3
   

Solar laser.

 
 
Glennn
 
Reply Mon 18 Jan, 2016 04:51 pm
If I take a 12’ magnifying glass and put it in the sun, and then position a 1’ magnifying glass just a little past the focal point of the larger lens in such a way that it will catch the diverging light from the larger lens and straighten it out, would I be able to burn things at a distance? A neighbor's barn, for instance?

Not that I'm thinking about doing that. I like my neighbors. Okay, I probably don't really like them, but I don't dislike them enough to burn down their barn. But then again, I just moved here, and I don't even really know them yet. I guess time will tell . . .
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Type: Question • Score: 3 • Views: 1,116 • Replies: 18

 
parados
 
  1  
Reply Mon 18 Jan, 2016 04:59 pm
@Glennn,
The short answer - No.

You might be able to heat up something fairly close but 2 magnifying glasses won't make a laser.

Glennn
 
  0  
Reply Mon 18 Jan, 2016 05:03 pm
@parados,
Not a true laser, but why wouldn't you be able to straighten the light coming off the focal point of the larger lens so that it forms a coherent beam the width of a pencil?

I believe it's the same principle as used in flashlights that have a twistable head to narrow or broaden the beam.
parados
 
  3  
Reply Mon 18 Jan, 2016 05:08 pm
@Glennn,
The light is focused, not coherent.


http://spaceplace.nasa.gov/laser/en/
Glennn
 
  0  
Reply Mon 18 Jan, 2016 05:14 pm
@parados,
Yes, it is focused by the larger lens down to a focal point of intense heat. Just past the focal point, the light begins to spread out. If a much smaller lens is there to intercept the light as it begins to spread back out, that smaller lens will act as a beam-straightener. Why is this any different from a flashlight with an adjustable focus?
rosborne979
 
  2  
Reply Mon 18 Jan, 2016 05:19 pm
@Glennn,
Glennn wrote:
I believe it's the same principle as used in flashlights that have a twistable head to narrow or broaden the beam.

As Parados said, this still doesn't create a coherent beam, nor a collimated beam. And you can see this by simply moving the focused circle of a one of those flashlights and shining it on a more distant surface... the focused area will be larger.

Commercial grade lasers also have a degree of de-cohererne and will get larger at a distance, but the change is far less pronounced in a laser (I think the de-coherence may be due to scattering, but I'm not sure). It may also be due to lower grade components and adjustments. Again, I'm not sure.
Glennn
 
  0  
Reply Mon 18 Jan, 2016 05:23 pm
@rosborne979,
Well, I don't need it to have a great range. I just need it to have an effect at about 100 feet.

EDIT: The fact that my neighbor's barn is almost exactly 100 feet from my porch is purely coincidental.
Glennn
 
  0  
Reply Mon 18 Jan, 2016 05:43 pm
Speaking of solar ideas, if you had five 12” lenses fitted into a large piece of plywood in such a way that they form a circle, and you then placed a mirror below each lens in such way that it would reflect the focal point of each lens to the center of the circle where there would be a piece of 1” diameter black iron pipe through which water would flow and become heated, wouldn’t that be cool . . . er, hot?
0 Replies
 
roger
 
  1  
Reply Mon 18 Jan, 2016 05:51 pm
You've got an interesting mind there, Glenn. I hope you're saving it for something important.
Glennn
 
  0  
Reply Mon 18 Jan, 2016 05:56 pm
@roger,
I've spent my internet career on the important **** in what I like to call "Operation _____ ____" I'm retired from that, and am just trying to have a good time now.
0 Replies
 
parados
 
  1  
Reply Mon 18 Jan, 2016 06:01 pm
@Glennn,
It's not much different but when you focus down a flashlight it doesn't start a neighbor's barn on fire. Nor will your attempt to make a straight beam of white light start your neighbors barn on fire. It may work as a fairly dim spotlight but it will lose intensity over distance because it is still just white light that is bouncing off itself.
Glennn
 
  0  
Reply Mon 18 Jan, 2016 06:17 pm
@parados,
But the light from the flashlight is coming from a small bulb which is powered by low voltage batteries--extremely low heat output--while the source of the light for the beam I am describing is concentrated sunlight capable of starting fires.
0 Replies
 
rosborne979
 
  1  
Reply Mon 18 Jan, 2016 06:29 pm
@Glennn,
You seem to be fixated on your neighbor's barn. Do you and the barn have a "history"?
Glennn
 
  0  
Reply Mon 18 Jan, 2016 07:05 pm
@rosborne979,
Fixated? Hell, this will be my fourth post in a row in which I haven't mentioned my neighbor's barn.

A "history"? Well, since you asked, that barn is where my sister lost her virginity to the son of the guy who now owns it. And that guy liked to use magnifying glasses to fry ants. I'm just into poetic justice.
0 Replies
 
neologist
 
  1  
Reply Tue 19 Jan, 2016 12:59 am
Definitely a thread worthy of 7 or maybe even 8 thumbs up.

But this is the best I can do for now:

Laughing Laughing Laughing Laughing Laughing Laughing Laughing Laughing Drunk
Glennn
 
  0  
Reply Tue 19 Jan, 2016 11:36 am
@neologist,
Quote:
But this is the best I can do for now:

Laughing Laughing Laughing Laughing Laughing Laughing Laughing Laughing Laughing Drunk

Yes, you've advertised that over and over again . . . Wink
0 Replies
 
parados
 
  1  
Reply Tue 19 Jan, 2016 04:55 pm


Forget your neighbors barn. Spend some time melting metal with the sun.
Glennn
 
  1  
Reply Tue 19 Jan, 2016 05:53 pm
@parados,
Quote:
Forget your neighbors barn.

If all goes as planned, I will definitely be forgetting about my neighbor's barn, as there will be nothing there to remind me of it.

Quote:
Spend some time melting metal with the sun.

But where's the poetic justice in that?
0 Replies
 
Glennn
 
  0  
Reply Tue 19 Jan, 2016 06:06 pm
Okay, so if you had a lens like the one in the video, and you focused it onto a small piece of black cast-iron tube, how much water would have to pass through that tube in order to keep it cool enough to not melt? And what possible uses would there be for the very hot water coming out the other end of that tube?

I'm going to get one and find out.
0 Replies
 
 

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