LIF scanning

LIF scanning

Portion of the fresco painted wall with delimitation of the canned area (4.5 m2)
Portion of the fresco painted wall with delimitation of the scanned area

The LIF scanning instrument capable to collect hyperspectral fluorescence images on large areas has been designed and Manufactured for ENEA. The system is aimed at identifying and detecting the fluorescence signature of samples from a remote station. For the purpose of the measurements, the system can be set up to detect the signature of pigment and consolidants on investigated samples; to this end the exciting laser is set up emitting in the UV at 266nm, while receiving detector is acquiring the full spectrum from 200nm to 850nm with a spectral resolution of 2.5nm. Former work already pointed out LIF capabilities as non destructive diagnostic tool on painted surfaces. The detection of the emitted fluorescence allows to identify the presence of substances capable to be excited by UV radiation; indeed the adopted experimental technique is proven to detect the occurrence superficial contamination, and to identify extraneous materials onto the surface (biodeterioration, pollutant, waxes, some kinds of biological attack such as microalgae and fungi, presence of superficial contaminants, pigments and consolidants.

Major achievements have been reached by a critical review of the optical design and consequently of the detector utilized:

  • the focalization mode has been changed into a line focalization by using a quartz cylindrical lens and a imaging spectrograph;
  • the linear array detector, responsible for the multichannel spectral resolution, has been replaced with a square ICCD sensor, mounted behind a slit parallel to the laser line footprint during the scanning.

This arrangement is characterized by having the spatial and spectral information on two mutually orthogonal directions imaged on the detector, with submillimetric spatial resolution and a spectral resolution better than 2nm. Additionally it is possible to implement time resolved measurements on the nanosecond scale by controlling the electronic detector gate.