A He–Ne laser, λ = 632.8 mm, is operated at a power level of 3-W CW. The laser aperture diameter is 0.9 mm, and the beam

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A He–Ne laser, λ = 632.8 mm,is operated at a power level of 3-W CW. The laser aperture diameteris 0.9 mm, and the beam divergence is 0.9 milliradian. If thepossibility
exists for momentaryaccidental intrabeam ocular exposure not exceeding 0.25second,
calculate the minimum requiredoptical densit,,y of protective goggles for
(a) exposure at thelaser,
(b) exposure at a distance of100 m, and
(c) continuous intrabeamviewing for up to 100 seconds at a distance of 100 m