A winter’s tale of spectrometric frustration

January and most of february flew with no updates, so here goes:

On the hardware front I’ve been playing with fiber optics and my laser. Having already spent a lot of money on this project (too much in fact), it seemed silly to patch up the spectrometer with sticky tac or chewing gum or whatever to allow a fiber to pass from one box to another without letting any light pass alongside. So I did the obvious: I bought more fibers..


Unfiltered 532 nm laser light, collimated and directed at a 1200 l/mm holographic diffraction grating. (Oh and you can see one of the orange fiber optic cables.)

After assuring myself the achromat and the spherical lens on either side of the fiber connection was in focus, I finally installed the diffraction grating, only to find out it will be harder than expected to focus it on the CCD.


The diffracted light from an EL-backlight’s fluorescence in 532 nm laser light. The much more intense laser light has been filtered out with an interference filter.

As can be seen on the picture the diffracted light is focused slightly above the pixels (well I guess you can’t really see because of the post-it on the CCD). I will probably print some linear stages to make my life easier, as the peltier elements hidden behind the copper bar behind the CCD make everything a little difficult to move.

Finally I’ve made a smaller version of the PCB for the TCD1304 CCD. There are no pictures yet, as I’m still waiting for the boards to arrive, but they’re roughly half the size of the original. Everything’s possible with today’s space age SMD-components and whatnot.


The first clumsy attempt at a TCD1304 PCB. Soon to be replaced.

The software has also received some attention. Most notably the raspberry pi can now read and display the data collected from the CCD:


Output from the TCD1304. Collected with the nucleo F401RE and displayed on the raspberry pi

I’ve done some cleanup of the source code for the software running on the raspberry pi, so it should be much easier to read. Cosmetically there’s nothing new compared to previous updates. It still looks like this (sorry for the old screenshot):


No roses without thorns, and somewhere in the roses an annoying bug is still hiding. I’m trying to learn debugging with GDB, but until I figure that out, I still need to press “record” twice to get proper data if the CCD has been previously over-saturated.

Finally I’ve been trying to figure out what to do once the Raman spectrometer is finished, and after throwing my love at “The cheapest decently resolving VIS-spectrometer in the history of mankind”, I’ll probably take a look at spatial heterodyne spectrometers.¹

Source code and eagle files are due shortly, dinner, a movie and a plane to Oslo are currently more urgent.

Update – the files:

Source code for TCD1304 driver

Source code for Raspberry pi TCD1304 GUI

Eagle files for the mini PCB for TCD1304


¹ Harlander, J.; Roesler, F. L., Proc. SPIE 1235, Instrumentation in Astronomy VII, 622 (July 1, 1990);  Spatial heterodyne spectroscopy – A novel interferometric technique for ground-based and space astronomy


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