Question

A laser beam was fired from the Air Force Optical Station on Maui, Hawaii, and reflected back from the shuttle Discovery as it sped by, 220 miles overhead. The diameter of the central maximum of the beam at the shuttle position was said to be 28 ft and the beam wavelength was 540 nm. What is the effective diameter of the laser aperture at the Maui ground station? Assume circular exit aperture of the laser beam.

Answer 1

The first minimum of the diffraction pattern due to circular aperture corresponds to the diffraction angle θ1 at which we have

where a is the diameter of the laser aperture.