Terahertz-Regime Attenuation Signatures in Bacillus subtilis and a Model Based on Surface Polariton Effects

A summary is provided for terahertz attenuation signatures measured in spore-laden samples of Bacillus subtilis in three different forms: 1) concentrated powder; 2) dilute powder; and 3) aerosol. In addition to a surprising spectral narrowness, some signatures also display an increase in peak signature strength (per spore) with dilution of the sample. A model is constructed to explain this phenomenology based on the presence of optical phonons and electromagnetic interaction with the spore wall. Specifically, the spheroidal Bacillus spores admit surface modes that interact with radiation via polaritonic coupling and are underdamped if isolated from each other through a dilution or aerosol levitation. Hence, the results defy longstanding assumptions that the biomolecular-related terahertz vibrations are necessarily overdamped and have immeasurably weak attenuation