What I want to do
We had some trouble at the recent oil testing kit meetup in New Orleans in getting strong enough light into the spectrometer. @mathew and I have been discussing possible solutions but we'd talked about having a very wide slit, to sacrifice resolution for brightness, as a worst-case solution. I gave it a try today.
My attempt and results
https://spectralworkbench.org/analyze/spectrum/32235
It seems we can get enough light to break the 25% intensity line, even without modifying exposure or anything in the webcam. I did not use a reflector or anything, just a UV laser. But the sharpness of the UV peak was very poor.
For reference, I set it up in a temporary setup like this with a webcam, DVD, and laser added:
Questions and next steps
We have some other options to explore:
- reflectors behind the sample jar
- more laser!
- longer exposure, maybe through UVC USB controls
- a more sensitive camera
- a bigger lens
Why I'm interested
We need to both simplify and increase sensitivity in the Oil Testing Kit to get clear enough results to try matching. I hope we don't have to give up resolution, but this did seem to work all right, and maybe we'd be able to distinguish spectra even with reduced resolution.
7 Comments
Warren, you might like this...
It is a resizeable slit.
It works like a zoom/focus on a camera
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slidey in, slidey out
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nice! @amysoyka. We're also thinking about cutting a bunch so they could be switched in and out at known widths.
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@matthew, I tried that. It drove me crazy, trying to cut the slit's varying distances apart. (Imm, 2mm, 5mm...etc)
Also, I found that I kept getting serrated bits at the top and bottom where the two sides of the slit connect.
Hence why I resorted to a slider.
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Warren, it's really exciting to see this sort of technology diffusing out of academia. All of your question are interesting, here are a few more thoughts: 1) Seeing that your baseline is almost half of your maximum signal, I wonder how much attention you've paid to isolating the sensor from external light sources? It can really improve your SNR to be very picky and careful about this--e.g. we would tape aluminum foil over all the windows and then black paper/cloth over that. Or is that baseline really the ccd/cmos thermal background?
2) Extraneous scattering from the laser can be tricky to eliminate as well; a long pass filter just in front of the sensor could help with that. They're not cheap, here's one possibility. 3) Adding multiple image captures of the same spectrum (e.g. in ImageJ) might be a cheap hack in place of, or at least for evaluating the benefit of, longer exposures. 4) By way of lab safety, there is research suggesting that the high energy end of the visible spectrum is energetic enough do damage to your retina; since I tend to be a nerd about lab safety, I might wear a good pair of blue blocker sunglasses while working with this laser. It would be nice if someone really knowledgeable about this could comment.
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You're right - it's a pretty high baseline. Something like 10%, no? I believe this is noise, but some may be related to infrared reflectivity inside the chamber -- we've found that it's hard to get a completely absorbent interior and the cameras are pretty sensitive to IR light once the filter's gone.
This particular test was done with paper that's not dark in the infrared range, too. I think we do a lot better when we use fully "infradark" materials, as in this example: https://spectralworkbench.org/analyze/spectrum/14919
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