A telescope can be used to enlarge the diameter of a laser beam and limit diffra

Question

A telescope can be used to enlarge the diameter of a laser beam and limit diffraction spreading. The laser beam is sent through the telescope in opposite the normal direction and can then be projected onto a satellite or the Moon. If this is done with the Otto Struve telescope, producing a 2.10 m diameter beam of 633 nm light, what is the minimum angular spread of the beam?

Neglecting atmospheric effects, what is the size of the spot this beam would make on the Moon, assuming a lunar distance of 3.84 × 108 m?

Explanation / Answer

(A) D = 2.1 m , ladam = 633 nm

theta = 1.22*lamda/D

theta = 1.22*633*10^-9/2.1

theta = 3.68*10^-7 m

(B) Theta = x/R

sin(3.04*10^-7) = x/(3.84*10^8)

x = 116.736 m

r = 2x =2*116.736

r = 234 m

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