Corneal Dosimetry in the 200–500 GHz Band Using Generalized Lorenz–Mie Theory

Abstract

This study presents a comprehensive dosimetric analysis of the human cornea exposed to continuous radiation in the 200–500 GHz frequency range. A semi-analytic approach is developed by combining Bruggeman effective-medium theory of the hydration-graded cornea with Generalized Lorenz–Mie Theory (GLMT) for arbitrary Gaussian-beam illumination, coupled to a Pennes bioheat equation to compute SAR, absorbed power density ($S_{ab}$) averaged over $1\;\mathrm{cm^{2}}$, and the temperature rise $\Delta T$. Validation at 100 GHz against established plane-wave results is obtained in the large-waist limit ($w_{0} = \text{60}\;\text{mm}$). Across 200–500 GHz at $w_{0} = \text{3}\;\text{mm}$, $S_{ab}$ and both peak and average temperature rises increase modestly with frequency, whereas the heating factor $\Delta T_{\text{peak}}/S_{ab}$ varies by less than 0.3%, establishing $S_{ab}$ as a frequency-stable surrogate for peak corneal temperature in this band. A beam-size sweep at $\text{300}\;\text{GHz}$ ($w_{0} = 2$–$\text{12}\;\text{mm}$) at fixed aperture-averaged incident power density demonstrates that beam geometry is the dominant determinant of peak corneal heating: $\Delta T_{\text{peak}}$ decreases by roughly a factor of four as the waist increases, while $S_{ab}$ increases only slightly. Peak and area-averaged quantities therefore vary in opposite directions as the beam narrows. Across all configurations, the calculated metrics at reference incident power densities of $40\;\mathrm{W/m^{2}}$ remain more than an order of magnitude below the $5\;^{\circ }\mathrm{C}$ Type-1 corneal operational threshold, and no abrupt change in dosimetric behaviour is observed across $\text{300}\;\text{GHz}$. Presented results quantify, for the cornea at sub-terahertz frequencies, the beam-size regime in which area-averaged $S_{ab}$ and local peak corneal temperature diverge.