Determining safety thresholds in high-powered lasers

High-powered near-infrared (NIR) lasers are used in manufacturing, communication, and medical applications, to name a few. To ensure user safety, guidelines on exposure limits are necessary. However, the computational models of tissue responses used to inform these limits – sometimes where experimental data does not exist – can be inaccurate in the NIR region due to higher amounts of scattering that occurs at these wavelengths.

DeLisi et al. updated the computational model to more accurately predict the response of porcine skin, which is often used as a proxy for human skin in biomedical and biological studies, to 1,070 nm laser irradiation, a commonly used wavelength in the middle of the NIR range. Compared with previous models, the update improves the prediction of damage thresholds for both continuous laser exposure as well as exposure to multiple smaller pulses.

According to the authors, one of their key innovations is the derivation and inclusion of realistic scattering and absorption coefficients for the epidermis at 1,070 nm, which relies on the water and melanin content in the tissue. Previous treatments do not adequately account for this, which leads to inaccuracies in predictions of the skin’s temperature distribution.

“The same principles could be applied to any wavelength if you know their optical properties,” said author Michael DeLisi. “The hope is that since it works well for this somewhat more complex case, it will also work well for simpler cases where there is more absorption at the surface.”

Additional factors, such as variations in melanin and the presence of hair follicles, need to be better understood to help develop informed safety requisites. Once these are accounted for, the model can help balance the tradeoff between safety and efficiency.

Source: “Computational modeling and damage threshold prediction of continuous-wave and multiple-pulse porcine skin laser exposures at 1070 nm,” by Michael P. DeLisi, Nicholas J. Gamez, Clifton D. Clark III, Semih S. Kumru, Benjamin A. Rockwell, and Robert J. Thomas, Journal of Laser Applications (2021). The article can be accessed at https://doi.org/10.2351/7.0000367 .