John Green
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LIBS spectrometry on the cheap
My main interest is geology and minerals which possessed me to try to construct a LIBS spectrometer. Knowing nothing about it and trying to build it
as cheaply as possible I began studying the problem and experimenting with different ways to accomplish that goal. I determined that I could probably
use a Q-switched Nd YAG laser from an M1 tank range finder along with a power supply and pulse forming network designed to work with the same unit.
For the spectrometer I used a section of DVD which has 1350 lines per mm as a reflection type diffraction grating, a couple lengths of PVC pipe and a
couple of single edge razor blades as the slit. Other than that an elevate-able table and some simple optics were required. I have been using an SLR
camera to capture spectra which can be loaded into Excel and graphed. Linear regression shows that the data are extremely linear . If anyone might
be interested in building a contraption like this I should be happy to offer any assistance I can. Thus far I am able to make qualitative
measurements (detect major element composition), quantitative measurements will take more work.
The laser, power supply, and pulse forming network were about $350. The rest was stuff I had lying around or bought cheaply at the local building
supply store. It was most helpful (though probably not essential) to have a bench-top lathe available.
The whole point of this is that I am considering acquiring a cheap spectrometer (or perhaps two as I am toying with building a Raman system as well).
There was quite a discussion on this board a while ago ( Cheap, Low-Resolution, Raman Spectroscopy) wherein there was a lot of talk about a $200
spectrometer from an outfit called Science-Surplus which might work. The trouble is I am reluctant to buy from someone who is afraid to list his
address or phone number. I sent an email to the company yesterday, so far no response. Radagast seems to have been pleased with his (though he
mysteriously broke one) has anyone else any experience with these?
 
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Marvin
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Really cool setup. I'm amazed you've done so much with so little, especially the grating. Do you have a collimating lens?
I looked at LIBS but what I read talked about a blanking delay to let the plume expand. Sometimes if done well enough things just work.
I was also concerned about eye damage and I thought I'd start with sparks.
I have a science surplus spectrometer but I've not realigned the optics, they are recycled bits of medical equipment.
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John Green
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Thanks Marvin. No I do not collimate the beam. I have toyed with the Idea but since it's working as it is there is not a lot of incentive. Also I
suspect that it would be best to use a mirror to avoid chromatic aberration which brings us back to Czerny-Turner configuration which is fine and
that's why I'm kind of looking for a cheap spectrometer.
Yes the blanking delay avoids a lot of incandescent light from the spark but I've had some luck selectively blocking the light from the initial spark.
I did some investigation of spark assisted LIBS but I suspect I was using way too much power and my spectra were dominated with lines from the
electrodes. I wish I could come up with a safe way to use microwaves.
With regard to eye damage I made a little cardboard box which covers the entire working stage and also lets me make exposures even in relatively high
ambient light.
I have emailed Science Surplus and gotten no response I'm beginning to suspect he may be out of business. Here's one for $749. http://www.aseq-instruments.com/
The photos below illustrate the sample table and dealing with the curved spectrum from a DVD (crop a small vertical segment with the least curvature).
fig.6 shows the plume projected on the spectrometer. By raising the table slightly one can move the high intensity spark out of the active area of
the slit, reducing somewhat the incandescent light.
  
[Edited on 7-2-2015 by John Green]
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m1tanker78
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Quote: Originally posted by John Green  | | I determined that I could probably use a Q-switched Nd YAG laser from an M1 tank range finder along with a power supply and pulse forming network
designed to work with the same unit. |
How did you source that range finder? Funny, I used one for years but never gave it a second thought. What's the output power and wavelength?
I'm building a bare-bones Raman system and working my way up to something I can put into an enclosure. I chose 650nm for the excitation wavelength. I
have a couple of Altera Cyclone IV FPGAs on PCIe cards as well as 16 bit A/D that I'll be using to generate pulses for and collect and process raw
data from a ~7500 element linear CCD. Edge and notch filters are in the mail.
How are you 'gating' the camera?
Tank
Chemical CURIOSITY KILLED THE CATalyst.
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Marvin
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The SSY-1 saturated the market some years ago as, appropriately enough, ex M1 tank parts. I think they moved to diode. I understand with the Q
switch removed it can punch through a razor blade. Meredith instruments still has some stock of parts.
Put the details of your Raman stuff in the Raman thread, I'm interested you are going a completely different way.
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John Green
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The laser I used (I understand) came from an early range finder used on the M-1 tank which was replaced by a later modification whereupon a lot of
these lasers became available on the surplus market. This laser is commonly referred to as a SSY-1. I believe this to be a misnomer. I have seen
pictures of the laser assembly stamped ASSY-######.
I do not remember the actual numbers but I suspect that someone unfamiliar with military nomenclature had one of these with some of the characters
obliterated so all he could see was SSY-1. At any rate a search on SSY1 will bring up many references to these devices which were widely available
just two years ago but seem to have disappeared. I got mine from Meredith Instruments https://www.mi-lasers.com/ but as far as I know he is out of them. He has most of the components but no Q-switches. One can find lots of info
on the SSY1 on Sam’s laser faq. http://www.repairfaq.org/sam/laserscl.htm including more detain than anyone would want on my system by searching within that page on “laser
induced breakdown spectroscopy” The SSY1 outputs 1064 nm radiation in a pulse about 1 nanosecond in length totaling about 10 milijoules. There
were recently some Israeli lasers very similar to the SSY1 that have been called SSY2’s . Adolf Cortel in Barcelona has used on to build a very
nice LIBS system using an Ocean Optics spectrometer. Some of Adolf’s (He’s done both LIBS and Raman) work can be found at: https://www.youtube.com/user/toc1955 I’ll be darned if I can find the SSY2 seller on EBay though. Similar units are sometimes used in
cosmetic laser systems so one might expect these lasers to be available but I haven’t seen any.
I don’t gate the camera I simply set the exposure to 30 sec. ASA 3200 f5.6 then depending on what I am trying to analyze fire the laser from 10 to
30 times at 1 sec intervals. Results depend a lot on what you are analyzing.
Note that the barium nitrate spectrum below is very clean but barium sulfate has a lot of background.
I will be most interested in following your progress on the Raman system.
Were there any restrictions on how many times you could fire the range finder in a given period of time in the tank?
 
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John Green
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Ok I'll put Raman stuff in Raman when I get some. It seems I remember one of the reasons for the change was eye saftey. Of course Marvin &
M1tanker would probably know more about that than I.
Since Libs tells one more about elemental composition and Raman more about molecular composition it would be nice to have both.
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m1tanker78
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| Quote: Originally posted by John Green | The laser I used (I understand) came from an early range finder used on the M-1 tank which was replaced by a later modification whereupon a lot of
these lasers became available on the surplus market.
[......]
Were there any restrictions on how many times you could fire the range finder in a given period of time in the tank?
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I dug out my old training manual. No mention (that I could see) of the LRF model number. I believe the LRF was updated when the M1A2 was upgraded to
the M1A2-SEP. Anyway, this is probably what you're after:
[Edited on 2-9-2015 by m1tanker78]
Chemical CURIOSITY KILLED THE CATalyst.
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John Green
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Hey thanks Tanker, that's exactly what I wanted.
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John Green
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I was going through some old emails for an unrelated reason and found this.
Looks like they sell Q-swiches for the sissy1 but I'll guess they're pretty expensive.
The other parts can be gotten from Meredith.
HiJohn,
Thank you for your e-mail.
We still manufacture the SSY-1 parts (M1 Pump Cavity) from time to time. However, we only supply the pump cavity and Q-switch.
We would be happy to send you a quote for the MK-367 .
Before we can quote, we will need your street address and phone number.
Please do not hesitate to call on us if we may be of service.
Best Regards,
Michael J. Myers
Kigre, Inc.
100 Marshland Road
Hilton Head Island, SC 29926
USA
PH# (843) 681-5800
Fax# (843) 681-4559
E-mail: mike@kigre.com
E-mail: michaelkigre@gmail.com
Web: www.kigre.com
[Edited on 9-2-2015 by John Green]
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John Green
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Here is the seller from Israel who was selling what have been called SSY2 (sissy 2) lasers. q-switched Nd-YAG lasers. http://stores.ebay.com/part2go/_i.html?_armrs=1&_dmd=1&a...
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