### Author Topic: Coherence  (Read 7135 times)

#### jdonnelly

• Newbie
• Posts: 1
##### Coherence
« on: February 04, 2008, 06:45:04 am »
I would really like to see applets demonstrating optical coherence. I can imagine two, based on the somewhat simplistic (but ok for us) description in our optics text:

1) a Michelson interferometer where a wave enters and is split in two at the beamsplitter and depending on the length of the wave train and the separation of the mirrors, the wave recombines in phase, out of phase, or not at all (coherence length exceeded.) I draw this on the board as a "worm" that splits in two- will it meet up with it's other half? I can't animate the board, however.
2) a double slit experiment illuminated by a source of varying size and distance. Fringes only form when the source is small enough/far enough away.

Coherence is hard to understand on any level, but my budding technicians just need to know why the two arms of the interferometer need to be approximately the same size and why the two slit experiment doesn't work when the source is a light bulb next to the slits.

Has anyone seen these?
thanks
/jd

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: Coherence
« Reply #1 on: February 16, 2008, 05:18:31 pm »
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I am sorry that I did not find your post earlier. (The time you posted the message was two days before Chinese New Years Eve).

I just create an applet for your first request. Because the interference pattern is due to phase distribution at different spaces. I have not figured out how to present simulation for your second request, yet. May be you can give me some ideas.
You can drag the left or top mirror to change path lengths.
Those arrows represente Efield strength and phase for the corresponding points.
You can drag those points to find out how phase change at different positions.

I hope this is what you want. Your suggestions will be highly appreciated.

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