The construction of the spectrometer is close to an end. Yesterday I spent the afternoon doing my best to focus the diffracted light onto the CCD. It's not as easy as collimating the slit - there are no tricks with mirrors that I know of.
By eye (and with a ruler), I simply tried to estimate the distance from the imaging lens that a 532 nm laser pointer would produce the most well defined line on a piece of paper, and then position the CCD at this position.
This morning after my girlfriend had left for work I recorded the lines from five different laser pointers. As I've still not come around to do any data handling in the software for the Linear CCD module, the data is upside down as usual. In short and for those who might have forgot, the TCD1304 outputs around 1.5V for a saturated pixel and 3.5-4V for an unexposed pixel, hence the scale on the y-axis.
It took a very short while to find the proper integration times. The 450, 520, 532 and 635 nm lasers were recorded in 40 µs. The 650 nm laser had an integration time of 143 µs. They're all supposed to be 5 mW, and they were not the cheapest laser pointers I could find, so I guess the batteries in the 650 nm are dying.
That or it's the spectral response of the CCD playing a part (or both of course), but looking at the spectral response curve I'd go with the batteries.
In the spectra it's a bit hard to see just exactly how well (or poor) the focusing is. It's also a matter of the slit width of course. Here's a cut-out of selected regions of the acquired data (pixel number on the left, CCD output on the right):
It looks like the sensor is more properly focused at the longer wavelengths. The 532 nm laser being a DPSS is the only proper laser - proper in the sense that it has a more well defined emission than the diode lasers - still it's not one line. Read more about that here: https://erossel.wordpress.com/2015/07/26/clear-as-the-mississippi/
All in all I'm quite satisfied with the results, and for this cheap spectrometer, I don't think I'll bother doing a better job of focusing.