Question

Apollo 11 astronauts Buzz Aldrin and Neil Armstrong placed laser reflectors on the moon on July 21, 1969. Use the expansion law of Gaussian beam to predict the diameter of a ruby laser (λ0 = 6943Å) beam of when it hits the moon (assume mean distance to the moon is 3.85x105 km) for the two cases:

a. A laser rod of 2 cm diameter.

b. This same laser sent through a telescope backward so that the beam starts with a diameter of 2m.

c. If the eye damage intensity is ~ 10 µW/cm2 , and the laser on earth produces 10 MW, was there a danger to the astronauts from the optical radiation? (you need to calculate the intensity for both the above cases).

Answer 1