Diffraction from a circular aperture: (A) What is the smallest optical spot whic
ID: 2084029 • Letter: D
Question
Diffraction from a circular aperture:
(A) What is the smallest optical spot which can be formed on the surface of the moon using a red laser beam which is perfectly collimated but transmitted through a circular aperture of 2 mm in diameter? (you have to come up with the numbers for red and the distance to the moon).
(B) How large does the (round) aperture need to be to create a spot which has it’s full width to the first zero in intensity less than 1mm in diameter? You would need to provide a lens in that aperture to form this spot; what is the F/number of the lens needed?
Explanation / Answer
(a) Distance to surface of moon is 3.77x108 m.
Redlight wavelength= 694.3 nm.
The minimum angular separation of the objects is
min = y/L = (480 m) /(3.77 × 108 m) = 1.3 × 106 rad
Therefore,
D = 1.22/min = 1.22(550 × 109 m) /(1.3 × 106 rad) = 0.52 m