The amount of problems we encountered in this lab went from comical to ridiculous. These significant problematic issues thwarted our progress substantially, and thus limited the scope of our experiment considerably. Outlined below are some major hindrances we conquered, and several we were unable to resolve.
Discovering the resolution of our Spectrometer was extremely difficult. The main source of difficulty was interpreting our data and finding out what exactly it meant. The phenomenon is easily understood by viewing the graph below. We at first thought that the smaller peaks were different modes in the laser, approaching the peak. This idea was nixed, however, when we observed that they were not symmetrical about the peak, as expected. Maybe this was a one time thing, so we tried again with the same setup. unfortunately we got the same exact pattern again and again. We decided to try out a Helium-Neon laser input, because with that we expect a much cleaner spectrum. Sadly, this too produced similar results. In looking at W. Demtröder, we were able to come up with a logical explanation. The grating within the spectrometer might have minute deviations between the adjacent grooves, or other inaccuracies. This problem can cause constructive interference and therefore propagate "wrong" wavelengths. These effects are known as grating ghosts (137). This may mean that the spectrometer is inaccurate, at least in the range we used. Because of these ghosts, we could not get our resolution measurement from the graphs, because we had no idea what was a real modal peak and what was a ghost. We finally proved they must be ghosts by discovering that their widths at half-max were 0.1 angstroms, far below the MAXIMUM resolution of the spectrometer, 0.4 angstroms. This was a great relief to all of us, because it was a nice way to explain such a strange problem.
Another goal of our lab procedure was to find the lasers wavelength dependence on temperature. The Wavemeter Jr. was to be used in this calculation, but a 5 hour problem stood in our way. The wavemeter requires a certain intensity of light to register a wavelength. The diode laser produces a very wide beam, and most of the light from this beam was to be focused into an optical fiber. Regrettably, the time spent rectifying the problem was ill-spent. Dr. Christian tried to fix the Wavemeter, but then we discovered that it was not broken by using the Helium-Neon laser. We were able to get plenty of light out of it. Strangely enough, as hard as we tried with as many as four optical lenses, accumulating enough light proved to be impossible. Thus, we spent some extra time in the lab taking the temperature data the hard (and long) way; we put the laser through the spectrometer at different temperatures, and actually came out with a great plot.
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