A telescope can be used to enlarge the diameter of a laser beam and limit diffra
ID: 1491993 • Letter: A
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 Mount Wilson telescope, producing a 2.54 m diameter beam of 653 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?
I have tried several different methods but I do not understand the clue of the 2.54 m. Thanks in advance!
Explanation / Answer
The minimium angular speed of the beam=tetha=1.22(lamda)/d
Lamda=653×10^-9m
Diameter of telescope=d=2.54m
Tetha= 1.22×653×10^-9/2.54
=313.64×10^-9
=3.1364×10^-7rad
Distance of the moon=D=3.84×10^8m
We know tetha= y/D
y=tetha×D
y=(3.13×10^-7)(3.84×10^8)
=12.01×10^1
=120.1m
the size of the spot this beam would make on the moon = 2y
=240.2m
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