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Probabilistic risk assessment is an acceptable technique for laser hazard analysis in uncontrolled environments. Risk is a combination of probability of exposure and probability of an injury resulting from that exposure. A dose-response model quantifies the probability of injury. In the present study, we developed a human dose-response model for laser induced retinal injuries. It consists of two sub-models, one for the mean and the other for the standard deviation of the dose-response probability distribution. The model for the mean fits experimental data to a simple three-parameter expression as a function of wavelength, exposure duration, and retinal tissue type. A scaling factor converts the fit to be appropriate for exposure of humans. A new human vulnerability model, based on the diversity of relevant physical characteristics within the human population, determines the standard deviation. Since the dose-response model is specific to retinal injuries, the variables are refractive error, ocular transmittance, and retinal absorptance. A Monte Carlo simulation with probability distributions for these variables, based on age, determines the standard deviation as a function of wavelength. We present details of the dose-response model along with their application to common human populations.Probabilistic risk assessment is an acceptable technique for laser hazard analysis in uncontrolled environments. Risk is a combination of probability of exposure and probability of an injury resulting from that exposure. A dose-response model quantifies the probability of injury. In the present study, we developed a human dose-response model for laser induced retinal injuries. It consists of two sub-models, one for the mean and the other for the standard deviation of the dose-response probability distribution. The model for the mean fits experimental data to a simple three-parameter expression as a function of wavelength, exposure duration, and retinal tissue type. A scaling factor converts the fit to be appropriate for exposure of humans. A new human vulnerability model, based on the diversity of relevant physical characteristics within the human population, determines the standard deviation. Since the dose-response model is specific to retinal injuries, the variables are refractive error, ocular transmi...

Reflections of high energy lasers from surfaces can present hazards to persons and instruments at significant distances. Heating from these lasers causes changes in the reflection characteristics of surfaces they illuminate. As such, reflections from these surfaces cannot be properly modeled with static bidirectional reflectance distribution functions (BRDFs), but require time- dynamic BRDFs. Moreover, the time-evolution of the surface reflections is not deterministic, but can vary even when the materials and illumination conditions are nearly identical, such that only probabilistic characterization is realistic. Due to the swiftly changing nature of the reflections, traditional BRDF measurements with goniometric instruments are impossible, so BRDFs must be deduced from images of the reflected light incident on a screen intercepting a portion of the reflection solid angle. A new BRDF model describes these complex probabilistic dynamic BRDFs with only four intuitive parameters for a given laser wavelength, irradiance, and duration, where these parameters have central values and statistical variances over discrete regimes corresponding to surface conditions. An automated procedure determines appropriate parameter values and variances from captured screen images, requiring only a single angle of laser incidence. Parameters from sample tests illustrate the model.Reflections of high energy lasers from surfaces can present hazards to persons and instruments at significant distances. Heating from these lasers causes changes in the reflection characteristics of surfaces they illuminate. As such, reflections from these surfaces cannot be properly modeled with static bidirectional reflectance distribution functions (BRDFs), but require time- dynamic BRDFs. Moreover, the time-evolution of the surface reflections is not deterministic, but can vary even when the materials and illumination conditions are nearly identical, such that only probabilistic characterization is realistic. Due to the swiftly changing nature of the reflections, traditional BRDF measurements with goniometric instruments are impossible, so BRDFs must be deduced from images of the reflected light incident on a screen intercepting a portion of the reflection solid angle. A new BRDF model describes these complex probabilistic dynamic BRDFs with only four intuitive parameters for a given laser wavelength,...

In cases where a laser source produces a pattern that is asymmetric on the retina, a modeling-based approach can be used to calculate a retinal thermal response to predict damage and make meaningful comparisons to exposure limit trends. The SESE (Scalable Effects Simulation Environment) model is a full 3D thermal finite-volume model that can simulate multiple independently controlled laser sources with unique wavelength, spatial profile, pulse duration, and power. The model is well suited to evaluate asymmetric sources since there is not an assumed axial symmetry and the spatial profile of the laser can be adjusted as a function of time. Several examples of asymmetric sources include multi-fiber bundle exposures, scanning beams, and scintillating sources. We use the SESE model to predict trends in retinal injury threshold for these cases and to help inform the laser safety community by providing estimates for safe and unsafe levels of exposure. We also introduce factors that inform hazard levels based on relative exposure conditions.In cases where a laser source produces a pattern that is asymmetric on the retina, a modeling-based approach can be used to calculate a retinal thermal response to predict damage and make meaningful comparisons to exposure limit trends. The SESE (Scalable Effects Simulation Environment) model is a full 3D thermal finite-volume model that can simulate multiple independently controlled laser sources with unique wavelength, spatial profile, pulse duration, and power. The model is well suited to evaluate asymmetric sources since there is not an assumed axial symmetry and the spatial profile of the laser can be adjusted as a function of time. Several examples of asymmetric sources include multi-fiber bundle exposures, scanning beams, and scintillating sources. We use the SESE model to predict trends in retinal injury threshold for these cases and to help inform the laser safety community by providing estimates for safe and unsafe levels of exposure. We also introduce factors that inform hazard levels based on ...

Computational models are capable of quantifying the expected thermal response of biological tissue to laser irradiation. A typical laser-tissue model accounts for optical energy deposition, heat transfer, and damage assessment, with the later often represented by calculation of the Arrhenius integral. Previous studies have successfully employed these methods to predict skin damage thresholds at laser wavelengths with high absorption in water, and usually for single continuous-wave exposures. However, there remains a need for a robust and accurate predictive model in low-absorption, high-scattering cases, such as for lasers in the near-infrared (NIR) region near 1 µm, where a large volume of tissue is heated simultaneously. This study presents a framework for modeling laser irradiation of skin tissue at 1070-nm for both continuous-wave and pulsed exposures with durations ranging from 10−2 to 101 seconds. We report the modeled skin thermal responses alongside thermal camera recordings of in-vivo porcine exposures as validation of simulation integrity. Comparisons of modeled damage thresholds calculated by the Arrhenius integral with past experimentally-determined minimum visible lesion ED50 data demonstrate a high degree of accuracy. The techniques outlined by this study provide a useful tool in assessing potentially hazardous near-infrared laser exposure scenarios while informing future investigations into modeling skin laser exposure at these wavelength regions.Computational models are capable of quantifying the expected thermal response of biological tissue to laser irradiation. A typical laser-tissue model accounts for optical energy deposition, heat transfer, and damage assessment, with the later often represented by calculation of the Arrhenius integral. Previous studies have successfully employed these methods to predict skin damage thresholds at laser wavelengths with high absorption in water, and usually for single continuous-wave exposures. However, there remains a need for a robust and accurate predictive model in low-absorption, high-scattering cases, such as for lasers in the near-infrared (NIR) region near 1 µm, where a large volume of tissue is heated simultaneously. This study presents a framework for modeling laser irradiation of skin tissue at 1070-nm for both continuous-wave and pulsed exposures with durations ranging from 10−2 to 101 seconds. We report the modeled skin thermal responses alongside thermal camera recordings of in-vivo porcine exp...

As solid-state laser technology continues to mature, high-energy lasers operating in the near-infrared (NIR) band are increasingly being utilized in manufacturing, medical, and military applications. Guidelines for the safe use of these systems have been established as formulations of maximum permissible exposure (MPE) limits for a given set of laser parameters, based on past experimental studies of exposure thresholds causing injury to the skin and eyes. However, in the case of skin, these formulations do not take into account the pulse characteristics of the exposure and only utilize the total exposure duration when calculating the MPE. The purpose of this study was to characterize the skin response to multiple-pulsed high-energy laser exposure at the NIR wavelength of 1070 nm, at a constant beam diameter of 1 cm, and using anesthetized Yucatan mini-pig subjects. A constant total laser-on time was explored as single- and multiple-pulse sequences. Multiple-pulse exposures had identical individual pulse durations, and different duty cycles were employed in order to characterize the effect of variable thermal additivity. Skin damage was quantified by the minimally visible lesion (MVL) metric as judged by a plurality of three observers at the 24-hour interval post-exposure. Injury thresholds for all exposure conditions were calculated as the median effective dose (ED50), based on varying laser power across subjects. The results of this study will provide a quantitative basis for the incorporation of multiple-pulsed laser exposure into existing standards and augment data contained in the existing ED50 database.As solid-state laser technology continues to mature, high-energy lasers operating in the near-infrared (NIR) band are increasingly being utilized in manufacturing, medical, and military applications. Guidelines for the safe use of these systems have been established as formulations of maximum permissible exposure (MPE) limits for a given set of laser parameters, based on past experimental studies of exposure thresholds causing injury to the skin and eyes. However, in the case of skin, these formulations do not take into account the pulse characteristics of the exposure and only utilize the total exposure duration when calculating the MPE. The purpose of this study was to characterize the skin response to multiple-pulsed high-energy laser exposure at the NIR wavelength of 1070 nm, at a constant beam diameter of 1 cm, and using anesthetized Yucatan mini-pig subjects. A constant total laser-on time was explored as single- and multiple-pulse sequences. Multiple-pulse exposures had identical individual pulse d...

Computational modeling of laser-tissue interaction in the retina can be used to predict the thermal response to a laser exposure. For in vivo photochemical damage threshold experiments, where temperature rise in retinal tissue cannot be conveniently measured, modeling was used to predict retinal temperature response. Laser exposures from sixteen in vivo experiments with wavelengths in the visible band were selected to represent a wide range of powers and exposure durations. It is hypothesized that photochemical damage mechanisms were responsible for changes to subjects’ retinal tissue and that thermal response is not a significant contribution to this observed damage.Results from the model predicted peak temperature responses of less than one Kelvin in the RPE layer of the retina where the largest temperature rise would be expected. These findings support the claim that changes to retinal tissue were not directly caused by a thermally induced mechanism.Computational modeling of laser-tissue interaction in the retina can be used to predict the thermal response to a laser exposure. For in vivo photochemical damage threshold experiments, where temperature rise in retinal tissue cannot be conveniently measured, modeling was used to predict retinal temperature response. Laser exposures from sixteen in vivo experiments with wavelengths in the visible band were selected to represent a wide range of powers and exposure durations. It is hypothesized that photochemical damage mechanisms were responsible for changes to subjects’ retinal tissue and that thermal response is not a significant contribution to this observed damage.Results from the model predicted peak temperature responses of less than one Kelvin in the RPE layer of the retina where the largest temperature rise would be expected. These findings support the claim that changes to retinal tissue were not directly caused by a thermally induced mechanism.

Laser safety control measures are often based upon the laser hazard class for the system. The Class 3R accessible emission limit is commonly used as a threshold hazard class for the assignment of laser eye protection, medical surveillance, and other administrative and engineering control measures. In this paper, we review the ANSI Z136.1-2014 exposure limits and class 3R accessible emission limits, and compare historical bioeffects data in order to examine risks for exposure at the 3R level. Focus areas of most concern are the consideration of exposure to extended-source and multi-pulse exposure limits. This information is of use to laser safety programs when making decisions regarding a specific laser system’s control measures assignment and is assembled to inform future revisions to national and international safety standards.Laser safety control measures are often based upon the laser hazard class for the system. The Class 3R accessible emission limit is commonly used as a threshold hazard class for the assignment of laser eye protection, medical surveillance, and other administrative and engineering control measures. In this paper, we review the ANSI Z136.1-2014 exposure limits and class 3R accessible emission limits, and compare historical bioeffects data in order to examine risks for exposure at the 3R level. Focus areas of most concern are the consideration of exposure to extended-source and multi-pulse exposure limits. This information is of use to laser safety programs when making decisions regarding a specific laser system’s control measures assignment and is assembled to inform future revisions to national and international safety standards.

The American National Standards Institute (ANSI) accredited standard committee for the development of user standards for laser safety is designated as the ASC Z136. Its subcommittees develop ten different standards and recommended practices for laser safety. For those involved in the practice and policy of laser safety, or in areas of research that influence exposure limits definition, involvement in the ASC Z136 is of great value to the community. This manuscript summarizes the organization, procedures, membership, and current activities of the ASC Z136 and its subcommittees.The American National Standards Institute (ANSI) accredited standard committee for the development of user standards for laser safety is designated as the ASC Z136. Its subcommittees develop ten different standards and recommended practices for laser safety. For those involved in the practice and policy of laser safety, or in areas of research that influence exposure limits definition, involvement in the ASC Z136 is of great value to the community. This manuscript summarizes the organization, procedures, membership, and current activities of the ASC Z136 and its subcommittees.

Recent changes in the maximum permissible exposure limits (MPE) for near-infrared (NIR) laser exposures are analysed in light of nonlinear optical phenomena. We have evaluated the thresholds for supercontinuum generation for ultrashort laser exposures in the NIR and compared these with the MPE’s. Because of the strong increase in ocular absorption in the 1.2 to 1.4 micrometer range, evaluation of this phenomenon is necessary because any shift in laser energy in the eye to shorter wavelengths could lead to unforeseen increases in hazards for the retina. Trends will be discussed regarding proposed changes to the safe exposure limits in the NIR regime.

Reflection of a laser beam from a surface depends on the optical properties of the surface, and can have components that are diffuse (in all directions) or specular (in one direction). Hazard distances tend to be short and easily calculated for diffuse reflections. However, specular reflections have longer hazard distances and their calculation poses challenges due to the spatial and temporal characteristics of the reflected beam. We have developed and refined a methodology to calculate hazard distances from specular reflections. This methodology uses analytical expressions to determine the irradiance and exposure time of the reflected beam, from which hazard distances are calculated. The method accounts for the properties of the incident beam, the material reflecting properties, and the shape of the surface.The motivations and concepts of the specular methodology are presented, along with the equations resulting from this approach. The spatial and temporal characteristics of the reflected beam for a specific laser and surface are calculated from the application of these equations. These characteristics are then used to determine either localization of hazardous regions in the surrounding space or a description of possible hazards at specific locations. Examples of the application of the specular methodology are presented with their corresponding hazardous conditions.Reflection of a laser beam from a surface depends on the optical properties of the surface, and can have components that are diffuse (in all directions) or specular (in one direction). Hazard distances tend to be short and easily calculated for diffuse reflections. However, specular reflections have longer hazard distances and their calculation poses challenges due to the spatial and temporal characteristics of the reflected beam. We have developed and refined a methodology to calculate hazard distances from specular reflections. This methodology uses analytical expressions to determine the irradiance and exposure time of the reflected beam, from which hazard distances are calculated. The method accounts for the properties of the incident beam, the material reflecting properties, and the shape of the surface.The motivations and concepts of the specular methodology are presented, along with the equations resulting from this approach. The spatial and temporal characteristics of the reflected beam for a spec...

Reflections of high energy lasers from targets present safety challenges, as the resulting hazard distances can be significant. We have developed two different but complementary simulations to determine hazard zones resulting from high energy laser reflections. One, the High Energy Laser Collateral Assessment Tool (HELCAT), is a high-fidelity successor to the Laser Range Safety Tool (LRST), which had been developed specifically for distant targets. HELCAT has an improved user interface and uses first-principle physics calculations to obtain reflected irradiances at observer locations for each time step in a simulation. The time histories of the irradiances are used to determine the hazard zone. It supports a variety of simple and complex targets, trajectories, reflecting properties of materials, and observer locations. The other, termed the Specular Methodology, considers only specular reflections to derive analytical expressions for the irradiance and exposure time at observer locations. The hazard zone is derived from these values. While the Specular Methodology is an approximation of reflected laser light compared to HELCAT, it performs calculations much more rapidly. Therefore, we have been able to incorporate probabilistic techniques into the Specular Methodology, which provides additional information for risk assessment. Comparisons between the two simulations indicate acceptable agreement for equivalent scenarios.Reflections of high energy lasers from targets present safety challenges, as the resulting hazard distances can be significant. We have developed two different but complementary simulations to determine hazard zones resulting from high energy laser reflections. One, the High Energy Laser Collateral Assessment Tool (HELCAT), is a high-fidelity successor to the Laser Range Safety Tool (LRST), which had been developed specifically for distant targets. HELCAT has an improved user interface and uses first-principle physics calculations to obtain reflected irradiances at observer locations for each time step in a simulation. The time histories of the irradiances are used to determine the hazard zone. It supports a variety of simple and complex targets, trajectories, reflecting properties of materials, and observer locations. The other, termed the Specular Methodology, considers only specular reflections to derive analytical expressions for the irradiance and exposure time at observer locations. The hazard zone ...

We measured threshold temperatures for cell death resulting from short (0.1 – 1.0 s) 514-nm laser exposures using an in vitro retinal model. Real-time thermal imaging at sub-cellular resolution provided temperature information that was spatially correlated with cells at the boundary of cell death, as indicated by post-exposure fluorescence images. Our measurements indicated markedly similar temperatures, not only around individual boundaries (single exposure), but among all exposures of the same duration in a laser irradiance-independent fashion. Two different methods yielded similar threshold temperatures with low variance. Considering the experimental uncertainties associated with the thermal camera, an average peak temperature of 53 ± 2 °C was found for laser exposures of 0.1, 0.25, and 1.0 s. Additionally, we found a linear relationship between laser exposure duration and time-averaged integrated temperature. The mean thermal profiles for cells at the boundary of death were assessed using the Arrhenius rate law using three different parameter sets (frequency factor and energy of activation) found in the literature.We measured threshold temperatures for cell death resulting from short (0.1 – 1.0 s) 514-nm laser exposures using an in vitro retinal model. Real-time thermal imaging at sub-cellular resolution provided temperature information that was spatially correlated with cells at the boundary of cell death, as indicated by post-exposure fluorescence images. Our measurements indicated markedly similar temperatures, not only around individual boundaries (single exposure), but among all exposures of the same duration in a laser irradiance-independent fashion. Two different methods yielded similar threshold temperatures with low variance. Considering the experimental uncertainties associated with the thermal camera, an average peak temperature of 53 ± 2 °C was found for laser exposures of 0.1, 0.25, and 1.0 s. Additionally, we found a linear relationship between laser exposure duration and time-averaged integrated temperature. The mean thermal profiles for cells at the boundary of death were assessed using the Arrheniu...

We report on the first of a series of modeling studies examining multiple-pulse damage thresholds in the retina. This effort focuses on near-infrared wavelength (1064nm – 1350nm) point source (small spot) thermal damage thresholds, but some general properties of multiple pulse exposures are obtained. We analyze the threshold trends as a function of wavelength, pulse width, inter-pulse spacing, and number of pulses, spanning a large parameter space.The rules used for determining multiple-pulse maximum permissible exposures (MPEs) in the current ANSI Z136.1 standard are evaluated, and we show that the MPE trends to not follow the damage threshold trends for many pulse train configurations, leading to large variations in the safety factor. We investigate a system for setting multiple-pulse MPEs that more closely follows the damage threshold trends, and also propose changes to the current multiple-pulse MPE rules.We report on the first of a series of modeling studies examining multiple-pulse damage thresholds in the retina. This effort focuses on near-infrared wavelength (1064nm – 1350nm) point source (small spot) thermal damage thresholds, but some general properties of multiple pulse exposures are obtained. We analyze the threshold trends as a function of wavelength, pulse width, inter-pulse spacing, and number of pulses, spanning a large parameter space.The rules used for determining multiple-pulse maximum permissible exposures (MPEs) in the current ANSI Z136.1 standard are evaluated, and we show that the MPE trends to not follow the damage threshold trends for many pulse train configurations, leading to large variations in the safety factor. We investigate a system for setting multiple-pulse MPEs that more closely follows the damage threshold trends, and also propose changes to the current multiple-pulse MPE rules.

The difficulty in creating retinal lesions in the near-infrared has been well known for many years. While it is expected that retinal lesions will not be created outside the retinal hazard regime (i.e. 400 nm – 1400 nm), the expectation is that they should be the first response of ocular tissues within that regime as laser exposure is increased. It was shown by previous authors that retinal lesions in the 1300-1400 nm range require very large powers to be created. We will elucidate the phenomena responsible for this dramatic increase in power required for retinal damage and propose new, novel mechanisms are at play for longer exposures in this interesting wavelength regime.The difficulty in creating retinal lesions in the near-infrared has been well known for many years. While it is expected that retinal lesions will not be created outside the retinal hazard regime (i.e. 400 nm – 1400 nm), the expectation is that they should be the first response of ocular tissues within that regime as laser exposure is increased. It was shown by previous authors that retinal lesions in the 1300-1400 nm range require very large powers to be created. We will elucidate the phenomena responsible for this dramatic increase in power required for retinal damage and propose new, novel mechanisms are at play for longer exposures in this interesting wavelength regime.

A practical approach to laser safety planning for the research laboratory must consider flexibility as a key component. Refinement of experimental design, a process of the scientific method, is inevitable. Each time the optical layout is modified, new hazards must be identified and neutralized before continuing normal experimental operation. In order to meet these changing technical demands, the development and implementation of a safe working environment should be both effective and flexible. Laser safety should be part of the culture of the research lab. A laser safety plan should consider the diverse nature of the research laboratory, with emphasis on the types of lasers used, end points of analysis, and duration of experimental procedures. Important factors for implementing a safety plan include the types of equipment required (influenced by the laser systems employed), detailed low-power alignment procedures, and control measures (both engineering and administrative) at key locations and times within the laboratory procedures. These control measures and procedures are required to maintain a safe working environment for all researchers in the laboratory. Overall, the approach to a laser safety plan must be logical and systematic with careful pre-planning for beam path layout. Together, these considerations work to promote the safe use of lasers in the research laboratory. We present a methodology that implements these approaches to laser safety and some real-world examples of how we have applied this methodology in our laboratory.A practical approach to laser safety planning for the research laboratory must consider flexibility as a key component. Refinement of experimental design, a process of the scientific method, is inevitable. Each time the optical layout is modified, new hazards must be identified and neutralized before continuing normal experimental operation. In order to meet these changing technical demands, the development and implementation of a safe working environment should be both effective and flexible. Laser safety should be part of the culture of the research lab. A laser safety plan should consider the diverse nature of the research laboratory, with emphasis on the types of lasers used, end points of analysis, and duration of experimental procedures. Important factors for implementing a safety plan include the types of equipment required (influenced by the laser systems employed), detailed low-power alignment procedures, and control measures (both engineering and administrative) at key locations and times within...

A three-dimensional thermal model is used to investigate the damage threshold for hazard assessments of lasers projecting non-uniform or non-symmetric images on the retina. The two source types considered are an array of sources and an elliptical source. In the array of sources, the spacing and size ratios of the sources are varied to determine their effect on the damage threshold. Additionally, it is determined where the spacing and size of the sources can be approximated by a large uniform source. For the elliptical source, the damage threshold is found as a function of the ratio of minor and major diameters. Short and long exposure times are considered for both the array of sources and the elliptical source.A three-dimensional thermal model is used to investigate the damage threshold for hazard assessments of lasers projecting non-uniform or non-symmetric images on the retina. The two source types considered are an array of sources and an elliptical source. In the array of sources, the spacing and size ratios of the sources are varied to determine their effect on the damage threshold. Additionally, it is determined where the spacing and size of the sources can be approximated by a large uniform source. For the elliptical source, the damage threshold is found as a function of the ratio of minor and major diameters. Short and long exposure times are considered for both the array of sources and the elliptical source.

High energy lasers present new challenges for safety evaluation. Not only is the direct beam hazardous, but the reflected beam may also cause injury. Two important issues with high energy laser safety have been addressed in simulations used to model reflected-beam hazards: the reflecting properties of materials and the time history of exposure. The reflecting properties are quantified by the Bi-directional Reflectance Distribution Function (BRDF), and a technique has been developed to extract parameters for BRDF models, primarily the Maxwell-Beard model, from measurement data and to calculate the reflected irradiance at an observer. In addition, the reflecting properties of materials often change upon heating, so a procedure using a camera and screen is being used to measure the time-varying BRDF of materials, which in turn is modeled empirically with spherical harmonics. Because the use of high energy lasers is often dynamic in nature, involving a moving laser, target, or observer, the time-history of exposure to the observer is calculated in the simulations. A sliding-window algorithm compares the time-history of exposure to maximum permissible exposure limits for a range of exposure times in order to determine if a hazardous condition exists for the observer.High energy lasers present new challenges for safety evaluation. Not only is the direct beam hazardous, but the reflected beam may also cause injury. Two important issues with high energy laser safety have been addressed in simulations used to model reflected-beam hazards: the reflecting properties of materials and the time history of exposure. The reflecting properties are quantified by the Bi-directional Reflectance Distribution Function (BRDF), and a technique has been developed to extract parameters for BRDF models, primarily the Maxwell-Beard model, from measurement data and to calculate the reflected irradiance at an observer. In addition, the reflecting properties of materials often change upon heating, so a procedure using a camera and screen is being used to measure the time-varying BRDF of materials, which in turn is modeled empirically with spherical harmonics. Because the use of high energy lasers is often dynamic in nature, involving a moving laser, target, or observer, the time-history of ex...

Many medical studies have investigated the safety threshold of ocular media at various wavelengths. Understanding and determining the damage threshold of laser exposure to the retina is important in order to set safety guidelines. A phenomenon known as thermal lensing where a media’s index of refraction changes as the laser energy is absorbed causes the beam profile and subsequently the position of the focal point of the beam to change as the temperature changes within the media. These changes in ocular media such as vitreous and aqueous humor, the cornea, crystalline lens, and retina all result in a slight change in the beam profile making the prediction of the focal point and laser spot size at the retina difficult to accurately predict. This paper describes how the effects of thermal lensing in the eye can be investigated to aid in determining the damage threshold for pulse durations of a few nanoseconds and continuous wave, CW, laser irradiation delivered to the retina and the relationship of how the damage is related to multiple pulse exposures. We present a first-order modeling effort for the thermal lensing effect in the eye along with initial estimates of impact on damage thresholds as predicted through computational biophysics thermal damage models.Many medical studies have investigated the safety threshold of ocular media at various wavelengths. Understanding and determining the damage threshold of laser exposure to the retina is important in order to set safety guidelines. A phenomenon known as thermal lensing where a media’s index of refraction changes as the laser energy is absorbed causes the beam profile and subsequently the position of the focal point of the beam to change as the temperature changes within the media. These changes in ocular media such as vitreous and aqueous humor, the cornea, crystalline lens, and retina all result in a slight change in the beam profile making the prediction of the focal point and laser spot size at the retina difficult to accurately predict. This paper describes how the effects of thermal lensing in the eye can be investigated to aid in determining the damage threshold for pulse durations of a few nanoseconds and continuous wave, CW, laser irradiation delivered to the retina and the relationship of how the ...

Laser-induced breakdown has been implicated in the threshold for damage of the retina below 100 fs. Laser pulses shorter than 50 fs possess enough wavelength bandwidth that during propagation, the pulse can lengthen or shorten because of the differences in refractive indices for different wavelengths. This phenomenon is called group velocity dispersion (GVD). We have modeled the dependence of the laser-induced breakdown threshold propagation in the eye in the wavelength band relevant for retinal damage (400 – 1400 nm). These computations take into account both aberrations and GVD while allowing for changes in the input pulse chirp. The computations were performed on a Beowulf-class parallel computer cluster. The trends in retinal damage were predicted to determine if extension of the 1 ps to 100 fs maximum permissible exposure levels provide significant protection from lasers with these pulse durations.

Recent laser and broadband bioeffects applications have extended the requirements of modeling damage to the retina beyond single-wavelength sources. Also, the creation and validation of safe exposure limits for arbitrary combinations of spectral content is extremely difficult due to the large parameter space available. We present recent updates to computational methods which provide predictions of damage thresholds under conditions of user-specified spectral and temporal content. The modeling results are compared with recent and historical multi-wavelength laser exposure and broadband emitter damage thresholds measured in the laboratory. In all cases, the computational biophysics model is able to predict damage thresholds and trends within the uncertainties of the laboratory measurements.Recent laser and broadband bioeffects applications have extended the requirements of modeling damage to the retina beyond single-wavelength sources. Also, the creation and validation of safe exposure limits for arbitrary combinations of spectral content is extremely difficult due to the large parameter space available. We present recent updates to computational methods which provide predictions of damage thresholds under conditions of user-specified spectral and temporal content. The modeling results are compared with recent and historical multi-wavelength laser exposure and broadband emitter damage thresholds measured in the laboratory. In all cases, the computational biophysics model is able to predict damage thresholds and trends within the uncertainties of the laboratory measurements.

Since Nov. 2001, the Optical Radiation Branch of the US Air Force Research Lab and the UK Military Laser Safety Committee have been collaborating on development of military laser safety models which use Probabilistic Risk Assessment (PRA) techniques. This collaboration was partly motivated by recent US development of military High Energy Laser systems, which require probabilistic analysis in order to properly assess the potential risks posed by testing and deployment. The US wishes to leverage UK expertise in this area, with the goal of producing a common probabilistic laser safety tool to meet future US/UK needs. The US has recently made a proposal for an expanded collaboration, in which an existing piece of USAF software, the LRMS/PRA Concept Demonstrator, will be used as a platform to host UK PRA mathematical models. The new code would be jointly owned and would be the common US/UK tool for performing military laser safety analyses.Since Nov. 2001, the Optical Radiation Branch of the US Air Force Research Lab and the UK Military Laser Safety Committee have been collaborating on development of military laser safety models which use Probabilistic Risk Assessment (PRA) techniques. This collaboration was partly motivated by recent US development of military High Energy Laser systems, which require probabilistic analysis in order to properly assess the potential risks posed by testing and deployment. The US wishes to leverage UK expertise in this area, with the goal of producing a common probabilistic laser safety tool to meet future US/UK needs. The US has recently made a proposal for an expanded collaboration, in which an existing piece of USAF software, the LRMS/PRA Concept Demonstrator, will be used as a platform to host UK PRA mathematical models. The new code would be jointly owned and would be the common US/UK tool for performing military laser safety analyses.

The Optical Radiation Branch of the Air Force Research Laboratory (AFRL/HEDO) has previously built the Laser Range Management System (LRMS) software to provide laser hazard analyses in support of realistic and safe training with military laser systems. LRMS makes use of laser safety standards and military-use tactics to calculate and display laser surface hazard zones on range maps that have been registered to digital tenain elevation data. LRMS is a totally integrated environment designed to provide Range Safety Officers with a realistic visualization of these zones in a training environment.The Optical Radiation Branch of the Air Force Research Laboratory (AFRL/HEDO) has previously built the Laser Range Management System (LRMS) software to provide laser hazard analyses in support of realistic and safe training with military laser systems. LRMS makes use of laser safety standards and military-use tactics to calculate and display laser surface hazard zones on range maps that have been registered to digital tenain elevation data. LRMS is a totally integrated environment designed to provide Range Safety Officers with a realistic visualization of these zones in a training environment.