Telescope and Lasers..?

gloryofblaze · Apr 13, 2010

So i was curious if anyone here has tried shining a laser through a telescope. Im curious if reversing the telescope could help the laser travel further? I know that just because you can see something bigger doesnt make it closer but how does the law of light speed affect a laser through a telesope? If im in the wrong place for this ? Sorry.Any one care to share opinion? I will be trying my own laser experiments when my green comes in.Untill then Im going to have to build my bluerays.

brando132 · Apr 13, 2010

From my understanding it would widen the beam and decrease the divergence, just like a beam expander, I may be wrong though.

f22warzone · Apr 13, 2010

If its the right telescope that is exactly right its just an over sized beam expander : )

GoRdOn_B · Apr 13, 2010

I have tried this.. Out of curiosity of course.

Thats pretty much how it went for me

Pontiacg5 · Apr 13, 2010

I used the finderscope (is that the right term?) as a beam expander for a while, it worked quite well especially with red diode lasers!

gloryofblaze · Apr 13, 2010

Is there a way to make it travel farther?

Pontiacg5 · Apr 13, 2010

Travel farther? Technically a laser travels to infinity, but if you want to see the dot further away as a small dot still you need better divergence. I'm no whiz at optics, but from what I infer a beam expander will "expand" the beam. For example so that instead of a 1mm beam you will have a 10mm beam but the beam will have a better divergence. I don't know exactly how but I think it is something like this

f1 and f2 are focal lengths, you want to match the focal point of the 2nd lens to the smallest beam diameter using the focal length of the first lens. (top example)

I odnt understand the bottom example

Damien · Apr 13, 2010

Pontiacg5 said:
I dont understand the bottom example

Appears to be an inverted dome lens.

RA_pierce · Apr 13, 2010

The principle behind a beam expander is this:
Large beam diameter --> lower possible divergence;

Beam diameter and divergence are inversely related.

The picture posted above shows two good examples of different methods of "expanding" a beam.
Either of the two methods can be used to create a beam expander.

A refracting telescope can be used as a beam expander and it has been done before. Binoculars will also work.
All three devices (beam expanders, telescopes, and binoculars) operate on the same principles of refraction.

A refracting telescope is basically a beam expander used in reverse.
Telescopes are used to collect light and project a small image (in order to artificially increase the "aperture" of the human eye)
Beam expanders are used to increase the area of the image of a (collected) light source.

kevinmassey · Apr 14, 2010

Yes, I have a pair of old binoculars that work as a 4x beam expander.

The bottom picture shows 2 lenses with different foci. It's saying if you have those kinds of lenses you have to line up the foci at the same spot. So you have your laser you shine it into the right lens from the right the focal point would be F2 distance away from the lens. Now you shine your laser in the left lens from the left. It should have a focal point back towards where the light is coming from at F1 distance towards the laser. You have to line them up to where the focal points F1, and F2 are at the same point. Then you shine your laser from the left through the 2 lenses and its expanded... I know i didnt describe it that well, but do you understand?

kevinmassey · Apr 14, 2010

It should look like this if you extend the lines. see how the foci meet at one point?

Pontiacg5 · Apr 14, 2010

Found this, I remember this from way back in 2006. I don't know if anyone ever used these plans, but there free

http://www.amazing1.com/download/COLMIN1.pdf

amazing1.com also has lots of other cool nerd stuff, its fun just to look around. (they're lasers are expensive though!)

phoenix77 · Apr 14, 2010

That particular set of DIY instructions have been posted several times on this Forum, (I even posted it once myself). To this day, I don't know of anyone who has built this assembly, (or even tried to). rob

gloryofblaze · Apr 15, 2010

I did not mean for this to merge to a topic of beam expansion. Rather i wanted to figure a way to make the visible beam visibly farther. Could a magnifying glass set at a point where the devergance of the laser hasnt gotten bigger than the glass if then the glass would make it small again for a greater diStance

Pontiacg5 · Apr 15, 2010

Not really, the only way to really decrease divergence is a beam expander. A magnifying lens at a spot like that would focus the wide beam into a very small point very quickly in front of the magnifying glass. After the beam reaches its smallest point it will expand again at the same slope.
I think it was daguin who posted an example using the letter X. The beam will focus down along the > side of the X then immediatly expand to the other side of the X, <

incoming beam >.< outgoing beam. The . would be the smallest point and the best for burning.

gloryofblaze · Apr 15, 2010

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..

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