Telescope and Lasers..?

[Pontiacg5]

Well, if you know the distance to the moon you can figure out what divergence with a certain starting beam size will focus down to a spot on the moon. As far as I know you would have to start out with a really large beam to focus down to a spot on the moon. A laser beam is like a cone, it can either be expanding or contracting, but it will be doing one or the other. The larger the beam size the longer it takes to switch from contracting to expanding.

NASA did leave a reflector on the moon, you can find out how far away the moon is using it, pretty interesting.
NASA - Accuracy of Eclipse Predictions

 

[RA_pierce]

Sorry,if i mislead ppl my point was really to try to find out say ''hypotheticy speaking'' how could you send a beam to the moon without covering a hundred sq miles? How do you keep the devergance dwn over long distance? That was my whole purpose of proposing the telescope but meant reversing the scope to send the beam further. I do not want beam expansion, unless it can somehow make the beam travel further more concentrated..

What I have been trying to explain is that the only way to "send the beam farther" is by beam expansion.

That is what a telescope will do- expand the beam and reduce divergence.

By the way, you will not be able to see the spot on the moon, telescope or not. There are many, many reasons that this cannot be done.

1. Distance--- The distance is enormous. You have to account for the trip there and back. Even with a beam expander or a telescope, the beam will be huge at that distance.

2. Atmosphere--- Turbulence in the air will distort the beam and the air itself will attenuate some light.

3. The Sun--- The sun will always be brighter than your laser. Sunlight on the surface of the moon will drown out any laser light you could possibly detect on its surface.

4. Reflection--- The surface of the moon will absorb some of your laser light. The photons that are reflected may not even be reflected in your direction. You can increase your chances of getting some back by hitting a retro-reflector, but the light still has to pass through the atmosphere again to reach your eye.

5. Your Eye--- What are the chances that the 10 or so photons that make it back to ground level will enter your eye? After all, each pupil dilates to only ~8mm diameter.

 

[gloryofblaze]

Well thats more like it..hmmmm..The hamster is turning the wheel.I guess that really does end that question i appreciate it..Now i can go back to trying to find where my laser was delivered to..

 

[Monco]

If you used a strong enough green laser, sent it through a very good telescope to collimate as well as possible (possibly use adaptive optics to reduce the effects of the atmosphere, off the shelf equipment these days), work with a very "young" moon and obscure the sunlight from it, and view the illuminated retroreflector with a very large telescope (>30" diameter), you might have a shot at chance to personally see your beam reflect off the moon. The human eye can detect a single photon of green light! All the equipment is now at the surplus and/or serious amateur astronomer level. An expensive project, but doable.

Refer to the LLR project (Lunar Laser Ranging) started in 1969 and still continuing on today.

"NASA's Jet Propulsion Laboratory has proposed a three-year mission that would outfit a spaceborne terminal with a telescope (12-cm aperture) and a transmitter (power of 250 mW). The earth terminal would have a 1-m telescope and transmit 3 mJ, 12 psec pulses at kHz rates."

that statement was a while back and APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is in use.

APOLLO

 

[Monco]

lol do you remember when the space shuttle was on ebay? it was epic (i don't think it sold though... seeing as how nasa still has it)

 

[kevinmassey]

I'm sure the people at nasa got a kick outa that haha^

 

[gloryofblaze]

Well thanks again to the brilliant minds on lpf...Really i think i have learned more on the forum than in most books i have started to read.So in theory it could work..:tinfoil::thanks:

 

[kevinmassey]

No, not in theory. It did work, but I think the laser used for reflecting off the moon was a multi-watt laser with a huge diameter to lower divergence... Good luck!

 

[Monco]

No, not in theory. It did work, but I think the laser used for reflecting off the moon was a multi-watt laser with a huge diameter to lower divergence... Good luck!

in terms we're all familiar with... 3,000,000,000 mW

hahahahaha

 

[Damien]

Sorry if I've missed the discussions up to this point; however may a static field around the lens [or lenses] amplify or modulate the frequency of the beam?

 

[Bluefan]

in terms we're all familiar with... 3,000,000,000 mW

hahahahaha

I've tested a 500,000,000,000 mW laser. Nasa has bigger.

 

[Cyparagon]

NASA did leave a reflector on the moon, you can find out how far away the moon is using it, pretty interesting.

He means of course "you" as second person, but more specifically people with ridiculous power lasers, absurdly large optics, and six-figure+ detecting equipment.

 

[MrGreenJeans]

I regularly use a shooters spotting scope as a beam expander. The lenses are AR coated across the visible spectrum and use pretty good quality lenses. Spotting scopes are a reasonable size and feature mounts for things like tripods making it easy to fix the scope in the beam path. Since they have variable focus controls and zooms you can adjust the beam characteristics in real time.