What is the explanation for this diffraction pattern?

[azdavesoul]

http://asymmetricphotons.davehewitt.com/__oneclick_uploads/2012/03/asymm.JPG

While playing with lasers in a simple home setup, I have produced asymmetrical diffraction patterns and have been unable to locate explanations in the public domain. By using a green led laser and two parallel panels to create a .5 mm single slit I got a normal diffraction pattern. Then moving one panel 1 cm closer to the laser source while maintaining the .5 mm gap, I got a pattern that changed from narrow bands on one side with progressively larger and wider spaced bands on the other extreme.

Is this new and interesting or have multiple physics students been playing with these patterns for years without bothering to publish.

 

[M Quack]

Sorry, but this is nothing new. You will get a diffraction pattern even from a single edge. The fringe spacing depends on the wavelength and the distance to the screen- which is different for your two edges.

 

[azdavesoul]

I understand that, what struck me as hard to understand is that the pattern was progressive. It varies from thin to thick. Is this just a example of a ‘wave’ pattern where each band is affected by both edges?

 

[azdavesoul]

Here is a clearer pattern and the setup I used.
http://asymmetricphotons.davehewitt.com/__oneclick_uploads/2012/03/asymetric1.jpg

http://asymmetricphotons.davehewitt.com/__oneclick_uploads/2012/03/setup.jpg

 

[sophiecentaur]

The pattern will depend, entirely, on the details of the diffracting shape involved. What is the actual shape and setup? (not a picture of the equipment but a diagram of the 'slot' or whatever). Remember, the slot depth is relevant as well as the basic width dimension. The simple formula is for a slot in an infinitely thin sheet. In general, the pattern will never be just symmetrical.

 

[azdavesoul]

Sophiecentaur,
The light source is a green led laser, 532 nm.
The target is a paper grid, ruled at 1 cm, 5 meters from the slit
The slit consists of two aluminum panels, .2 mm thick, painted flat black, perpendicular to the laser beam.
The panel on the left side is 1 cm closer to the laser.