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SRH
2012-Jul-08, 02:44 PM
I would like to see the results of the interference pattern given certain changes to the setup.

I would be willing to pay someone a nominal fee if they can make these changes (nothing too crazy) and email me the results.

(I'm not looking for a software simulation, but an actual real experiment)


Thanks!

caveman1917
2012-Jul-08, 03:49 PM
I'm sure you could probably fix something up yourself using thick black paper and a LED, given that the LED is monochromatic enough.

caveman1917
2012-Jul-08, 04:31 PM
The noncoherence of the LED light may mess up the interference though, meaning you'll have to go with a laser diode. Something like a standard laser pointer should do.

korjik
2012-Jul-08, 05:46 PM
The noncoherence of the LED light may mess up the interference though, meaning you'll have to go with a laser diode. Something like a standard laser pointer should do.

Or a pinhole that the LED light shines through. Depends on how old school you want to get.

antoniseb
2012-Jul-08, 05:49 PM
The noncoherence of the LED light may mess up the interference though, meaning you'll have to go with a laser diode. Something like a standard laser pointer should do.

The light doesn't have to be coherent. It just has to be from a source that is small compared to the interference pattern. Otherwise this effect couldn't have been observed before the invention of the laser.

When we did this experiment in high school, we painted a glass slide with tar or graphite or some other easy to slice through opaque medium, and then made the slits using two razor blades that were taped together, and sliced by pressing their wide side against a cork-backed ruler to get a straight line. Our light source was incandescent.

It might be interesting to try it again now using my green star-pointing laser... but I wouldn't want my kids to think this was an effect from coherence.

Swift
2012-Jul-08, 05:53 PM
One on-line instruction for doing it yoursefl (http://www.instructables.com/id/Double-slit-Interference-Experiment/?ALLSTEPS)

a1call
2012-Jul-08, 06:05 PM
The light doesn't have to be coherent. It just has to be from a source that is small compared to the interference pattern. Otherwise this effect couldn't have been observed before the invention of the laser.

When we did this experiment in high school, we painted a glass slide with tar or graphite or some other easy to slice through opaque medium, and then made the slits using two razor blades that were taped together, and sliced by pressing their wide side against a cork-backed ruler. Our light source was incandescent.

It might be interesting to try it again now using my green star-pointing laser... but I wouldn't want my kids to think this was an effect from coherence.

The fact that light from a pinhole can interfere with itself is the proof that it is coherent. out of phase light cannot form interference fringes. Parallel light/wave passing through a pinhole produces concentric waves centered at the pinhole.
If the light is not monochromatic, a spectrum of fringes will form.

ShinAce
2012-Jul-09, 02:46 AM
I did it in my hallway with a 1$ laser pointer. Even that cheap laser did great! Taped the button down to keep the laser on, mounted in a shoe box and shone the light on a piece of foil that had been pin pricked. Voila! Single pinhole and double pinhole with the same setup. Total cost, 1$. You just have to find a room dark enough.

I had taken pictures of the single slit and double slit diffraction patterns and linked them from http://www.bautforum.com/showthread.php/98706-How-to-set-up-the-two-slit-experiment. However, the original thread seems to have been nuked.

Jens
2012-Jul-09, 03:35 AM
I would like to see the results of the interference pattern given certain changes to the setup.


Out of curiosity, what do you plan to change?

Van Rijn
2012-Jul-09, 04:25 AM
I had taken pictures of the single slit and double slit diffraction patterns and linked them from http://www.bautforum.com/showthread.php/98706-How-to-set-up-the-two-slit-experiment. However, the original thread seems to have been nuked.

Would this be the original thread?

http://www.bautforum.com/showthread.php/81076-double-slit-experiment.html

For older threads where the link contains the name of the forum section you need to change that part to "showthread.php". So in this case you would start with:




http://www.bautforum.com/space-astronomy-questions-answers/81076-double-slit-experiment.html


and change it to:



http://www.bautforum.com/showthread.php/81076-double-slit-experiment.html (http://www.bautforum.com/showthread.php/81076-double-slit-experiment.htm)

ShinAce
2012-Jul-09, 04:32 AM
Thanks! That's the one. Still can't find my own photos, but that'll do.

The last post shows three pics. The first image is a double slit(pinholes, actually) but you see two patterns. The circular rings(like single slit diffraction), and the vertical lines(interference fringes).
The second photo looks like a closeup of the first, showcasing the fringes of the "double slit" pattern. The last photo is what happens when the holes are made too large. The pinhole obviously isn't perfectly circular, and the shape of the prick is affecting the pattern. The way I did it was to lay the aluminium foil on a hard surface and press the pin down. Even if it looks like you failed to get through, hold it up to a light and see if there's a hole in it after all.

SRH
2012-Jul-09, 11:27 AM
Out of curiosity, what do you plan to change?

I PM'd you.

Hornblower
2012-Jul-09, 11:50 AM
I PM'd you.Why don't you just show all of us your ideas out in the open. You might get some useful feedback in the process.

Swift
2012-Jul-09, 12:53 PM
Why don't you just show all of us your ideas out in the open. You might get some useful feedback in the process.
I have a guess, and that is that TOEfetish's ideas may be non-mainstream, and as he has been warned about advocating non-mainstream ideas in Q&A, he is being wisely cautious. If that is the case, he is doing this exactly correct - getting his information in Q&A and presenting his ideas privately or in ATM.

trinitree88
2012-Jul-09, 02:44 PM
The light doesn't have to be coherent. It just has to be from a source that is small compared to the interference pattern. Otherwise this effect couldn't have been observed before the invention of the laser.

When we did this experiment in high school, we painted a glass slide with tar or graphite or some other easy to slice through opaque medium, and then made the slits using two razor blades that were taped together, and sliced by pressing their wide side against a cork-backed ruler to get a straight line. Our light source was incandescent.

It might be interesting to try it again now using my green star-pointing laser... but I wouldn't want my kids to think this was an effect from coherence.

mmmm ...an incandescent source is not incoherent, but partially coherent...which helps the fringes S/N ratio...

a1call
2012-Jul-09, 03:59 PM
mmmm ...an incandescent source is not incoherent, but partially coherent...which helps the fringes S/N ratio...

Without a single slit in front of the double slits to turn the light from incandescent source coherent, no fringes will ever form.

caveman1917
2012-Jul-09, 07:39 PM
It might be interesting to try it again now using my green star-pointing laser... but I wouldn't want my kids to think this was an effect from coherence.

It is an effect from coherence, or perhaps better stated, a coherent light source is necessary for the effect. But you and korjik are correct that first putting it through a pinhole also works (by making the light coherent), though that's an extra step in the experiment that seems unnecessary now that cheap laser pointers are widely available.

SRH
2012-Jul-30, 11:57 PM
Is there a cheap laser pointer that I could buy on Ebay that is:
1. coherent
2. has an adjustable frequency?

If anyone could recommend a brand name, I would really appreciate it...thanks!

Jeff Root
2012-Jul-31, 07:24 PM
They are all more-or-less coherent. How coherent do you need?

None have adjustable frequency, that I know of. Lasers don't
make frequency adjustment possible. You could use two lasers
of different frequencies.

Don't worry too much about the price. If you need to spend
$100 to get what you want, instead of $10 to get something
that isn't really adequate, spend it.

On the other hand, if you don't really need it, don't spend it.
You can probably get by just fine with less than you expect.

-- Jeff, in Minneapolis

SRH
2012-Jul-31, 09:31 PM
thanks jeff. nice website btw.

does the wavelength matter? 650nm? 532nm?
there are keychain lasers on ebay for $1...good enough?

caveman1917
2012-Aug-01, 12:08 AM
thanks jeff. nice website btw.

does the wavelength matter? 650nm? 532nm?
there are keychain lasers on ebay for $1...good enough?

Well, for one dollar it can't hurt to give it a try and see whether it's good enough for your purposes or if you'll require something better.