Propagation of higher-order annular Gaussian beams in biological tissues.

The propagation characteristics of a higher-order annular Gaussian (HOAG) beam in biological tissue turbulence are investigated. Average intensity at the receiver plane is found when the HOAG source field is used as excitation. The effects of the HOAG beam on different tissue types of the upper dermis (human), liver parenchyma (mouse), intestinal epithelium (mouse), and deep dermis (mouse) are studied. Variations of the average intensity versus the source and medium parameters such as the strength coefficient of the refractive-index fluctuations, propagation distance, wavelength, and beam size are presented. The results show that all modes of the HOAG beam can successively transmit beam energy at different levels of turbulence for all tissue types. At the same turbulence strength, HOAG beams having larger mode numbers transmit higher intensity to receivers than the modes with smaller mode orders, which is valid for all the examined tissue types. As the strength of tissue turbulence increases, the HOAG beam slowly turns into a pure Gaussian beam. For the different tissue types, the highest beam intensity at the receiver was observed for the deep dermis (mouse) tissue type. Despite the change in wavelength, refractive-index fluctuations, and source beam size, the highest beam transmission through the tissue in a turbulent environment was also observed for this same tissue type. This research may be useful in understanding the fundamentals of light-tissue interaction of HOAG laser beams, which may improve noninvasive disease detection and therapy methods through tissue in biophotonic technologies.