Background

Depending on wavelength and pigmentation, human skin can reflect up to 70% of incident laser light.

Aims

We tested the hypothesis that returning (“recycling”) this diffusely reflected light to the site of laser exposure would increase cutaneous response.

Materials and Methods

Thirteen adult volunteers with Fitzpatrick skin types I–IV participated in this IRB-approved study. Matched contralateral test sites on the volar forearms 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 one arm, the laser handpiece was fitted with an aluminized hemispherical mirror with a reflectance of 67%. The minimum fluence causing skin purpura, and the purpura lesion diameter were measured.

Results

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.

Conclusion

Consistent with a theoretical model and in vitro measurements, this human study confirms that “recycling” reflected laser light can increase skin response. Potentially, the therapeutic response can also be improved with “photon recycling.”