Laser question?

Question

A 30.0 W laser emits a beam of light 6.0 mm in diameter. The laser is aimed at the Moon. By the time it reaches the Moon, the beam has spread out to a diameter of 85 km. Ignore absorption by the atmosphere.

What is the intensity of the light just outside the laser?

What is the intensity of the light where it hits the surface of the Moon?

Answer 1

If I understand the question you are looking for power densities ant the just outside the laser and on the Moon's surface

a) p=P/A = P/(pi r^2) diameter D =2r
p=30.0/(pi (.006/2)^2)
p=1,061,033 W/m^2 (yes it is over 1Million W/m^2)

b) p=30.0/(pi (85,000/2)^2)

p=5.3 E-9 W/m^2