100-megawatt power Q-switched Er-glass laser

Optical Interactions With Tissue and Cells XVII

et al. 2006

Self Cite

The reflectance and absorption of the skin plays a vital role in determining how much radiation will be absorbed by human tissue. Any substance covering the skin would change the way radiation is reflected and absorbed and thus the extent of thermal injury. Hairless guinea pigs (cavia porcellus) in vivo were used to evaluate how the minimum visible lesion threshold for single-pulse laser exposure is changed with a topical agent applied to the skin. The ED 50 for visible lesions due to an Er: glass laser at 1540-nm with a pulse width of 50-ns was determined, and the results were compared with model predictions using a skin thermal model. The ED 50 is compared with the damage threshold of skin coated with a highly absorbing topical cream at 1540 nm to determine its effect on damage pathology and threshold. The ED 50 for the guinea pig was then compared to similar studies using Yucatan minipigs and Yorkshire pigs at 1540-nm and nanosecond pulse duration. 1, 2 The damage threshold at 24-hours of a Yorkshire pig for a 2.5-3.5-mm diameter beam for 100 ns was 3.2 Jcm -2 ; very similar to our ED 50 of 3.00 Jcm -2 for the hairless guinea pigs.

Section: Lasermentioning

confidence: 99%

Injury thresholds for topical-cream-coated skin of hairless guinea pigs ( cavia porcellus ) in the near-infrared region

Pocock

Zohner

Optical Interactions With Tissue and Cells XVII

et al. 2006

Self Cite

“…Table-top laser systems are capable of producing microsecond pulses with tens of joules of energy per pulse. 1 Once the first experimental data showed the benefits of picosecond and femtosecond pulses compared to nanosecond pulses for ablation-mediated, precise tissue removal in fairly transparent tissue 2 , few studies have explored the damage mechanism of surface LIB plasma damage on skin from nanosecond pulses in the NIR. Due to the proliferation of high-peak-power systems in the NIR for military and industrial applications, the damage mechanisms associated with these systems are now of interest from a laser-safety perspective.…”

Section: Introductionmentioning

confidence: 99%

Comparative analysis of histological results of visible lesion thresholds for thermal and LIB induced skin damage at 1.3 μm and 1.5 μm

Zohner¹,

Pocock³

et al. 2007

SPIE Proceedings

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An assessment of skin damage caused by near-IR laser exposures is reported. The damage from two distinct laser-tissue temporal regimes is compared at two wavelengths (1.3 µm and 1.5 µm). Skin damage caused by thermal effects from single laser pulses is compared to damage caused by LIB (laser induced breakdown) using histological examinations. Modeling applications are explored to determine crossover points between thermal and photomechanical damage thresholds.

“…For the longer pulse durations at 1540 nm, pulse energies of 100 joules or more can be obtained at pulse durations of ~1 ms. For nanosecond pulses at this wavelength, a mechanical Q-switch is generally used to shorten the pulse duration. A system developed in our laboratory 1 can generate ~31 ns pulses. The American National Standards Institute (ANSI) 2 divides the electromagnetic spectrum into bands of wavelength regions.…”

Section: Introductionmentioning

confidence: 99%

Infrared laser damage thresholds for skin at wavelengths from 0.810 to 1.54 microns for femto-to-microsecond pulse durations

Cain

Roach²,

et al. 2007

SPIE Proceedings

Self Cite

In this paper we report on our combined measurements of the visible lesion thresholds for porcine skin for wavelengths in the infrared from 810 nm at 44 fs to 1318 nm at pulse durations of 50 ns and 350 µs to 1540 nm including pulse durations of 31 ns and 600 µs. We also measure thresholds for various spot sizes from less than 1 mm to 5 mm in diameter. All three wavelengths and five pulse durations are used extensively in research and the military. We compare these minimum visible lesion thresholds with ANSI standards set for maximum permissible exposures in the infrared wavelengths. We have measured non-linear effects at the laser-tissue interface for pulse durations below 1 µs and determined that damage at these short pulse durations are usually not thermal effects. Damage at the skin surface may include acoustical effects, laser ablation and/or low-density plasma effects, depending on the wavelength and pulse duration. Also the damage effects may be short-lived and disappear within a few days or may last for much longer time periods including permanent discolorations. For femtosecond pulses at 810 nm, damage was almost instant and at 1 hour had an ED 50 of 8.2 mJ of pulse energy. After 24 hours, most of the lesions disappeared and the ED 50 increased by almost a factor of 3 to 21.3 mJ. There was a similar trend for the 1.318 µ laser for spot sizes of 2 mm and 5 mm where the ED 50 was larger after 24 hours. However, for the 1.54 µ laser with a spot size of 5 mm, the ED 50 actually decreased by a small amount; from 6.3 Jcm -2 to 6.1 Jcm -2 after 24 hours. Thresholds also decreased for the 1314 nm laser at 350 µs for spot sizes of 0.7 mm and 1.3 mm diameter after 24 hours. Different results were obtained for the 1540 nm laser at 600 µs pulse durations where the ED 50 decreased for spot sizes 1 mm and below, but increased slightly for the 5 mm diameter spot size from 6.4 Jcm -2 to 7.4 Jcm -2