This past week at LASP was fun and productive. Since we have completed our training from last week we were able to participate much more in the experiments. With Dimitri out at a conference in Alaska, Hugh and I had the chance to run a few sessions of our UV fiber cut-back experiment on our own. The “cut-back” is simply cutting the UV fiber to a shorter length to gain a understanding of how the length affects the light transmission. It was a good chance to really get familiar with the setup and work through the process more independently. We practiced cleaving the UV fiber with the ruby cleaving knife, which takes a bit of finesse and a steady hand but started feeling pretty natural after a lot of practice.
A big part of the week was troubleshooting the optical alignment. We had to make sure the fiber was properly aligned with both the deuterium lamp light source and the monochromator. The fiber needed to sit right in the focal plane so the light could couple efficiently, and that was a little tricky to dial in. At one point we realized the fiber mount was just a bit too low, so we machined a simple aluminum shim to lift it by a couple millimeters, and that ended up making a big difference. We also adjusted the collimating optics on the input side of the monochromator to better match the divergence of the beam from the fiber. At the end of the fiber, the tip usually bends and this is very hard to see with the naked eye and fix.
We spent a fair bit of time working with the vacuum chamber too, learning all the procedures and safety. For our experiment we were pumping it down to around 3 × 10⁻⁶ torr, which took a while, usually overnight. We double-checked the O-rings and made sure the turbopump was running smoothly. Once everything was stable, we ran a few spectral scans using the monochromator, stepping through different wavelengths and measuring the transmitted power through the fiber. The deuterium lamps gave us a solid signal across the UV range, though we had to watch out for drift as the lamp warmed up.
Outside the lab, Hugh and I made the most of the free time—we went to the CU Rec Center most evenings and got in a few good hikes, including Mount Sanitas, which had awesome views. Overall it was a good balance of troubleshooting, experimenting, and getting some fresh air.
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