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SupaVillain
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DIY FTIR
Okay so on all the other FTIR threads I found in the search here and on google errbody's like "the hardest part is building an interferometer" and
searching into these interferometers all I get is these
http://www.instructables.com/id/Do-It-Yourself-Lab-Ware/step...
now whats the difference between that and what is really required
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Marvin
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That set up gets you interference fringes, which is equivalent to the information in a few micrometers of path difference. To get a useful FTIR
spectrum needs of the order of 10mm path difference. This is usually done with a travelling mirror tracked within a fraction of a micrometer and
absolutely parallel. Far IR is absorbed by glass, so it also needs different optics. The KBr/Ge beamsplitter used in commercial instruments is
sensitive to moisture.
Building an optical interferometer with a travelling arm is feasible and the tolerances for FIR are easier to reach but that may be balanced by the
low availability of FIR optics. Then you need to add FIR sensors, electronics and computer control. I think this would be a big project and the
kind of thing that with a big effort would work reliably once.
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SupaVillain
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Honestly the hardest part is finding out what I actually need in order to build one.
If I know what I need to get and what I need to do, then it's made. Everything electronic and computerized is not hard for me to accomplish, Im an IT
major and know a lot of people in the field.
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SupaVillain
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FOR THE SLIDING MIRROR
okay so Ive found theres simple programmed arduinos that can control linear actuators, or small electric motors.
im thinking small electric motor would prolly be better for this "fractions of a micrometer" movement using VERY FINE AND TEENY TINY TOOTHED GEARS and
can be tracked simply by how it is commanded, in programming this would tell the motor to move it "x" micrometers and a couple lines of code could
tell it to retain the amount it moved and display it back to you, even though you already know its movements if youre typing them into command it. Im
assuming these movements would be prepogrammed anyways though instead of entered in by the operator.
Now as far as planning for every other component, i need to know details, for example exactly what spectrum, size, and intensity of IR laser light for
the laser. This would be easier if i could reverse engineer a broken FTIR but the parts are so expensive there really is no such thing i dont believe.
Havent done extensive research but have only found pdfs to be like user manuals and not designs or specifications n such
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SupaVillain
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Just realized how small micro meters are, gonna have to see how others do it in order to make something that can be that accurate
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SupaVillain
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Annnnd google helps me find out about "nanometer positioning stages" so still proving to be possible. Learning as im going.
so actually now im seeing what you mean by optics, an "optical linear encoder" preferably via arduino is gonna make it happen
[Edited on 9-11-2014 by SupaVillain]
[Edited on 9-11-2014 by SupaVillain]
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SupaVillain
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So as far as the infrared detector, there arent any sources for this info on wikipedia but i guess it suggests the following....
"In IR spectrometers the pyroelectric detectors are the most widespread."
-For the sliding mirror again, this may actually be moved by something that doesnt move it by nanometers per second for example, and could just be
moved by an electric motor, i think as long as the movements are TRACKED nanometer by nanometer
[Edited on 10-11-2014 by SupaVillain]
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smaerd
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This is one of those big dreams I've had for a long time. There are some hurdles but it is very possible. The biggest hurdle imo is the detector.
Those puppies are expensive. I'm not sure what could be built in a home experimenters budget from commercial parts.
You're right in that you don't have to position the mirror nanometer by nanometer but instead can 'track' the movements to that resolution while
recording information. An idea for this that comes to mind would be a very fine screw thread. Yes there would be hysterisis but if secured properly it
could play the part. The ones I've seen/fixed in commercial FT-IR's at my university had some sort of linear actuator with mounted springs to reduce
vibrations and made their 'scan routines' very quickly. A home instrument could afford to sacrifice some time (longer scan's) if everything else can
be mounted and handled properly. This would likely be important for data chucking over USB to a computer for example.
Another big issue is simply housing the optics/mechanics securely. It's really easy to over-look this but before making the plunge for parts have a
game-plan for this. Even the most basic dynamic optic paths are not easy to make reliable.
There's a lot to consider but it's totally possible. I'd love to see some attempts here. If I had the free-time and the money and didn't have a
million other projects to finish I'd be right there with you.
Edit - also, I'm not sure if a laser source is necessary. I think heating certain metals (nichrome type stuff through joule heating) is a common way.
Those are called Globar sources. A laser can be used to align the optics though so it's not flying blind. Would be a lot cheaper as well. A Globar
source should be very cheap to construct with a little research.
Edit2- yea know what I might need to make a globar source for a different project I have been working on. If I go that route I will share my
findings/efforts.
[Edited on 11-11-2014 by smaerd]
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Marvin
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The HeNe laser in an FTIR has a use, by tracking the interferogram of the this line it can be precise about the position of the mirror. Tricks in the
optical path can do this in phase quadrature. Runners made from metal dowelling and ball bearings and pushed by a micrometer have been used for
optical interferometers with success. These parts are usually made to high tolerances. Might be that a CD-ROM sled would work. There is apparently
something to be said for angle aluminium glued to a flat surface to fabricate the rest.
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WGTR
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I know nothing about FTIR, but for nano-positioning, using piezoelectric actuators is a standard way of doing it. For example:
http://www.physikinstrumente.com/technology.html
The displacement of the piezoelectric stack changes with applied voltage. Different configurations work in different ways. Some devices flex, others
compress. You don't have to use the world's most expensive actuator:
http://www.steminc.com/PZT/en/stack-piezo-actuators
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Little_Ghost_again
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Piezo is also used in some microscope stages like some electron microscopes. They can be very very precise
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SupaVillain
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Thank you so much for the help i will make sure that i show ya'll what I come up with.
i think ive decided for the optics i can probably buy the KBr windows (so that i dont have to cut crystals perfectly or polish them) and coat them
with germanium myself (using PVD of some sort and a cheap calotester to assure the perfect coating job is done) - this will be the beamsplitter which
is the most expensive part i think, therefore the most vital part to work on making cheaper. For $100 i think i can order a couple KBr windows.
yes the fact that i dont have to move it with nanometers but just TRACK it by some amount of nanometers is a huge help.
I would love to start a small business just doing analysis with this FTIR and maybe move on to making UV-Vis and other spectrometers.
a person has informed me of a problem called "chirping" that is fixed with a "compensator" in which the person had to cut an identical piece of KBr
crystal to place before the detector.
the hardest part is finding all the required information in high detail, no other task is as difficult when determination is involved.
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SupaVillain
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Im pretty sure theres a lot of schematics/wiring diagrams for FTIR's online via google images. At first i had imagined circuit boards and software but
now that i see how it works and is built i think i may just need a switch to turn every component on and activate it, then from the detector the
information is sent to the interferogram which im sure theres open source programs for
but maybe this needs its on switch and then an actual button to activate an arduino that controls the mirror, and the completing of the full range of
motion that the mirror makes will determine the start and finish of the scanning of the chemical sample.
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IrC
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I wonder if the parts from a DVD optical assembly could be used. The lens is adjusted by current variation on a coil which magnetically moves the
focus. Also I found a link which may be useful on this subject.
http://www.fc.up.pt/pessoas/peter.eaton/tutorial/webCT/
"Science is the belief in the ignorance of the experts" Richard Feynman
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Little_Ghost_again
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It might be worth looking at hard drive heads as well.
Dont ask me, I only know enough to be dangerous
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SupaVillain
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Infrared Source:
globar is best, but will require water cooling or something or the sort.
"Advances in ceramic metal alloys have lead to the production of Globars that no longer require water cooling. However these newer Globars are
typically not operated at as high a temperature as 1300K"
Beamsplitter:
i've actually found in catalog, rectangular KBr crystals that are like almost an inch tall and almost two inches long, for $40 so im thinking of
cutting these in half and making $20 KBr windows that are about a square inch big. Then with prolly "Ge" magnetron sputtering I'll put the germanium
coating on them.
As far as testing the coating, every coating thickness test like calo test and such seem to require some kind of liquid to work like diamond paste or
whatever and i worry about the KBr window taking in all the moisture from that. Either way I would only translate these test results to the light
intensity of the transmission half and the reflection half, and to the amount of time spent in "Ge" magnetron sputtering. So what im saying is it's
pointless to test the thickness if i can just compare seconds spent in sputtering with the actual correct performance of the beamsplitter. This would
be tested with a photometer, comparing light intensities of the relflected and transmitted beams.
also, ebay is a very good friend for finding things cheap, but always remember when ordering KBr type stuff, it's safer bought from the manufacturer
because of how hygroscopic it is
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SupaVillain
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Globars are also called non inductive resistors it seems, maybe theyre a type of those. Only problem is that these things look like straight tubes,
how do I hook up and use something like that????
Either way the most modern IR source is a globar that does not need water cooling. All this heat and water cooling combined with KBr and electronics
has me worried...
after looking at this page: http://chemwiki.ucdavis.edu/Analytical_Chemistry/Instrumenta...
i realize ill have to look into "air bearings" as they say they use for the sliding mirror
also a "collimator" can be addd to the front of a globar or any IR source so that it can be more direced in a path rather than omnidirectional
[Edited on 19-11-2014 by SupaVillain]
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SupaVillain
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Theres something about having had to use mechanical bearings and ruby ball bearings for the sliding mirror to be able to oscillate every millisecond,
and now currently they use air bearings because theres air in between the parts making them longer lasting from not having friction and crap like
that, however ive heard otherwise about them....
Now theres also the sample compartment that im gonna have to look at but i think thatll be a simpler part compared to others.
Now the worst and most hardest part possibly.... is the detector. This is because you cant just buy a little infrared detector, those only do like
100um to 1mm or something, right before the wavelength of microwaves. Not even in the same ballpark of what we need. In order to get what I need, im
either going to have to "liquid phase epitax" some HgCdTe, or the cheapest and most likely thing that I do is to make a pyroelectric bolometer with
PZT or LiTaO3 crystals then figure out how to hook that up to electronics that convert the beam into electronic signal that goes to the interferogram.
Deuterium for DTGS detector aint happenin.
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SupaVillain
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Check out this file for a basic idea of what to use for a detector and why,
http://shop.perkinelmer.com/Content/applicationnotes/app_lit...
so basically DTGS is a standard, but LiTaO3 is "at least as good" except for S/N which can be made up for by running more scans with a little more
time. The benefits massively destroy DTGS as a competitor. Also cheap cheap cheap! Or cheapER at least...
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SupaVillain
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Ive realized i can get a small lithium tantalate crystal for like $50 bucks but then i still have to build the tiny electrical component with its
electrodes and field effect transistor crap, at the time i dont know anything about electronics and if i just pay $50-60 bucks more i can get a
lithium tantalate detector that I know will work and will be far more effective than what I can make myself due to the fact that these manufacturers
have all put their little signature thin films and other such pieces on that they have designed through extensive research.
ive pretty much figured something out for every single component in my head but now im trying to see how everything will work as an assembly with the
electronics
im also thinking of keeping the IR source as a separate outer part instead of it being right up close with all the other parts because of how hot it
is
ive found HeNe lasers at 632nm and .8mw to 5mw for like 40 bucks or so, are these strong enough? There are lasers just like these available for $1000
which is ridiculous, i hope i dont need a certain strength of laser
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quantumcorespacealchemyst
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OK, so this kind of defeats the purpose
but http://www.ebay.com/itm/PERKIN-ELMER-1600-FTIR-SOFTWARE-AND-...
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SupaVillain
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I dont understand why you would post that it doesnt defeat any purpose it's just spam. What you posted is literally exactly the reason why this thread
exists. Im in the 300-500 dollar price range after pricing almost every single part and Im gaining and will soon share the knowledge of how to prepare
this entire machine for cheap.
You have achieved nothing but insist that my efforts are valuable in the thousand dollar range. From what Ive learned and the capabilities one gains
from the experience of building something like this, this FTIR, and several spectrometers of other kinds can be made for the same price as buying a
single machine that you have no reason to believe can work as it's bought from a stranger off the internet. They always say never buy a used
beamsplitter so theres also a high risk of having to repair that, as well as other certain parts. Also consider, why are they selling it? Maybe
because their laboratory cannot build enough profits to pay off their bills as they have thrown too much money around on making themselves look fancy
with crap like this. Also, they have to pay to repair this thing, which isnt cheap. If something breaks in a machine that you built yourself, youre
going to know EXACTLY what went wrong and how to fix it. Then you dont have to have your business inoperable until the repairman can schedule an
appointment with you and order repair parts from a facility that takes days to process and ship your part.
I can probably make an entire other FTIR for the price of one repair after labor, parts cost, and not losing business over waiting for service. Maybe
Nicolet has a warranty that says theyll work on your machine for free. Still gonna take a long time before you can operate it for your business.
And no i dont care if anyone is going to come to me and tell me that the way Im doing things works for me and not for others.
I dont do things MY way i do them the RIGHT way, in which all else is inferior.
also, not everyone can afford to buy something that overpriced or wont be willing to gamble with taking a loan out for one. In this way however, it
can be affordable and operable for those who are willing to do the work it takes.
Id like to put on my resume that i can beat the price of these big companies and make the exact same thing they do with the same quality analysis.
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smaerd
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I am pretty gungho on home made instruments for a few reasons. Go ahead buy an old FT-IR on e-bay. I would if I could afford one. The real downside is
say, if a detector goes bad a replacement is 3k+ or an opportunistic(or should I say optimistic) ebay purchase. Whereas a home instrument can be
modified/improved on and fixed when something goes wrong. Almost always for significantly cheaper. There are always drawbacks though. Cost is the most
prohibitive for me, however, lately time is becoming another. But to get back on track...
I don't believe the laser needs to be high power ( <= 1mw). I think it's moreso about the beam quality/character. Maybe also the pulse time
(probably not though). Keep in mind the purpose of the beam.
[Edited on 29-11-2014 by smaerd]
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SupaVillain
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Yea i mean i think all that matters for the laser is that it's "632 nm", i mean the stronger ones burn things and are used for engravings. Not trying
to burn every component and cost hundreds in damage, so it must not need to be one of those.
DOES ANYBODY KNOW HOW FAST THE SLIDING MIRROR MOVES??? what is the full action between the moving mirror and the detector? For example, does the
detector receive the input signal as a single picture as the mirror moves from point A to point B or does it "take a picture" every single micrometer
of movement until the whole movement is made? This is pretty much the area in which i know nothing about and dont know how to find. The electronics
are the most complex but, like i said i will learn them with time.
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smaerd
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I don't see how the velocity of the mirror would really matter. Seems to me, more like a variable you should tune based on limitations of your design.
Edit - Unless you choose to design the instrument by interpolating the mirrors position from say it's velocity. Then you'd want to tune the velocity
of the mirror based on how fast you can sample/process the data. I don't think the 'flying blind' approach would ever be acceptable. Even a lot of
position tracking method's have downsides which can give outright wrong measurements. So definitely look into how you'll handle that.
A good starting point might be to first see how long of a throw you will need, and then see what your options are for inducing the motion. Then see
what your options are for tracking.
Keep in mind that mirror's motion is the essence of the instrument. Definitely recommend looking up some of the math and crunching some numbers with
available components before moving forward.
Good starting point -
http://www.shimadzu.com/an/ftir/support/tips/letter8/tech.ht...
Great over-view -
http://mmrc.caltech.edu/FTIR/Understanding%20FTIR.pdf
[Edited on 6-12-2014 by smaerd]
[Edited on 6-12-2014 by smaerd]
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