Depending on wavelength and pigmentation, human skin can reflect up to 70% of incident laser light. Now a human study has confirmed the theoretical model that “photon recycling” of reflected laser light can improve skin response to treatment with a laser.
Noting that laser treatment effects are created only by the light that is absorbed, the researchers examined the potential to return this diffusely reflected light—which can be considered wasted energy—to the skin to increase treatment response. The article, published in Lasers in Surgery and Medicine (LSM), the official journal of the American Society for Laser Medicine and Surgery, Inc. (ASLMS), was written by Drs. Edward V. Ross, Jill Raythen, and laser pioneer R. Rox Anderson.
“We performed the study to determine if there was a real role for photon recycling in a clinical device,” Dr. Ross said in a press release. “We made a working prototype photon recycler and showed that it increases skin response to laser exposure. The recycler recovers lost photons and returns them like a boomerang to the skin surface. In the red and near-infrared spectral region, photon recycling could produce very large improvements in the energy available for treatment.”
In this study, 13 adult volunteers with Fitzpatrick skin types I–IV were exposed to a pulsed dye laser operated at 585 nm, 450 microseconds pulse duration in a uniform 5 mm circular exposure spot without skin cooling on matched contralateral test sites on the volar forearms.
A laser handpiece fitted with an aluminized hemispherical mirror with a reflectance of 67% was used on one arm. Results showed that the mean purpura threshold fluence with the reflector was 3.1 J/cm² (0.5 SD), and 3.7 J/cm² without the reflector (0.36 SD) (p<0.001). The mean laser-induced purpura lesion diameter was approximately 5.3 mm with the reflector and 5.0 mm without the reflector. These results indicate that recycling reflected laser light can increase skin response and potentially improve the therapeutic response.