Trapping Neutral Mercury

Laser Technology

Laser system to produce the 253.7-nm radiation necessary for trapping neutral mercury. The bottom right part shows the disc laser operating at 1014.8 nm. On top the frequency doubling unit can be seen. The frequency quadrupling unit is shown on the left together with the saturation spectrocopy setup for laser stabilization.

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:

  1. disc laser operating at 1014.8 nm with consecutive frequency quadrupling.
  2. Yb:doped fiber amplifier seeded by an external cavity diode laser operating at 1014.8 nm with consecutive frequency quadrupling.
  3. 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



Magneto-Optical Trap

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

Principle of the Magneto-Optical Trap
Photograph of our Setup


Prof. Dr. Thomas Walther

Laser und Quantenoptik
Institut für Angewandte Physik
Fachbereich 05 - Physik
Technische Universität Darmstadt
Schlossgartenstr. 7
D-64289 Darmstadt

+49 6151 16-20831 (Sekretariat)

+49 6151 16-20834 (Fax)




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