Hyperspectral imaging and directional reflectance for predicting interaction of laser radiation with biodeteriorated objects threatening human health

The aim of this study was an attempt to use hyperspectral imaging and hemispheric directional reflectance, supported by GLCM and quadtree decomposition methods, for non-invasive analysis of historical objects. The research was carried out to adjust the wavelength of laser light, which could be used for decontamination, to the characteristics of historical materials from the Auschwitz-Birkenau State Museum. Historical leathers and fabrics from original children's shoes are contaminated with bacteria at the level of 105–106 CFU/100 cm2 and 104 CFU/100 cm2 with fungi, on average, including microorganisms posing threat to the objects and people. Two proposed methods allowed for a quantitative, repeatable and absolute assessment of interaction of electromagnetic radiation with tested materials. The dependence of reflectance on the wavelength was roughly similar for all materials, i.e. slight fluctuations or gradual increase in the spectral range of 400–700 nm, then increase for 700–1700 nm and a decrease for 1700–2500 nm. In general, higher reflectance was recorded for historical fabrics than for historical leathers. The most suitable range of laser radiation for disinfection was set at 700–1000 nm. Irradiation with a diode laser (λ = 808 nm) caused statistically significant differences in the numbers of all tested microbial strains and reduction by 56.03–99.10%.