Author Topic: Making IR optics.  (Read 4189 times)

Offline S. Heslop

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Making IR optics.
« on: June 10, 2016, 04:05:10 PM »
This is somewhat silly but i've been thinking lately about how possible it would be to make a relatively cheap FTIR spectrometer (or several) at home. I'm still at the phase where i'm trying to figure out if it'd be even possible though, but i've got a few ideas. This thread is sort of a sanity check since I'm sure there's people that know more about this stuff on here than the crap i've been able to find through google.

The things i'd like to make myself are off-axis parabolic mirrors, IR windows, and a beam splitter.

For the IR windows i've been thinking about using zinc selinide co2 laser cutter lenses and grinding them flat-enough. The most i've found about grinding lenses, flats, and mirrors at home is from the amateur astronomy world where they're grinding large chunks of glass. I'm not sure of the same techniques would translate as easily to a single 20mm diameter blank, but I'm thinking it might be possible to stick/ clamp them all to a surface and grind a whole bunch of them at once. But i'm not so sure on a good method for sticking them that would be easy to remove once the job is done.

For the beam splitter i'm thinking it might be possible to sputter a half mirror onto one of those flat-enoughs. There's alot of stuff online about sputtering at home. But I think I might need to find more info on other optical coatings to reduce internal reflections or the mirror from corroding. Not been able to find much on stuff in the mid IR region though.

I feel sort of half confident about the windows and the beam splitter, but where i'm really stuck is on the off-axis parabolic mirrors. From what i've seen (https://www.youtube.com/watch?v=rJ8U5kwCZDk#t=2m37s) they're made with fancy CNC machines. I'm not sure if there's a way to make one (or several) at home to a high standard, but I've been wondering if it'd be possible to cast or press one if I was able to get a die made. I don't think regular resins would retain their shape to a high degree, nor would anything that needed to be heated up. And then assuming i'm sputtering the mirror surface onto it then it'd need to be able to survive some temperature.

Any information or advise would be appreciated.

Offline PK

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Re: Making IR optics.
« Reply #1 on: June 10, 2016, 06:25:35 PM »
A tiny CNC lathe (like a taig) and a diamond tool.  You get your off axis bit with a fixture on a faceplate...
????

Offline S. Heslop

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Re: Making IR optics.
« Reply #2 on: June 10, 2016, 09:20:01 PM »
It'd need a fairly large swing for that I feel. Although i'm beginning to think it might not need to be a super fine surface finish since with acrylic I could try that vapour polishing thing to smooth the result out.

I might've jumped the gun a bit with this thread since i'm still trying to learn stuff about optics. The main purpose of the off axis mirrors is to gain a collimated beam from the IR source, and then to focus that beam back down to a point on the detector at the end. It seems like something that aught to be fairly accurate, but accurate is a relative term!

Offline S. Heslop

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Re: Making IR optics.
« Reply #3 on: June 11, 2016, 02:28:46 PM »
Are there any good websites/ forums for CNC stuff out there? Most of what i've found googling about has been absolute crap.

Offline PK

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Re: Making IR optics.
« Reply #4 on: June 11, 2016, 04:32:47 PM »
www.cnczone.com is good. Big, but good

Here's one I prepared earlier http://www.caswa.com/cncathome/lathe.html
Ignore all the bits about the electronics. The advent of low cost stepper drives has changed everything and it's all COTS now.
PK

Offline S. Heslop

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Re: Making IR optics.
« Reply #5 on: June 26, 2016, 12:26:54 PM »
Been looking at this a bit more and found this great video.

<a href="http://www.youtube.com/watch?v=fnoVV-RWIWY" target="_blank">http://www.youtube.com/watch?v=fnoVV-RWIWY</a>

This style of old video are always great to watch. More info and less 'mercial.

One thing it doesn't say though is how youre supposed to clean out the embedded grits. Maybe a disposable pitch lap would work well for the lapping plate with optical parts.

I'm keen to try this stuff out but i'm really jumping the gun, as always, and i've got a couple other projects I need to finish first.

Offline awemawson

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Re: Making IR optics.
« Reply #6 on: June 26, 2016, 12:57:31 PM »
Years ago when I worked for Mullards, we were lapping Yttrium Iron Garnet into fine wafers for use as IR detectors, and the thinner you could get the wafer the less back ground boltzmann noise was produced improving the signal to noise ratio of the detectors (these things were cooled with liquid nitrogen, and sometime liquid air again to reduce the thermal noise). One day my colleague managed to sneeze on a wafer, and something in his outpouring managed to dissolve some of the YIG producing an area significantly thinner than the rest of the area around it. It went undetected and the wafer was used.

When I did the testing of the bucket brigade 256 element array that was laid on that particular bit, all of a sudden I found a far higher signal than expected  :clap: It took a long time to repeat the experiment and find something more reliable than a sneeze to produce the same effect

These things were used in early spy satellites - a bit un-nerving having armed guards on the lab  :bugeye:
Andrew Mawson
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Offline Joules

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Re: Making IR optics.
« Reply #7 on: June 26, 2016, 01:44:40 PM »
Love the video   :D  3D printed lapping machine coming right up....    :thumbup:
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline S. Heslop

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Re: Making IR optics.
« Reply #8 on: June 28, 2016, 11:32:53 AM »
These things were used in early spy satellites - a bit un-nerving having armed guards on the lab  :bugeye:

It sounds like a job like that would pay you well enough to make up for it though!


I had this arrive yesterday. It's a UV-VIS spectrometer, but an old and somewhat weird one.


(i've given it another scrub to remove some of the stains since taking these photos. and i'm making sure to wash my hands every time i touch it)

I didn't expect it to work, but it was listed fairly cheaply on ebay so I figured i'd have a punt at it and maybe at least get a diffraction grating and some mirrors out of it, and maybe a deuterium lamp if I was lucky. But it powered on fine. I couldn't find much information about it online so I emailed Biochrom asking about it and they sent me the manual almost immediately, which was very kind of them. The manual suggests it was made in about 1987.


Got some thermal paper for it today and was at first a bit disappointed by the stepped chart. But reading the manual carefully I found out that 'calibration' isnt the same as recording a baseline.

I'm really thrilled it works. I'll need to think of something interesting to do with it though. My big dream for a while has been to try making chemistry videos, but i'm still not sure exactly what i'm going to go for. I'd like to at least avoid using stuff that isn't so easy to get ahold of.

Offline S. Heslop

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Re: Making IR optics.
« Reply #9 on: July 01, 2016, 04:28:31 PM »
Also got a balance, a Sartorius LA230S. It didn't have a power supply with it and i'm not sure exactly what it requires. The back says 12 and 30 volts DC but its some weird custom 4 pin connector. I might be able to figure it out from the circuit board but I'll try emailing the company that makes it first.


There's not alot of information on these things online, and photos of their innner workings are as rare and low resolution as photos of bigfoot. I've attached a bunch of higher resolution photos just in case anyone interested finds this via google.


I'm probably mucking up the calibration by taking this cover off.


From what little i've been able to find online, they work on balancing the weight in the pan against an electromagnetic coil (the big round bit in the middle-right), sensing it's position via an optical position sensor (I assume to be that gold package on the far right) and adjusting the current to get it balanced. Then measuring the current to deduce the weight. The lever itself is a parallelogram flexure so the weight's position on the pan doesnt affect the reading. There might be some extra lever to amplify the travel of the coil too, but i'm going cross-eyed looking at this thing to make anything out.

There's one other electronic device on the flexure too that i'm not so sure about. It might be a temperature sensor to correct for things expanding.


I think this has something to do with automatically calibrating itself. My best guess is that it lowers those weights onto those brackets screwed onto the pan to use as a reference.

While I had the cover off I took Andrew's advise and made sure to sneeze on it to boost it's performance. I also made sure to touch all the chips without grounding myself and poked everything possible with a sharp screwdriver.

Offline S. Heslop

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Re: Making IR optics.
« Reply #10 on: July 02, 2016, 12:33:45 PM »
Had a closer look at the curcuits and connector and it only seems 2 of the pins are connected. Kinda weird they used such a connector but maybe it's not as custom as I though. The boards are a multi-layer affair and I couldn't trace the traces to figure out where they went.

The back specifically says "Input voltage 12V-30V = (DC)". I wonder if that means it'll accept anything between 12 and 30 volts. That seems like a wide range. If I work the courage up I could shove in 12 volts and see what happens. I at least know which pin is ground and positive now.

Offline S. Heslop

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Re: Making IR optics.
« Reply #11 on: July 02, 2016, 01:46:01 PM »
Always another problem... Could just be a loose cable somewhere. But at least it seems to just be the display at fault. I tried to tare it but my desk is so wobbly it couldn't get a stable reading.

Offline S. Heslop

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Re: Making IR optics.
« Reply #12 on: July 02, 2016, 02:38:28 PM »
The problem was easy to find. Looks like this pin has bent and also torn it off the PCB. I'd solder in a bodge wire, but continuing the theme my soldering iron doesn't work any more. I guess I might go buy a new one tomorrow.

Offline S. Heslop

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Re: Making IR optics.
« Reply #13 on: July 02, 2016, 06:16:30 PM »
It didn't work. I spent a while making sure I hadn't shorted anything. I guess the problem must be in the LCD itself. The whole modules (LMG7380QHFC) are quite expensive at around 120. Looking at the data sheet it seems theres a LC7942N OFU2 responsible for the horizontal pixels. My best guess, as an idiot with no clue, is that replacing that could solve the problem. Or it could be something inside the module like a ribbon cable coming loose.

The weight is still perfectly readable with the screen in this condition but i'm keen to try fix it for its own sake, even if i'm risking making it worse. But at least the screens are available if I really muck it up.

Offline S. Heslop

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Re: Making IR optics.
« Reply #14 on: July 04, 2016, 11:39:34 AM »
I decided it was probably unlikely the chip had gone and the most likely cause is the ribbon cable between that circuit and the LCD itself.

So I carefully removed it and... ay caramba.


Seems like alot of the conductive scub from the ribbon cable has come off and there's not alot of cable left to work with.


This stupid module is built like calculators I remember pulling apart as a kid, with that big conductive rubber lump that's difficult to re-align. I don't know enough about these things to really pass judgement, but i'm not convinced this is worth 120 or being called 'industrial'.


Thing's are looking up. I think i've at least found the real source of the problem! I just need to read up how to work with these sorts of ribbon cables. I might be able to extend the existing one a bit with some more cable, or there could possibly be just enough material left to try re-attach it.

Offline Noitoen

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Re: Making IR optics.
« Reply #15 on: July 06, 2016, 08:53:17 AM »
Looks like a standard graphic display to me. You could probably change it without hassle.

Offline S. Heslop

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Re: Making IR optics.
« Reply #16 on: July 06, 2016, 06:14:11 PM »
Looks like a standard graphic display to me. You could probably change it without hassle.

If I was smarter I could probably look at the data sheet for it and try figure out if theres a cheaper display out there that would accept the same inputs (I still don't know much about electronic engineering!), but i've got a few things to try first.

I've been wanting to get a temperature controlled soldering iron for a bit now, and this gives me an excuse to get one. Then I can try maybe melting the glue back together with that and a bit of silicon rubber to stop the iron directly contacting the plastic.

I'm fairly sure, after googling about a bit, that it's ACF bonded. Most ACF bonding stuff i've found is videos of Chinese/ Romanian people trying to make a living refurbishing various broken LCD screens, and pdfs from companies selling the glue. Yet to find a firm in the UK that looks like it'd accept a one-off order, but looking at the methods used it just seems to be a hot bar constructed similar to a solder gun tip (but wide) and a cylinder to apply a specific pressure. The companies that make the tape supply information on the recommended pressures and temperatures. It could be in the realm of something I could do myself if I can find a supplier for small amounts of the flex and tape.

Either way i'm skint at the moment since some things came up. So i'm sitting on it for now.

Offline Joules

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Re: Making IR optics.
« Reply #17 on: July 07, 2016, 01:40:09 AM »
I've repaired a number of LCD connectors by cleaning (Isopropanol, fibre glass brush) all the gunk off the cable and connector and make my own pressure pad/gasket.   Using two sheets of glass or polished metal use shim to space them apart.  Apply Vaseline or cling film as release and squeeze a layer of bath sealant, leave till set.  Using a scalpel make a strip to apply pressure to the connection when you re assemble the display or cable connector.  You can then nudge the cable position till your display comes back to full life.  If you made plenty of gasket and the connection is near the edge of the board, a bulldog clip can apply temporary pressure.  Once the right position is found use the rear of the scalpel blade to scratch aligment lines on the cable and PCB where it won't be damaged.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline S. Heslop

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Re: Making IR optics.
« Reply #18 on: July 18, 2016, 03:42:51 PM »
I've repaired a number of LCD connectors by cleaning (Isopropanol, fibre glass brush) all the gunk off the cable and connector and make my own pressure pad/gasket.   Using two sheets of glass or polished metal use shim to space them apart.  Apply Vaseline or cling film as release and squeeze a layer of bath sealant, leave till set.  Using a scalpel make a strip to apply pressure to the connection when you re assemble the display or cable connector.  You can then nudge the cable position till your display comes back to full life.  If you made plenty of gasket and the connection is near the edge of the board, a bulldog clip can apply temporary pressure.  Once the right position is found use the rear of the scalpel blade to scratch aligment lines on the cable and PCB where it won't be damaged.

This display uses a ribbon cable for the rows and a zebra connector for the columns so there's no easy way to get at the ribbon cable under the display's can when it's all assembled. It also comes with its own rubber lump to put pressure on the cable.

I tried the lump of silicon rubber with a soldering iron to try get the connector to stick again and it seemed to be working, till I slipped and poked a hole in the ribbon cable. I've now got enough rows working again that I can read the numbers and navigate the menus, albeit with a bit of guessing, so i'm leaving it like this before I wreck it further. But there's yet another problem; sometimes the whole thing becomes unresponsive. Not sure at all what could be causing that, but perhaps i'm somewhat under-volting it. The back says 12-30 volts which suggests it could take all the way up to 30 volts input. But of course i'm a bit hesitant to just start sending more volts in.

Offline S. Heslop

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Re: Making IR optics.
« Reply #19 on: August 13, 2016, 11:48:02 AM »
I can't help myself. I saw a totally broken one for sale and bought it to try help solve the few remaining mysteries.


The brass part is the system for lowering a calibration weight.


This arrangement is starting to get familiar. It's a much less panic inducing way of constructing it though than it being machined from solid.


The fault with this balance was that this part had snapped. It's a double flexure to connect the voice coil lever beam to the main parallelogram (i'm making these names up).


This is the inside of the voice coil. There's a pair of fairly strong opposing magnets that go in the middle of it. The lever beam floats on a pair of reasonably stout flexures and is electrically connected by two extremely thin flat wires. The optical position sensor is just a slot cut in a metal bar in between a transmitter and reciever.


Measuring the resistance of the coil. I'm not sure if this gives me any really useful information but it seemed like a clever thing to do!


The circuit has a bunch of op amps on it, a precision voltage reference in the middle, what I assume to be some sort of thermocouple, and this unidentified blob. It was hidden under an aluminium can filled with rubber, and it's quite well isolated. For thermal stability I assume. Might try dissolving that resin off to see whats underneath.


I need to take a closer look at the main board before I can really take a guess at what does what, but i'm leaving that for now. For the record I have no idea what i'm doing when it comes to electronics and i'm mostly just googling the chip numbers.