First order fringes being reflected back to the 0 order

[cseanm]

I heard that if you put a laser through a diffraction grating, and then reflect the first order fringes back to the middle point you will create a second diffraction pattern within the bright spot you are creating. I have been asked to try to test this and would like to know whether or not it is true before spending time trying to get the experiment to work correctly (I briefly tried and could not see any diffraction pattern whatsoever).

Thanks!

 

[0xDEADBEEF]

The reflected beam is coming in at an angle, so I think there should be fringes.

 

[cseanm]

So, if the mirrors were 5cm apart would the equation d*sin(theta) = m(lambda) still work for the new fringes created? With d now being 5cm?

ie, would it would turn into something similar to a double slit experiment, just with light sources quite far apart and distance between the fringes extremely small?

 

[0xDEADBEEF]

The inner rays have a shorter distance then the outer ones, so you should get a stripe pattern. The result will differ a bit from the double slit I think, because the distance from the source to the mirror is also relevant. If you split a beam in two parts and let one beam interfere with the other beam at an angle this will always produce stripes.