# Location of a diffraction pattern

• A
I am trying to make a spectrometer. At the moment, I have an optical setup consisting of a laser, diffraction grating and a screen/detector in a straight line. I am trying to understand how to estimate the location of the diffraction pattern of the slit on the screen? Is it the same location on the screen as the location of the laser/source?

ZapperZ
Staff Emeritus
I am trying to make a spectrometer. At the moment, I have an optical setup consisting of a laser, diffraction grating and a screen/detector in a straight line. I am trying to understand how to estimate the location of the diffraction pattern of the slit on the screen? Is it the same location on the screen as the location of the laser/source?
Wait, what?

A "diffraction pattern" from a diffraction grating using a laser will consist of more than just one dot on the screen. So how can it even be "the same location on the screen as the location of the laser"? Or are you looking at just the 0th order?

The location of the diffraction dots will follow the standard diffraction equation for diffraction grating.

Zz.

Hi,
Thanks for your reply. Apologies for the confusion. What I really want to know is how to calculate the location of the entire diffraction pattern on the screen to place the linear CCD array.

I hope this clarifies the confusion.

Ibix
2020 Award
It depends on your diffraction grating - you can make one to produce more or less any pattern you want. Assuming it's a set of parallel lines, then the pattern is (at least theoretically) infinitely wide. The brightest part, however, should be more or less where the laser would strike the screen if the grating wasn't there.

I am only targetting to capture the first and central spot. I think it should be on the sample plane as the point source.

ZapperZ
Staff Emeritus
Hi,
Thanks for your reply. Apologies for the confusion. What I really want to know is how to calculate the location of the entire diffraction pattern on the screen to place the linear CCD array.

I hope this clarifies the confusion.
This question makes no sense especially after I've given you the diffraction equation. Why can't you find the location of the spots from that?

Zz.

Andy Resnick
Hi,
Thanks for your reply. Apologies for the confusion. What I really want to know is how to calculate the location of the entire diffraction pattern on the screen to place the linear CCD array.

I hope this clarifies the confusion.
The diffraction pattern is not imaged onto any particular plane. Varying the distance between screen/CCD array and slit(s) will simply result in the diffraction pattern size changing. The diffraction pattern is more cleanly described in terms of angles, not linear dimensions.

Cryo and Ibix
The diffraction pattern is not imaged onto any particular plane. Varying the distance between screen/CCD array and slit(s) will simply result in the diffraction pattern size changing. The diffraction pattern is more cleanly described in terms of angles, not linear dimensions.
Correct. But as a while (the central and the other orders) are located on the same plane as the point source? Assume that you have a point source (the laser), would the entire diffraction pattern be located on the same plane as the point source?

Thanks for taking time to reply.

Andy Resnick
Correct. But as a while (the central and the other orders) are located on the same plane as the point source? Assume that you have a point source (the laser), would the entire diffraction pattern be located on the same plane as the point source?

Thanks for taking time to reply.
I'm sorry, I don't understand what you are asking- specifically "[...] entire diffraction pattern be located on the same plane as the point source?" doesn't make sense (to me).

berkeman
Mentor
But as a while (the central and the other orders) are located on the same plane as the point source?
Assuming a 1-D grating, I would think so...