arXiv subjects

A. F. Borghesani

Publications and source records attributed to A. F. Borghesani.

At least 19 recordsLinked to original sources

arXiv2026

Evidence for multiple scattering effects in the electron mobility in dense argon gas

We report measurements of the electron drift mobility in dense argon gas over an extended range of densities, temperatures, and electric fields, supplementing our earlier work. The measurements confirm the validity of the heuristic model we previously developed by introducing multiple scattering effects in the classical kinetic theory description of the electron mobility in a dilute gas. We definitively show that, in the argon gas, because of the particular energy dependence of its electron-atom momentum-transfer scattering cross section, none of the multiple scattering effects we have identified in the past can be neglected if the mobility behavior is to be accurately rationalized over the whole investigated parameter range.

physics.plasm-ph↗

arXiv2023

Electron thermalization length in solid para-hydrogen at low-temperature

We report the first ever measurements of the thermalization length of low-energy electrons injected into solid para-hydrogen at a temperature $T\approx 2.8\,$K. The use of the pulsed Townsend photoinjection technique has allowed us to investigate the behavior of quasi-free electrons rather than of massive, slow negative charges as reported in all previous literature. We have found an average thermalization length $\langle z_0\rangle\approx 260\,$Å which is 3 to 5 times longer than that in liquid helium at the same temperature.

physics.chem-ph↗

arXiv2022

Validation of the Heuristic Model for the Electron Mobility in Dense Helium Gas

The investigation of the mobility $μ$ of quasi-free electrons in dense, cold helium gas as a function of its density $N$ is made difficult by the fact that a significant fraction of electrons is localized in low mobility bubbles. The measured mobility is a weighted average of the contributions of the slow electron bubbles, whose mobility is determined by hydrodynamics, and of the fast quasi-free electrons. A precise description of the fast electron mobility is thus required. In the past we have developed a heuristic model that proved succesful at rationalizing the electron mobility in argon and neon gases. In order to validate it, we have carried out new accurate %electron mobility measurements in helium gas in the temperature range $\textbf{26} \, \text{K} < \text{\em T} < \textbf{300}\,$K at densities, in which the presence of localized states is negligible. The analysis of these new data confirms the validity of the model.

physics.chem-ph↗

arXiv2019

Influence of irreversible demagnetization on the polarization of thermal radiation emitted by a hot cobalt wire

thermal radiation emitted by a %hot cobalt wire in the temperature range from $T\approx 400\,$K up to melting. The radiation is linearly polarized perpendicular to the wire. $P$ decreases from $30\,\%$ just above room temperature down to $6.5\,\%$ near melting and does not show any particular behavior neither at the martensitic {\em hcp}$-${\em fcc} transition at $\approx 700\,$K nor at the Curie point at $ \approx 1400\,$K. However, $P$ shows a rapid decrease for $T\gtrsim 1000\,$K and, contrary to previous measurements with tungsten wires, it hysteretically behaves if the temperature change is reversed. This behavior is rationalized by %taking into account accounting for the irreversible thermal demagnetization of the wire with magnetic domain size change.

cond-mat.mtrl-sci↗

arXiv2019

Resonant low-energy electron attachment to O$_{2}$ impurities in dense neon gas

We report measurements of resonant low-energy electron attachment to O$_2$ molecular impurities in neon gas in the temperature range $46.5\,\mbox{K}\le T\le 101\,\mbox{K}$. The reduced attachment frequency $ν_A/N$ shows a well defined peak as a function of the gas density $N$ when the electron energy is resonant with the 4th vibrational level of O$_2^-$. For $46.5\,\mbox{K}\le T\le 48.4\,$K a second peak has been detected at a much higher density, which is due to the formation of ions in the 5th vibrational level. The temperature dependence of the first peak position can be explained within an ionic bubble model by computing the electron excess free energy as a function of $T$ and $N$. The peak shape is rationalized by taking into account the density dependent shift of the electron energy distribution function and the density of states of excess electrons in a disordered medium, and by assuming that electrons sample the gas density over a region of the order of the ionic bubble radius.

physics.plasm-ph↗

arXiv2019

O2- Ion Mobility in Dense Ne Gas: the Free Volume Model

We report data of the O2- ion mobility in neon gas over broad density and temperature ranges along with its theoretical description in terms of the thermodynamic, free volume model that has successfully been adopted for the interpretation of electron and ion mobility in superfluid and normal helium. The free volume model, which is aimed at computing the free volume accessible for the ion motion, along with the Millikan- Cunningham slip factor correction, is able to describe the ion mobility in the crossover region connecting the dilute gas regime described by the classical Kinetic Theory to the high density region ruled by the laws of hydrodynamic transport.

physics.chem-ph↗

arXiv2018

Infrared and visible scintillation of Ho$^{3+}$-doped YAG and YLF crystals

In our effort to develop a new kind of detector for low-energy, low-rate energy deposition events we have investigated the cathodo- and radioluminescence of Ho:YAG and Ho:YLF single crystals in an extended wavelength range from $200\,$nm to $2200\,$nm. The emission spectra of both crystals show a much more intense emission in the infrared range than in the visible one. We estimate an infrared light yield of $40\,$photons/keV when exciting the crystals with X-rays of energy $\approx 30\,$keV. The main reason of this high value is due to the Ho$^{3+}$ ions energy levels scheme that allows efficient cross relaxation processes to occur even at low dopant concentration.

physics.atom-ph↗

arXiv2017

Molecular Dynamics Simulations of the O2- Ion Mobility in Dense Ne Gas at Low Temperature: Influence of the Repulsive Part of the Ion-Neutral Interaction Potential

New Molecular Dynamics simulations have been carried out in order to get an insight on the physical mechanisms that determine the drift mobility of negative Oxygen ions in very dense Neon gas in the supercritical phase close to the critical point. Two ion-neutral interaction potentials have been used that differ by their repulsive part. We have observed that the potential with a harder repulsive part gives much better agreement with the experimental data. The differences with the softer repulsive potential previously used are discussed. We propose that the behavior of the ion mobility as a function of the gas density is related to the number of neutral atoms loosely bound in the first solvation shell around the ion.

physics.chem-ph↗

arXiv2017

Cathodo- and radioluminescence of Tm$^{3+}$:YAG and Nd$^{3+}$:YAG in an extended wavelength range

We have studied the cathodo- and radioluminescence of Nd:YAG and of Tm:YAG single crystals in an extended wavelength range up to $\approx 5\,μ$m in view of developing a new kind of detector for low-energy, low-rate energy deposition events. Whereas the light yield in the visible range is as large as $\approx 10^{4}\,$photons/MeV, in good agreement with literature results, in the infrared range we have found a light yield $\approx 5\times 10^{4}\,$photons/MeV, thereby proving that ionizing radiation is particularly efficient in populating the low lying levels of rare earth doped crystals.

physics.optics↗

arXiv2017

Molecular Dynamics Simulations of the O2- Ion Mobility in Dense Neon Gas

We report here the results of Molecular Dynamics simulations of the drift mobility of negative oxygen ions in very dense neon gas in the supercritical phase. The simulations relatively well reproduce the trend of the experimental data. The rationalization of the mobility behavior as a function of the gas density is given in terms of the number of atoms correlated in the first solvation shell around the ion.

physics.chem-ph↗

arXiv2016

A new technique for infrared scintillation measurements

We propose a new technique to measure the infrared scintillation light yield of rare earth (RE) doped crystals by comparing it to near UV-visible scintillation of a calibrated Pr:(Lu$_{0.75}$Y$_{0.25}$)$_{3}$Al$_5$O$_{12}$ sample. As an example, we apply this technique to provide the light yield in visible and infrared range up to \SI{1700}{nm} of this crystal.

physics.ins-det↗

arXiv2016

Microwave emission by nonlinear crystals irradiated with a high-intensity, mode-locked laser

We report on the experimental investigation of the efficiency of some nonlinear crystals to generate microwave (RF) radiation as a result of optical rectification (OR) when irradiated with intense pulse trains delivered by a mode-locked laser at $1064\,$nm. We have investigated lithium triborate (LBO), lithium niobate (LiNbO$_3$), zinc selenide (ZnSe), and also potassium titanyl orthophosphate (KTP) for comparison with previous measurements. The results are in good agreement with the theoretical predictions based on the form of the second-order nonlinear susceptibility tensor. For some crystals we investigated also the second harmonic generation (SHG) to cross check the theoretical model. We confirm the theoretical prediction that OR leads to the production of higher order RF harmonics that are overtones of the laser repetition rate.

physics.optics↗

arXiv2015

Particle detection through the quantum counter concept in YAG:Er$^{3+}$

We report about a novel scheme for particle detection based on the infrared quantum counter concept. Its operation consists of a two-step excitation process of a four level system, that can be realized in rare earth-doped crystals when a cw pump laser is tuned to the transition from the second to the fourth level. The incident particle raises the atoms of the active material into a low lying, metastable energy state, triggering the absorption of the pump laser to a higher level. Following a rapid non-radiative decay to a fluorescent level, an optical signal is observed with a conventional detectors. In order to demonstrate the feasibility of such a scheme, we have investigated the emission from the fluorescent level $^4$S$_{3/2}$ (540 nm band) in an Er$^{3+}$-doped YAG crystal pumped by a tunable titanium sapphire laser when it is irradiated with 60 keV electrons delivered by an electron gun. We have obtained a clear signature this excitation increases the $^{4}I_{13/2}$ metastable level population that can efficiently be exploited to generate a detectable optical signal.

physics.ins-det↗

arXiv2015

Temperature dependent polarization of the thermal radiation emitted by thin, hot tungsten wires

We report measurements of the temperature $T $ dependence of the linear polarization $\langle P\rangle $ of the thermal radiation emitted by thin, incandescent tungsten wires. We investigated an interval ranging from a little above room temperature up to melting, $T_m\approx 3700\,$K. These are the first measurements in such wide a range. We found that $\langle P\rangle $ decreases with increasing $T.$ We obtained a satisfactory agreement with the theoretical predictions based on the Kirchhoff's law by using a Drude-type formula for the optical properties of tungsten. The validity of such formula is assessed in literature for $T\leq 2400 \,$K and for wavelengths in the range from visible up to $λ\approx 2.6\,μ$m. We have extended the range of validity of this formula for $T$ up to $T_m$ and for $λ$ up to $\approx 12\,μ$m.

physics.optics↗

arXiv2014

A contactless microwave-based diagnostic tool for high repetition rate laser systems

We report on a novel electro-optic device for the diagnostics of high repetition rate laser systems. It is composed of a microwave receiver and of a second order nonlinear crystal, whose irradiation with a train of short laser pulses produces a time-dependent polarization in the crystal itself as a consequence of optical rectification. This process gives rise to the emission of microwave radiation that is detected by a receiver and is analyzed to infer the repetition rate and intensity of the pulses. We believe that this new method may overcome some of the limitations of photodetection techniques.

physics.optics↗

arXiv2013

Electron swarm experiments in dense rare gases: a review

Swarm techniques have largely been used to investigate electron transport in very dilute gases in order to shed light on the electron-atom (molecule) scattering cross section and, hence, on the interaction potential. The theoretical basis for the analysis of these experiments is classical Kinetic Theory. However, electron transport in dense media, either in gaseous- or condensed phase, is a physical phenomenon of fundamental and practical interest. Dense rare gases are model systems for disordered media. They are particularly well suited to investigate how the dynamics and energetics of quasifree electrons change as the environment density is gradually increased. A review on the electron swarm experiments in dense rare gases is presented here.

physics.plasm-ph↗

arXiv2013

Generation of microwave radiation by nonlinear interaction of a high-power, high-repetition rate, 1064-nm laser in KTP crystals

We report measurements of microwave (RF) generation in the centimeter band accomplished by irradiating a nonlinear KTiOPO$_4$ (KTP) crystal with a home-made, infrared laser at $1064\,$nm as a result of optical rectification (OR). The laser delivers pulse trains of duration up to $1\,μ$s. Each train consists of several high-intensity pulses at an adjustable repetition rate of approximately $ 4.6\,$GHz. The duration of the generated RF pulses is determined by that of the pulse trains. We have investigated both microwave- and second harmonic (SHG) generation as a function of the laser intensity and of the orientation of the laser polarization with respect to the crystallographic axes of KTP.

physics.optics↗

arXiv2012

Collection efficiency of photoelectrons injected into near- and supercritical argon gas

Injection of photoelectrons into gaseous or liquid dielectrics is a widely used technique to produce cold plasmas in weakly ionized systems for investigating the transport properties of electrons. We report measurements of the collection efficiency of photoelectrons injected into dense argon gas for $T=152.7 $K, close to the critical temperature $T_{c}\approx 150.9 $K, and for $T=200.0 $K. The high-field data agree with the Young-Bradbury model and with previous measurements below $T_{c}$ and at an intermediate temperature above $T_c .$ The effective, density-dependent electron-atom momentum transfer scattering cross section can be deduced. However, the weak-field data near $T_{c}$ show large deviations from the theoretical model. We show that the electron behavior at weak field is influenced by electrostriction effects that are only important near the critical point.

physics.chem-ph↗