A particular difficulty in trapping mercury is the generation of continuous wave UV radiation at the trapping frequency of mercury, i.e. the well-known 253.7 nm transition. We are following two independent approaches:
- disc laser operating at 1014.8 nm with consecutive frequency quadrupling.
- Yb:doped fiber amplifier seeded by an external cavity diode laser operating at 1014.8 nm with consecutive frequency quadrupling.
- In either case, frequency doubling is achieved in a build-up cavity using a LBO crystal followed by doubling in an external build-up cavity using BBO
Our magneto optical trap is relatively standard with a background pressure of 5 x 10-10 mbar. The Laser radiation is split in three branches of identical intensity and aligned via retro-reflectors in the typical 'crossing (see image of principle).' configuration of MOTs. The Anti-Helmholtz coils are water cooled. And we use a UV enhanced EMCCD camera to image the cloud of cold Hg atoms.
Special attention was given to the Hg reservoir. It consists of a copper double walled tube and is held at a temperature of -40°C using a compressor cooler. A two-stage Peltier element then enables cooling of the reservoir to temperatures between -40°C and -72°C.