| Ultrashort Laser Retinal Damage Threshold Mechanisms |
15 Jan 2010 |
11 pages |
| Authors:
Benjamin A Rockwell; Robert J Thomas; Alfred Vogel; TASC INC SAN ANTONIO TX
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 | Ultrashort lasers have been adapted for use in a variety of applications from micromachining of dielectrics to atmospheric spectro-chemistry. These lasers emit almost exclusively in the retinal hazard wavelength regime, making them potential sources for both accidental vision loss, but also candidates for biomedical applications where precise alteration of tissues is an objective. We review the mechanisms for damaging the retina at the threshold for the lowest energy where any ... |
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| Roles of Tunneling, Multiphoton Ionization, and Cascade Ionization for Femtosecond Optical Breakdown in Aqueous Media |
Sep 2009 |
207 pages |
| Authors:
Alfred Vogel; Benjamin A Rockwell; LUBECK MEDICAL UNIV (GERMANY) MEDICAL LASER CENTER
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| The interplay of the various ionization mechanisms reveals itself through the dependence of breakdown events on laser parameters such as pulse duration, wavelength, and pulse energy. In the past, the dependence of the breakdown threshold on pulse duration has attracted most attention because of the lowering of the energy threshold with decreasing pulse duration that enables precise material processing. In the present study, these aspects are included because we use ... |
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| First-Order Model of Thermal Lensing in a Virtual Eye |
Mar-2009 |
12 pages |
| Authors:
Clark; Robert J Thomas; Rebecca L Vincelette; Ashley J Welch; Benjamin A Rockwell; Clifton D III; TEXAS UNIV AT SAN ANTONIO
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| An ABCD beam-propagation method was used to build a first-order mathematical model of a thermal lens effect from a near-infrared laser beam in water and ocular media. The model was found to fit experimental z-x scan data best when the thermo-optic coefficient dn/dT of liquid water at 292 K was -4.46x10(-5) K(-1). The physiological parameters of the human eye were simulated in a simple eye model using this fitted dn/dT ... |
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| Trends in Retinal Damage Thresholds from 100-Millisecond Near-Infrared Laser Radiation Exposures: A Study at 1,110, 1,130, 1,150, and 1,319 nm |
Jan 2009 |
10 pages |
| Authors:
Rebecca L Vincelette; Benjamin A Rockwell; Jeff W Oliver; Semih S Kumru; Robert J Thomas; Kurt J Schuster; Gary D Noojin; Aurora D Shingledecker; Dave J Stolarski; Ashley J Welch; AIR FORCE RESEARCH LAB BROOKS AFB TX HUMAN EFFECTIVENESS DIR/BIODYNAMICS AND PROTECTION DIV
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| Retinal damage thresholds from 100-millisecond exposures to laser radiation for wavelengths between 1,100 and 1,350nm have never previously been established. We sought to determine the retinal damage threshold for 100- millisecond exposures of near-infrared (NIR) laser radiation wavelengths at 1,110, 1,130, 1,150, and 1,319 nm. These data were then used to create trends for retinal damage thresholds over the 1,100?1,350nm NIR region based upon linear absorption of laser radiation in ... |
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| Thermal Lensing in Ocular Media Exposed to Continuous Wave Near-Infrared Radiation: the 1150-1350-nm Region |
Oct-2008 |
11 pages |
| Authors:
Robert J Thomas; Rebecca L Vincelette; Ashley J Welch; Benjamin A Rockwell; David J Lund; TEXAS UNIV AT AUSTIN DEPT OF BIOMEDICAL ENGINEERING
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| Abstract. Ocular damage threshold data remain sparse in the continuous wave CW, near-infrared NIR radiation region save for the 1300-nm area that has been investigated in the past several decades. The 1300-nm ocular damage data have yielded unusual characteristics where CW retinal damage was observed in rabbit models, but never in nonhuman primate models. This paper reviews the existing 1300-nm ocular damage threshold data in terms of the fundamental criteria ... |
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| Infrared Laser Damage Thresholds for Skin at Wavelengths from 0.810 to 1.54 Microns for Femtosecond to Microsecond Pulse Durations |
Jan 2007 |
12 pages |
| Authors:
Clarence P Cain; William P Roach; David J Stolarski; Gary D Noojin; Semih S Kumru; Kevin L Stockton; Justin J Zohner; Benjamin A Rockwell; NORTHROP GRUMMAN SAN ANTONIO TX
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| 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. ... |
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| Modeling of Surface Thermodynamics and Damage Thresholds in the IR and THz Regime |
Jan 2007 |
12 pages |
| Authors:
Clark; C D III; Robert J Thomas; Paul D Masebergh; Gavin D Buffington; Lance J Irvin; Jacob Stolarski; Benjamin A Rockwell; NORTHROP GRUMMAN SAN ANTONIO TX
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| The Air Force Research Lab has developed a configurable, two-dimensional, thermal model to predict laser-tissue interactions, and to aid in predictive studies for safe exposure limits. The model employs a finite-difference, time-dependent method to solve the two-dimensional cylindrical heat equation (radial and axial) in a biological system construct. Tissues are represented as multi-layer structures, with optical and thermal properties defined for each layer, are homogeneous throughout the layer. Multiple methods ... |
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| Comparative Analysis of Histological Results of Visible Lesion Thresholds for Thermal and LIB Induced Skin Damage at 1.3 microns and 1.5 microns |
Jan 2007 |
10 pages |
| Authors:
Justin J Zohner; David J Stolarski; Ginger M Pocock; Jerry R Cowart; Clark; Clifton D III; Robert J Thomas; Clarence P Cain; Semih S Kumru; Benjamin A Rockwell; AIR FORCE RESEARCH LAB MESA AZ HUMAN EFFECTIVENESS DIRECTORATE
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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 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. |
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| Thermal Lensing in the Ocular Media |
Jan 2007 |
7 pages |
| Authors:
Rebecca L Vincelette; Robert J Thomas; Benjamin A Rockwell; Ashley J Welch; AIR FORCE RESEARCH LAB BROOKS AFB TX
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| A tissue phantom of water with an absorbing dye, Allura Red, was used to observe the effects of thermal lensing in a thick sample exposed to a CW 532 nm Verdi laser. A collimated beam was sent through a sample 2.9 cm thick. Results from the collimated beam revealed qualitative information about thermal lensing in a liquid media. The studies presented here argue the relevance of incorporating oscillating factors such ... |
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| Visible Lesion Laser Thresholds in Cynomolgus (Macaca fascicularis) Retina with a 1064-nm, 12-ns Pulsed Laser |
Jan 2007 |
12 pages |
| Authors:
Jeffrey W Oliver; David J Stolarski; Gary D Noojin; Harvey M Hodnett; Michelle L Imholte; Benjamin A Rockwell; Semih S Kumru; AIR FORCE RESEARCH LAB BROOKS AFB TX OPTICAL RADIATION
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| 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 ... |
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| Damage Thresholds for Exposure to NIR and Blue Lasers in an In Vitro RPE Cell System |
Jul 2006 |
10 pages |
| Authors:
Michael L Denton; Michael S Foltz; Larry E Estlack; David J Stolarski; Gary D Noojin; Robert J Thomas; Debbie Eikum; Benjamin A Rockwell; AIR FORCE RESEARCH LAB BROOKS AFB TX OPTICAL RADIATION
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| Until reliable nonanimal systems of analysis are available, animal models will be necessary for ocular laser hazard analysis and for evaluating clinical applications. The purpose of this work was to demonstrate the utility of an in vitro system for laser bioeffects by identifying photothermal and photochemical cytotoxicity thresholds for continuous-wave (cw) and mode-locked (ml) laser exposures. Exogenous melanosomes were added to hTERT-RPE1 cells in exposure wells 1 day before laser ... |
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| Visible Lesion Thresholds with Pulse Duration, Spot Size Dependency, and Model Predictions for 1.54-mum Near-Infrared Laser Pulses Penetrating Porcine Skin |
22 Mar 2006 |
9 pages |
| Authors:
Clarence P Cain; Kurt J Schuster; Justin J Zohner; Kevin L Stockton; David J Stolarski; Robert J Thomas; Benjamin A Rockwell; William P Roach; NORTHROP GRUMMAN SAN ANTONIO TX
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| 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 ... |
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| Photochemical Damage from Chronic 458-nm Laser exposures in an Artificially Pigmented hTERT-RPE1 Cell Line |
Feb 2006 |
13 pages |
| Authors:
Michael S Foltz; Norris A Whitlock; Larry E Estlack; Manuel A Figueroa; Robert J Thomas; Benjamin A Rockwell; Michael L Denton; AIR FORCE RESEARCH LAB BROOKS AFB TX OPTICAL RADIATION
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| Artificially pigmented hTERT-RPE1 cells were exposed to a mode-locked or continuous wave (CW) laser at 458 run for one hour in a modified culture incubator. Exposure conditions were selected to give greatest likelihood of damage due to a photochemical mechanism, with interest in possible differences between CW and mode-locked damage thresholds. After post-exposure-recovery (PER) for either 1-hour or 24-hour, cells were concurrently stained with annexin V and 6-CFDA to determine ... |
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| Precision Targeting With a Tracking Adaptive Optics Scanning Laser Ophthalmoscope |
Jan 2006 |
12 pages |
| Authors:
Daniel X Hammer; R D Ferguson; Chad E Bigelow; Nicusor V Iftimia; Teoman E Ustun; Gary D Noojin; David J Stolarski; Harvey M Hodnett; Michelle L Imholte; Semih S Kumru; Michelle N McCall; Cynthia A Toth; Benjamin A Rockwell; PHYSICAL SCIENCES INC ANDOVER MA
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| Precise targeting of retinal structures including retinal pigment epithelial cells, feeder vessels, ganglion cells, photoreceptors, and other cells important for light transduction may enable earlier disease intervention with laser therapies and advanced methods for vision studies. A novel imaging system based upon scanning laser ophthalmoscopy (SLO) with adaptive optics (AO) and active image stabilization was designed, developed, and tested in humans and animals. An additional port allows delivery of aberration-corrected ... |
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| Threshold Damage of In vivo Porcine Skin at 2000 nm Laser Irradiation |
Jan 2006 |
10 pages |
| Authors:
Bo Chen; Daniel C O'Dell; Sharon L Thomsen; Benjamin A Rockwell; Ashley J Welch; AIR FORCE RESEARCH LAB BROOKS AFB TX OPTICAL RADIATION
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| A series of experiments were conducted in vivo on female Yucatan mini-pigs to determine the ED50 damage thresholds for 2000 nm continuous wave laser irradiation. These results provide new information for refinement of Maximum Permissible Exposure (MPE). The study employed Gaussian laser beam exposures with spot diameters (1/e2) of 4.83 mm, 9.65 mm and 14.65 mm and exposure durations of 0.25 s, 0.5 s, 1.0 s and 2.5 seconds as ... |
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| An Alternative Method of Evaluating 1540nm Exposure Laser Damage Using an Optical Tissue Phantom |
Jan 2006 |
11 pages |
| Authors:
Nichole M Jindra; Manuel A Figueroa; Lucas J Chavey; Justin J Zohner; Benjamin A Rockwell; AIR FORCE RESEARCH LAB BROOKS CITY-BASE TX
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| An optical phantom was designed to physically and optically resemble human tissue, in an effort to provide an alternative for detecting visual damage resulting from inadvertent exposure to infrared lasers. The phantom was exposed to a 1540-nm, Erbium:Glass, Q-switched laser with a beam diameter of 5 mm for 30 ns at varying power levels. Various materials were tested for use in the phantom; including agar, ballistic media, and silicone rubber. ... |
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| Injury Thresholds for Topical-Cream-Coated Skin of Hairless Guinea Pigs (cavia porcellus) in the Near Infrared Region |
Jan 2006 |
12 pages |
| Authors:
Ginger M Pocock; Justin J Zohner; David J Stolarski; Kelvin C Buchanan; Nichole M Jindra; Manuel A Figueroa; Lucas J Chavey; Michelle L Inholte; Robet J Thomas; Benjamin A Rockwell; AIR FORCE RESEARCH LAB BROOKS AFB TX OPTICAL RADIATION
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| 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 ... |
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| Visible Lesion Thresholds and Model Predictions for Q-Switched 1318-nm and 1540-nm Laser Exposures to Porcine Skin |
Jan 2006 |
10 pages |
| Authors:
Justin J Zohner; Kurt J Schuster; Lucas J Chavey; David J Stolarski; Semih S Kumru; Benjamin A Rockwell; Robert J Thomas; Clarence P Cain; AIR FORCE RESEARCH LAB BROOKS AFB TX OPTICAL RADIATION
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| 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 ... |
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| Detection of 2-Photon Oxidation from a NIR Laser Using Confocal Microscopy |
Jan 2006 |
10 pages |
| Authors:
Kurt J Schuster; Larry E Estlack; Benjamin A Rockwell; Michael L Denton; AIR FORCE RESEARCH LAB BROOKS AFB TX OPTICAL RADIATION
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| Recent studies have determined that photochemical oxidation in cultured cells can be detected at peak irradiances as low as 8.5x10(8) W cm(-2) (87-fs pulse). Fluorescent dyes, such as CM-H(2)DCFDA, enable us to quantify the oxidation response of cells to mode-locked near-infrared (NIR) laser exposure. Using a modified confocal microscope, we characterize the time-dependent 2-photon induced fluorescence generated from a given NIR laser exposure. When cultured cells were then pre-loaded with ... |
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| A Comparison of a First-Order Thermal Lensing Model to a Closed Aperture Z-Scan for the Propagation of Light in Ocular Media |
Jan 2006 |
10 pages |
| Authors:
Rebecca L Vincelette; Robert J Thomas; Benjamin A Rockwell; Ashley J Welch; AIR FORCE RESEARCH LAB BROOKS CITY-BASE TX
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| The phenomenon of thermal lensing was investigated in water using a Z-scan method and corresponding first-order mathematical models. Data from first-order thermal lensing models and ABCD beam propagation methods were used to simulate the non-linear absorption of water held in a thin sample cuvette for a Z-scan optical set up of CW cases at 1313 run. The single beam closed aperture Z-scan was then used to determine the non-linear absorption ... |
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| ED50 Study of Femtosecond Terawatt Laser Pulses on Porcine Skin |
13 Jun 2005 |
6 pages |
| Authors:
Semih S Kumru; Clarence P Cain; Gary D Noojin; Mary F Cooper; Michelle L Imholte; David J Stolarski; Duane D Cox; Carrie C Crane; Benjamin A Rockwell; AIR FORCE RESEARCH LAB BROOKS CITY-BASE TX HUMAN PERFORMANCE WING (711TH)
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| 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 ... |
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| Porcine Skin ED50 Damage Thresholds for 2,000 nm Laser Irradiation |
Jan 2005 |
10 pages |
| Authors:
Bo Chen; Daniel C O'Dell; Sharon L Thomsen; Benjamin A Rockwell; Ashley J Welch; TEXAS UNIV AT AUSTIN BIOMEDICAL ENGINEERING LAB
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| The objectives of this research are to gain refinement in safe-exposure limits, indicated by the maximum permissible exposure (MPE) limits, the minimum visible lesion thresholds for three spot sizes (5-15 mm) and four exposure durations (0.25-2.5 seconds) were determined for the skin at 2,000 nm continuous wave laser irradiation. A series of experiments were conducted in vivo on female Yucatan mini-pigs to determine the ED50 damage thresholds for 2,000 nm ... |
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