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 Post subject: Relatively low cost hand held Raman Spectrometers
PostPosted: Fri May 12, 2017 1:33 pm 
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I recently found out about the Ahura FirstDefender and wanted to share what I'd learned. The FirstDefender is a Raman Spectrometer designed for forensics and similar applications, mostly meant for government use. They can often be found on ebay for relatively low prices. This spectrometer uses a 785 nm laser. While it internally does a comparison of the resultant spectra against a database (which is full of industrial chemicals rather than minerals), it can also export collected Raman spectra onto an SD card or Compact Flash (depending on which model of FirstDefender). With a bit of editing the spectrum can be put into a format readable by free Raman spectra programs--for instance, CrystalSleuth is a free program that can compare against the RRUFF database. (The FirstDefender also displays the spectrum on screen for quick visual comparisons.)

I have obtained 4 of these (so far) and managed to get all of them to work.
I did have to write some special purpose software to convert the .spc file that the original First Defender exports into something that Crystal Sleuth can use, but it was not hard. (There is some free software that converts .spc to text files anyway, so all that is necessary is to transpose it).

We have found that it works fine on some minerals and not at all on others. Some it just takes a long time on. Dioptase doesn't work at all, for example (apparently it fluoresces when hit with 785 but not with 582 - one of the real weirdos of Raman). The instrument also warns not to aim it at gunpowder because apparently it could ignite it. So the laser is pretty strong, though it doesn't seem to warm samples significantly even after long exposures.

Devices usually come without accessories, including charging cables, batteries, vials for internal scanning, nose cones, SD cards and Compact Flash cards. Fortunately the batteries they use are also used by the Trimble GPS, so they are not too expensive and readily available. Compact flash cards are also cheap. You can also directly plug the FirstDefender into the wall, but I don't have the transformer for that.

I am working on trying to figure out how to change the internal databases so they will work on minerals. I am having some success at cracking the internal format, but am not "there" yet and anyone that wants to help would be appreciated.


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Fri May 12, 2017 2:49 pm 
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Hi there,
what do you need to do?
Let me know

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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Fri May 12, 2017 3:34 pm 
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I heard y'all had acquired some of these. That's pretty cool.

Apparently gunpowder (black powder) is still black at 785 nm, absorbing that wavelength like it absorbs visible light wavelengths. Most gems should be transparent at that wavelength, but cupric tourmaline is not.


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Fri May 12, 2017 5:42 pm 
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I should mention that there are 3 of these for sale on ebay right now for less than $700. (O.K, it is $695 or best offer).


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Mon May 15, 2017 9:12 pm 
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Apparently the Ahura uses Windows CE internally, on an ARM processor (running the THUMB api set). I wonder if it would be difficult to port CrystalSleuth?


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Sat Sep 02, 2017 6:09 pm 
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Just wanted to share a crazy thing that happened today. We were showing off one of our spectrometers (hoping to sell one). One of the dealers had shown some interest so we asked him if he had any stones he would like us to scan. He handed us a blue zircon, 2.37 carats with a nice deep blue color. The spectrum looked odd though, a bit of noise in the low frequencies and then one large peak.
Long story short it was a diamond. We borrowed a diamond tester to double check which confirmed it. He had gotten it in an old collection, and it was in a beat up plastic gem jar with a label and everything. We tested all the other zircons he had and they were just zircon. I have no idea how that would have happened---looking closer of course there was no facet doubling which should have made it really obvious if viewed closer than a couple feet.

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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Sun Sep 03, 2017 10:33 am 
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Stephen Challener wrote:
Just wanted to share a crazy thing that happened today. We were showing off one of our spectrometers (hoping to sell one). One of the dealers had shown some interest so we asked him if he had any stones he would like us to scan. He handed us a blue zircon, 2.37 carats with a nice deep blue color. The spectrum looked odd though, a bit of noise in the low frequencies and then one large peak.
Long story short it was a diamond. We borrowed a diamond tester to double check which confirmed it. He had gotten it in an old collection, and it was in a beat up plastic gem jar with a label and everything. We tested all the other zircons he had and they were just zircon. I have no idea how that would have happened---looking closer of course there was no facet doubling which should have made it really obvious if viewed closer than a couple feet.

I was running the tablet computer on this one - and when I ran the software and the first 13 matches were "diamond" - i murmured to Stephen "You are going to want to see this". aside from some noise around 200 nm, there was only one tall (narrow) peak at 1332. I read that when they were developing the RRUFF database they found that over 25% of the minerals they got from museums and private collections had been mis-identified (they used mass spec and XRD to identify things before they put them in the database.). But I really never expected to find a large blue diamond mis-identified as a zircon. And it was the FIRST ONE he asked us to run.


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Thu Sep 07, 2017 9:38 pm 
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Have you had any luck masking the fluorescence (dioptase) by using a UV filter?


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Fri Sep 08, 2017 12:33 am 
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When i was reading an article about Raman spectroscopy, it mentioned that there was one mineral that fluoresces at 784 but not at 532. (This is unusually as it is usually the other way around.) It was either dioptase or diopside - I'll have to look it up.

I have not heard of using a UV filter - do you have a reference?


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Tue Sep 19, 2017 11:14 pm 
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Here are a few general observations, which may or may not hold up with further testing.

I ran into a CZ (obvious from size, appearance and SG) which had an unusual spectrum, including a peak near where diamond's peak would be (though shifted a bit and too broad). My guess is that this stone has the much-touted diamond-like carbon coating. The match was good enough to make the software suggest diamond as a result, but not good enough to actually be convincing if you've seen a real diamond spectrum.

London blue topaz seems to have some shifted peaks, presumably from lattice defects. Nothing surprising there but it's cool to be able to see it with the spectrometer.

Lead-glass filled rubies seem to have some extra peaks in the low inverse centimeters which resemble some SiO2 polymorphs. I haven't tested too many of these but I've seen it in all three or so of the lead glass filled corundums I have tested and in no other corundums. I will report back when I've scanned more.

Zircon's spectrum seems to be the most variable of the ones I've seen, even above and beyond the various levels of metaminction--I assume rare earth elements are contributing different peaks here and there.

Overall, this is a great tool for sorting stones quickly and accurately. We picked up a big tray of estate gems, obviously from a JTV customer, which had been sorted by color into plastic gem jars. It's pretty satisfying to take a big pile of red and orange stones and separate them into their component pyrope-almandines, spessartines, zircons, (likely synthetic) sapphires, spinels and citrines, quickly and with strong assurance that they are correctly identified.

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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Fri Sep 22, 2017 7:25 pm 
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Stephen Challener wrote:
Here are a few general observations, which may or may not hold up with further testing.

I ran into a CZ (obvious from size, appearance and SG) which had an unusual spectrum, including a peak near where diamond's peak would be (though shifted a bit and too broad). My guess is that this stone has the much-touted diamond-like carbon coating. The match was good enough to make the software suggest diamond as a result, but not good enough to actually be convincing if you've seen a real diamond spectrum.

London blue topaz seems to have some shifted peaks, presumably from lattice defects. Nothing surprising there but it's cool to be able to see it with the spectrometer.

Lead-glass filled rubies seem to have some extra peaks in the low inverse centimeters which resemble some SiO2 polymorphs. I haven't tested too many of these but I've seen it in all three or so of the lead glass filled corundums I have tested and in no other corundums. I will report back when I've scanned more.

Zircon's spectrum seems to be the most variable of the ones I've seen, even above and beyond the various levels of metaminction--I assume rare earth elements are contributing different peaks here and there.

Overall, this is a great tool for sorting stones quickly and accurately. We picked up a big tray of estate gems, obviously from a JTV customer, which had been sorted by color into plastic gem jars. It's pretty satisfying to take a big pile of red and orange stones and separate them into their component pyrope-almandines, spessartines, zircons, (likely synthetic) sapphires, spinels and citrines, quickly and with strong assurance that they are correctly identified.


Hi guys, not exactly sure about how far you got by now with integration of a mineral database into the handheld, but I wanted to let you know that my optical spectroscopy software Spectragryph has now combined spectra acquisition and spectral database search. Thus, it takes only two clicks from measured spectrum to search result. I made a Youtube video showing mineral identification, where Spectragryph drives a 785nm Raman spectrometer and uses RRUFF data for identification:
DIRECT LINK: https://youtu.be/O5KB1dnLlEM



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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Sat Sep 23, 2017 3:36 pm 
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Hi -
We have gotten pretty far. It reads the spectra directly (wirelessly) from our Raman. You then click to remove background, and click to match. We had it translated to work on a phone. Having lots of fun with it. It is sure nice to pull out my phone and run the matching after using the Raman! That will be particularly useful at Tucson, I think.


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Sat Sep 23, 2017 4:11 pm 
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Sounds good =D> So you use the FirstDefender for measuring and then CrystalSleuth ported to Android/ iOS for matching?

A special turn to "mobile phone spectroscopy" and most probably a reasonable one :D Wish you great success!


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Sat Sep 23, 2017 4:15 pm 
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oh, and I posted the wrong link before, that one is showing the x axis calibration for direct transformation from pixels to RamanShift. Here is the link for mineral identification I wanted to post: https://youtu.be/QPYunSwUTS4


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Wed Mar 14, 2018 5:31 pm 
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Well I *finally* have managed to port gem and mineral spectra *into* the Ahura Spectrometer. So now it is point and shoot (or put it in a bottle and shoot) and have it display the answer.

WooHoo!!


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