At select wavelengths, near infrared (IR) light is absorbed in the preretinal media of the eye. This produces small transient increases in temperature that temporarily alter the local index of refraction. If the IR exposure is sufficiently high, a momentary reduction in the focusing power of the eye can be induced through an effect known as thermal lensing. Fundamental optical interaction and safety aspects of this phenomenon have been demonstrated previously in animal and artificial eye models. However, whether the effect will induce an observable visual change in human subjects has not been explored. Here, results of a pilot study are shown where eight human subjects were exposed to an IR laser at levels that were below the safe exposure limit. The exposures did induce a transient visual distortion if sufficiently high levels were used. While the description of the visual change varied between subjects, this experiment was able to determine a general guideline for power needed to induce significant effects in human subjects.
Iris recognition is considered to be one of the most accurate biometrics, but user inconvenience during the image
acquisition phase has limited its widespread use. Image capture is largely constrained to well-controlled situations,
where subjects must remain relatively stationary or within a capture "volume" close to the camera. As a consequence,
iris recognition systems have a reputation for being borderline intrusive, and less friendly for both subjects and
operators. To support the development of a more natural and acceptable iris capture system, we have sought to develop
a pre-processor driven imaging system that predicts a maximal opportunity window for iris capture for a subject engaged
in natural motion based on predictive head and eye movement algorithms. This paper describes a first-generation
prototype iris capture system that utilizes this approach. A wide field of view camera is used to track a person's face and
provide head pose data as input to the predictive algorithm. The algorithm is then used to direct a second narrow field of
view camera to capture the iris image more reliably. This system serves as a platform for further development of head
movement prediction algorithms used to enhance the probability of iris capture in moving or uncooperative subjects.
The U.S. Dept. of Defense (DOD) is currently developing and testing a number of High Energy Laser (HEL) weapons systems. DOD range safety officers now face the challenge of designing safe methods of testing HEL's on DOD ranges. In particular, safety officers need to ensure that diffuse and specular reflections from HEL system targets, as well as direct beam paths, are contained within DOD boundaries. If both the laser source and the target are moving, as they are for the Airborne Laser (ABL), a complex series of calculations is required and manual calculations are impractical. Over the past 5 years, the Optical Radiation Branch of the Air Force Research Laboratory (AFRL/HEDO), the ABL System Program Office, Logicon-RDA, and Northrup-Grumman, have worked together to develop a computer model called teh Laser Range Safety Tool (LRST), specifically designed for HEL reflection hazard analyses. The code, which is still under development, is currently tailored to support the ABL program. AFRL/HEDO has led an LRST Validation and Verification (V&V) effort since 1998, in order to determine if code predictions are accurate. This paper summarizes LRST V&V efforts to date including: i) comparison of code results with laboratory measurements of reflected laser energy and with reflection measurements made during actual HEL field tests, and ii) validation of LRST's hazard zone computations.
The Department of Defense has an increasing number of high-energy laser weapons programs with the potential to mature in the not too distant future. However, as laser systems with increasingly higher energies are developed, the difficulty of the laser safety problem increases proportionally, and presents unique safety challenges. The hazard distance for the direct beam can be in the order of thousands of miles, and radiation reflected from the target may also be hazardous over long distances. This paper details the Air Force Research Laboratory/Optical Radiation Branch (AFRL/HEDO) High-Energy Laser (HEL) safety program, which has been developed to support DOD HEL programs by providing critical capability and knowledge with respect to laser safety. The overall aim of the program is to develop and demonstrate technologies that permit safe testing, deployment and use of high-energy laser weapons. The program spans the range of applicable technologies, including evaluation of the biological effects of high-energy laser systems, development and validation of laser hazard assessment tools, and development of appropriate eye protection for those at risk.
As laser systems with increasingly higher energy are developed for military applications, the difficulty of the laser safety problem increases proportionally. The hazard distance for the direct beam can be in the order of thousands of miles, and the potential exists for radiation reflected from the target to be hazardous over long distances. It then becomes impractical to contain the laser beam within the confines of test ranges. This, together with a rapidly changing environment with fast moving laser source and target, has led to the requirement for an integrated modeling and simulation tool to perform the complex series of calculations which are needed to ensure the safe testing and use of these lasers outdoors. The Laser Range Safety Tool (LRST) is being developed to meet this requirement. LRST predicts laser intensity distributions in the physical space surrounding an illuminated target and provides a highly interactive and graphical visualization of the scenario geometry, scattered intensity, and potential hazard zones. A comprehensive validation and verification program involving measurements during high-energy laser range tests is also being undertaken. The inclusion of models for stochastic processes such as aiming and tracking errors, atmospheric turbulence, and risk criteria is also being considered to extend the tools to provide quantitative risk assessment data to support risk management decisions. Finally, as high-energy laser programs move out of the testing phase to training and operational deployment, tools such as these can be enhanced and integrated into real time mission planning and commanders' decision aids.
A deterministic approach to laser hazard assessment is used in most laser safety standards. Personnel are protected from hazardous laser radiation is by defining a space withm which the direct, reflected, or scattered radiation during laser operation exceeds the safe Maximum Permissible Exposure level. Controlling access to this space insures safety. Although this approach has satisfied the commercial and industrial laser communities for many years, it may not be applicable to the highpower (up to megawatt) laser systems currently being developed by the US military. These systems will have extremely long laser hazard distances, and controlling access to this space will be unrealistic, especially when the likelihood of hazardous human exposure is low. For these situations, an alternative analytical approach that estimates both the level of risk and the degree of risk reduction achievable by controlling key contributors can be applied. Analytic risk assessment tools are finding increasing application in a wide variety of hazard assessments, m both industrial and commercial situations. These tools use scientific data, assumptions, and mathematical models to estimate the likelihood, frequency, and severity of harm to people exposed to the hazard. This paper will discusses application of such tools to laser safety and considers the uncertainties associated with probability density functions applied to key factors such as atmospheric scmtillation, reflected radiation, population distribution and ocular injury.
The dependence of retinal damage threshold on laser spot size was examined for two pulsewidth regimes; nanosecond- duration Q-switched pluses from a doubled Nd:YAG laser and microsecond-duration pulses from a flashlamp-pumped dye laser. Threshold determination were conducted for nominal retinal image sizes ranging form 1.5 mrad to 100 mrad of visual field, corresponding to image diameters of approximately 22 micrometers to 1.4 mm on the primate retina. Together, this set of retinal damage threshold reveals the functional dependence of threshold on spot size. The threshold dose was found to vary with the area of the image for larger image sizes. The experimental results were compared to the predictions of the Thompson-Gerstman granular model of laser-induced retinal damage. The experimental and theoretical trends of threshold variation with retinal spot size were essentially the same, with both data sets showing threshold dose proportional to image area for spot sizes >= 150 micrometers . The absolute values predicted by the model, however, were significantly higher than experimental values, possibly because of uncertainty in various biological input parameters, such as the melanosome absorption coefficient and the number of melanosomes per RPE cell.
The dependence of retinal damage threshold on laser spot size was examined for two pulsewidth regimes; nanosecond- duration Q-switched pulses from a doubled Nd:YAG laser and microsecond-duration pulses from a flashlamp-pumped dye laser. Threshold determinations were conducted for nominal retinal image sizes ranging from 1.5 mrad to 100 mrad of visual field, corresponding to image diameters of approximately 22 μm to 1.4 mm on the primate retina. In addition, baseline collimated-beam damage thresholds were determined for comparison to the extended source data. Together, this set of retinal damage thresholds reveals the functional dependence of threshold on spot size. The threshold dose was found to vary with the area of the image for larger image sizes. The results are compared to previously published extended source damage thresholds and to the ANSI Z136.1 laser safety standard maximum permissible exposure levels for diffuse reflections.
The paper represents the results of the intermediate stage of a Ph.D. program exploring an alternative vision system based on an image sensor which would ideally match the characteristics of visual data by the use of spatially adaptive homogeneous low level processing techniques. The work is based on the empirical analysis of simulations of simple analogue resistive networks driven by a linear array of photoreceptors. The feasibility of a homogeneous spatially adaptive space modulated filter is explored and the results of investigations into a dynamic closed loop system are presented.
Laser safety standards and eye protection (filters) are designed to limit ocular exposures to prevent retinal lesions yet " eyesafe^" laser exposures can disrupt vision by causing glare and flashblindness. Protective filters can have opposing effects on visual function. They reduce laser exposures but also reduce task luminance and contrast. Filters alone may interfere with vision and consequently reduce work safety and performance. It is therefore important to be able to predict the effects of both laser exposures and protective filters to assess trade-offs between protection and visual function. This paper briefly reviews the methods concepts and experimental database used in our laboratory to predict laser filter and laser-plus-filter effects on tasks involving visual detection. The modeling approach uses estimates of the spatial distribution of light in the retinal image of the laser source to predict glare flashblindness and retinal lesions. It also considers the non-uniformity of visual abilities across the retina in predicting the impact of a laser exposure of a given size and retinal location. The proposed modeling approach provides a general framework for the interpretation integration and application of data from various studies. It has the potential to assess the effects of lasers and eye-protection devices on vision and to guide visualsimulations of the appearance of displays and scenes after laser exposures. The model is far from complete and is complicated by the number of variables affecting laser
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