The explosive vaporization of melanosomes in situ in skin during pulsed laser irradiation (pulse duration less than 1 microsecond) is observed as a visible whitening of the superficial epidermal layer due to stratum corneum disruption. In this study, the ruby laser (694 nm) was used to determine the threshold radiant exposure, H0 (J/cm 2 ), required to elicit whitening for in vitro black (Negroid) human skin samples which were pre-equilibrated at an initial temperature, Ti , of 0, 20, or 50°. A plot of H0 vs Ti yields a straight line whose x -intercept indicates the threshold temperature of explosive vaporization to be 112±7° (SD, N = 3 ). The slope=\Delta H0/\Delta Ti , specifies the internal absorption coefficient, µa , within the melanosome: µa = -\rho c/(slope(1 + 7.1 Rd)) , where \rho c is the product of density and specific heat, and Rd is the total diffuse reflectance from the skin. A summary of the absorption spectrum ( µa ) for the melanosome interior (351-1064 nm) is presented based on H0 data from this study and the literature. The in vivo absorption spectrum (380-820 nm) for human epidermal melanin was measured by an optical fiber spectrophotometer and is compared with the melanosome spectrum.
S. L. Jacques, D. J. McAuliffe, "The melanosome: threshold temperature for explosive vaporization and internal absorption coefficient during pulsed laser irradiation," Photochemistry & Photobiology,53, 769-75 (1991).