Draft ANSI standard for the evaluation of laser eye protection

Abstract

The first commercially available laser eye protection was based on absorptive technology. As the name implies, the incident energy is absorbed and then dissipated as heat. Product testing consisted of assessing the optical properties of the eyewear (optical power, haze, distortion, abrasion resistance, etc.), optical density, potential for saturable absorption, and damage threshold. Common of absorptive technologies, the absorption bandwidth was broad with considerable secondary absorption. The unwanted absorption resulted in low transmittance and high spectral distortion. As the usage of lasers spread and the number of possible wavelengths increased, R&D efforts in multiwavelength laser eye protection expanded to explore alternative filter technologies such as holograms or dielectric stacks. The dielectric equivalent of the early neodymium protection had 80% transmittance as opposed to the 45% of the absorptive eyewear. The angular sensitivity, however, required that the bandwidth increased to prevent the filter from shifting off the critical wavelength for off-axis exposures. This new type of eye protection dramatically increased the demands and rigor of performance testing. No longer could one assess just the critical area. Now the required angular protection had to be determined. The required angular coverage was a function of the eye relief, pupil diameter, range of eye movements, and range of interpupillary distances. If the filter is eye centered, and as implied, alignment and fit critical, then one also needs to determine how the filter performs as misalignment is introduced. The safety zone and fit parameters determine the number of points and angular coverage at each point which must be measured to assess the protection offered. This is all in addition to the standard optical tests required to certify a product. Depending on the number of wavelengths, filter complexity, and surface area the time and cost of testing can increase dramatically.