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 Post subject: More Details About Cheap, DIY Raman Spectroscopy
PostPosted: Sat Feb 23, 2013 10:07 pm 
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Hi all,

I'm Radagast from Sciencemadness.org, an amateur-chemistry forum. I came across posts by the member "Mikko" here, describing his experience constructing a DIY Raman spectrometer from the Science-Surplus/B&WTek spectrometer, and was instantly fascinated by the possibilities for using that instrument as a relatively inexpensive tool to analyze and fingerprint organic compounds.

I'm intrigued to see so many experts in spectroscopy in a gemology forum (and interested to learn that Mikko now is himself an expert in Raman technique), and hope to learn more from you here. In the meantime, I've logged my progress on my DIY raman spectrometer at the following link at Sciencemadness.org:

http://www.sciencemadness.org/talk/view ... ?tid=23422

I'm not sure this will be useful to you from a gemological perspective, but hope that the other DIY'ers on this site will be able to get something out of it.

Best,

Greg


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 Post subject: Re: More Details About Cheap, DIY Raman Spectroscopy
PostPosted: Thu Mar 14, 2013 2:36 am 
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Thanks for the post! Going to read it (when I'm not so sleepy).


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 Post subject: Re: More Details About Cheap, DIY Raman Spectroscopy
PostPosted: Thu Mar 14, 2013 11:32 am 
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The availability of lasers that are essentially free, and the further availability of almost free Raman filters (from Omega Bob on ebay) makes it very easy for people to experiment with Raman spectroscopy.

Make sure you get a pair of safety glasses for the laser wavelength you are using.
Many of the lasers sold are jazzed up or intended to be jazzed up by the buyer by increasing the feed power. You don't want to get the beam or a specular reflection of the beam (as could come out of a faceted gemstone) square into the eye.

I am normally NOT much of a safety Nazi but you can sustain injuries to the eye very quickly. A pair of goggles is all you need. And keep others out of the room while you experiment. NEVER look at anything illuminated by a laser through ANY optical system even a loupe. Raman and FTIR microscopes all have shutters to the eyepieces and video observation systems to prevent those temptations.

I had not looked at the linked to thread in a while but he seems to be onto something. I will get caught up on his thread and report back.

He is using the inexpensive BW Tek spectrometer that is available on ebay for $200. The seller is Science Surplus. Another seller called goodgadgets2U who sells lots of laser items buys these and calibrates them and sells them at a modest mark up.


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 Post subject: Re: More Details About Cheap, DIY Raman Spectroscopy
PostPosted: Thu Mar 14, 2013 2:40 pm 
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http://www.sciencemadness.org/scipics/ed800081t.pdf

Here is a reprint on how to make your own Raman spectrometer.
Something personally amusing to me is that the article is edited by a Professor
from my own alma mater under whom I did an electronics construction project in about 1971.
I built a silver coulometer for him. It too was for educational laboratory purposes.

Here are details and photographs:
http://www.sciencemadness.org/scipics/si002.pdf

The Semrock filter specified is very good but probably expensive. (They are the ones to beat these days) A similar filter could be had from Omega Bob for $50 or so. He probably would also be happy to make the right angle elliptical reflector. Alternatively you could just use "90 degree geometry and point the laser in and collect the light at a right angle.

A less expensive lens than the microscope objective they specify would also probably work just fine.
A 20X objective has a focal length of eight to ten millimeters.


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 Post subject: Re: More Details About Cheap, DIY Raman Spectroscopy
PostPosted: Thu Mar 14, 2013 3:19 pm 
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Thanks, Gene. Lots to read. :)


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 Post subject: Re: More Details About Cheap, DIY Raman Spectroscopy
PostPosted: Thu Mar 14, 2013 3:48 pm 
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@Beryllagem

No problem -- I based this design off of Mikko's work in the following thread, and consider the project at Sciencemadness to be essentially a fork of his original work:

viewtopic.php?f=11&t=14016&start=30

By the way, I read GemmoRaman's posts about having a more-open raman database, and have to say that this alone is a reason to support that company. One of the most frustrating aspects of any kind of spectroscopy is that commercial databases are very expensive. Any movement to a more open spectral database would be amazing.

I'll keep this thread updated with any significant developments (knock on wood). Mostly, I (and the other SciMad members) are working on the mundane details of how to get better spectra from organic compounds, e.g. varying the laser power and focus, integration times, sample distance, etc. There are more advanced suggestions on time-resolved spectroscopy, single-mode lasers, and the like, but I'm taking baby steps at the moment.

Recently I obtained better results from reducing the power of the laser by a simple Radioshack potentiometer, which afforded a much flatter baseline for my aspirin spectra. If you build your own raman spec, I hope you'll post your results in this thread since gems are, after all, inorganic compounds and therefore interesting to amateur chemists like me.

@G4Lab

That's quite a coincidence re: your work for one of the authors. And, I agree 100% with your safety suggestions, particularly when aligning the laser with the beam-splitter. More than once, I took an indirect hit from the overspec'd 532 nm laser while fiddling with the beam-splitter (fortunately with my 532 nm/IR-protective glasses on), and the specular reflection even from a rough white surface (an aspirin tablet) is blindingly bright even at a distance. I imagine that working with gems would be riskier.

The spectra I've collected so far were actually based on either on Brian's or your suggestion (probably years ago, can't find the post at the moment) of using OmegaBob's raman filter. Although the Mohr et al. article included a supplementary parts list, that list did not include the optical breadboard and posts, so I've extended that list here:

http://www.sciencemadness.org/talk/file ... &aid=22437

Although the resolution is still quite low and the spectra are a bit messy, I believe we're making progress and the spectrometer is already capable of supplying the dominant peaks appearing in spectra taken by professional instruments. I welcome any suggestions or comments by you and the other wizards on this forum.

@all

I recall seeing some posts inquiring about the specific details of how to configure the breadboard and posts. I'm only a beginner but if you'd like pictures of my setup, just let me know and I'd be glad to post them. In the meantime, I leave you with the LEGO raman spectrometer:


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IMG-20130307-00097_reduced.jpg [ 72.85 KiB | Viewed 2435 times ]
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 Post subject: Re: More Details About Cheap, DIY Raman Spectroscopy
PostPosted: Thu Mar 14, 2013 5:27 pm 
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One the photomacrography forum there is a Canadian engineering student whose first effort at Z stacking photography was done with a LEGO rig that he built. It seemed to work quite well. He has since built a "real" set up and gone crazy about Z stacking like everyone else over there.

Also a list member here was going to use LEGOs to prototype a Brewster Angle refractometer for OTL use. I don't know how far he got.

On Radagast's Raman thread at Science madness bfesser posted this picture which I repost here for the general amusement.


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narrow top-ramen.jpg [ 60.98 KiB | Viewed 2427 times ]


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