The development of a wide-field infrared spectroscopic imaging apparatus using a bolometer camera and feasibility test for forensic examination

Abstract A wide-field infrared spectroscopic imaging apparatus that uses a bolometer camera instead of a mercury cadmium telluride detector has been developed. The apparatus is equipped with a projection lens and utilizes, for Fourier spectroscopy, an imaging type interferometer resistant to vibrations. In contrast to the conventional systems, the apparatus has several advantages including short measurement times for large samples, low cost, and future portability. To test the applicability of this apparatus to forensic examination, a polystyrene film and different types of ink on an Al plate were tested. When the spectroscopic imaging of a 40-μm-thick polystyrene film was obtained in transmission mode via the developed apparatus, very clear spectra were recorded. In reflection mode, the spectroscopic imaging of writing pen inks on a 10 cm × 10 cm aluminum plate could also be obtained. The developed apparatus could record spectra of 240 × 320 = 76,800 points with a wavelength resolution of approximately 5 cm −1 in ca. 1 min. Considering the time required for the analysis of the interferogram, the total time was ca. 2 min. By changing the projection magnification, the size of the area to be examined could be easily modified. The measurement time was constant regardless of the size of the area. As the developed apparatus is very compact and portable, in situ observation of crime material will be possible.