The Photometry and Radiometry Department carries out basic and applied research and develops measurement methods relevant for photometry, radiometry, colorimetry and optometry from near infrared to ultraviolet. Furthermore, know-how in Quantum Optics is applied to researches in the field of Quantum Information and Foundations of Quantum Mechanics. The national SI standards of luminous intensity, illuminance and luminous flux are realised and extended to luminance and transmittance. SI units are maintained and disseminated with the status of national reference laboratory (Italian law no. 273/1991). Dissemination is provided by calibration activity, through the Italian Calibration Service (SIT). Main results achieved throughout 2005 are reported.
The studies concerning foundations of quantum mechanics and applications to quantum information and metrology have been carried on. More in detail, in collaboration with Moscow University, research addressed to characterizing fiber transmission of polarisation entangled states of photons has been performed. Interesting interference effects in the II order Glauber correlation function have been showed. Furthermore, we studied if Parametric Down Conversion (PDC) quantum correlations can be used to realise a scheme for absolute calibration of analog detectors. Preliminary results showed that these researches are worth further investigation. In collaboration with Milano and Insubria Universities a systematic study on the use of an innovative scheme, based on on/off detectors, for reconstructing the statistics of quantum optical states has been performed. The results demonstrate the interesting potentialities of this method. Research addressed to verifying the feasibility of an Earth-space quantum communication channel is being carried on in collaboration with Politecnico di Torino and Alenia Spazio. Together with Torino and Catania Universities, a preliminary research concerning the preparation of a highly spectrally selected photon source for applications to the realisation of quantum optical gates has been completed. Finally, the studies on local realism (connection between CP violation and such tests by using K mesons) have been pursued.
Optical bench for fiber quantum communication.
An experiment, in which photon pairs from a pulsed PDC source were coupled into single-mode fibers with heralding efficiencies (obtained for a range of down-conversion beam-size configurations) as high as 70%, has been carried out. Analysis of spatial and spectral mode selection and of their mutual correlation provides a practical guide for engineering PDC-produced single photons in a definite mode and spectral emission band. A single photon source at 1550 nm with high conversion-efficiency in periodically-poled crystals has been produced. The goal is the development of an appropriate PDC source at Telecom wavelengths, meeting the requirements of high-efficiency pair production and collection in single spectral and spatial modes (single-mode fibres ). A protocol to optimize photon collection, noise levels and uncertainty evaluation has been proposed. A scheme for a photon-counting detection system that can be operated at incident photon rates higher than otherwise possible, by suppressing the effects of detector dead-time, has been presented. The method uses an array of N detectors and a 1-by-N optical switch with a control circuit to direct input light to live detectors. Calculations and models (both for continuous and pulsed light sources) highlighted the advantages of the technique: in particular a group of N detectors provides an improvement in operation rate that can exceed the improvement that would be obtained by a single detector with dead-time reduced by 1/N, even if it were feasible to produce a single detector with such a large improvement in dead-time.
Heralded single-photons at 1550 nm.
To increase the quantum efficiency of transition-edge sensors (TES) it is necessary to reduce the reflection losses at the film surface. In 2005 different solutions based on the deposition of few layers of amorphous silicon-nitrogen alloys as antireflection coatings have been studied. Solutions that minimize the reflectivity to less than 1% simultaneously at different telecommunication wavelengths or to a few percent in a continuum band have been designed and produced for Ti TES. The characterization of a cryogenic RF-preamplifier, in view of its possible applications to very fast superconducting photodetectors, has been started too. The short response times (~100ps) of these detectors, in fact, require an amplification stage set as close as possible to the superconducting devices, to improve the frequency response and reduce the effect of external interferences. Finally, the study about the noise produced during the resistive transition of MgB2 polycrystalline thin film has been carried on. The power spectrum of the current noise has been interpreted with a model that makes it possible to fit both the shape and intensity of the spectrum, which presents a large electrical noise of 1/f n type (n = 3) over a quite wide range of frequencies.
The reflectivity of a Ti film (red dots) can be reduced nearly to zero for 1310 nm and 1550 nm with a proper antireflection coating design (green line).
The spectrophotometric characterisations of ancient Egyptian statues were performed to fully evaluate their behaviour and colour rendering under several artificial lighting systems. A new measurement device to characterise materials with strong diffusing properties, based on two integrating spheres (one to produce uniform illumination and one to evaluate the hemispherical transmission), was completed. The device arranged is expected to lower measurement uncertainty: a comparison with goniophotometric measurement is scheduled in 2006. The mobile laboratory "Tiresia" (outcome of collaboration with ANAS) for digital photometric measurements in the field started its activity in road lighting characterisation, with several measurements of tunnel lighting systems and urban lighting pollution.
Hemispherical transmittance measurement system.