Dependence of light transmission through human skin on incident beam diameter at different wavelengths

For many people who use light for skin treatment, it is important to let the photon penetrate into the skin. Since photons are absorbed and scattered by the skin tissue, the color and diameter of the incident light will affect the penetration depth of the photons.

In this study, at six wavelengths (532nm, 632nm, 675nm, 810nm, 911nm, and 1064nm), the wavelength dependence of light transmission through human skin tissue (between the earlobe and finger) was measured in vivo.

The study found:

1) Under a given incident beam diameter, the penetration depth of photons with a wavelength of 1064nm is deeper than other wavelengths;

2) The transmittance at a specific wavelength gradually increases as the diameter of the incident beam increases. For some skin tissues, the transmittance of 532nm photons flattens out at about 8mm, while for all other wavelengths, the transmittance tends to saturate at about 12mm