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Very low laser beam divergence






steve001 said:
Here's a video using a laser to prove the earth is flat (it ain't), but the reason I posted this is it shows what a low diverging beam the spot size looks like at some distance.
Start watching at 13 minutes.
https://www.youtube.com/watch?v=GBhDFO4NMrw

Optical and laser specifications: Laser: 3W laser – adjustable collimator – 0.08mRad divergence
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Nice find -special purpose made low divergence set up, for sure.
 
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Encap said:
Nice find -special purpose made divergence for sure.
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Your average DPSS green with a 10x BE should be able to get to 0.08mRad without much trouble. Will need to give that video a watch later though, at the very least it'll be a good laugh.
 
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diachi said:
Your average DPSS green with a 10x BE should be able to get to 0.08mRad without much trouble. Will need to give that video a watch later though, at the very least it'll be a good laugh.
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Are you sure? With your average 1- 1.5 mrd 532nm green dpss laser a 10x would give a beam reduction 10x less or 0 .1- 0.15 mrd. You'd have to use a 100x beam expander to get down to such low divergence as seen in the video.
 
steve001 said:
Are you sure? With your average 1- 1.5 mrd 532nm green dpss laser a 10x would give a beam reduction 10x less or 0 .1- 0.15 mrd. You'd have to use a 100x beam expander to get down to such low divergence as seen in the video.
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0.8mRad is low for sure, but far from unheard of for a green DPSS, maybe not the super cheap china jobs, but even they have rather good divergence. 10x would bring that down to 0.08mRad. 100x Would bring your 1mRad beam down to 0.01mRad.

That said, at 3W that's pretty impressive. But looking at the video, they're using a real big DPSS unit with a BE on the end. Probably dropped a large amount of cash for that setup...
 
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All it takes is a temperature gradient to throw their measurements off.
 
Watched that whole video and it's easily bs. Air temperature bends light, and with such precise measurements of only a meter or two, at 800-2000 meters away, the slightest thing can change that including air temperature. I've also heard of mirage effects and things like that bending light around the earth from ships behind the horizon.
 
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That's a nice video IMO, not because of the experiment, but because of laser they used and showed it how the dot looks in various far distances during a day.
 
Alaskan said:
All it takes is a temperature gradient to throw their measurements off.
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diachi said:
Yep, and I don't particularly trust their methods either... Doesn't seem at all accurate.
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Crazlaser said:
Watched that whole video and it's easily bs. Air temperature bends light, and with such precise measurements of only a meter or two, at 800-2000 meters away, the slightest thing can change that including air temperature. I've also heard of mirage effects and things like that bending light around the earth from ships behind the horizon.
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Agree, inaccurate pseudoscience based delusional flat earther belief BS/propaganda
 
Radim said:
That's a nice video IMO, not because of the experiment, but because of laser they used and showed it how the dot looks in various far distances during a day.
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That's the reason why I posted this video.
 
I was struck by the fact that by 3 miles out they could no longer see the dot/spot/light of any kind. A three watt 532nm laser with a good BE should have been visible still at that distance.
 
paul1598419 said:
I was struck by the fact that by 3 miles out they could no longer see the dot/spot/light of any kind. A three watt 532nm laser with a good BE should have been visible still at that distance.
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That could be do to scattering and or refraction of the beam do to different air densities close to the water surface.
 
That is possible, but I tend to think it is because this whole thing was a sloppy attempt at science.
 
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