Historically many different agencies and standards organizations have proposed laser occupational exposure limits (EL1s) or maximum permissible exposure (MPE) levels. Although some safety standards have been limited in scope to manufacturer system safety performance standards or to codes of practice most have included occupational EL''s. Initially in the 1960''s attention was drawn to setting EL''s however as greater experience accumulated in the use of lasers and some accident experience had been gained safety procedures were developed. It became clear by 1971 after the first decade of laser use that detailed hazard evaluation of each laser environment was too complex for most users and a scheme of hazard classification evolved. Today most countries follow a scheme of four major hazard classifications as defined in Document WS 825 of the International Electrotechnical Commission (IEC). The classifications and the associated accessible emission limits (AEL''s) were based upon the EL''s. The EL and AEL values today are in surprisingly good agreement worldwide. There exists a greater range of safety requirements for the user for each class of laser. The current MPE''s (i. e. EL''s) and their basis are highlighted in this presentation. 2. 0
Since laser exposure in humans is usually limited to accident cases precise definition of its effects on visual function is difficult to come by. In order to determine more precisely these effects and at what exposure levels they occur animal models are required. This immediately poses the problem of how to appropriately ask the animal what it can see. Under the assumption that the visual system of lower primates is sufficiently similar to our own electrophysiological techniques allow us to trace the production of neuroelectric currents in the visual nervous system and thus to make conclusions of function based on signal analysis. These techniques (pattern and luminance electroretinograms and visual evoked potentials) are useful especially in delineating short-term effects (seconds). Since these signals are " large scale " responses their specificity can only be set by precisely delineating the stimuli used to evoke them a variant of the GIGO (garbage in garbage out) rule. The results while obtainable in no other way are therefore limited. Long term effects (chronic alterations in visual function) can also be demonstrated with these techniques. This paper will review both the techniques and the questions to which these techniques have been applied for laser exposure energies ranging from long-term low-level exposures to acute lesion-level exposures in the primate model. 2.
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
Laser applications have proliferated in recent years and as to be expected their presence is no longer confined to the laboratory or places where access to their radiation can be easily controlled. One obvious application where this is so is in military operations where various devices such as laser range finders target designators and secure communications equipment elevate the risk of exposure specifically eye exposure to unacceptable levels. Although the need for eye protection in the laboratory and other controlled areas has been appreciated since the invention of the laser the use of lasers in circumstances where safety or the risk of temporary loss of vision which can not always be ensured by administrative procedures has made adequate eye protection essential. It is the critical nature of many military operations that has driven the search for eye protection against both nuclear and laser radiation. At the same time the requirement to maintain useful vision during irradiation as well as advances in laser technology have complicated the problem enormously. Pertinent aspects of the problem such as laser characteristics- -pulse width repetition rate laser wavelength tunability or agility as well as laser power or energy have been placed in perspective. In addition possible effects on vision for various exposures have been estimated as have the characteristics required of eye protective devices. Various classes of devices are discussed and advantages and disadvantages noted. 1.
Ultraviolet radiation in the ambient environment or from artificial sources may pose both acute and chronic hazards to the skin and the ocular tissues. In general terrestrial conditions have evolved such that there are only narrow safety margins between ambient UV levels and exposure levels harmful to the human. Obvious examples of acute consequences ofUV overexposure are sunburn and snowblindness as well as analogous conditions induced by artificial sources such as the welder''s arc mercury vapor lamps and UV-emitting lasers. Further chronic UV exposure is strongly implicated as a causative agent in certain types of cataract and skin cancer. This presentation will summarize a number of specific cases where UV radiation affected the primate cornea. Data presented will include the action spectra for far- and near-UV induced ocular damage the pulsewidth and total energy dependencies of ocular thresholds studies of cumulative effects of repeated UV exposures and quantitative determinations of tissue repair or recovery rates. Depending on the exposure parameters utilized photochemical thermal or photoablative damage mechanisms may prevail. 1.
Infrared radiation from a CO2 laser at a wavelength of 10.6 im is strongly absorbed by the cornea. Indeed, 99% is absorbed within the first 50 itm of tear film and epithelium. This energy is rapidly converted to heat that initially is concentrated in the volume of absorption and subsequently is conducted to deeper layers of the cornea and beyond. Consequently, various layers of the cornea can sustain thermal damage, depending on the exposure conditions. In this review we summarize very briefly our past work on: epithelial damage thresholds for single- and multiple-pulse exposures having individual pulse durations between 1 ms and 10 s12; endothelial damage thresholds and endothelial temperature histories34; and damage thresholds for stromal cells.5 For very short duration pulses that have extremely high peak irradiance, the possibility for acoustic as well as thermal damage exists. Here we give a more extensive report of new epithelial damage thresholds for single- and multiple-pulse exposures with an individual pulse duration of 80 ns. We note that material is ejected from the corneal surface at near-threshold exposures. This observation is used in conjunction with lesion histology and temperature computations to discuss possible damage mechanisms.
Laser field exposure effects on visual function involve produc tJon of minimal spot irradiation on or near the huntan fovea. Functional effects of such exposure may involve transient or perinanent change in visual function depending upon exposure dose. While Maximun Permissible Exposure (MPE) lirrtits define exposure in terins of threshold retinal niorphological change such limits are not applicable with regard to transient changes in visual function below MPE limits induced by alteration in retinal physiological processes. Mechanisms of transient and permanent functional change reported in these exper iments point out the need to examine laser safety limits in terms of both the functional as well as the morphological disturbance induced in retinal tissue. L
The heat shock response is a phenomenon common to all cells and is characterized by an increase in the rate of synthesis of intracellular heat shock proteins (HSPs) . The response occurs following rapid transient increases in terrerature sufficient to cause stress but not cell death. HSPs appear to perform protective functions that raise the cell''s tolerance to diverse noxious stimuli. Thus we postulated that we could limit laser-induced retinal darriage through induction of the heat shock -response. Corrmon goldfish (C. auratus) made hyperthermic by immersion in 35C water for 15 minutes and radiolabeled with methionine showed retinal liSPs with apparent molecular weights of 110 90 70 and 35 kilodaltons. To test the protective effects of HSPs against laser injury goldfish were made hyperthermic and 4 and 24 hr later their retinas were irradiated with argon laser light (51 4 . 5 nm spot size at the cornea 3. 0 mm irradiance 125 mW/cm2) . NonhyperLhermic animals served as controls. Following 24 hr of recovery fish were terminated and retinas fixed for histology. Fundus photographs were taken irrunediately after laser exposure . Lesion diameters were measured from fundus photographs and evaluated statistically. The mean retinal lesion diameters of fish not subjected to hyperthermJ. a laser exposed 4 hr post hyperLhermia and laser exposed 24 hr post hyperthermia were 10. 25 1. 4 SD 8. 82 2. 1 SD and 6. 78
We present an approach for solving nonlinear coupled differential equations using personal computer spreadsheet programs. This approach is used to model the phenomena of bleaching and dynamic filtering in saturable absorbing media. The numerical results are presented. Because of their convenient features 3-D spreadsheet programs are useful for modeling many similar physical phenomena. 1.
A number of approaches are being explored to provide eye protection against visible wavelength lasers while maintaining adequate transirtission for visual performance. Real protection at this time is provided by fixed wavelength reflectors and absorbers and if a plastic substrate is required only absorbers have been reliably produced. An absorber useful in the visible spectruit must have a very narrow absorption band centered at the appropriate laser wavelength with minimum attenuation outside that band. With such restrictions the choice of absorbers is liirited and many of the choices that do exist are saturable absorbers. A saturable absorber becomes increasingly transparent to an incident laser beam as the irradiance of that beam increases thus it would seem to be a poor choice for ocular protection. Nevertheless for some wavelengths saturable absorbers are the only absorbers available. We have performed some tests with a phthalocyanine dye in a plastic substrate to explore limits within which a saturable absorber can be used without comproruising eye safety. 1
The tristimulus optical interference filter announced last year at the Orlando SPIE Symposium on Aerospace Sensing has been improved by increasing the light transmission in the three passbands and by the addition of an absorptive dye toblock the " blue shift^" of interference filters. Work is in progress to develop comfortable polycarbonate eyewear in place of the bulky prototype goggles. TEXT There is a need to provide eye protection to laboratory personnel at risk from a variety of laser beams and we have demonstrateda unique approach: an optical filter that blocks the entire visible spectrum except for three very narrow passbands - one in the red one in the green and one in the blue. This filter blocks all popular laser wavelengths yet vision through it is bright and clear - and in full natural color. The transmission spectrum is shown in Figure 1. The initial work was reported at the SPIE Technical Symposium on Aerospace Sensing in Orlando 27-31 March 1989 and a prototype goggle was shown there. This filter was originally conceived by Dr. W. A. Thornton and me in late 1987. The basic idea was not new with us it has been known since at least 1860 and is used in the picture tube of every color television set in the world. What was new was the idea''s embodiment in a practical optical filter that could be incorporated
This paper examines the effects of angle of incidence changes on the optical properties of rugate filters. Like quarterwave dielectric stacks rugate filters are sensitive to tilting: their reflectance bands shift to shorter wavelengths and their optical properties become polarization dependent. Tilting a quarterwave stack also produces a drop in the transmittance in the middle of the passband this drop is called the halfwave hole. In single line rugate filters a similar behavior is observed and multiple holes corresponding to harmonics of the main reflectance bands appear in the pass band. In multiline rugate filters the situation is even more complicated: the large number of harmonics already present is increased by supplementary peaks produced by beating between each family of harmonics. All these reflecting bands are located on the short wavelengths side of the main bands and they can be such that most of the light is reflected. Some possible solutions are suggested involving the use of aperiodic structures. 1.
An optical system for laser eye protection application is presented. The optical device includes a first lens having a positive power of magnification a second lens having a negative power of magnification and a flat interference based reflector(s) between the two lenses. Incoming light rays are redirected by the lenses so that they pass through the interference filter at normal incidence. 1.
It is shown that the nonlinearity in the response function of a holographic medium can lead to formation of gratings at the sum and difference frequencies of the exposing standing wave patterns. This nonlinear feature can be ultilized to create reflection holograms at spectral regions where the conventional techniques are not applicable. Specifically it is suggested that NIR or JR rejection filters which are sensorcentered can be obtained using this approach. 1.
The performance of eyesafe erbium:glass lasers operating at a wavelength of 1. 54 urn has been tested under various natural and manmade obscurants. To obtain the maximum amount of information two distinct system configurations were employed. The first a laser cloud mapper was designed to provide a direct depth profile of smoke density and reflectivity as well as target position. The second configuration was a production military laser rangefinder. It is representative of systems currently incorporated in tactical armored vehicles and was used to provide a direct indication of target range. 1.
In 1980 the Army fielded the AN/GVS-5 Nd:YAG hand held laser rangefinder. The use and widespread deployment of the AN/GVS-5 was limited due to concerns for eyesafe operation in training and forceonforce battlefield simulation scenarios. In 1983 the Arniy awarded contracts to develop 1. 54 nticron laser rangefinders to provide eyesafe operation for both training and tactical use. Following the early developmental efforts the Army awarded in 1988 a Development Production Prove Out (DPPO) contract to finalize the design and establish the system to produce thousands of these devices. The product is designated as the AN/PVS-6 Mini Eyesafe Laser Infrared Observation Set (MELIOS) . This paper summarizes the system''s history projected performance and the present status of the program. 1. THE NEED FOR A LASER RANGEFINDER There has always been a need for accurate range information in military operations. Until the advent of the laser the ability to satisfy this need was at best extremely limited. Manual rangefinding techniques include the use of maps and compasses and the estimation of distance to a target by its relative size in sighting optics. These techniques are slow difficult to master and the skills quickly erode unless constantly practiced. Studies have shown that manual range estimation techniques typically have an error of 27. Personal experience indicates that this error is usually an underestimation of the actual range to a target. It is desirable to
Laser rangefinders operating at 1. 54 jtm are of increasing interest because of their eyesafe property. We report on technology and hardware developed at Hughes Aircraft Company based on using Stimulated Raman Scattering (SRS) of the Nd:YAG 1. 06 im output to the eyesafe 1. 54 jtm wavelength. This technology has been extended from the 1 Hz repetition rate to the 10 to 20 Hz range for air defense applications by use of circulating gas Raman cells and several resonator configurations have been developed to improve conversion efficiency and beam divergence. The eye safety and the atmospheric penetration of the 1. 54 jim wavelength is discussed.
A 10. 6 micron eyesafe laser rangefinder (LRF) has been designed for use on the M1A2 tank. Prototypes have been fabricated and extensive engineering tests have been performed. The unit is characterized by extreme optomechanical rigidity a high brightness projected LED array highly modular packaging and advanced built-in test capability for ease of I-level maintainability. Several LRFs have been delivered to date for testing under field conditions to verify performance. Reliable range returns have been demonstrated against canvas targets at ranges to 4500 meters (the length of the range) over swampy terrain under conditions of rain during the summer in Florida. Likewise reliable returns have been demonstrated against targets of opportunity at ranges to 5700 meters under conditions of rain during mid-latitude winter conditions. Required range sensitivity has been demonstrated by ranging against the common module FUR and by numerous attenuation filter tests. Trends in LIDAR performance against theoretical predictions are discussed. Large sample size test methods are required to detect low frequency of occurrence phenomena and to control their rate.
There is an increase in international laser safety requirements as part of the emphasis on world-wide standardization of products and regulations. In particular the documents which will evolve from the 1992 consolidation efforts of the European Community (EC) will impact both laser manufacturers and users. This paper provides a discussion of the current status of the various laser radiation standards. NORTH AMERICAN REQUIREMENTS United States Requirements on manufacturers from the Food and Drug Administration (FDA) have been in effect since 1975. The Center for Devices and Radiological Health (CDRH) within that agency ensures that these mandatory requirements  are satisfied. The CDRH regulations include the division of products into classes depending on their potential for hazard criteria for power measurement and requirements for product features labels and manuals and records and reports. Manufacturers must test products and certify that they comply with the CDRH requirements. User requirements are found in a standard published by the American National Standards Institute (ANSI) and in requirements from several individual states. Specific ANSI standards have also been published for fiber communications systems  and for lasers in medical applications . Please note that the Appendix includes additional information on the standards discussed in this paper including sources for obtaining the documents. Canada In the past Canada has had requirements for two specified product categories (bar code scanners and educational lasers) [26 These will be replaced
The eye hazard problem of pulsed lasers being used in fire control systems causes considerable safety concern during training exercises. For this reason the eye safe requirement was placed on all of the new laser systems being developed for the West German armed forces. The Rainan shifted Nd:YAG laser and the Erbium laser both operating at 1. 54 tm become the competitive technologies for many requirements. After extensive competitive trials at the proving grounds the system using the Raman technique was awarded the production contract. This paper describes the attributes of the Raman shift technology for laser range finders (LRF) and results obtained. SPIE Vol. 1207 Laser Safety Eyesafe Laser Systems and Laser Eye Protection (1990) / 155
e have realized a new Q-switch of controling total reflection. In this Q-switch total reflection of a prisni is controled by modulating the spacing between a glass plate and the prisa''s reflection surface. To control the spacing we drive a glass plate using a piezoelectric actuator. Ejuploying this Q-switch coiupact laser oscillator and Hand-Held Eye-Safe Laser Range Finder have been developed. 1.
In the past terrestrial optoelectronic distance measurement in the kilometer range was only possible by marking targets with reflector prisms or by increasing the optical output power far beyond the eyesafety limits. These requirements are unacceptable for many measurement tasks and this paper describes how they can be avoided by using a low power semiconductor laser and modern signal processing techniques. 1. DESIGN GOALS A number of manufacturers have fielded optoelectronic rangefinders which must be supported by reflector prisms mounted on the target if distances beyond 100 m are to be measured. These devices based on semiconductor lasers are very accurate (to the order of mm) and because of their low optical output power they are generally eyesafe. Devices are also available for measurements without reflector prisms (non-cooperative targets) to large distances beyond 5000 m where poor target reflectivity and atmospheric attenuation are overcome by high power output usually from an NdYAG crystal laser. The very high intensity laser radiation however is dangerous to the human eye and therefore these devices are constrained to operate under rigorous safety measures. Between these two extremes there are numerous applications where not extreme range or accuracy but eyesafety non-cooperative targets small size and low cost are of primary importance. This is the case not only for civilian applications but also for military use e. g. in force-on-force exercises or special operations. Other design goals
Excimer laser linear excisions are performed on both rabbit and human cadaver corneas by varying the excision direction and the laser pulse number. The shape , width and depth of the excisions as a function of these parameters are studied. Excisions parallel to the limb ( used for astigmatism correction ) appear to be much more reliable than radial excisions.
Organic dyes often are dissolved in plastic materials to produce filters which serve as laser eye protection. In two recent studies performed on one such filter nonlinear changes in the absorbance of the filter were observed with changes in radiant exposure (J/cm ). The nonlinear changes were noted at a laser wavelength of 694 nm but not at 1064 nm. One proposed mechanism for the changes in absorbance involves " entrapment^" of the excited chromophores in a stable excited triplet state during . the descent to the ground state. This mechanism involves electronic transitions which photons with a wavelength of 694 nm would produce . However photons with a wavelength of 1 0 6 4 nm usually would not be expected to cause electronic transitions. The preseht study was performed to investigate the relationship of wavelength and nonlinear changes in absOrbances . At an intermediate near infrared wavelength the absorbances of three different commercially available plastic laser protective goggles were measured at various radiant exposure levels. A decrease in absorbance with increase in radiant exposure was observed in at least two of the samples. These results suggest that a triplet state may be involved in the region of approximately 750 nm but further investigation is required 2 . BACKGROUND In one frequently used laser eye protective filter designed to absorb at both 694. 3 and 1064 nra a decided drop in