Hyperspectral imaging (HI) are generally called the techniques and devices which combine in a single data set the information coming from a digital picture with the one coming from a spectrophotometer. The obtained data set, known as "hyperspectral cube", is a 3D matrix where a 2D image is combined with a third dimension giving the spectral composition of each pixel of the same image. Most popular applications of hyperspectral imaging are in chemical analysis, fluorescence microscopy, cultural heritage, thermal imaging, and spaceborne applications like Earth survey for environment or security.

A new technology

At INRiM a novel technique to obtain hyperspectral imaging has been demonstrated and an imaging device has been constructed. The device is based on a scanning Fabry-Perot interferometer where the mirrors move from contact to a maximum distance by means of piezo actuators. During the cavity length scanning, a video is captured so that the light intensity variations occurring on each pixel are recorded. The interferogram obtained for each pixel is mathematically elaborated to give the spectral composition of the light hitting the same.

Advantages

With respect to commercially available hyperspectral devices the luminosity of our device is higher because it is based on an interferometer instead of a monochromator (Jacquinot and Felgett advantages) allowing shorter exposure times. Furthermore the F-P interferometer can be realized in a very compact form, thus can be easily integrated in optical imaging set up.

Applications

The potentiality of the instrument for spectral analysis has been demonstrated in the visible region (400-720 nm) with a resolution of about 2 nm @ 532 nm, but the technique can be used in the infrared (simply changing the CCD technology, e.g. by using InGaAs instead of silicon) where the absorption spectra of chemical substances is rich in information. Eventually a possible application in colour imaging has been demonstrated: the technique could be used to obtain colour images from a monochromatic CCD with the advantage of the higher resolution of the latter with respect to colour sensors.
Besides classical spectroscopic analysis for remote recognition of chemical compounds, other applications are foreseen in the field of fluorescence microscopy where more fluorescent markers can be observed and discriminated on the same biological sample, in thermal imaging where the temperature can be accurately calculated from the shape of the emission spectrum, and in preservation of cultural heritages.