Cryogenic calibrators

A full-sky in your pocket.

Measuring the sky temperature at millimeter and sub-millimeter wavelengths (from several GHz to 1 THz) from Space, at about -270 C, and with a precision of a part over a million, is a very challenging task. The solution is to build  dedicated  reference  sources at cryogenic temperature.  These calibrators allow either to accurately characterize your detectors during ground tests or to provide a very stable reference signal to the microwave detectors during the observations.

Operational temperature (about 4K), very high emissivity ( close to a ‘black-body’, with emitted radiation higher than 99,99%) , polarization purity, thermal stability, compactness (from a few millimeters to one meter): this is the business card of such smart pieces of sky.

The IASF-Bo team,  within the ESA-ASI Planck-Satellite Collaboration,  have designed, manufactured and characterized in  operational conditions, the three on-ground calibrators for the Low Frequency Instrument (LFI, 27 GHz- 77 GHz) and High Frequency Instrument ( HFI, 100 GHz – 900 GHz) onboard the Planck Satellite, together with the cryogenic flight reference (4K Reference Load) for the Planck- LFI pseudo-correlation radiometers. Extremely accurate  electromagnetic, thermal and mechanic studies allowed our Institute to reach the state of the art technological level in  the passive cryogenic calibrators for microwave detectors.

Laue lenses

The scientific challenges that the space missions for hard X-ray and gamma astrophysics in the next decade shall face will require a radical improvement (x100) of the observational sensitivity with respect to instrumentation now in operation. A solution particularly challenging to meet these requirements rely on the development of hard X-ray and gamma focusing systems as Laue lens. These lenses exploit the ability of crystals to deflect, by means of diffraction, the path of the incident X photons. Assembling a number of crystals devices capable of focusing incident X/gamma-rays at the same point can be obtained, just as a conventional lens does with visible light. The construction of Laue lenses for space requires the development of sophisticated technologies both for the realization of the more suitable crystals both for their mechanical assembly. Our institute, in collaboration with the Department of Physics, University of Ferrara is engaged since several years in the development of wide band Laue lens for focusing X-rays from about 100 to several hundred keV.

Semiconductor spectrometers at room temperature

How do we can get an image in various colours (photon energies) of the X-and gamma ray sky?

With detectors designed for this purpose made of cadmium telluride (CdTe) or cadmium telluride with the addition of zinc (CdZnTe), semiconductor materials which allow the realization of device sensible to the X/gamma photons interaction position and operating at room temperature with good resolution in position and energy.

Currently detectors made with this technology are successfully operating on board of the ISGRI INTEGRAL (ISGRI) and Swift (BAT) satellites, and are used in various fields, in addition to the space.

IASF-Bologna is engaged since the 90’s in developing this type of X-ray and gamma ray sensors and in the design of advanced detectors for space missions able to perform also measurements of the polarization of the photons using the Compton scattering. Our group has proposed one of the first, the use of CdTe/CZT segmented detectors for hard X and soft gamma ray polarization measurements with the realization of a series of experiments (POLCA), the results of which have become an international reference. In the same context the activity of the group has recently oriented, as part of an European collaboration, the development of detectors capable of determining the position of interaction of photons at each energy in 3 dimensions. This capability is a key requirement for the new astrophysics instrumentation in the X and gamma ray energy range as it will significantly increase the sensitivity of simultaneous measurement of energy, location and polarization of cosmic sources through the more precise determination of the parameters of each photons interaction with the detector.

Single photon avalanche diodes (SPAD)

What kind of detectors will be used in the next decades to improve the performance of the gamma-ray detectors currently onboard space missions such as AGILE and Fermi? One of the possibilities is the use of plastic scintillating fibers with thickness less than 1 mm, which are less expensive and can be much longer than standard silicon detectors. These fibers produce light when radiation passes through them, but the light produced has a very low intensity, therefore extremely sensitive detectors are needed to detect it. For this reason we are studying Single Photon Avalanche Diodes (SPAD), capable to trigger even when hit by a single photon, the minimum amount of light possible. These devices, realized by the IMM Institute of the National Research Council (CNR) based in the same research district where IASF Bologna is located, were initially conceived for on-ground applications and for the first time are now studied as possible detectors for space. This is a remarkable example of synergy between institutes working on different topics.

BATMAN

In the common digital video projectors there is a high technology component that astronomers believe can be used to build a new type of detector for visible and infrared light. Its name is DMD (Digital Micromirror Devices).

It is a an electromechanical component in the form of a grid of more than a million small mirrors that can be moved using an electric signal.

By placing a DMD along the optical path of a telescope, it is possible to address the light of each star or galaxy in the field toward the light detector or to block it.

This is important when collecting spectra of celestial objects because this way it is possible to select only the objects of interest among those present in the field.

Moreover these spectra will not be “polluted” by those of the other objects and by the diffuse light of the sky, and no mechanichal component has to be moved!

BATMAN is a demonstrator spectrometer that will use 2048×1080 mirrors DMD and will be installed at the Telescopio Nazionale Galileo (Canary Islands).