Porcine skin damage thresholds for 0.6 to 9.5 cm beam diameters from 1070-nm continuous-wave infrared laser radiation

Abstract

There is an increasing use of high-power fiber lasers in manufacturing and telecommunications industries operating in the infrared spectrum between 1000 and 2000 nm, which are advertised to provide as much as 10 kW continuous output power at 1070 nm. Safety standards have traditionally been based on experimental and modeling investigations with scant data available for these wavelengths. A series of studies using 1070-nm infrared lasers to determine the minimum visible lesion damage thresholds in skin using the Yucatan miniature pig (Sus scrofa domestica) for a range of beam diameters (0.6, 1.1, 1.9, 2.4, 4.7, and 9.5 cm) and a range of exposure durations (10 ms to 10 s) is presented. Experimental peak temperatures associated with each damage threshold were measured using thermal imaging. Peak temperatures at damage threshold for the 10-s exposures were ∼10°C lower than those at shorter exposures. The lowest and highest experimental minimum visible lesion damage thresholds were found to have peak radiant exposures of 19 and 432 J/cm2 for the beam diameter-exposure duration pairs of 2.4 cm, 25 ms and 0.6 cm, 10 s, respectively. Thresholds for beam diameters >2.5 cm had a weak to no effect on threshold radiant exposure levels for exposure times ≤0.25 s, but may have a larger effect on thresholds for exposures ≥10 s.

Thermal damage thresholds for multiple-pulse porcine skin laser exposures at 1070 nm

“…The relationship also fits a power function, specifically: where m T is the aforementioned thermal slope term (°C∕J∕cm 2 ) and t is the total sequence duration (s). This finding is compatible with the observations made by Vincelette et al 8 and Oliver et al, 12 who noted lower peak temperature changes at longer exposure duration ED 50 s compared to shorter exposure duration ED 50 s.…”

“…Oliver et al 12 observed that for CW exposures to 1319-nm laser radiation for 0.25, 1, 2.5, and 10 s at two different beam diameters, only the 0.25-s cases featured a 1-h ED 50 that was greater than its 24-h counterpart. However, Vincelette et al 8 found that the 1-h ED 50 was greater than the 24-h ED 50 in 13 of 16 cases for 1070-nm laser radiation, across a wide range Table 3 Probit results for lesions 1 and 24 h after exposure to 1070-nm laser pulses with a beam diameter of 0.973 cm (1∕e 2 ). The laser total on-time for each set of parameters is 10 s. of exposure durations and beam diameters.…”

“…Subsequent studies also explored the 1060-nm wavelength for both human and porcine subjects, for 1-s 4,5 and 0.2-to 0.3-s 6,7 exposures. A recent study by Vincelette et al 8 determined the contribution of beam diameter to porcine skin MVL thresholds for 1070-nm laser exposure durations ranging from 10 ms to 10 s. DeLisi et al 9 further investigated skin injury response to 1070-nm lasers but at suprathreshold endpoints for 3-and 100-ms exposures in excised porcine tissue. Cain et al 10 and Montes de Oca et al 11 presented porcine skin MVL thresholds for light near 1315 nm and pulse durations of 0.35 ms, whereas Oliver et al 12 provided thresholds at 1319 nm for exposure durations of 0.25, 1, 2.5, and 10 s. Several porcine skin MVL threshold studies for 1540-nm laser are available, including for 30-ns, 13,14 0.6-, 13 0.8-, 15 and 60-ms pulses.…”

“…38,39 This observation is due to a significant disparity between the optical absorption coefficients of hair (10 −1 cm −1 ) and skin tissues (10 −1 cm −1 ) for this wavelength region. [40][41][42][43][44] Vincelette et al 8 reported that high-energy exposures of porcine skin at 1070 nm often resulted in distinctly observable incineration events, with hair follicles catching fire and burning away. High-speed thermal imagery from that study reveals the drastically higher temperatures of hair follicles when compared to the baseline tissue within the beam.…”

“…In order to address part of this data gap and as a continuation of the work started by Vincelette et al, 8 we performed a series of in vivo experiments using Yucatan mini-pigs to determine the MVL limits for 1070-nm multiple-pulse skin exposure to relatively "long" pulses (100 μs to 10 s). Given the average power limitations of the lasers and the recognition that the primary damage mechanism would be photothermal, we subdivided pulse train parameters into "total on-times" (TOTs) of 0.01, 0.1, and 10 s and differentiated them with duty cycle as opposed to the PRF.…”