What are „extended sources“ (TROS) and why do they matter?

„Extended sources“ is a term from TROS laser radiation (Technical Rule on Optical Radiation – the national German counterpart to EN 60825-1). Line lasers, cross-line lasers and DOE positioning lasers fall into this category because they spread their radiation across an area geometry – in contrast to „collimated sources“ (point lasers), which concentrate all power in a narrow beam. Consequence: at equal total power the irradiance per point is lower, and the extended source is classified into a lower laser class than the collimated one. Practical example: a 50 mW line laser can fall into Class 2 while a 50 mW point laser already reaches Class 3R.