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The damage patterns on the skin indicated the number of filaments in the laser pulse. Many of the pulses produced only superficial damage that disappeared in 24 hours and that nearly three times the pulse energy was required to cause subdural or cellular damage. With further research, non-thermal tissue ablation using TW laser pulses could provide a viable alternative to current techniques of laser use in dermatology.

A series of experiments in a new animal model for retinal damage, cynomolgus monkeys (Macaca fascicularis), have been conducted to determine the damage threshold for 12.5-nanosecond laser exposures at 1064 nm. These results provide a direct comparison to threshold values obtained in rhesus monkey (Macaca mulatta), which is the model historically used in establishing retinal maximum permissible exposure (MPE) limits. In this study, the irradiance level of a collimated Gaussian laser beam of 2.5 mm diameter at the cornea was randomly varied to produce a rectangular grid of exposures on the retina. Exposures sites were fundoscopically evaluated at post-irradiance intervals of 1 hour and 24 hours. Probit analysis was performed on dose-response data to obtain probability of response curves. The 50% probability of damage (ED50) values for 1 and 24 hours post-exposure are 28.5(22.7-38.4) LJ and 17.0(12.9-21.8) PU, respectively. These values compare favorably to data obtained with the rhesus model, 28.7(22.3-39.3) lJ and 19.1(13.6-24.4) pJ, suggesting that the cynomolgus monkey may be a suitable replacement for rhesus monkey in photoacoustic minimum visible lesion threshold studies.

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We report on our measurements of the Minimum Visible Lesion (MVL) thresholds for porcine * skin [Yucatan mini-pig (Sus scrofa domestica)] for laser exposures at 810 nm and sub-50 femtosecond (fs) laser pulses. In this study we measured the ED 50 skin thresholds from laser pulses that produced multiple self-focusing filaments while propagating from the laser to the skin. These high-powered (1-2 terawatt) filaments were focused on the flank of mini-pig and three trained readers determined the number of lesions becoming visible at 1-hour and 24-hour post-exposure. The observed damage patterns on the skin surface indicated the number of filaments in the laser pulse and these were photographed for future reference. Histological sections were obtained after both readings and the results will be reported later for sub-surface damage. The threshold using preliminary data at 1-hour was 9 mJ of energy and increased to 25 mJ after 24 hours. This increase in threshold indicated that many of the laser pulses produced only superficial damage (erthemia) that disappeared in 24 hours and that nearly 3 times the pulse energy was required to cause subsurface or cellular damage.