175mw Laserglow into 900mm FL Telescope

[Alaskan]

Found a 900 mm focal length 60mm telescope on ebay for 20 bucks and taped my Laserglow Aries 175mw 532nm laser to it, now that's a fat beam

 

[upaa27]

Haha that is pretty cool! Always wondered what such a fat beam would look like.

 

[Alaskan]

Wish it were a clear night and not cloudy and drizzle raining, as it is now. I took the photo with a cheap cell phone. I will try again when clear outside and post new photo's with a better camera some other time.

 

[shokkunlasers]

Looks awesome!
I Love fat beams in addition to the fact that with expanding comes low divergence
Do that with a 1W green and people will think that you're building a deathstar laser^^
Link to the telescope on ebay please

 

[Alaskan]

With such a fat beam and the low clouds above, when shooting at a low angle I am fairly sure someone on the far side of the spot a couple of more miles beyond it might not be able to see the beam, just a green orb moving around in the clouds, aliens are coming

Here's what I bought, I didn't realize the seller had more until I went back and looked just now. They do not come with an eye piece:

Celestron 60mm Refractor Telescope OTA 1 25" Focuser 900mm F L | eBay

Without an eye-piece lens I used two large 35mm diameter plano-concave lenses with identical negative focal lengths of -53mm to expand the laser beam before collimation. I happened to have a few of them from an ebay purchase, one alone would not expand the laser beam enough to fill close to the entire lens on the end of the telescope.

So what happens when you put two -53mm focal length plano-concave lenses together? Now 26.5mm focal length? I'm new to optics, don't know but if that is how it works, my beam was expanded by a ratio of over 30 times. If true, my 1.2 mRad laser became a .04 mRad. A laser with that low of a divergence would produce a spot just over 2 feet wide 10 miles away, now that's delivering a lot of light for the distance to one spot. At 1000 miles away, about 200 feet diameter, amazing. Imagine how bright that would be to a theoretical observer, could it challenge the light coming from a small city?

 

[IsaacT]

Anyone in the USA should check out Craigslist for cheap telescopes. There are always super cheap ones. And make sure you get a refractor not a reflector. A reflector would make the laser into a tube of light if you had the right FL eyepiece.

 

[paul1598419]

Nice job. I was wondering how that might look as well. Unfortunately, I won't be doing it myself anytime soon as I made a huge purchase and my funds are now depleted for the time being. But, still, what a nice job, and the divergence is incredible.

 

[Alaskan]

Now you have me wondering what kind of goodies you bought

I have another lens I'd like to set up for use as a beam expander someday, I've posted a photo of it here before, about 12 inches diameter. With that lens and the right expander lens the beam can travel a long way before expanding much, at ten miles the spot would be only 5 percent bigger than the lens diameter, at one hundred miles just 50 percent bigger at only a foot and a half wide, at the distance of the moon only 1200 some feet wide. These figures amaze me.

I have a 3 watt output 532nm laser which would go great with this lens IF I ever get it interfaced to a TEC controller! I bought it but haven't wired it all up yet. That one isn't the Halfnote, another one.

PS: the fact that no one can see it 100 miles away because it would be pointing into space is moot to me, it's the reality that impresses me, whether viewed or not, I would know it can go that far while maintaining a tight divergence. A lot more fun would be to point it into a cloud layer to see a brilliant spot in the sky, but not a good idea if an airplane were in the vicinity

 

[paul1598419]

My purchase was unrelated to lasers, so not worth going into here. I looked over your lens, prism set up and the figures for the beam expansion, and I can find no fault with it. I, too, would like to get a laser system with a vey low divergence not unlike what you have planned here, That DPSSL at 3 watts would be perfect to start out and with the wavelength being so high in the visual acuity, would probably give you a beam that would leave a spot at ten miles out that one could see. Have you ever thought of doing it in the summer and from a mountain top at night where you could have one person observing and the other lining the beam up with a telescope to aid you in this endeavor? Nice job, BTW.

 

[Alaskan]

I originally bought the 12 inch lens surplus for use at IR to do just that, but to modulate the signal to pass data between the two using a telescope just that way. I have too many such projects I've bought parts for and not put anything together yet. The only big project I have finished is this one, it started out with lofty plans to use as a IR beacon for a work related project, but turned into a toy instead, added 800 watts of RGB LED's to it too, they are sure cool, but the divergence is horrible, as you can imagine.