Location of a diffraction pattern

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Discussion Overview

The discussion revolves around the estimation of the location of a diffraction pattern produced by a diffraction grating in an optical setup involving a laser and a screen. Participants explore how to calculate the positions of the diffraction spots on the screen and whether these positions correspond to the location of the laser source.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks to understand if the location of the diffraction pattern on the screen is the same as the location of the laser source.
  • Another participant clarifies that a diffraction pattern from a grating will consist of multiple spots, suggesting that the location of these spots follows the standard diffraction equation.
  • There is a discussion about the nature of the diffraction pattern, with some participants noting that it can be infinitely wide depending on the grating design.
  • One participant expresses a focus on capturing only the first and central spots of the diffraction pattern, suggesting they should align with the sample plane of the point source.
  • Several participants emphasize that the diffraction pattern is better described in terms of angles rather than linear dimensions, indicating that varying the distance between the screen and the slit will change the size of the pattern.
  • There is confusion among participants regarding the relationship between the diffraction pattern and the plane of the point source, with some questioning the clarity of the original query.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the diffraction pattern and the point source plane. While some agree that the central and other orders may be located on the same plane as the point source, others find the question unclear and do not reach a consensus.

Contextual Notes

Participants note that the diffraction pattern's characteristics depend on the specific diffraction grating used and that assumptions about the setup may affect the interpretation of the pattern's location.

shahbaznihal
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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?
 
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shahbaznihal said:
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.
 
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.
 
shahbaznihal said:
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.
 
shahbaznihal said:
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.
 
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Andy Resnick said:
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.
 
shahbaznihal said:
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).
 
  • #10
shahbaznihal said:
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...

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1566849170520.png
 

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