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A series of experiments are conducted in vivo using Yucatan mini-pigs (Sus scrofa domestica) to determine thermal damage thresholds to the skin from 1940-nm continuous-wave thulium fiber laser irradiation. Experiments employ exposure durations from 10 ms to 10 s and beam diameters of approximately 4.8 to 18 mm. Thermal imagery data provide a time-dependent surface temperature response from the laser. A damage endpoint of minimally visible effect is employed to determine threshold for damage at 1 and 24 h postexposure. Predicted thermal response and damage thresholds are compared with a numerical model of optical-thermal interaction. Results are compared with current exposure limits for laser safety. It is concluded that exposure limits should be based on data representative of large-beam exposures, where effects of radial diffusion are minimized for longer-duration damage thresholds

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 microsecond to 1540 nm including pulse durations of 31 ns and 600 microseconds. 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 microseconds 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 ED50 of 8.2 mJ of pulse energy. After 24 hours, most of the lesions disappeared and the ED50 increased by almost a factor of 3 to 21.3 mJ. There was a similar trend for the 1.318 mu laser for spot sizes of 2 mm and 5 mm where the ED50 was larger after 24 hours. However, for the 1.54 mu laser with a spot size of 5 mm, the ED50 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 microseconds for spot sizes of 0.7 mm and 1.3 mm diameter after 24 hours. Different results were obtained for the 1540 run laser at 600 microsecond pulse durations where the ED50 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)., Prepared in collaboration with the U.S. Air Force Research Laboratory, Brooks City AFB, TX. Presented at the Optical Interactions with Tissue and Cells (18th) held in San Jose, CA on 22-24 Jan 2007. Published in Progress in Biomedical Optics and Imaging, v8 n12, ISSN 1605-744; Proceedings of the SPIE, v6435 paper 64350W, Feb 2007, ISBN 9780819465481. This article is from ADA484275 Conference on Optical Interactions with Tissue and Cells (18th) Held in San Jose, California on January 22-24, 2007

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 microns and 1.5 microns). 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., Prepared in collaboration with Northrop Grumman, San Antonio, TX. Presented at the Optical Interactions with Tissue and Cells (18th) held in San Jose, CA on 22-24 Jan 2007. Published in Progress in Biomedical Optics and Imaging, v8 n12, ISSN 1605-744; Proceedings of the SPIE, v6435 article 643504, Feb 2007, ISBN 9780819465481. This article is from ADA484275 Conference on Optical Interactions with Tissue and Cells (18th) Held in San Jose, California on January 22-24, 2007

Skin damage thresholds were measured and compared with theoretical predictions using a skin thermal model for near-IR laser pulses at 1318 nm and 1540 nm. For the 1318-nm data, a Q-switched, 50-ns pulse with a spot size of 5 mm was applied to porcine skin and the damage thresholds were determined at 1 hour and 24 hours post-exposure using Probit analysis. The same analysis was conducted for a Q-switched, 30-ns pulse at 1540 nm with a spot size of 5 mm. The Yucatan mini-pig was used as the skin model for human skin due to its similarity to pigmented human skin. The ED50 for these skin exposures at 24 hours post-exposure was 10.5 J/cm2 for the 1318-nm exposures, and 6.1 J/cm2 for the 1540-nm exposures. These results were compared to thermal model predictions. We show that the thermal model fails to account for the ED50 values observed. A brief discussion of the possible causes of this discrepancy is presented. These thresholds are also compared with previously published skin minimum visible lesion (MVL) thresholds and with the ANSI Standard's MPE for 1318-nm lasers at 50 ns and 1540-nm lasers at 30 ns., Published in Optical Interactions with Tissue and Cells XVII, Proceedings of SPIE, V6084, 60840E, 2006.

Er:glass lasers have been in operation with both long pulses (hundreds of microseconds) and Q-switched pulses (50 to 100 ns) for more than 35 yr. The ocular hazards of this laser were reported early, and it was determined that damage to the eye from the 1.54-microns wavelength occurred mainly in the cornea where light from this wavelength is highly absorbed. Research on skin hazards has been reported only in the past few years because of limited pulse energies from these lasers. Currently, however, with pulse energies in the hundreds of joules, these lasers may be hazardous to the skin in addition to being eye hazards. We report our minimum visible lesion (MVL) threshold measurements for two different pulse durations and three different spot sizes for the 1.54-microns wavelength using porcine skin as an in vivo model. We also compare our measurements to results from our model, based on the heat transfer equation and the rate process equation. Our MVL-ED50 thresholds for the long pulse (600 microsecs) at 24 h postexposure were measured to be 20, 8.1, and 7.4 J cm2 for spot diameters of 0.7, 1.0, and 5 mm, respectively. Q-switched laser pulses of 31 ns had lower ED50 (estimated dose for a 50% probability of laser-induced damage) thresholds of 6.1 J cm(2) for a 5-mm-diam, top-hat spatial profile laser pulse., Published in Journal of Biomedical Optics, v11 n2 p024001-1-024001-8 March/April 2006.

Terawatt (TW) lasers have become commonplace since the development of the chirped-pulse amplification method using Ti:sapphire and Nd:glass laser rods. We have measured the minimum visible lesion (MVL) thresholds for porcine1 (Yucatan minipig) skin using TW laser pulses. Our system produced laser pulses at 810 nm and sub-50 femtoseconds. These 1-2 TW laser pulses created multiple self-focusing (SF) filaments during propagation and were directed on the flanks of mini-pigs under anesthesia. We measured the pulse energies necessary to determine the ED50 skin damage thresholds., The original document contains color images. Pub. in Lasers in Surgery and Medicine, v37, p59-63, 2005.

Applications of ultrashort pulse laser systems have increased dramatically in the past several years. Retinal exposure to these laser pulses can produce visible lesions with pulse energies of less than 1 microjoule (microJ) per pulse. Our research has found a reduction in the energy required for retinal damage as pulse duration is decreased from the nanosecond (ns) to femtosecond (fs) regime. With this data, new laser safety standards are being proposed to reduce the dangers and uncertainties when working around these lasers., The original document contains color images. All DTIC reproductions will be in black and white.

This report describes the ultrashort pulse laser system, USP-II, installed in the research laboratory and which is comprised of components manufactured by both Spectra-Physics and Coherent Laser Group. This laser system uses state of the art laser technology to provide very high energy single pulses in the visible and near IR spectra for pulsewidths near 100 femtoseconds This report describes in detail the turn-on and operating procedures so that the system operator can bring it up to specificationc and fine-tune the subsystems to give optimum pulsewidth and energy pulse outputs. The basic system has been configured to operate on a single 4 by 12 ft optical bench with some diagnostic instruments permanently mounted to the table. The major subsystems which comprise the USP-II are described briefly as to their operating characteristics and how the output characteristics of each unit affects the output of the following unit. This report is not designed to replace the operating procedures of each subsystem but rather to describe how the complete system works in unison. Each subsystem is described ir the same order as required to turn on the system and reach specified outputs. The theory of operation is incorporated into this turn-On procedure along with optimizing procedures. If any subsystem output does not meet its specifications, the operator is referred to the manufacturer's operating and maintenance procedures for that particular laser. Correct output signals for each laser are described and optimizing procedures for obtaining these optimum levels are also described. This report should be adequate for the daily operation of the system if no problems occur within any subsystem.

A study of the various probit methods to analyze biological data was undertaken to understand the various methods and to determine the requirements for the input data as to distribution, number, and tightness of data for the desired results. Calculations were run for many data sets, and results were compared. Graphical analysis and the Karber method were used along with the SAS Probit Procedure and EZ-Probit. All four methods provided very close agreement on most data sets, and the EZ-Probit program provided almost identical information to the SAS Probit Procedure. Real biological data sets were used for comparison purposes, and three other data sets were made up to simulate real data (with variations in the number and distribution of data points). Fiducial limits at the 95% confidence level were also calculated and compared. For those data sets which had no fiducial limits with SAS Probit at the 95% confidence interval, 85% confidence levels were calculated with the EZ-Probit method because it is not possible to adjust the confidence levels with SAS Probit. Different data sets were run in an attempt to minimize the amount of additional data points needed for an existing data set to tighten the fiducial limits and to show the correlation with a chi square distribution. Finally, it will be shown that the probability distributions from 0.01 to 0.99 are identical out to four decimal places for the SAS Probit and EZ-Probit and that there are only minor differences in the fiducial limits between the two methods for some data sets. Appendix A contains the program required to run the SAS Probit on a PC computer. The EZ-Probit method is included in Appendix B.

In vivo retinal injury studies using ultrashort-pulse lasers at visible wavelengths for both rabbit and primate eyes have been completed, and the results are presented herein for laser-induced breakdown (LIB) and bubble generation. Results of previous measurements for the millimum visible lesion (MVL) threshold doses for both primate and rabbit eyes were reported earlier for pulsewidths from 4 nanoseconds (ns) to as low as 90 femtoseconds (fs). We have recorded on video the first in vivo LIB in vitreous using both albino (New Zealand white) and pigmented (Dutch-belted) rabbit and rhesus monkey eyes with 580-nanometer (nm), 120-fs pulses. We believe the phenomena responsible for bubble generation to be LIB because of the extremely high irradiances within the focused beam and because of the very low absorption properties of the vitreous humor. The laser-generated LIB-ED(50) bubble threshold for the monkey eye was 0.56 uJ at 120 fs. Results of our nonlinear modeling and calculations for self-focusing within the eye and for LIB thresholds are presented and are compared with our experimental results. Data is presented which show that LIB thresholds cannot be reached with MVL-ED(50) doses until the pulsewidth drops to <600 fs and the retinal image diameter is close to 10 micrometers (um). Self-focusing and LIB are the two nonlinear effects shown to affect the visible lesion thresholds, and our results also explain why it is so difficult to produce hemorrhagic lesions in either the rabbit or primate eye with visible 100-uJ, 100-fs laser pulses.