Development of a radiometric sensor for the hazard assessment of scattered high-power laser radiation

Abstract

The outdoor operation of lasers involves the potential risk of unintentionally exposing the human eye and skin to radiation. In addition to direct exposure, indirect scattered radiation of high-power lasers may pose a threat to operators, working personnel, and third parties. Hazard assessments are usually performed based on laser safety standards. However, these standards are limited in their applicability regarding outdoor environments and therefore it is advisable to corroborate models and safety calculations with measurements of the absolute scattered radiant power under realistic conditions.For the determination of scattered radiation, a radiometric detection system has been developed. The system consists of an optical, electronic, and mechanical unit. Two realizations of the optical unit with a side-on photomultiplier tube (PMT) and a photodiode amplifier (PDA) have been built according to laser safety standards (e.g. German safety policies). Two detectors facilitate the detection of scattered radiation over a wide power range. The electronic unit contains the data acquisition and processing system and peripheral devices (i.e. environmental sensors and GPS module). A lock-in amplifier is used to reduce the contribution of unwanted background radiation. The optical and electronic units are separately housed in a weather-resistant case on a tripod and a mobile container, respectively.Radiometric calibration is performed for each optical detection unit. The calibration involves a two-step procedure allowing for a direct conversion of the output voltage of the lock-in amplifier into an absolute scattered power considering the detector area and collection solid angle of the optical detection unit. Goniometer-based light scattering measurements of solid samples are carried out for the characterization of the performance of the optical detection system in terms of dynamic range, accuracy, reproducibility, and the influence of background noise and contribute to a better understanding of the detection system in the future field deployment.

Field validation of a mobile detection system for laser scattering measurements in the NIR range

“…10 The details of the detection system have been described in a previous contribution. 11 Therefore, only a brief outline of the main features is given: The detection system is capable of measuring the scattered laser radiation originating from solid targets as well as from extended sources (i.e. a scattering volume filled with aerosol particles) by using different types of detectors.…”