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 Post subject: Raman with DSLR and stacking software...
PostPosted: Fri Oct 12, 2012 12:34 pm 
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I'd like to start experimenting with a Raman setup. I want to develop a good understanding of the technology and for me, that means DIY. I have no interest at all in buying a turnkey product.

I have many dpss laser choices already available and I think most components for the spectrometer seem easy enough to get hold of. However there are many variables to consider with the CCD including software etc so I don't want to commit to choosing just yet. At this stage I just want to try out a rough setup to see if I can capture a Raman spectra and I was wondering if a DSLR camera would do it?
Using stacking software, I have no problem imaging very very faint deep sky objects with the camera through my telescope and that has me wondering whether I could take multiple short exposures from the spectroscope and stack up the result. There will be no scale of course but Im hoping at least I might just see some peaks at the expected intervals apart for that sample??


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 Post subject: Re: Raman with DSLR and stacking software...
PostPosted: Fri Oct 12, 2012 4:00 pm 
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Having a Dslr you are already at a great advantage to Dr. C.V. Raman who recorded his first and Nobel prize winning spectra on photographic plates with very long exposures.

There is an ebay seller who sells a spectrometer whose frequency range you have to set yourself anyway. Furthermore any ocean optics spectrometer is tunable but you lose the factory calibration.
Units like the science-surplus one are so cheap that it doesn't pay to fool around with a camera.
You would need to devise a sample holder, light collector, edge filter and dispersing element. Dr. Raman used prisms and probably prism trains because when he did his work suitable gratings were not available to him.

http://www.ebay.com/itm/Compact-Fiber-C ... 7675.l2557


http://www.ebay.com/itm/Laser-Lab-Fiber ... 1c2c11dfa3


http://www.ebay.com/sch/i.html?_nkw=fib ... =1&_ipg=50

http://www.ebay.com/sch/science-surplus/m.html

Stacking software won't do you much good. I guess you are wanting to signal average which all fiber optic spectrometer software can do.

Its a good idea to get an interference filter to keep the laser light out of the spectrometer. These are also available on fleabay.

http://www.ebay.com/itm/Optical-Filter- ... 51918bb462

This seller can furnish any wavelength you need and is reasonable.


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 Post subject: Re: Raman with DSLR and stacking software...
PostPosted: Sat Oct 13, 2012 12:34 pm 
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Thanks for that most helpful reply! Unfortunately there doesn't appear to be any more of those science-surplus spectrometers available at the moment.

I was a little concerned that these types of spectrometers designed for wideband spectra may not have the resolution to take full advantage of Raman and got thinking of using the DSLR. Are there any applications in gem identification where it's helpful to have more resolution than these units offer or do the peaks tend to be far enough apart?

Also, what is the most useful laser wavelength for gem identification (for use on one of these spectrometers)?


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 Post subject: Re: Raman with DSLR and stacking software...
PostPosted: Sun Oct 14, 2012 2:58 pm 
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Quote:
Thanks for that most helpful reply! Unfortunately there doesn't appear to be any more of those science-surplus spectrometers available at the moment.

Have you emailed them and asked? They have offered these repetitively. If there are no more they are probably out of them for good since it is likely they bought a large lot of them at surplus.

The auction from "goodgadgets2u" is the same spectrometer tuned up. That seller is very reliable. A laser nut. If science-surplus is out of them you might consider that auction.

Quote:
I was a little concerned that these types of spectrometers designed for wideband spectra may not have the resolution to take full advantage of Raman and got thinking of using the DSLR. Are there any applications in gem identification where it's helpful to have more resolution than these units offer or do the peaks tend to be far enough apart?

The resolution is a function of starting wavelength and bandwidth. And the grating in used. All ccd based spectrometers are going to have a limitation in resolution unless multiple units are ganged as has been done with fiber optic based LIBS spectrometers.
They still make more sense than trying to use a Dslr. You would need the correct amount of dispersion as well as throughput at the Dslr sensor and you are very unlikely to get them with a gemological spectroscope stuck in front of Dslr. (although you might get lucky)

http://en.wikipedia.org/wiki/Etendue

Quote:
Also, what is the most useful laser wavelength for gem identification (for use on one of these spectrometers)?

Shorter wavelengths give more Raman signal but are likely to cause fluorescence. This is why "real" Raman spectrophotometers usually have two or more lasers to choose from.


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