Penetration Depth of 635 nm Laser Light Into the Biological Tissue

Optical parameters of the target tissue are important to know for all kinds of phototherapy. In photodynamic therapy, for example, the knowledge of the penetration depth for the light is needed in order to ensure that the optical energy received by the tumorous tissue. In the present study, the optical penetration depths of 635 nm laser light in chicken breast tissue have been measured by using 11 tissue samples with different thicknesses between 3.0 mm and 8.0 mm. Transmitted light intensities through the tissue samples have been measured for the optical powers of 200 mW, 450 mW and 650 mW. Measurement results for each power value have been analyzed according to the Beer-Lambert law. Optical penetration depths have been found to be 5.98±0.47 mm, 5.88±0.36 mm and 5.94±0.37 mm for 200 mW, 450 mW and 650 mW optical powers, respectively. These results show that the optical penetration depth of the light in biological tissue does not depend on its optical power.