Fast, multi-band photon detectors based on quantum well devices for beam-monitoring in new generation light sources

In order to monitor the photon-beam position for both diagnostics and calibration purposes, we have investigated the possibility to use InGaAs/InAlAs Quantum Well (QW) devices as position-sensitive photon detectors for Free-Electron Laser (FEL) or Synchrotron Radiation (SR). Owing to their direct, low-energy band gap and high electron mobility, such QW devices may be used also at Room Temperature (RT) as fast multi-band sensors for photons ranging from visible light to hard X-rays. Moreover, internal charge-amplification mechanism can be applied for very low signal levels, while the high carrier mobility allows the design of very fast photon detectors with sub-nanosecond response times. Segmented QW sensors have been preliminary tested with 100-fs-wide 400 nm laser pulses and X-ray SR. The reported results indicate that these devices respond with 100 ps rise-times to such ultra-fast laser pulses. Besides, linear scan on the back-pixelated device has shown that these detectors are sensitive to the position of each ultrashort beam bunch

First results of a novel Silicon Drift Detector array designed for low energy X-ray fluorescence spectroscopy

We developed a trapezoidal shaped matrix with 8 cells of Silicon Drift Detectors (SDD) featuring a very low leakage current (below 180 pA/cm2 at 20 \ub0C) and a shallow uniformly implanted p+ entrance window that enables sensitivity down to few hundreds of eV. The matrix consists of a completely depleted volume of silicon wafer subdivided into 4 square cells and 4 half-size triangular cells. The energy resolution of a single square cell, readout by the ultra-low noise SIRIO charge sensitive preamplifier, is 158 eV FWHM at 5.9 keV and 0 \ub0C. The total sensitive area of the matrix is 231 mm2 and the wafer thickness is 450\u3bcm. The detector was developed in the frame of the INFN R&D project ReDSoX in collaboration with FBK, Trento. Its trapezoidal shape was chosen in order to optimize the detection geometry for the experimental requirements of low energy X-ray fluorescence (LEXRF) spectroscopy, aiming at achieving a large detection angle. We plan to exploit the complete detector at the TwinMic spectromicroscopy beamline at the Elettra Synchrotron (Trieste, Italy). The complete system, composed of 4 matrices, increases the solid angle coverage of the isotropic photoemission hemisphere about 4 times over the present detector configuration. We report on the layout of the SDD matrix and of the experimental set-up, as well as the spectroscopic performance measured both in the laboratory and at the experimental beamline. \ua9 2015 Elsevier B.V

The Low Density Matter (LDM) beamline at FERMI: Optical layout and first commissioning

The Low Density Matter (LDM) beamline has been built as part of the FERMI free-electron laser (FEL) facility to serve the atomic, molecular and cluster physics community. After the commissioning phase, it received the first external users at the end of 2012. The design and characterization of the LDM photon transport system is described, detailing the optical components of the beamline

An ASIC for multichannel data acquisition systems

In this paper, we describe the realization of an ASIC which may signi"cantly simplify the instrumental apparatus for measures in UHV (ultra-high vacuum, p410~9 mbar) while permitting very fast acquisitions. The chip will "rst be used in ESCA experiments; however, its parallel architecture and the fast serial protocol for data transmission may increase the e$ciency of the measure process in any experiment where multichannel acquisition is a key issue

Meso-Pancreatectomy: New Surgical Technique for Wirsung Reconstruction

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Synchrotron Radiation Study of Gain, Noise, and Collection Efficiency of GaAs SAM-APDs with Staircase Structure

In hard X-ray applications that require high detection efficiency and short response times, such as synchrotron radiation-based Mössbauer absorption spectroscopy and time-resolved fluorescence or photon beam position monitoring, III–V-compound semiconductors, and dedicated alloys offer some advantages over the Si-based technologies traditionally used in solid-state photodetectors. Amongst them, gallium arsenide (GaAs) is one of the most valuable materials thanks to its unique characteristics. At the same time, implementing charge-multiplication mechanisms within the sensor may become of critical importance in cases where the photogenerated signal needs an intrinsic amplification before being acquired by the front-end electronics, such as in the case of a very weak photon flux or when single-photon detection is required. Some GaAs-based avalanche photodiodes (APDs) were grown by a molecular beam epitaxy to fulfill these needs; by means of band gap engineering, we realised devices with separate absorption and multiplication region(s) (SAM), the latter featuring a so-called staircase structure to reduce the multiplication noise. This work reports on the experimental characterisations of gain, noise, and charge collection efficiencies of three series of GaAs APDs featuring different thicknesses of the absorption regions. These devices have been developed to investigate the role of such thicknesses and the presence of traps or defects at the metal–semiconductor interfaces responsible for charge loss, in order to lay the groundwork for the future development of very thick GaAs devices (thicker than 100 [Formula: see text] m) for hard X-rays. Several measurements were carried out on such devices with both lasers and synchrotron light sources, inducing photon absorption with X-ray microbeams at variable and controlled depths. In this way, we verified both the role of the thickness of the absorption region in the collection efficiency and the possibility of using the APDs without reaching the punch-through voltage, thus preventing the noise induced by charge multiplication in the absorption region. These devices, with thicknesses suitable for soft X-ray detection, have also shown good characteristics in terms of internal amplification and reduction of multiplication noise, in line with numerical simulations

A two-dimensional detector for pump-and-probe and time resolved experiments

We present a new bidimensional detector setup, based on cross delay line technology, specifically developed for time resolved experiments and particularly suited to work in conjunction with pump-and-probe systems. Thanks to the particular architecture of the acquisition electronics, the detector is able to correlate each event with the time it occurred in a way which preserves the picoseconds time resolution of pump-and-probe techniques and, more generally, can perform time resolved acquisition in the nanosecond or picoseconds scale. The acquisition setup count rate, up to more than 4 Mcounts/s in time resolved mode, exceeds the performances of the best two-dimensional detectors working in counting mode presently available on electron analysers. First experimental results, obtained both on bench tests and in UHV conditions, where the detector has been mounted on an electron analyser, confirm the validity of the approach and show the potentiality of time resolved acquisition applied to electron spectroscopy analysis

Investigation of the behaviour of GaAs/AlGaAs SAM-APDs for synchrotron radiation

11noThis work reports on the fabrication and characterization of a novel high-speed, low-noise X-ray Avalanche Photodiode based on III-V compound semiconductors operating over an extended photon energy range. These materials were suggested as their higher atomic numbers allow for the absorption of higher photon energies; hence, shorter response times can be achieved by growing APDs with thinner active regions. In addition, the use of staircase hetero-junctions enhances electron multiplication and results in lower noise if compared with conventional p-i-n diodes. In this work, molecular beam epitaxy was used to produce GaAs/AlGaAs APDs with separated absorption and multiplication regions. The multiplication region, separated from the absorption region by a δ p-doped layer of carbon, contains a staircase structure composed of nanometric layers of AlGaAs and GaAs, which alternate periodically. The periodic modulation of the band gap enables a well-defined charge multiplication and results in low multiplication noise. Several devices were characterized in terms of dark current, photocurrents generated utilizing visible and hard X-ray sources as well as noise generated under laser light.openopenNichetti, Camilla; Steinhartova, Tereza; Antonelli, Matias; Cautero, Giuseppe; Menk, Ralf Hendrik; Pilotto, Alessandro; Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca; Arfelli, Fulvia; Biasiol, GiorgioNichetti, Camilla; Steinhartova, Tereza; Antonelli, Matias; Cautero, Giuseppe; Menk, Ralf Hendrik; Pilotto, Alessandro; Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca; Arfelli, Fulvia; Biasiol, Giorgi

Experimental Characterization of Separate Absorption–Multiplication GaAs Staircase Avalanche Photodiodes under Continuous Laser Light Reveals Periodic Oscillations at High Gains

In this work, we experimentally analyze the periodic oscillations that take place in staircase APDs with separate absorption and multiplication regions when operating under continuous laser light. These oscillations increase in frequency when the APD gain increases. We have verified that they are not affected by the parameters (gain and bandwidth) of the transimpedance amplifier, and thus originate inside the APD. The phenomenon is analyzed systematically by considering devices with different thicknesses of the absorption region. Possible physical interpretations related to the flux of holes generated by impact ionization are provided