Refractive index measurement of biological particles in visible region

Optical cross-sections of biological warfare simulants, killed agents, and live agents are needed to assess the standoff detection performance of active lidar and passive FTIR systems. To aid in this investigation, Johns Hopkins University Applied Physics Laboratory (JHU/APL) has developed a technique to determine the index of refraction of biological materials in the visible region using a combination of transmission measurements and anomalous diffraction theory (ADT). The spectral measurements using a dual beam grating spectrometer provide a basis for calculating the optical cross section of suspended particles. ADT is then used to convert the cross section result into index of refraction. A summary of this procedure is described along with the results for silica microspheres and Bacillus globijii (BG). A comparison of these results to published data is also presented.