Marco Pisani

Angle amplification for nanoradian measurements

A method to amplify the rotation angle of a mirror, based on multiple reflections between two quasi-parallel mirrors, is presented. The method allows rotations of fractions of nanoradians to be measured with a simple setup. The working principle, the experimental setup, and the results are presented.

A Johnson noise thermometer with traceability to electrical standards

The paper presents an absolute Johnson noise thermometer (JNT), an instrument to measure the thermodynamic temperature of a sensing resistor, with traceability to voltage, resistance and frequency quantities. The temperature is measured in energy units, and can be converted to SI units (kelvin) with the accepted value of the Boltzmann constant kB; or, conversely, it can be employed to perform measurements at the triple point of water and obtain a determination of kB. The thermometer is composed of a correlation spectrum analyzer and a calibrator. The calibrator generates a pseudorandom noise (at a level suitable for traceability to an ac voltage standard) by digital synthesis, scaled in amplitude by a chain of electromagnetic voltage dividers and cyclically injected in series with the Johnson noise. First JNT measurements at room temperature are compatible with those of a standard platinum resistance thermometer within the estimated combined uncertainty of 60 µK K −1 of both instruments. A path towards future improvements of JNT accuracy is also sketched.

A multi-electrode plane capacitive sensor for displacement measurements and attitude controls

A novel, multi-electrode capacitive sensor has been designed, realized and tested at INRiM (Istituto Nazionale di Ricerca Metrologica). The circular active electrode of a guarded plane-parallel capacitive sensor is sub-divided into four sectors of equal area. The four output signals from each independent sensor are acquired, normalized and summed, to obtain the displacement. Similarly, by a combination of summing and differencing, the tip and tilt between the relative electrodes can be determined. An angular sensitivity up to 70 mV µrad-1 with a noise level of approximately 85 µV Hz−1/2 has been achieved with a working distance of 50 µm. The angular sensitivity decreases to a few mV µrad-1 for plate separations larger than 200 µm. The measuring electronics was set for a full-scale displacement range of several hundreds of micrometers.

A hyperspectral imager based on a Fabry-Perot interferometer with dielectric mirrors

In this paper we present a new hyperspectral imager based on a Fabry-Perot interferometer with low reflectivity dielectric mirrors. This set-up has been validated by measuring hypercubes of scenes containing emitting bodies and reflective surfaces in the visible region and compared with success with reference spectra. The system is based on dielectric mirrors which, with respect to similar systems based on metallic mirrors, have lower losses at lower cost and are available off-the-shelf. The spectra calculation is carried out with a Fourier transform based algorithm which takes into account the not negligible dispersion of the mirrors.

Fabry–Perot-based Fourier-transform hyperspectral imaging allows multi-labeled fluorescence analysis

We demonstrate the ability of our hyperspectral imaging device, based on a scanning Fabry-Perot interferometer, to obtain a single hyper-image of a sample marked with different fluorescent molecules, and to unambiguously discriminate them by observing their spectral fingerprints. An experiment carried out with cyanines, fluorescein, and quantum dots emitting in the yellow-orange region, demonstrates the feasibility of multi-labeled fluorescence microscopy without the use of multiple filter sets or dispersive means.

A Hyperspectral Camera in the UVA Band

We present a hyperspectral camera based on a Fabry-Pérot interferometer designed to work in the UVA range (315-400 nm). The measured hypercube contains about 400 × 400 pixels, for a total of 160 000 spectra. Each spectrum has a spectral resolution of about 5 nm at the wavelength of 315 nm. Spatial and spectral discrimination capability has been demonstrated by imaging a target with five different ultraviolet (UV) light-emitting diodes. Spectral resolution is demonstrated by aiming at the sky and observing spectral features of the diffused solar light in the UV. A possible application of the hyperspectral camera is the measurement of the UVA content of the diffused light of the whole sky.

A comparison of sensitivity standards in form metrology—final results of the EURAMET project 649

Results of an intercomparison measurement of sensitivity standards are presented. The standards circulated were a flick and two multi-wave standards (MWS). The measurands were form deviation and, for the MWS only, the height of the dominant spectral components. For the flick, influences from mechanical filtering and calibration are discussed. For the MWS several influencing quantities are identified and discussed. Some of these influencing quantities may dominate the result under certain circumstances. It can be shown that standard measurement uncertainties of smaller than 25 nm can be achieved for the amplitude heights of MWS, whereas the form deviation results disagree a little more than expected compared to standard uncertainties of the order of 50 nm.

A device for hyperspectral imaging in the UV

We present an optical device for hyperspectral imaging designed to work in the 300-400 nm range. The system is basically based on a scanning Fabry-Pérot interferometer with reflective mirrors in the range of interest. The instrument allows capturing the UV spectrum of each pixel of an image generating a 3D matrix called “hyperspectral cube” with spatial and spectral information. This system can be integrated with a digital camera provided with a UV sensitive sensor and a UV fisheye optic for the measure of the UV sky radiance.

Practical realization of Nyquist’s gedanken experiment

If two noisy electrical dipoles are connected with an electric line, noise power can flow through the line. Such power can be measured, in the audio frequency range, with a wattmeter with spectral display capabilities. If the dipoles are two equal resistors in thermodynamic equilibrium, the power depends exclusively on the temperature difference, giving a differential noise thermometry method. If the dipoles are at the same temperature, but one is out of thermodynamic equilibrium (because of a flowing dc current), noise power depends on excess noise only, and it is possible to measure excess noise far below Johnson noise threshold.

Fourier Transform Hyperspectral Imaging for Cultural Heritage

Hyperspectral imaging is a technique of analysis that associates to each pixel of the image the spectral content of the radiation coming from the scene. This content can be helpful to recognize the chemical nature of the materials within the scene or to calculate their colours under particular conditions. Different solutions of hyperspectral imager have been realized with different spatial resolution, spectral resolution and range in the elec‐ tromagnetic spectrum. In particular, improving the spectral resolution allows discrimi‐ nating smaller features in the spectrum and the unambiguous detection of the absorption bands characteristic of superficial materials. Hyperspectral imagers based on interfer‐ ometers have the advantage of having a spectral resolution that can be varied according to the needs by changing the optical path delay of the interferometer. A spectrum for each pixel is obtained with an algorithm based on the Fourier transform of the calibrated interferogram. We present the results of the application of a hyperspectral imager based on Fabry‐Perot interferometers to the field of cultural heritage. On different artworks, the hyperspectral imager has been used for pigment recognition, for colour rendering elaborations of the image with different light sources or standard illuminants and for calculating the chromatic coordinates useful for specific purposes.