Optical properties of Bacillus subtilis spores from 02 to 25 µm

Abstract

We have used spectral reflectance and transmittance measurements combined with Kramers-Krönig analyses to obtain the real (n) and imaginary (k) parts of the complex refractive index, N = n + ik, of Bacillus subtilis spores over a wavelength interval from 0.2 to 2.5 mum. Samples were in the form of thin solid films, pressed pellets, and suspensions in water and glycerol. The optical constants of spores suspended in water were found to differ from those of spores suspended in glycerol. In addition, spores previously exposed to water in earlier experiments and subsequently dried exhibited different optical constants from spores that had not been exposed to water.