How does a Reflection diffraction grating work?

p3t3r1

Hello, I am wondering how does a reflection diffraction grating work. Most physics text simply ignore this topic or talk in very ambigious terms. I understand that in transmission diffraction grating, you have parallel grooves so that light can pass through and produce an interference pattern. How does a reflection diffraction work? Do you still have open silts? Or is light is divided in half by making the diffraction grating material reflective? i.e. half of the pass throguh the open silts while the others hit the non-open parts and get reflected back? The problem with that is light is not diffracted though since it does not pass through a narrow opening. Thanks for any help.

ice109

you always have partial reflection when going from one refractive index to another?

p3t3r1

Well, you do have some partial reflection if you don't shine the light at the normal incidence... But how is it related? This is diffraction we are talking about.. not some normal reflection pattern.

ice109

what i mean is what is a reflection diffraction grating if every diffraction grating relfects and diffracts?

p3t3r1

Well, you see, my textbook is kind of unique because it introduce new concepts that most other university level textbooks don't even mention. (It is a grade 12 physics textbook). It usually doesn't explain these unique features well since it sometimes talk in very ambigious terms. One of the unique features for the section on diffraction grating is the difference between transmission and reflection diffraction gratings. Usually, I would just ignore it but my teacher placed a special stress on it.

According to the book, diffraction gratings are made by diamond tip cutters. They produce opaque lines with open silts in betwee. Transmission diffraction grating is what a normal diffraction grating is.. Basically, light passes through many many silts and produce an interference pattern that is sharp and narrow. That I can understand very well. For the reflection diffraction grating, it explains..:

When the lined glass is used as a reflection grating, light falling on it is reflected only in the untouched segments. This reflected light effectively comes from a series of equally spaced sources that provide the diffraction grating interference pattern reflected onto the screen.

Now, what does it mean by untouched segments???? This is what I have no clue about. I seached on Google and turned up nothong.

ice109

is this textbook in english or are you translating?

p3t3r1

The textbook is in English... Is a Canadian physics textbook for Ontario students..

ice109

sorry dude i have no clue what you're talking about

Doc Al

Think of the reflecting strips (between the grooves) as narrow parallel mirrors. The strips of reflected light interfere--and produce a diffraction pattern--exactly as light would if it passed through narrow slits. When light passes through a narrow slit, you have a narrow strip of light--same with light reflected from a narrow mirror; you still get a narrow strip of light.

Between the grooves are the untouched (ungrooved) narrow strips that act like mirrors. Those mirror-like strips are the "untouched" segments they refer to.

Note that there are different ways to make reflection gratings--you can make the grooves at set blaze angle--the light reflecting from the grooved portions. But the basic idea is the same: break the incoming light into narrow strips of reflected light. Note that this is essentially the same as breaking the light into narrow strips by sending it through the slits of a transmission grating. You get similar diffraction patterns either way.

Make sense?

p3t3r1

Yep, thanks for the help.

ice109

does that mean you can make a reflection diffraction grating that produces interference patterns emanating from both sides?