Resolving Power - Disadvantages

  • Thread starter elemis
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  • #1
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So I know resolving power is given by :

Resolvance = λ/Δλ = nN

Where n = order of fringe being observed and N is the no. of slits.

So I was thinking there are a few ways of increasing resolvance :

1.) Decrease the slit width
2.) Increase the order of the fringe we observe.
3.) Increase the number of slits.

However, wouldn't the first option cause a decrease in transmitted light and hence wouldnt our spectra have decreasing intensity ?

Also, for the second option, it is known that intensity of maximas decreases quite quickly from one order to the next... Hence, would our peak have poor intensity as well ?
 

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  • #2
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However, wouldn't the first option cause a decrease in transmitted light and hence wouldnt our spectra have decreasing intensity ?
Right. You'll have to find the best slit width, taking both effects into account.
Also, for the second option, it is known that intensity of maximas decreases quite quickly from one order to the next...
Not if the slits are narrow ;).
 
  • #3
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increasing the number of slits increases resolution AND intensity
 
  • #4
Andy Resnick
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So I know resolving power is given by :

<snip>

I'm not sure what you are asking about- technologies used for high resolution spectroscopy, grating design, something else....?
 
  • #5
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I'm not sure what you are asking about- technologies used for high resolution spectroscopy, grating design, something else....?

I'm in interested in grating designs that could increase resolving power and the subsequent disadvtages.
 
  • #6
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increasing the number of slits increases resolution AND intensity

So what changes could I implement that would have some disadvantages ?
 
  • #7
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Are you sure you want to get additional disadvantages?
- reduce the number of slits
- use a different width for different slits
- make the slits too small, or too wide
- use the screen too close to the grating, or too far away

If you want to have advantages, avoid all those points.
 
  • #8
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Are you sure you want to get additional disadvantages?
- reduce the number of slits
- use a different width for different slits
- make the slits too small, or too wide
- use the screen too close to the grating, or too far away

If you want to have advantages, avoid all those points.

Thanks !! You see what I'm really interested in is the possible trade off's.
 
  • #9
Andy Resnick
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I'm in interested in grating designs that could increase resolving power and the subsequent disadvtages.

Grating design is a complex subject that must take into account not just the density of 'lines' but also the detailed shape (the 'blaze angle', for example). I recommend starting by reading this:

http://gratings.newport.com/library/handbook/handbook.asp

It's the gold-standard reference. Also, I recommend looking at what equipment NIST or other standards labs use to perform precision (say, 1 part in 10^15) spectroscopy.
 

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