Question: When a laser pointer is projected on a screen we see a red (λ = 670 nm) spot with an area of ∼1mm2. The intensity of the light reaching the screen is 3mW.
a. Find the number of laser photons reaching the screen per unit time.
b. If you think of these photons as uniformly distributed through the volume of the laser beam, how far apart are they? (Hint: How fast are they going?)