What I want to do
Scott Eustis and I and others have made a number of attempts to get clear fluorescence spectra by shining a green laser through mineral oil which has had small amounts of crude oil dissolved in it. But we've struggled to get enough brightness into a Desktop Spectrometer.
My attempt and results
Today over lunch I was fiddling with a UV laser (~405 nanometers: buy on Amazon here for $8) with Matt Hirsch and we suddenly realized that it produces a much stronger spectrum than green lasers had. This may be because a laser can only create fluorescence at longer (lower energy) wavelengths than its own -- so green lasers could never create blue fluorescence. See the setup in the lead image for how we did it -- it was pretty easy. But PLEASE be careful not to shine this in your eye, and don't look at the laser dot directly as this could be a strong UV laser and could damage your eye even though it's hard to see with the naked eye.
The spectra were remarkably strong:
This is very exciting because it has a pretty good signal to noise ratio, and it's a lot to work with for potentially matching oils.
Questions and next steps
We were also able to measure the spectrum of Bertolli olive oil and an unidentified fuel liquid which is probably paraffin. So one thing we should do is take a lot of spectra of different oils and see if we can reliably distinguish them! If you do this, tag your spectra with "oil" please!
Finally, I created a little black cardboard box with the whole setup taped down inside to streamline the process. It includes space to store your laser pointer and samples, and standardizes the position and orientation of the laser and sample container. It's VERY helpful in doing these sorts of tests, especially for reducing stray light:
Update: Link to sample containers I used: http://www.sciplus.com/p/WHITCAP-BOTTLE_48212