Laser Safety—What Is the Laser Hazard Distance for an Electro-Optical Imaging System?

Abstract

Laser safety is an important topic. Everybody working with lasers has to follow the long-established occupational safety rules to prevent people from eye damage by accidental irradiation. These rules comprise, for example, the calculation of the Maximum Permissible Exposure (MPE), as well as the corresponding laser hazard distance, the so-called Nominal Ocular Hazard Distance (NOHD). At exposure levels below the MPE, laser eye dazzling may occur and is described by a quite new concept, leading to definitions such as the Maximum Dazzle Exposure (MDE) and to its corresponding Nominal Ocular Dazzle Distance (NODD). In earlier work, we defined exposure limits for sensors corresponding to those for the human eye: The Maximum Permissible Exposure for a Sensor, MPES, and the Maximum Dazzle Exposure for a Sensor, MDES. In this publication, we report on our continuative work concerning the laser hazard distances arising from these exposure limits. In contrast to the human eye, unexpected results occur for electro-optical imaging systems: For laser irradiances exceeding the exposure limit, MPES, it can happen that the laser hazard zone does not extend directly from the laser source, but only from a specific distance to it. This means that some scenarios are possible where an electro-optical imaging sensor may be in danger of getting damaged within a certain distance to the laser source but is safe from damage when located close to the laser source. This is in contrast to laser eye safety, where it is assumed that the laser hazard zone always extends directly from the laser source. Furthermore, we provide closed-form equations in order to estimate laser hazard distances related to the damaging and dazzling of the electro-optical imaging systems.

An approach for laser safety calculations for electro-optical imaging systems

“…For the NSeHD, we found approximative estimates both for the upper and lower value of 𝜈 hd [9] 𝑣 uhd…”

“…Then, in a second step, the terms of the equations to be solved, which depended on the truncation factor 𝜈, were substituted by approximations that allowed solutions for 𝜈 hd in closed-form. We refer the reader to reference [9] for detailed explanations and will present here the results only.…”

“…These approximations are well usable to determine hazard distances for sensor damage. In reference [9], approximative values of NSeHD calculated using Equations ( 39) and (40) (𝑁𝑆𝑒𝐻𝐷 appr ) were compared to values computed by numerically solving Equation (36) (𝑁𝑆𝑒𝐻𝐷 num ). The calculations were performed for a total of 5734 different parameter sets.…”

“…In this publication, we summarize our work on laser safety calculations for electro-optical imaging systems, which was presented in detail in several journal articles [8][9][10][11]. This includes the derivation of equations to estimate exposure limits (Section 4) and dazzle spot sizes (Section 5), approximations to estimate hazard distances (Section 6), suggestions for values of non-standard parameters (Section 7) and the validation of the this work by modeling and field trials (Section 8).…”

“…We will not go into details here but mainly present the results of our work. Image taken from reference [9].…”