A beam of 632.8 nm photons from a He-Ne laser strikes a detector area of 5.0 mm2. The laser has a flux of 3.18 x 1015 photons s-1.
(a) What is the laser radiant power in watts?
(b) What is the laser irradiance at the detector?
(c) Express the answer for part (b) in terms of photons s-1 rather than watts.