BEaTriX (Beam Expander Testing X-ray facility) is the new facility available at the INAF-Osservatorio Astronomico Brera (Merate, Italy) for the calibration of X-ray optics. Specifically designed to measure the point spread function (PSF) and the effective area (EA) of the mirror modules (MM) of the ATHENA X-ray telescope at their production rate, BEaTriX gives the unique possibility to test the optics with a source that approximate an astronomical source, i.e. with a large, parallel X-ray beam (170 × 60 mm2) that fully covers the entrance pupil of the MM. For a fast and precise testing, BEaTriX is a compact facility (9 × 18 m2) with fast vacuum pump-down (to 10-6 mbar), and an optical setup able to create the X-ray beam with a residual divergence of about 2-3 arcsec, HEW, and with a flux of 60 photons/s/cm2. The first beam line at the energy of 4.51 keV is now operative, and a second beam line, working at the energy of 1.49 keV, will be implemented in the coming future. The unique characteristics of the BEaTriX X-ray beam are obtained with an X-ray microfocus source placed in the focus of a paraboloidal mirror, a monochromation stage with 4 symmetrically cut crystals, and an expansion stage where the beam is diffracted and expanded by an asymmetrically-cut crystal. The beam, reflected by the MMs, is then imaged at 12 m distance, where a directly-illuminated CCD camera is placed. This paper presents the facility, the calibration of the beam and the latest results with the ATHENA MMs.
The BEaTriX (Beam Expander Testing X-ray) facility is now operative at the INAF-Osservatorio Astronomico Brera (Merate, Italy). This facility has been specifically designed and built for the X-ray acceptance tests (PSF and Effective Area) of the ATHENA Silicon Pore Optics (SPO) Mirror Modules (MM). The unique setup creates a parallel, monochromatic, large X-ray beam, that fully illuminates the aperture of the MMs, generating an image at the ATHENA focal length of 12 m. This is made possible by a microfocus X-ray source followed by a chain of optical components (a paraboloidal mirror, 2 channel cut monochromators, and an asymmetric silicon crystal) able to expand the X-ray beam to a 6 cm × 17 cm size with a residual divergence of 1.5 arcsec (vertical) × 2.5 arcsec (horizontal). This paper reports the commissioning of the 4.5 keV beam line, and the first light obtained with a Mirror Module.
BEaTriX (beam expander testing x-ray) is the compact (18m×9m) x-ray facility being implemented at INAF for the acceptance tests of the ATHENA silicon pore optics mirror modules (MM) working at the two energies of 1.49 and 4.51 keV. It adopts an innovative design based on a collimating mirror and Bragg crystals in proper configuration to provide a large and parallel beam. The 4.51 keV line provides a parallel beam with 170 mm×60 mm size and it has been calibrated and characterized in terms of intensity, uniformity, divergence and stability. This paper traces the path taken for the best-achieved alignment of the different optical components, from the preliminary phases to the final step where the function of merit was obtained directly from the parallel beam itself. The alignment method used a combination of optical and mechanical tools: laser tracker, micro-alignment telescope (MAT), 3D measuring machine (CMM) and self-designed holed plates. The final characterization of the x-ray beam is presented.
BEaTriX (Beam Expander Testing X-ray) is the X-ray facility under construction at the INAF-Osservatorio Astronomico Brera (Merate, Italy) to prove that it is possible to perform the X-ray acceptance tests (PSF and Aeff) of the ATHENA mirror modules at the required rate and with the required accuracy. The unique optical setup makes use of a micro-focus X-ray source with anode in Titanium, a paraboloidal mirror with small radius of curvature, and a set of crystals to monochromate and expand the beam to fully illuminate the entrance pupil of the ATHENA MMs. The quality of the optical components, and their precise alignment, guarantees the production of a parallel beam at 4.51 keV, to be extended in a second phase to 1.49 keV in order to complete the acceptance requirements for the ATHENA MMs. The completion of the facility is expected to occur in July this year, while the commissioning will start in September. In this paper, we present the current status.
The ATHENA X-ray telescope comprises an optical system with several hundreds of Silicon Pore Optics (SPO) Mirror Modules (MM) to be assembled. All the MMs have to be tested for acceptance before integration. INAF-Osservatorio Astronomico Brera is building in its premises of Merate (Italy) a unique pathfinder facility, BEaTriX, which is characterized by a broad (170 ×60 mm2), uniform and parallel X-ray beam (divergence ≤ 1.5 arcsec HEW) at the energies of 1.49 and 4.51 keV. BEaTriX prime goal is to prove that it is possible to perform the acceptance tests (PSF and Aeff) of the ATHENA SPO MM’s at the production rate of 3 MM/day. The system is very compact (9 × 18 m2) and it is designed with modular compartments where the vacuum can be broken independently to replace the optics under test. It works at a vacuum level of 10-3 mbar, easily evacuated in a short time. The expanded and parallel beam is obtained with an X-ray microfocus source placed in the focus of a paraboloidal mirror, a monochromation stage with 4 symmetrically cut crystals, and an expansion stage where the beam is diffracted and expanded by an asymmetrically-cut crystal. The key axes of all the optical components are motorized in vacuum for a proper beam alignment. The expanded beam fully illuminates the aperture of the MMs, imaging the focused beam at 12 m distance on a CCD camera, with the sensor in vacuum and motorized in air for XYZ movements. A thermal box is also present to radiatively heat the MM and check its optical performances under different temperatures. The design of the facility started in 2012 and has been finalised under an ESA contract. After completing the design, the facility is now in the realization phase. This paper provides an overview of the current status of the facility realization.
ATHENA Silicon Pore Optics (SPO) Mirror Modules (MM) have to be tested and accepted prior to integration in the full ATHENA Mirror Assembly (MA). X-ray tests of the MMs are currently performed at the PTB laboratory of the BESSY synchrotron facility in pencil beam configuration, but they require a PSF reconstruction. Full illumination X-ray tests could be performed using a broad, low-divergent X-ray beam like the one in use at PANTER (MPE, Neuried, Germany), but the large volume to be evacuated makes it impossible to perform the functional tests at the MMs production rate (3 MM/day).
To overcome these limitations, we started in 2012 to design a facility aimed at generating a broad (170 x 60 mm2), uniform and low-divergent (1.5 arcsec HEW) X-ray beam within a small lab (∼ 9 x 18 m2), to characterize the ATHENA MM. BEaTriX (the Beam Expander Testing X-ray facility) makes use of an X-ray microfocus source, a paraboloidal mirror, a crystal monochromation system, and an asymmetrically-cut diffracting crystal for the beam expansion. These optical components, in addition to a modular low-vacuum level (10-3 mbar), enable to match the ATHENA SPO acceptance requirements.
The realization of this facility at INAF-OAB in Merate (Italy) is now on going. Once completed, BEaTriX can be used to test the Silicon Pore Optics modules of the ATHENA X-ray observatory, as well as other optics, like the ones of the Arcus mission. In this paper we report the advancement status of the facility.
The construction of the BEaTriX (Beam Expander Testing X-ray) facility is ongoing at INAF/Osservatorio astronomico di Brera. The facility will generate a broad (170 x 60 mm2 ), uniform and low-divergent (1.5 arcsec HEW) X-ray beam within a small lab (∼ 9 x 18 m2 ), using an X-ray microfocus source, a paraboloidal mirror, a monochromation system based on a combination of symmetrically cut and asymmetrically-cut crystals in Bragg diffraction configuration. Once completed, BEaTriX can be used to test the Silicon Pore Optics modules of the ATHENA X-ray observatory, as well as other optics, like the ones of the Arcus mission. The facility is designed to operate at 1.49 keV and 4.51 keV, by using two fixed beam lines, equipped with the necessary optical elements. The first beam line to be completed will be at 4.51 keV and will prove the BEaTriX concept. Silicon crystals are used at this energy and four symmetric diffractions, with appropriate tilt of some crystals, will provide the spectral filtering at the required level to return the desired divergence. Owing to the quite short range necessary to obtain a parallel beam with this setup, a low vacuum level (10-3 mbar) can be used without a significant beam extinction. In addition to a modular vacuum approach, the low vacuum will allow us to reduce the time required to evacuate the tank, thus enabling to demonstrate a test rate that will match the ATHENA SPO production of 3 MM/day. In this paper, we report the design of the facility and the construction progress.
The BEaTriX (Beam Expander Testing X-ray facility) project is an X-ray apparatus under construction at INAF/OAB to
generate a broad (200´60 mm2), uniform and low-divergent X-ray beam within a small lab (6´15 m2). BEaTriX will
consist of an X-ray source in the focus a grazing incidence paraboloidal mirror to obtain a parallel beam, followed by a
crystal monochromation system and by an asymmetrically-cut diffracting crystal to perform the beam expansion to the
desired size. Once completed, BEaTriX will be used to directly perform the quality control of focusing modules of large
X-ray optics such as those for the ATHENA X-ray observatory, based on either Silicon Pore Optics (baseline) or Slumped
Glass Optics (alternative), and will thereby enable a direct quality control of angular resolution and effective area on a
number of mirror modules in a short time, in full X-ray illumination and without being affected by the finite distance of
the X-ray source. However, since the individual mirror modules for ATHENA will have an optical quality of 3-4 arcsec
HEW or better, BEaTriX is required to produce a broad beam with divergence below 1-2 arcsec, and sufficient flux to
quickly characterize the PSF of the module without being significantly affected by statistical uncertainties. Therefore, the
optical components of BEaTriX have to be selected and/or manufactured with excellent optical properties in order to
guarantee the final performance of the system. In this paper we report the final design of the facility and a detailed
performance simulation.
KEYWORDS: Sensors, Interference (communication), Signal detection, Prototyping, Electrodes, Gamma-ray astronomy, Signal to noise ratio, Collimation, Space telescopes, Electrons
At DTU Space we have developed a high resolution three dimensional (3D) position sensitive CZT detector for high energy astronomy. The design of the 3D CZT detector is based on the CZT Drift Strip detector principle. The position determination perpendicular to the anode strips is performed using a novel interpolating technique based on the drift strip signals. The position determination in the detector depth direction, is made using the DOI technique based the detector cathode and anode signals. The position determination along the anode strips is made with the help of 10 cathode strips orthogonal to the anode strips. The position resolutions are at low energies dominated by the electronic noise and improve therefore with increased signal to noise ratio as the energy increases. The achievable position resolution at higher energies will however be dominated by the extended spatial distribution of the photon produced ionization charge. The main sources of noise contribution of the drift signals are the leakage current between the strips and the strip capacitance. For the leakage current, we used a metallization process that reduces the leakage current by means of a high resistive thin layer between the drift strip electrodes and CZT detector material. This method was applied to all the proto type detectors and was a very effective method to reduce the surface leakage current between the strips. The proto type detector was recently investigated at the European Synchrotron Radiation Facility, Grenoble which provided a fine 50 × 50 μm2 collimated X-ray beam covering an energy band up to 600 keV. The Beam positions are resolved very well with a ~ 0.2 mm position resolution (FWHM ) at 400 keV in all directions.
In a Laue lens made of single crystals oriented to diffract parallel x-rays at the lens focus, the energy and angular resolution are limited by the crystal size and by the crystal mosaicity. The use of extended crystals bent according to the lens curvature provides better focusing, with the resolution given essentially by the crystal mosaicity. With this approach, a crystal mosaicity as low as 15–25 arcsec, well below the mosaicity value of copper crystals, was found suitable for the new design of the Laue lens. The reflectivity and transmission profiles and the integrated intensity have been measured in flat and bent GaAs and Si crystals prepared by the method of surface damaging by using sandpaper of different grain size. The surface grinding induces a local lattice strain which produces a self-standing bent crystal. Bent crystals with radius of curvature lower than a critical value given by the extinction length behave as ideal mosaic crystals, maximizing the diffraction efficiency at high x-ray energies. It is found that the surface grinding does not affect the crystal diffraction efficiency, the damage thickness being limited to a few tens microns near the crystal surface.
We will describe the LAUE project, supported by the Italian Space Agency, whose aim is to demonstrate the capability to build a focusing optics in the hard X-/soft gamma-ray domain (80{600 keV). To show the lens feasibility, the assembling of a Laue lens petal prototype with 20 m focal length is ongoing. Indeed, a feasibility study, within the LAUE project, has demonstrated that a Laue lens made of petals is feasible. Our goal is a lens in the 80-600 keV energy band. In addition to a detailed description of the new LARIX facility, in which the lens is being assembled, we will report the results of the project obtained so far.
Curved crystals used as optical elements of a Laue lens for hard x- and gamma-ray astronomy have a larger diffraction
efficiency with respect to perfect flat crystals. In this work we show how to achieve the bending of the crystals by a
controlled surface damaging which introduces defects in a superficial layer of few tens micrometers in thickness
undergoing a highly compressive strain.
Several silicon, gallium arsenide and germanium wafer crystals have been treated. The local and mean curvature radii of
each sample have been determined by means of high resolution x-ray diffraction measurements in Bragg condition at
low energy (8 keV). (100) oriented silicon and (111) oriented germanium samples showed spherical curvatures, whereas
(100) oriented GaAs treated samples evidenced an elliptical curvature with major axes corresponding to the <011<
crystallographic directions. Curvature radii between 3 and 70 m were easily obtained in wafers with thicknesses up to 2
mm.
Several 3x1x0.2 cm3 GaAs crystals (100) oriented with a radius of curvature of 40 m were prepared for the Laue Lens.
Using a x-ray tube set at a distance of 20 m from the crystal for the first time the focusing of the (022) diffracted beam at
a distance of 20 m was observed.
In a Laue lens made by single crystals oriented to diffract parallel x-rays at the lens focus, the energy and angular
resolution are limited by the crystal size and by the crystal mosaicity. The use of extended crystals bent according to
the lens curvature provides a better focusing, with the resolution given essentially by the crystal mosaicity.
With this approach a crystal mosaicity as low as 15-25 arcseconds, well below the mosaicity value of copper crystals,
was found suitable for the new design of the Laue lens.
The reflectivity and transmission profiles and the integrated intensity have been measured in flat and bent GaAs and
Si crystals prepared by the method of surface damaging by using sandpaper of different grain size. The surface
grinding induces a local lattice strain which produces a self standing bent crystal.
Bent crystals with radius of curvature lower than a critical value given by the extinction length behave as perfect
mosaic crystals or strongly bent perfect crystals, maximizing the diffraction efficiency at high x-ray energies. It is
found that the surface grinding does not affect the crystal diffraction efficiency, the damage thickness being limited to
a few tens microns near the crystal surface.
We present the status of LAUE, a project supported by the Italian Space Agency (ASI), and devoted to develop
Laue lenses with long focal length (from 10–15 meters up to 100 meters), for hard X–/soft gamma–ray astronomy
(80-600 keV). Thanks to their focusing capability, the design goal is to improve the sensitivity of the current
instrumention in the above energy band by 2 orders of magnitude, down to a few times 10−8 photons/(cm2 s keV).
The development of new focusing optics based on wide band Laue lenses operating from ~60 keV up to several hundred
keV is particularly challenging. This type of hard X-ray or gamma ray optics requires a high performance focal plane
detector in order to exploit to the best their intrinsic capabilities. We describe a three dimensional (3D) position sensitive
detector prototype suitable as the basic module for a high efficiency Laue lens focal plane detector. This detector
configuration is currently under study for use in a balloon payload dedicated to performing a high significance
measurement of the polarization status of the Crab between 100 and 500 keV. The prototype is made by packing 8 linear
modules, each composed of one basic sensitive unit bonded onto a thin supporting ceramic layer. Each unit is a drift strip
detector based on a CZT crystal, irradiated transversally to the electric field direction. The anode is segmented into 8
detection cells, each comprising one collecting strip and 8 surrounding drift strips. The drift strips are biased by a voltage
divider. The cathode is divided into 4 horizontal strips for the reconstruction of the Z interaction position. The detector
readout electronics is based on RENA-3 ASIC and the data handling system uses a custom electronics based on FPGA to
provide the ASIC setting, the event handling logic, and the data acquisition. This paper mainly describes the components
and the status of the undergoing activities for the construction of the proposed 3D CZT prototype and shows the results
of the electronics tests.
Today it is widely recognised that a measurement of the polarization status of cosmic sources high energy emission is a
key observational parameter to understand the active production mechanism and its geometry. Therefore new
instrumentation operating in the hard X/soft γ rays energy range should be optimized also for this type of measurement.
In this framework, we present the concept of a small high-performance spectrometer designed for polarimetry between
100 and 1000 keV suitable as a stratospheric balloon-borne payload dedicated to perform an accurate and reliable
measurement of the polarization status of the Crab pulsar, i.e. the polarization level and direction. The detector with 3D
spatial resolution is based on a CZT spectrometer in a highly segmented configuration designed to operate as a high
performance scattering polarimeter. We discuss different configurations based on recent development results and
possible improvements currently under study. Furthermore we describe a possible baseline design of the payload, which
can be also seen as a pathfinder for a high performance focal plane detector in new hard X and soft gamma ray focussing
telescopes and/or advanced Compton instruments. Finally we present preliminary data from Montecarlo undergoing
studies to determine the best trade-off between polarimetric performance and detector design complexity.
Curved crystals, instead of flat mosaic crystals, can be used as optical elements of a Laue lens for hard x- and gamma-ray astronomy to increase the diffraction efficiency. We propose to achieve the bending of the crystals by a controlled surface damaging, which introduces defects in a layer of few tens nanometers in thickness undergoing a highly compressive strain. Several oriented silicon and gallium arsenide wafer crystals have been treated. The local and mean curvature radii of each sample have been determined by means of high resolution x-ray diffraction measurements in Bragg condition at low energy (8 keV). Silicon samples showed spherical curvatures, whereas GaAs-treated samples evidenced elliptical curvatures with major axes corresponding to the 〈110〉 crystallographic directions. Curvature radii between 3 and 70 m were easily obtained in wafers of different thicknesses. The characterization of GaAs samples performed in Laue geometry at gamma-ray energy of 120 keV confirmed the increase of the diffraction efficiency in the bent crystals.
GaAs, Cu, CdTe, and CdZnTe crystals have been studied as optical elements for lenses for hard x-ray astronomy. High-resolution x-ray diffraction at 8 keV in Bragg geometry and at synchrotron at energies up to 500 keV in Laue geometry has been used. A good agreement was found between the mosaicity evaluated in Bragg geometry at 8 keV with x-ray penetration of the order of few tens of micrometers and that derived at synchrotron in transmission Laue geometry at higher x-ray energies. Mosaicity values in a range between a few to 150 arcsec were found in all the samples but, due to the presence of crystal grains in the cm range, CdTe and CdZnTe crystals were found not suitable. Cu crystals exhibit a mosaicity of the order of several arcmin; they indeed were found to be severely affected by cutting damage which could only be removed with a very deep etching. The full width at half maximum of the diffraction peaks decreased at higher x-ray energies showing that the peak broadening is affected by crystallite size. GaAs crystals grown by Czochralski method showed a mosaic spread up to 30 arcsec and good diffraction efficiency up to energies of 500 keV. The use of thermal treatments as a possible method to increase the mosaic spread was also evaluated.
Curved crystals can be used as optical elements of a x-ray lens for hard x-ray astronomy in order to increase the
diffraction efficiency. In this work we propose to obtain bent crystals by a controlled surface damaging, which introduces
defects in a superficial layer of few tens nanometers in thickness undergoing a highly compressive strain.
Several (100) oriented silicon and gallium arsenide wafer crystals have been treated. By using high resolution x-ray
diffraction measurements in Bragg condition at low energy x-rays the local and mean curvature radius of each sample
have been determined. Curvature radii between 3 and 70 m were easily obtained in wafers of different thicknesses.
In particular, spherical curvatures have been determined in silicon samples whereas GaAs treated samples showed an
elliptical curvature with the major axes corresponding to the <011> crystallographic directions.
The characterization of GaAs samples performed in the Laue geometry at gamma-ray energy of 120 keV confirmed the
increase of the diffraction efficiency in the bent crystals.
We have analyzed GaAs, Cu, CdTe, and CdZnTe crystals as possible optical elements for hard x-ray lenses for x-ray
astronomy. We used high resolution x-ray diffraction at 8keV in Bragg geometry and Laue transmission diffraction at
synchrotron at energies up to 500 keV. A good agreement was found between the mosaicity evaluated in Bragg
diffraction geometry with x-ray penetration of the order of few tens micrometers and in Laue transmission geometry at
synchrotron.
All the analyzed crystals showed mosaicity values in a range between a few to 150 arcseconds and suitable for the
application. Nevertheless
-CdTe and CdZnTe crystals exhibit non-uniformity due to the presence of low angle grain boundaries;
-Cu crystals exhibit mosaicity of the order of several arcminutes; they indeed suffer by a severe cutting damage that had
to be removed with a very deep etching. The FWHM was also rapidly decreasing with the x-ray energy showing that the
mosaic spread is not the only origin of peak broadening;
-GaAs crystals grown by Czochralski method show mosaicity up to 30 arcseconds and good diffraction efficiency up to
energies of 500 keV.
The use of thermal treatments as a possible method to increase the mosaic spread is also evaluated.
KEYWORDS: Sensors, Prototyping, Electronics, Phase transfer function, Spectroscopy, Telescopes, Crystals, Spectrometers, Analog electronics, Detector development
We report on the development of a 3D position sensitive prototype suitable as focal plane detector for Laue lens
telescope. The basic sensitive unit is a drift strip detector based on a CZT crystal, (~19×8 mm2 area, 2.4 mm thick),
irradiated transversally to the electric field direction. The anode side is segmented in 64 strips, that divide the crystal in 8
independent sensor (pixel), each composed by one collecting strip and 7 (one in common) adjacent drift strips. The drift
strips are biased by a voltage divider, whereas the anode strips are held at ground. Furthermore, the cathode is divided in
4 horizontal strips for the reconstruction of the third interaction position coordinate. The 3D prototype will be made by
packing 8 linear modules, each composed by one basic sensitive unit, bonded on a ceramic layer. The linear modules
readout is provided by a custom front end electronics implementing a set of three RENA-3 for a total of 128 channels.
The front-end electronics and the operating logics (in particular coincidence logics for polarisation measurements) are
handled by a versatile and modular multi-parametric back end electronics developed using FPGA technology.
Recently the design of a Laue lens with field of view of 30 arcseconds and for x-rays in the energy range from 100 keV
to 1 MeV has been proposed in which mosaic crystals are used as focussing elements. The proper mosaic angular spread is chosen as a compromise between intensity and energy resolution of the Laue lens.
In the present work we consider the use of GaAs crystals as optical elements for hard x-ray astronomy. GaAs crystals have essentially the same electron density and lattice spacing as germanium, and are characterized by spontaneous formation of "cellular structures" with dislocations distribution at the boundaries between perfect zones of the crystal. Because of the presence of cellular structures Czochralsky grown GaAs show a natural degree of mosaicity. Several GaAs ingots grown by liquid encapsulating Czochralsky technique have been characterized by high resolution x-ray diffraction. Bragg diffraction profiles have been measured along ingot axes and diameters of doped, undoped or stoichiometry deviated GaAs crystals. Full width at half maximum values ranging from 15 to 40 arcseconds depending on the position were measured close to the proposed 30 arcsecond mosaicity required for the Laue lens. Appropriate growth conditions allow the control of the dislocation density and the modification of cellular structure responsible of the crystal mosaicity so that the possibility of obtaining crystals with a given degree of mosaicity by tuning the LEC growth conditions is proposed.
The importance of hard X-ray astronomy (>10 keV) is now widely recognized. Recently both ESA and NASA have
indicated in their guidelines for the progress of X- and γ-ray astronomy in the next decade the development of new
instrumentation working in the energy range from the keV to the MeV region, where important scientific issues are still
open, exploiting high sensitivity for spectroscopic imaging and polarimetry observations. The development of new
concentrating (e.g. multilayer mirror) telescopes for hard X-rays (10 -100 keV) and focusing instruments based on Laue
lenses operating from ~60 keV up to a few MeV is particularly challenging. We describe the design of a threedimensional
(3D) depth-sensing position sensitive device suitable for use as the basic unit of a high efficiency focal
plane detector for a Laue lens telescope. The sensitive unit is a drift strip detector based on a CZT crystal, (10×10 mm2
area, 2.5 mm thick), irradiated transversally to the electric field direction. The anode is segmented into 4 detection cells,
each comprising one collecting strip and 8 drift strips. The drift strips are biased by a voltage divider, whereas the anode
strips are held at 0 V. The cathode is divided in 4 horizontal strips for the reconstruction of the Z interaction position.
The 3D prototype will be made by packing 8 linear modules, each composed of 2 basic sensitive units, bonded onto a
ceramic layer together with the readout electronics.
Recently, some of the authors showed that it is possible to grow CZT crystals by the boron oxide encapsulated vertical
Bridgman method. The most important feature of the technique is that the crystal, during the growth, is fully
encapsulated by a thin layer of liquid boron oxide, so that the crystal-crucible contact is prevented. The stress of the
crucible to the crystal is strongly reduced also during the cooling, because the boron oxide layer is molten down to about
500°C. A number of detectors have been prepared out of these crystals. The transport properties (μτ product) have been
studied by photoconductivity measurements as well as by determining the response to hard X-ray irradiation. The
transport properties have been studied as a function of the indium content and of the position of the wafer which the
detector was cut out.
A 2 X 2 optical switch performing bidirectional cross-bar on optical communication signals at 1550 nm is presented and experimented. The switch is based on electro-optic effect in bulk CdTe crystals. Operation is totally independent by input state of polarization of the optical beams to be addressed. The proposed free-space architecture grants high compactness, reliability and fast response time compared with common switching solutions.
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