Seeing through smoke and flames is a great challenge for imaging capabilities and any advance has applications of wide impact in the industrial and the safety field. The existing thermographic detectors employ Infrared (IR) bolometers which are able to see clearly the targets through smoke, as the infrared radiation is just slightly scattered by the soot particles [1]. However, they are blinded whenever a flame is present on the scene being imaged, due to its emission which is focused by the bolometer lens and saturates the detector elements. This results in blind areas in the images. On the contrary, lensless Digital Holography (DH) [2] at 10.6µm overcomes this limitation thanks to the possibility to acquire holograms out of the focus plane and to perform the focusing process by means of a numerical simulation of the diffraction integral [3]. In this way, the flame emission is distributed on the whole array of the detector and a clear imaging of the targets is achievable with no blind areas. Moreover, the employed wavelength allows to detect human size targets. The combination of these capabilities can lead to new imaging devices able to see clearly alive people in fire scenes, independently on the extension of the flame and the involved burning material. Experiments have been carried out to demonstrate the capability of IR-DH to look beyond curtains of smoke and flames. In particular, holographic imaging of small objects and alive people has been achieved through smoke and flames generated in safely way in laboratory and the results have been compared with white light images and the vision obtainable with thermographic techniques. From Fig.1 is apparent that only holographic imaging is able to discard the unwanted radiation, and images of human targets are obtained behind the flames with no blind areas. For these reasons we claim that Digital Holography at far infrared can pave the way for a new kind of imaging device which can help fire departments to coordinate the rescue operations and to operate safely in case of fire accidents.

© 2013 IEEE

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