Historically, safety analyses for radio frequency emission and optical laser exposures have been designed to define the threshold level for tissue damage. To date, no experimental studies have documented damage thresholds to living tissues in the terahertz (THz) range of electromagnetic frequencies (0.1 - 10 THz). Exposure limits exist as extrapolated estimates at the extreme bounds of current occupational safety standards for lasers and radio frequency sources. Therefore, due to the lack of published data on the safety of terahertz emissions, an understanding of the bioeffects of tissue exposures to terahertz beams is necessary. The terahertz frequency band represents an intermediate range in which both optical and radiofrequency methods of theory and experimentation can be selectively employed and compared for consistency. We report on work recently completed to reconcile the theoretical methods of optical and radio-frequency radiative transport modeling, while additionally discussing preliminary theoretical estimates of damage thresholds to skin tissue from terahertz energy and work planned to validate these findings experimentally.
To properly assess skin damage caused by photonic exposure, the mechanisms of photon attenuation and subsequent heat
production are investigated. Currently, voids exist in frequency specific electromagnetic properties such as the complex
dielectric permittivity and conductivity necessary to define refractive index and attenuation values. We investigate these
properties in several tissues such as blood, bone, skin, vitreous humor, cornea, retina and many others. Inside these
tissues, exponential decrease in photon energy occurs due to attenuation. Because photon energy absorbed in tissue is
expressed as heat in many instances, it follows that the dielectric properties of the material will also change as a function
of the heating patterns as well as with frequency or wavelength. Conversely, changes in tissue thermal properties should
change photon behavior as dispersion properties change. In our case we are concerned with existing data and theoretically determining dispersion properties over a large range of frequencies or wavelengths.
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