Ultraviolet spectrometry

This page will sum-up as much information as possible on the subject of ultraviolet or UV/visible spectrometry. It will concentrate on the task of improving the methods to collect data in the 350 - 400nm and possibly below 350nm wavelengths, cameras and gratings permitting

CMOS camera sensors

some data shows that rear- or back-illuminated CMOS sensors are sensitive down past 200nm in the ultraviolet.

CMOS graph

Non-glass optics

Presumably glass lenses will cut off anything below 350nm, so to take full advantage of this we might consider using a pinhole instead of a glass lens. Luckily webcam lenses just unscrew. Please post here if you try this!

Quartz lenses

Mathew sez: Quartz UV passing lenses are available from Universe Kogaku. http://Ukaoptics.com The m12 mount ones for security/industrial cams are small and probably cheaper.

Jack Summers sez: According to these guys: http://dx.doi.org/10.1016/j.aca.2006.09.001, you can detect CO2 at 193 nm... You would, however, need a specialized lamp to do absorbance measurements, and things like plastic and normal glass optics are not going to work at that wavelength.

ToF sez: Pyrex-Lenses should work, but between 200 and 150nm the O2 in the air is very absorbing.

Below comparative specta for Borosilicate glass (Pyrex, BK7...) plotted against regular Soda-Lime glass:

Borosilicate vs Soda-Lime Glass absorption spectra

We see that regular glass lenses and optics would start curring off significantly below 350nm where Borosilicate glasses would start filtering below 335nm

And now the absorption spectra of PMMA (Polymethylmetacrylate, Lexan, Plexyglass..) and PC (Polycarbonate, the DVD material)

Absorption spectra of PMMA and PC

In comparison, the almost perfect transmittance of Fused Silica down to 175nm

Fused Silica transmittance

UV light tests

Recent tests have shown that 360nm and higher is possible, by calibrating a spectrometer and then pointing it at an ultraviolet light. The spectrometer was near-IR capable (had been modified). These tests were based on this work from Feb 2012 and were done with glass optics still in place.