technique, data analyses in optical ellipsometry tend to be complicated and require the use of a predetermined model, therefore indirectly linking the sample properties to the measured ellipsometric parameters. The aim of this tutorial is to provide an overview of terahertz (THz) time-domain ellipsometry, which is based instead on a coherent detection approach and allows in a simple and direct way the measurement of the material response. After giving a brief description of the technology presently used to generate and detect THz radiation, we introduce the general features of an ellipsometric setup operating in the time domain, putting in evidence similarities and differences with respect to the classical optical counterpart. To back up and validate the study, results of THz ellipsometric measurements carried out on selected samples are presented
Enhanced relaxation dynamics in silver-doped chitosan nanocomposites: Probing the charge carrier dynamics and terahertz dielectric response
Full text linkThis study investigates the influence of silver nanoparticle incorporation on the electro-optical properties of chitosan, a biocompatible and versatile polymer with promising applications in biomedicine, energy storage, and sensing technologies, to name a few. Silver nanoparticles were synthesized by nanosecond laser ablation of the silver target in the polymeric solution. Terahertz time-domain spectroscopy was used to determine the complex dielectric function of pure chitosan and chitosan-silver nanocomposite films over a broad frequency range. The experimental data were analyzed using theoretical models, based on the Drude-Smith and Havriliak-Negami equations, to elucidate the underlying charge carrier dynamics and dielectric relaxation processes. Additionally, complex impedance and complex dielectric modulus analyses were conducted, incorporating Cole-Cole plots. The findings reveal a significant enhancement in the relaxation dynamics of the nanocomposite compared to pure chitosan, evidenced by a shift towards higher frequencies in the imaginary part of the dielectric function and a characteristic quarter-circle arc in the Cole-Cole plot. This study provides valuable insights into the structure-property relationships governing the electro-optical behavior of chitosan-based nanocomposites, paving the way for their tailored design and optimization for advanced technological applications
Engineering of high quality factor THz metasurfaces by femtosecond laser ablation
Full text linkWe report on the realization of high Q metasurfaces operating in the THz frequency range by femtosecond laser ablation applied to a nanometric metallic layer over a silicon substrate. Two different fabrication methods are used to develop periodic patterns whose basic elements are in form of an array of through-holes or metallic islands. The response of the resulting structures is characterized using a time-domain spectrometer in the frequency range 0.3–1.5 THz. The experimental findings are compared with the predictions of full wave electromagnetic simulations. The fairly good agreement between simulation predictions and experimental findings evidences that the proposed approach can offer a facile way to the elaboration of THz metasurfaces
Perspective on the use of nanoparticles to improve LIBS analytical performance: nanoparticle enhanced laser induced breakdown spectroscopy (NELIBS)
No full textIn this paper, the new approach for Laser Induced Breakdown Spectroscopy (LIBS) based on nanoparticle
deposition on the sample surface is reviewed from both fundamental and application points of view. The
case of Nanoparticle-Enhanced LIBS (NELIBS) of metal samples is used for describing and discussing the
main causes of the emission signal enhancement. A set of test cases is presented, which shows
enhancements up to 1–2 orders of magnitude obtained using NELIBS with respect to LIBS. The feasibility
and potential of NELIBS are also discussed for several analytical applications, including analysis of
metallic samples, transparent samples and aqueous solution
Accurate THz ellipsometry using calibration in time domain
No full textWe report on the realisation of a customized THz time domain spectroscopic ellipsometer (THz-TDSE) based on fiber-coupled photoconductive antennas, operating in a wide range of incident angles and allowing also standard transmission spectroscopy without any optical realignment. To ensure accurate parameter extraction for a broad range of materials, we developed a fast and effective algorithm-assisted method to calibrate the setup and compensate for the nonideality in the response of the THz system. The procedure allows to minimise errors induced by imperfect response of the antennas and polarizers, imprecise setting of the impinging and receiving angles in the goniometric mechanical arms, and unavoidable mismatches in the THz beam optics. Differently from other calibration methods applied in the literature, our approach compares in time domain the ellipsometric derived electric field s- and p-polarised components at a given angle of incidence with the reconstructed ones, attained by using the complex dielectric function of a known sample. The calibrated response is determined with high precision by setting the system in transmission mode. In order to validate the technique, ellipsometric measurements have been carried out at various angle of incidences on a number of materials both in solid and liquid form, and their data compared with what obtained by conventional THz spectroscopy. Results show that THz-TDSE accompanied with an accurate calibration procedure is an effective technique for material characterization, especially in case of samples with a high absorption rate that are not easily investigated through transmission measurements
Reply to Comment on "nanoparticle Enhanced Laser-Induced Breakdown Spectroscopy for Microdrop Analysis at subppm Level"
Full text linkIn this paper, nanoparticle enhanced laser-induced breakdown spectroscopy (NELIBS) was applied to the elemental chemical analysis of microdrops of solutions with analyte concentration at subppm level. The effect on laser ablation of the strong local enhancement of the electromagnetic field allows enhancing the optical emission signal up to more than 1 order of magnitude, enabling LIBS to quantify ppb concentration and notably decreasing the limit of detection (LOD) of the technique. At optimized conditions, it was demonstrated that NELIBS can reach an absolute LOD of few picograms for Pb and 0.2 pg for Ag. The effect of field enhancement in NELIBS was tested on biological solutions such as protein solutions and human serum, in order to improve the sensitivity of LIBS with samples where the formation and excitation of the plasma are not as efficient as with metals. Even in these difficult cases, a significant improvement with respect to conventional LIBS was observed
Fundamental study and analytical applications of nanoparticle-enhanced laser-induced breakdown spectroscopy (NELIBS) of metals, semiconductors and insulators
No full textNanoparticle-Enhanced Laser-Induced Breakdown Spectroscopy (NELIBS) is a recently proposed method to efficiently increase the LIBS emission signal of metals up to 2 orders of magnitude, by depositing metal nanoparticles (NPs) on the sample surface (De Giacomo A, Gaudiuso R, Koral C, Dell’Aglio M, De Pascale O Anal Chem 85). This considerable emission enhancement has been ascribed to two effects: (1) an improvement in the ablation effect, and (2) a more efficient production of seed electrons by field emission, in turn due to the enhancement of the laser electromagnetic field induced by the NPs themselves (De Giacomo A, Gaudiuso R, Koral C, Dell’Aglio M, De Pascale O Acta Part B, 98)
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