Search

This article presents the measurements of the luminescence and scintillation under X-ray of undoped, Si-doped, and Si, B codoped gallium-arsenide (GaAs) samples at cryogenic temperature over a wide infrared (IR) region using Si and InGaAs photodetectors. The undoped GaAs has a narrow emission band at 838 nm (1.48 eV) and a low light output of about 2 ph/keV. The GaAs:Si has three broad luminescence bands at 830 nm (1.49 eV), 1070 nm (1.16 eV), and 1335 nm (0.93 eV) and a light output of about 67 ph/keV. GaAs:(Si, B) has four luminescence bands at 860 nm (1.44 eV), 930 nm (1.33 eV), 1070 nm (1.16 eV), and 1335 nm (0.93 eV) with a light yield of approximately 119 ph/keV. With advances in photodetection, GaAs promises to be a useful cryogenic scintillator for the detection of electron recoils from MeV/c2 dark matter.

Searches for dark matter axion involve the use of microwave resonant cavities operating in a strong magnetic field. Detector sensitivity is directly related to the cavity quality factor, which is limited, however, by the presence of the external magnetic field. In this paper we present a cavity of novel design whose quality factor is not affected by a magnetic field. It is based on a photonic structure by the use of sapphire rods. The quality factor at cryogenic temperature is in excess of $5 \times 10^5$ for a selected mode., 6 pages, 7 figures

In this work, we experimentally explore the possibility to realize a sensor whose basic building block is a laser cavity that hosts a target crystal for the incident ionizing radiation. Two possible detection mechanisms are considered: a process of coherent scintillation related to the rapid decay via stimulated emission of the excited atomic or molecular levels of the target material and the activation of states that absorb intracavity photons. We use a solid-state laser to study the dynamic response of our prototype sensor and the related intrinsic limitations and demonstrate capability to detect x-ray energy down to 10 GeV.

We investigated the possibility to use a liquid as insulator in a High Voltage generator which is wireless powered by a laser system. The liquid must be transparent to the laser light wavelength, must not attack the control circuits, which are immersed in it, and the support materials. An adequately performing liquid was identified and we characterized the liquid performance in intense electric field, by measuring its breakdown voltage and the leakage current, and checked its optical and thermal behaviour.

The emission spectrum of Erbium-doped fluoride crystals excited by soft X-rays in the (400–1700) nm wavelength range is investigated between 3.2 K and 300 K. The largest component of the crystals emission is observed in the infrared range, which corresponds to a light yield of several tens of photons/keV. Such a large value is caused by energy transfer processes between the Erbium ions which convert the excitation of a dopant ion at high energies into the emission of multiple infrared photons. The present results show that this mechanism could be exploited to realize scintillators of high light yield.

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., Comment: 15 pages, 5 figures, to be submitted to Journal of Luminescence

We demonstrate an all-optical method for manipulating the magnetization in a 1-mm YIG (yttrium-iron-garnet) sphere placed in a $\sim0.17\,$T uniform magnetic field. An harmonic of the frequency comb delivered by a multi-GHz infrared laser source is tuned to the Larmor frequency of the YIG sphere to drive magnetization oscillations, which in turn give rise to a radiation field used to thoroughly investigate the phenomenon. The radiation damping issue that occurs at high frequency and in the presence of highly magnetizated materials, has been overcome by exploiting magnon-photon strong coupling regime in microwave cavities. Our findings demonstrate an effective technique for ultrafast control of the magnetization vector in optomagnetic materials via polarization rotation and intensity modulation of an incident laser beam. We eventually get a second-order susceptibility value of $\sim10^{-7}$ cm$^2$/MW for single crystal YIG., 5 pages, 4 figures

The feasibility of an electron-polarized, active target to be used as detector in neutrino scattering experiments, suggested by several theoretical papers, has been investigated. We report on the properties of the paramagnetic crystal Gd2SiO5 (GSO), in which 7.7% of the total number of electrons present can be polarized by lowering the temperature and applying an intense external magnetic field. The material magnetic susceptibility has been measured down to cryogenic temperatures showing that for H¼ 5 T and T¼ 4 K about 80% of the maximum allowed magnetization can be attained. Also the spectral and time response of the crystal have been characterized and the scintillation process has been studied using a photomultiplier to measure the response to gamma rays irradiation and cosmic rays operating the GSO crystal at 13.5 K. An avalanche photodiode (APD) readout of the scintillation signal from the GSO crystal has also been performed, since the magnetic field-independent response of this device allows it to be placed close to the crystal in the cryogenic environment.

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., Comment: submitted to NIM A

A silicon p-i-n diode of thickness 1 cm has been studied experimentally at liquid helium temperature. This preliminary study is aimed at the construction of a much bigger detector to detect low energy neutrino events.

We show that a very thin conducting film (whose thickness can be much smaller than the skin depth), placed nearby a wall of an electromagnetic cavity, can produce the same shift of the resonance frequency as a bulk conducting slab, provided the displacement of the film from the wall is much bigger than the skin depth. We derive a simple analytical formula for the frequency shift and compare it with exact numerical calculations and experimental data.

Relative light yield (LY) dependence on temperature for Yb:YAG crystals containing 10% to 100% of Yb dopant is studied for γ and α excitation. The maximum LY is achieved at 120 K T K . LY=(13.5±2.5)×103 Ph/MeV at T=140 K for (Yb 25%) YAG. Linearity of the light output is checked. α/γ ratio is found to be 0.42±0.02. Pulse shapes induced by γ and α particles and cosmic rays are investigated by analysing a set of single events recorded. γ events are fast (τ

Ytterbium-doped yttrium aluminum garnets (Yb:YAG) are known as IR laser crystals. Previously, we have shown that they are also fast scintillators in the near UV region. In this work we report on the measurements of I R scintillation properties of Yb(10%):YAG crystal. It emits at room temperature at 1.03 mum with a light yield of (79+/-8) x 103 photons/MeV and a decay time of 1.9 ms when excited by 90 keV electrons. With decreasing temperature both light yield and decay time decrease. (C) 2001 Elsevier Science B.V. All rights reserved.

High count rate detectors are of particular interest in nuclear medicine as they permit lower radiation doses to be received by the patient and allow dynamic images of high statistical quality to be obtained.We have developed a high-speed gamma camera based on a multi-wire proportional chamber, The chamber is filled with a xenon gas mixture and has been operated at pressures ranging from 5 to 10 bar. With an active imaging area of 25 cm x 25 cm, the chamber has been equipped with an advanced, high rate, digital, electronic read-out system which carries out pulse shaping, energy discrimination, XY coincidence and cluster selection at speeds of up to a few megahertz. In order to ensure stable, long-term operation of the camera without degradation in performance, a gas purification system was designed and integrated into the camera. Measurements have been carried out to determine the properties and applicability of the camera using photon sources in the 20-120 keV energy range.We present some design features of the camera and selected results obtained from preliminary measurements carried out to measure its performance characteristics. Initial images obtained from the camera will also be presented. (C) 2002 Elsevier Science B.V. All rights reserved.

An InGaAs large area photodiode has been employed for detection of a-particles in the energy range of 0.412-5.5 MeV. W- value for InGaAs is determined. W = 2.94 +/- 0.16 eV. (C) 2000 Elsevier Science B.V. All rights reserved.

Infrared emission from CsI(TI) excited by similar to 70 keV electrons was detected with an InGaAs PIN photodiode, Some parameters of infrared scintillation were studied. The emission spectrum is located between 1.55 and 1.70 mu m with a maximum at 1.60 mu m. The light yield of infrared scintillation is (4.9 +/- 0.3) x 10(3) photons/MeV. Infrared scintillation caused by 3 MeV alpha-particles is detected as well. (C) 2000 Elsevier Science B.V. All rights reserved.

We report on our efforts to give direct limits to the existence of forces other than gravitational ones in the submillimetre range. The technique used involves looking at the expected shifts to the resonant frequency of microresonators whose motion is monitored through a fibre optic interferometer.

We present a preliminary study to develop a large area photodetector, based on a semiconductor crystal placed inside a superconducting resonant cavity. Laser pulses are detected through a variation of the cavity impedance, as a consequence of the conductivity change in the semiconductor. A novel method, whereby the designed photodetector is simulated by finite element analysis, makes it possible to perform pulse-height spectroscopy on the reflected microwave signals. We measure an energy sensitivity of 100 fJ in the average mode without the employment of low noise electronics and suggest possible ways to further reduce the single-shot detection threshold, based on the results of the described method.

We report about a novel technique to generate microwave radiation by the irradiation of a nonlinear optical crystal with uniformly spaced, ultrashort optical pulses delivered by a mode-locked laser. We study systematically the laser polarization and intensity dependence of the microwave signal to conclusively show that it is a nonlinear phenomenon and that it originates from optical rectification. The measurements have been conducted using KTP, LBO and ZnSe crystals. The observed pulsed microwave signals are harmonically related to the laser pulses repetition rate, a feature that can be exploited to develop an innovative ultrafast laser detector.

The feasibility of fully floating high voltage (HV) generation was demonstrated producing a prototype of a modular HV system. The primary power source is provided by a high efficiency semiconductor power cell illuminated by a laser system ensuring the floating nature of each module. The HV is then generated by dc-dc conversion and a HV multiplier. The possibility of series connection among modules was verified.

A high voltage generator built by a series connection of 100 kV modules was produced. The series connection feasibility is ensured by the inherent floating character of each module which is wireless powered by high efficiency photovoltaic cells illuminated by a laser system. Each module is equipped with a control and monitoring board allowing excellent stabilization of the high voltage output. The performance of the system in terms of reliability, stability, and efficiency was evaluated. In particular using a three module setup, we achieved a maximum voltage of 234 kV with stability better than 0.1%.

In this paper we present theoretical and experimental studies of the modifications of the thermal spectrum inside a microwave resonator due to a parametric amplification process. Both the degenerate and nondegenerate amplifiers are discussed. Theoretical calculations are compared with measurements performed with a microwave cavity parametric amplifier

In this paper, we present the experimental study of a single-mode thermal field carried out using a microwave parametric amplifier tuned at 1.5 GHz and working at room temperature. The parametric amplifier is based on a variable capacitance diode placed inside a microwave resonant cavity. The measured distribution of the thermal photons inside the resonator follows the expected Bose–Einstein distribution probability.

The use of radio frequencies (RF) superconducting re-entrant cavities has been suggested in the framework of some research to detect photon generation from the vacuum, due to the dynamical Casimir effect. A thin semiconducting slab, put inside the cavity, will be excited by a train of laser pulses of a frequency twice the resonant frequency of the cavity, so that a periodic modulation of the dielectric constant of the slab will be realized. In order to produce a RF cavity that can safely work at temperatures larger than 4 K, we have designed and constructed a MgB2 re-entrant cavity having a resonant frequency in the range of 2-3 GHz. The cavity is made by a cylindrical cup of about 40 mm of internal diameter and 40 mm of height and on its base is standing a cylindrical coaxial nose on which the semiconductor slab will be deposited. The details of the construction of the MgB2 cavity will be presented as well as the measurements of its quality factor, as a function of the temperature.

We describe recent improvements in the development of the high power laser system used in the motion induced radiation (MIR) experiment to amplify electromagnetic fields inside a microwave cavity. The improvements made on the oscillator stabilization, the pulse train shaping device, and the spatial beam uniformity are reported.

We detected the infrared light (at wavelength about 1 mum) emitted in an Ar-Xe gaseous mixture during the multiplication process near a thin wire and measured the light signal dependence on gas pressure and wire gain. (C) 2001 Elsevier Science B,V. All rights reserved.

Light yield and spectrum of infrared (IR) scintillation in Xe are different in gaseous and liquid phases. In gas, the spectrum consists mainly of a broad line centered at 1300 nm. In liquid, light is emitted primarily below 1200 nm and with a lower yield. (C) 2001 Elsevier Science B.V. All rights reserved.

We report on measurements of the light yield, emission spectrum, and time response of YAG:Yb crystals. The temperature dependence of light yield was investigated. Data show that YAG:Yb crystals are good scintillators, suitable for applications to neutrino detection and spectroscopy. (C) 2001 Elsevier Science B.V. All rights reserved.

In this work we present measurements of the sensitivity of a low noise microwave receiver developed with the aim to detect a feeble quantum electrodynamics effect known as dynamical Casimir effect. We study the performance of the receiver when it is connected to a transmission line ending with an antenna coupled to a resonant microwave cavity. The noise temperature of the receiver is measured with the method of the variable temperature load resistor. The noise generated by the cavity is measured in a similar way. An equivalent input noise of ( 2.0 ± 0.2 ) × 10 - 22 W / Hz is measured at the receiver input. This is equivalent to a sensitivity of approximately 100 photons, well below the expected signal from the quantum vacuum photons.

In this paper we report the status of the experiment MIR (Motion Induced Radiation), aimed at the experimental verification of the dynamical Casimir effect. The stringent theoretical requirements to observe the effect are satisfied in a scheme in which the conductivity of a semiconductor inside a superconducting microwave resonant cavity is varied in time. Free carriers in the semiconductor are periodically excited and recombine at 5 GHz. In this process vacuum and thermal photons are parametrically amplified in a time interval of 200-500 ns.

We have carried out a systematic study of the electron multiplication in liquid argon on an array of 52 sharp tips. We found a multiplication factor for a single tip of at least 100 and a plateau region in the counting-rate vs tip-voltage curve of about 150 V. The results make us hopeful in exploiting such mechanism for a new kind of detectors.

In this paper, the status of the experiment MIR (motion induced radiation) is reported. This experiment aims at measuring for the first time the dynamical Casimir effect by using an effective motion of a wall of a superconducting microwave resonant cavity. Effective motion is produced by periodic illumination of a semiconductor slab by means of an ultra-high-frequency amplitude modulated laser.

We report new measurements of the linear polarization of thermal radiation emitted by incandescent thin tungsten wires, with thicknesses ranging from five to hundred microns. Our data show very good agreement with theoretical predictions, based on Drude-type fits to measured optical properties of tungsten., Comment: 12 pages, 4 encapsulated figures. This new version matches the one published in New. J. Phys.. Improved presentation, more references added, and one new figure included

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.

Several massive silicon and germanium home-made detectors, working at cryogenic temperature, have been studied. They are the benchmarking schemes to check the possibility of realizing a semiconductor time projection chamber that could have various interesting applications in weak interaction problems. Reported here are the first results on investigations of charge collection efficiency and metal–semiconductor contact hardness. The leakage current, total depletion voltage and alpha or gamma spectroscopy are presented.

According to QED a metallic mirror set in motion in quantum vacuum gives rise to “dissipated” energy in the form of real photons. This phenomenon, called dynamical Casimir effect, has never been observed due to unsolved technical difficulties: in order to obtain an experimentally measurable number of photons from vacuum fluctuations a reflecting surface has in fact to vibrate at very high frequencies (≃109 Hz). As these frequencies are too high to be achieved with a purely mechanical oscillation, our idea is to switch an effective microwave mirror on and off at very short intervals of time changing the reflectivity of a semiconductor layer by shining a pulsed laser beam on its surface. The first step to study the feasibility of this technique is to show that a semiconductor slab when illuminated by a laser behaves indeed as a metal. This article presents the measurements that confirm this demand, obtained by uniformly illuminating large (several square centimeters) surfaces of silicon and GaAs.

Nearly massless particles coupling weakly to two photons constitute suitable candidates as dark matter components: experimental searches investigating this effect by optical techniques have recently been conducted. PVLAS is an experiment designed to measure the vacuum magnetic birefringence and to improve the detection sensitivity for the above particles. It is based on a very sensitive ellipsometer and a 9 T superconducting dipole magnet especially developed for this purpose. With a sensitivity of about 10−8 rad/√Hz and an integration time of 106 s we plan to be able to detect a dichroism corresponding to the production of particles with a coupling constant to two photons of 10-8 GeV-1, provided that particles masses are less than 10−3 eV. With our experimental parameters, the vacuum birefringence effect would give to an ellipticity of 10−11 rad

The infrared scintillation yield from gaseous xenon excited by an α source has been measured in the wavelenght range 0.7–1.6 μm. The infrared light yield has been found to be ≥2.1×104 ph/ MeV.

We present experimental results on infrared emission induced by protons in some solid-state samples, Infrared scintillation occurs ill many crystals, with different yield values and time-response behaviours, A rough measurement of the emission wavelength of CsI(TI) is also reported, (C) 2000 Elsevier Science B.V. All rights reserved

We report on the design of a new type of electron gun to be used for experiments of infrared emission spectroscopy of rare gas excimers. It is based on a filament heated by means of a pack of rechargeable batteries floated atop the high-voltage power supply. The filament current is controlled by a feedback circuit including a superluminescent diode decoupled from the high voltage by means of an optical fiber. Our experiment requires that the charge injection is pulsed and constant and stable in time. This electron gun can deliver several tens of nC per pulse of electrons of energy up to $100\,$keV into the sample cell. This new design eliminates ripples in the emission current and ensures up to 12 hrs of stable performance., Comment: 1o pages, 8 figures, to be submitted to Review of Scientific Instruments

In 1948 Hendrick Casimir published a short article predicting that (neutral) ideal metallic plates attract each other. This attraction is widely ascribed to the quantum vacuum fluctuations of the electromagnetic field (even though away from the limit of ideal metals it depends demonstrably on the physics of the charge carriers vanishing when they cease to carry). Casimir's remarkable discovery, nowadays called the Casimir effect, has charmed several generations of physicists. In the last decade alone, more than a thousand publications have addressed its many consequences, generalizations, and possible applications in different areas from particle physics to cosmology. Interest in the field is still growing driven by impressive progress in experimental skills and its importance for the recently opened-up area of micro- and nano-electromechanical systems: according to the Thompson ISI Web of Science database, in 2005 the number of papers related to the Casimir effect or to Casimir forces jumped to over 125, compared to approximately 60 in 2000 and 30 in 1995. The increase continues, with more than 170 papers in 2008. The International Workshop '60 Years of the Casimir Effect' took place on 23–27June 2008, in Brasilia (Brazil) organized by the International Center for Condensed Matter Physics (ICCMP). The purpose was to celebrate this anniversary of Casimir's pioneering paper by inviting the leading specialists in the area, both theorists and experimentalists, together with young researchers and post-graduate students interested in hearing about the most recent achievements in the field. The Workshop was attended by 65 participants from 14 countries, who presented 41 talks and 12 posters. These Proceedings contain extended versions of almost all the talks and some posters, plus several papers by authors who had planned to attend but for various reasons could not. The contributions are divided (with some inevitable arbitrariness) into four groups. The largest one consists of work devoted to the current status of the theory and measurements related to Casimir forces. Readers must be warned that some topics in this field of research remain controversial (especially the dependence on temperature): they can and do generate debates that sometimes become quite heated. These controversies are reflected in the papers. We believe that at present it is not the business of conference organisers to adjudicate such issues, and hope that detailed expositions of different approaches and different points of view will help readers to formulate their own, and will eventually lead to a better understanding of the problems and of the solutions proposed. The other three groups contain contributions bearing on (1) topics related to causes and consequences of Casimir effects in quantum field theory and gravitation; (2) the so-called dynamical (or nonstationary) Casimir effect and motion-induced radiation, (3) some new manifestations and applications of the Casimir effect. We are grateful to the authors for making their papers so interesting; to the referees for their careful reading of the initial versions, and for their many helpful comments and suggestions; to the Institute of Physics for its kindness in offering to publish these Proceedings in Journal of Physics: Conference Series; and to the Institute of Physics office at the Lebedev Physical Institute in Moscow for essential help in the preparation of this volume. On behalf of the participants of the workshop, we thank the direction and staff of the ICCMP for their splendid organization of the event. Finally we acknowledge the support of the Brazilian scientific funding agencies FAP-DF and CNPQ, which covered the local and travel expenses of many participants. The Editors Gabriel Barton (University of Sussex, Brighton, UK) Giovanni Carugno (INFN - Sezione di Padova, Italy) Victor Dodonov (University of Brasilia, Brazil) Margarita Man'ko (Lebedev Physical Institute, Moscow, Russia) Workshop Organizers Gabriel Barton and Victor Dodonov International Advisory Committee of the Workshop Michael Bordag (Leipzig, Germany) Giovanni Carugno (Padova, Italy) Emilio Elizalde (Barcelona, Spain) Francisco Mazzitelli (Buenos Aires, Argentina) Kimball Milton (Norman, USA) Vladimir Mostepanenko (St Petersburg, Russia) Serge Reynaud (Paris, France)

An experimental set-up for the measurement of the Casimir effect at separations larger than a few microns is presented. The apparatus is based on a mechanical resonator and uses a homodyne detection technique to sense the Casimir force in the plane-parallel configuration. First measurements in the 3-10 micrometer range show an unexpected large force probably due to patch effects., Proceedings of the workshop On the 60 Years on Casimir Effect

We describe the principle and the status of the PVLAS experiment which is being assembled at INFN Laboratori Nazionali di Legnaro (Legnaro, Padua, Italy) to look for coherent effects, related to the QED vacuum structure, on the propagation of a polarized light beam in a strong magnetic field.