Advanced Physics

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

exists for momentary accidental intrabeam ocular exposure not exceeding 0.25 second,

calculate the minimum required optical densit,,y of protective goggles for

(a) exposure at the laser,

(b) exposure at a distance of 100 m, and

(c) continuous intrabeam viewing for up to 100 seconds at a distance of 100 m