Physics : Diffraction through a privacy filter

I was wandering through the scraps and parts shop one day in the merry month of May and saw a stack of what appear to be privacy filters torn off old ATM machines. Knowing that they contain a mesh of fine fabric, I gambled that they would serve as a grating. I bought them for a song; they were 80 cents a piece because the owner didn't know what they were.

A trip home and a flash of the laser pointer later, the filters showed a promising diffraction pattern right off the bat. I set up the expriment in the manner shown below:

The first task at hand is to estimate the pitch of the grating.

At a distance of 50cm between grating and screen, I measured the distance between the zeroth and 7th maxima to be 2.05 cm. Using the formula nλ= dsinθ, with tanθ=2.05/50, and nλ=7X650nm, d works out to be 0.111 millimeters, which seems reasonable considering the grating is made of fabric fibers of some sort or other.

I also obtained an enveloped diffraction pattern with a red and green laser. Granted the lasers have different spot sizes and frequencies, they both show how the diffraction pattern on the screen is subjected to an envelope when multiple aperatures are involved. Estimating a beam spot size of approximately 1mm, we would expect the laser to pass through about 9 aperatures.

The diffraction pattern obtained with a red 650nm laser.

The diffraction pattern obtained with a green 532nm laser.

Physics : Diffraction by CD

Comparison of the wavelengths of green and red laser beams by diffraction from a Compact Disc.

The CD used is a regular stamped music CD. The specifications for the grating-like surface of the metal layer of the CD is 500nm track width and 1600nm track pitch.

Red Laser (650nm)

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Green Laser (532nm)

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I will be posting photos and videos of physics experiments that I have constructed and performed. Feedback welcome, and I'd be glad to help out if you wish to replicate it!

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This is intended to be a repository of Physics experiments and questions that I would collect over the years. Please feel free email any O-levels or A-levels Physics questions to me. I would try my best to answer them and post the question and answers in my blog within 48hours.
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