Computational Analysis of 635 nm Diode Laser Absorption in Epidermal Layers of Light and Dark Skin Types

Abstract

Laser tissue interaction for photobiomodulation is significantly dependent on the skin pigmentation due to the difference in melanin concentration. This affects the optical absorption and the depth of penetration of the laser beam. The computational model developed was aimed at analyzing the interactions between the diode laser beam of wavelength 635 nm and the light and dark layers of epidermis skin tissue. The power output of the laser was varied from 2 to 20 mW. The absorption coefficient of optical power (mW·mm⁻³) was determined in respect to different depths of epidermis skin tissues (0.015 to 0.1025 mm). The findings indicated that the rate of absorption was greater in dark skin compared to light skin because the volume absorbed optical power was 2.39 times higher due to a higher concentration of melanin in the dark skin. Absorption of energy occurred at a lesser depth of 0.019 to 0.0317 mm in dark skin but occurred at a greater depth in light skin. There was a strong correlation between the rate of energy absorbed and power, where R²>0.98. The findings revealed that there were marked variations in the energy absorption mechanisms among various skin types, with far-reaching implications for fine-tuning the process of photobiomodulation. Notably, no biological effect was assessed in the study.