We’ve finished installing the bowtie cavity in the 3DMOT chamber, and attached our new fused silica “science” cell made by Precision Glassblowing. The windows have a graded-index surface-relief AR coating, done by Tel Aztec, and it’s really strange to see no reflections, and none of the angle-dependent chromatic effects characteristic of multilayer thin film AR coatings.
Preliminary tests of coupling to the cavity in-vacuum show that it is aligned within the chamber as intended, and confirmed that the linewidth is <100 kHz. We’ve already been able to lock the laser to the cavity using only piezo feedback on the fiber laser, in spite of the excess vibrations from the pumping station temporarily attached to the chamber. Full characterization of the cavity will have to wait until after the bakeout.
Alignment and assembly took most of the last 3 days, but went surprisingly smoothly. Preliminary measurements (in-air) show a cavity linewidth of about 100 kHz and a finesse of 10,000, exactly in line with predictions for the mirrors we chose. (The FSR is 1.05 GHz) Since we’ll be trapping atoms at the beam intersection, we verified that the cavity beams are coplanar (to within the accuracy we can measure) by monitoring losses from a sharp tungsten tip on a 3-axis translation stage. After an overnight UV/ozone cleaning, we’ll break vacuum in the main chamber and install the cavity and the new “science” cell tomorrow.
Congratulations are in order for group member Jesse Evans, who successfully defended a Masters thesis on Construction of monolithic all-glass optical cavities for trapping ultracold atoms.
The novel optical assembly techniques he helped develop are going to allow us to build some rather special cavity-based dipole traps, such as the symmetric ring-bowtie depicted in the rendering above. That cavity will undergo final cleaning and installation in our 3DMOT chamber very soon. We’re waiting to break vacuum on the main chamber, since our custom fused silica “science cell” from Precision Glassblowing (rendering below) will be delivered next month, and we want to install them in one operation.
If this is the world’s best lab, it has more to do with the awesome and enthusiastic students than the professor. Thanks for making us “group mugs” Lucas!
We’re now offically a dual-species experiment. It’s not as big and bright as our lithium-7 MOT, but we’ve managed to magneto-optically trap lithium-6, even though the lithium vapor source currently installed in the 2DMOT only contains about 7% lithium-6 (that’s the natural isotope abundance). After we install an enriched Li-6 vapor source and make some other improvements (grey molasses cooling beams) we’ll be ready to load both isotopes into an optical dipole trap. Quantum degeneracy here we come!