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- Jan 5, 2011
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If you want a 1 mm speck on the moon, it's certainly possible to use a lens to focus the laser--essentially making it non-collimated, so we increase the spread in angle to decrease the spread in position. The governing quantity for how small you can focus the beam with a lens is the f-number: the distance between the lens and the focus divided by the diameter of the laser beam when it enters the lens. So, you could place a small lens close to the moon so the beam is focused rapidly to the 1 mm spot, or you could place a huge lens on earth so it converges over its entire journey to the moon.
Would like to know how big is that lens to get a spot of 1 mm on the Moon :drool: (I'm lazy to calculate myself
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