Saturday, July 6, 2013

Card Interference

Last night I shined laser light onto the edge of a playing card in hopes of forming an interference pattern on my wall. (I believe Thomas Young also used a card in his initial interference experiments by using sunlight that had passed through a pinhole) The following is a brief account of what I saw. I don't have any quantitative results on this yet, but will try to work out details in a later post. In principle it should be easily possible to measure the wavelength of light with this setup, or assume the wavelength (it is 650 nm) and measure the thickness of the card. (Of course we might as well measure the thickness of a deck and divide by 52 !) 

Here are some pictures of the setup. The red laser pointer is mounted on a mini tripod while the card is held up by a slit cut into a cardboard box. The idea is that the card splits the laser beam into two beams which can interfere with each-other. 
Image 1: Card splitting a beam of laser light 

Image 2: Other view

The beam is deflected horizontally (perpendicular to the card) as can be seen in the distance.

Image 3: Back view

Image 4: Lights out

Here's a closer look at the wall, notice that the fringes on the left are different than those on the right. There seems to be a much longer spacing between nulls on the RHS.
Image 5: Pattern observed on wall, notice differences between RHS and LHS
Image 6. LHS image from one of my attempts, looks like fairly even spacing. Can see variation in height of fringes.  
Image 7: Close look at the LHS from another attempt

An attempt at measuring spacing between the maxima  (of image 7)

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