Evaluating extended source hazards

Abstract

Although the direct beam from a collimated laser is often more hazardous than a diffuse reflection, both must be considered when considering the hazards in a laboratory environment. Diffuse reflections are often extended sources and many times the direct beam could be an extended source when a lens is used to partially collimate the output from an extended source such as a laser diode or vertical cavity surface emitting laser (VCSEL). Evaluating the hazards from extended sources often involves a consideration of both thermal and photochemical injury processes. The retinal thermal exposure limits are provided as irradiance or radiant exposure on the cornea; the photochemical limit is provided as integrated radiance. Some scientists find it difficult to draw a direct comparison between the thermal and photochemical hazards, especially those laser sources with an elongated shape. In the American National Standard for Safe Use of Lasers, ANSI Z136.1 (2014), correction factors to the maximum permissible exposure (MPE) are available for both circular and elongated beams for thermal hazards, but correction factors are not used with the photochemical MPE. The author explains the rationale for the thermal correction factors and provides a similar correction factor method that can be used to express the photochemical MPE as irradiance or radiant exposure on the cornea, for both circular and elongated sources. Also, the differences in analysis methods for extended sources, between the ANSI Z136.1 (2014) and the International Electro-technical Commission (IEC) Safety of Laser Products, 60825-1 (2014), are explained.Although the direct beam from a collimated laser is often more hazardous than a diffuse reflection, both must be considered when considering the hazards in a laboratory environment. Diffuse reflections are often extended sources and many times the direct beam could be an extended source when a lens is used to partially collimate the output from an extended source such as a laser diode or vertical cavity surface emitting laser (VCSEL). Evaluating the hazards from extended sources often involves a consideration of both thermal and photochemical injury processes. The retinal thermal exposure limits are provided as irradiance or radiant exposure on the cornea; the photochemical limit is provided as integrated radiance. Some scientists find it difficult to draw a direct comparison between the thermal and photochemical hazards, especially those laser sources with an elongated shape. In the American National Standard for Safe Use of Lasers, ANSI Z136.1 (2014), correction factors to the maximum permissible exposu...