Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 15/06/2010 17:43:59

Title: How small a spot could you focus from earth to the moon using a laser?
Post by: thedoc on 15/06/2010 17:43:59

With the best laser, how small a spot could you focus from earth to the moon?
Asked by Oilinky, via Twitter          

Title: Re: How small a spot could you focus from earth to the moon using a laser?
Post by: thedoc on 15/06/2010 17:44:00

We posed this question to Graeme Hirst from the STFC Central Laser Facility...

Graeme -   You're trying to fight a thing called diffraction and that depends on how big you can make your laser beam down at the earth.  A back of the envelope calculation - laser light spreads out about one wavelength in 10 metres.  It’s 400,000 kilometres to the moon.  You’ll probably get something about 40 metres across [on the moon].  As a football metaphor, we’d be looking at something about twice the size of the 18 yard box.


               
Go to the show page for more. (http://www.thenakedscientists.com/HTML/podcasts/show/2010.06.13/)

Title: How small a spot could you focus from earth to the moon using a laser?
Post by: syhprum on 15/06/2010 18:16:02

I always understood that the ranging laser that utilises the reflectors placed on the moon by the Apollo astronauts has a spot size of about 4 Km but I am sure this is not the ultimate that can be achieved.