# Effect of stacking diffraction gratings

• mun
In summary: I came up with. In summary, the conversation revolves around the question of whether adding a second diffraction grating of the same pattern to a laser beam transmitted through a first diffraction grating would result in more spots/maximas. The expert summarizer notes that the conversation becomes more complicated as the questioner introduces a non-typical diffraction grating and a 2D diffraction pattern, and questions why the questioner did not use a simpler scenario to test their idea. The questioner explains that they did not have access to the necessary equipment and were curious to know the answer.
mun
Hi

I have a basic question about the effect of transmitting a laser beam through multiple diffraction gratings. Suppose a diffraction grating was used to produce many spots as follows:

Would adding a second grating of the same pattern result in more spots/maximas? If so, would the resulting number be n^2 where n is the original number of spots/maximas? If not, what is the expected visual effect?

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mun said:
Hi

I have a basic question about the effect of transmitting a laser beam through multiple diffraction gratings. Suppose a diffraction grating was used to produce many spots as follows:

View attachment 262123

Would adding a second grating of the same pattern result in more spots/maximas? If so, would the resulting number be n^2 where n is the original number of spots/maximas? If not, what is the expected visual effect?

Back up a bit.

First of all, a typical diffraction grating does not produce 2D spot pattern like that. Have you not played with one?

So now start with the straightforward diffraction grating that even most General Physics students know of, and ask your question again.

Zz.

Vanadium 50
ZapperZ said:
Back up a bit.

First of all, a typical diffraction grating does not produce 2D spot pattern like that. Have you not played with one?

So now start with the straightforward diffraction grating that even most General Physics students know of, and ask your question again.

Indeed, it's not a typical diffraction grating. This isn't the type with N lines per mm, but rather I believe this is based on FFTs. Still, these are diffraction gratings. The grating pattern looks something like this:

My question is mainly will each beam detracted by the first grating be independently detracted again by the second grating?

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mun said:
Indeed, it's not a typical diffraction grating. This isn't the type with N lines per mm, but rather I believe this is based on FFTs. Still, these are diffraction gratings. The grating pattern looks something like this:

View attachment 262154

My question is mainly will each beam detracted by the first grating be independently detracted again by the second grating?

But see, this is what I find puzzling, and why I don't know why you can't see the issue with your question.

Typically, if we want to test an idea, we use the SIMPLEST CASE, something that is well known and UNADORNED with unnecessary complexities. You don't test the validity of Newton's laws in the very beginning by finding the trajectory of an object in high winds over large range of altitudes! You try to test it in the simplest, controlled manner that eliminates as much complexities as possible.

So why are you using a non-typical scenario, and not even something you can easily test, to ask such a question? What is wrong with testing this with typical diffraction gratings? After all, it is almost trivial to stick another diffraction grating at a spot's location after it has passed through the first grating, isn't it? Why don't you try it?

Zz.

vanhees71
ZapperZ said:
But see, this is what I find puzzling, and why I don't know why you can't see the issue with your question.

Typically, if we want to test an idea, we use the SIMPLEST CASE, something that is well known and UNADORNED with unnecessary complexities. You don't test the validity of Newton's laws in the very beginning by finding the trajectory of an object in high winds over large range of altitudes! You try to test it in the simplest, controlled manner that eliminates as much complexities as possible.

So why are you using a non-typical scenario, and not even something you can easily test, to ask such a question? What is wrong with testing this with typical diffraction gratings? After all, it is almost trivial to stick another diffraction grating at a spot's location after it has passed through the first grating, isn't it? Why don't you try it?

Zz.

I'm asking because I don't have the equipment or gratings. And in the current climate, parts can be hard to come by. Also I'm asking purely out of curiosity and thought this would have been experimented many times and an established answer exists. For experimenters that have the resources, adding/multiplying multiple gratings should have been rather straightforward, so I didn't expect novelty in my question.

mun said:
I'm asking because I don't have the equipment or gratings. And in the current climate, parts can be hard to come by. Also I'm asking purely out of curiosity and thought this would have been experimented many times and an established answer exists. For experimenters that have the resources, adding/multiplying multiple gratings should have been rather straightforward, so I didn't expect novelty in my question.

Then why ask this using a complicated scenario in the first place? You have never made any attempt to explain this.

Zz.

ZapperZ said:
Then why ask this using a complicated scenario in the first place? You have never made any attempt to explain this.

Zz.

mun said:
I'm asking purely out of curiosity and thought this would have been experimented many times and an established answer exists.

mun said:
I'm asking purely out of curiosity and thought this would have been experimented many times and an established answer exists.

That does NOT explain at all on why you picked a complicated scenario to test what is essentially an easy test. Why did you picked a horribly complicated "diffraction grating" and a 2D diffraction pattern to test an idea that can be easily tested by MUCH SIMPLER setup that is available in practically all intro physics labs?

THAT is what I do not understand, and that is what you have failed to explain.

Zz.

ZapperZ said:
That does NOT explain at all on why you picked a complicated scenario to test what is essentially an easy test. Why did you picked a horribly complicated "diffraction grating" and a 2D diffraction pattern to test an idea that can be easily tested by MUCH SIMPLER setup that is available in practically all intro physics labs?

THAT is what I do not understand, and that is what you have failed to explain.

Zz.

No one deliberately PICKED a scenario to ensure no one in this forum won't have an answer for. That's the scenario I came up with because that's what I have in hand from an old Christmas shower light. Whether it could be reduced to a simple toy example using 1D gratings is a separate issue. This is going in circles and you really have issues. Have a nice day.

mun said:
Hi

I have a basic question about the effect of transmitting a laser beam through multiple diffraction gratings.

Would adding a second grating of the same pattern result in more spots/maximas? If so, would the resulting number be n^2 where n is the original number of spots/maximas? If not, what is the expected visual effect?

The short 'B- rated' answer is 'it depends'. In a sense, you can imagine that the second grating will create a new diffraction pattern for every diffracted component created by the first grating.

Going past that is an I- or A-rated response...

## 1. What is the purpose of stacking diffraction gratings?

The purpose of stacking diffraction gratings is to increase the overall diffraction efficiency and improve the spectral resolution of the grating. By stacking multiple gratings, the diffracted light from each grating can be combined to create a more precise and detailed spectrum.

## 2. How does stacking diffraction gratings affect the diffraction pattern?

Stacking diffraction gratings can result in a more complex diffraction pattern with multiple diffraction orders. The intensity and direction of the diffracted light will depend on the spacing and orientation of the stacked gratings.

## 3. What factors should be considered when stacking diffraction gratings?

When stacking diffraction gratings, factors such as the grating spacing, orientation, and alignment must be carefully considered. The materials and coatings of the gratings can also affect the overall performance.

## 4. Can stacking diffraction gratings improve the spectral range of a spectrometer?

Yes, by stacking gratings with different groove densities, the spectral range of a spectrometer can be extended. This allows for the detection of a wider range of wavelengths and finer details in the spectrum.

## 5. Are there any limitations or drawbacks to stacking diffraction gratings?

One limitation of stacking diffraction gratings is the increased complexity and cost of the spectrometer system. Additionally, stacking too many gratings can result in overlapping diffraction orders and decrease the overall efficiency of the system.

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