Ultracold molecules offer a vast number of applications, ranging from searches for novel physics, probes for possible variations of fundamental constants, precision measurements, studies of many-body quantum systems, and manipulation of the outcome of chemical reactions. In order to realize these applications, an ultracold and dense sample of molecules is required. Among the different types of molecules, polar molecules are of particular interest since their electric dipole moment introduces a long-range interaction between the molecules.
At the heart of our experiment is a cryogenic buffer-gas beam source which creates a high-flux beam of molecules at a few Kelvin. Such a beam is slow enough to apply laser radiation pressure to slow the molecules below the capture velocity of a magneto-optical trap and trap them. Subsequent cooling techniques then allow for eventually reaching the ultracold regime.
Our goal is to cool and trap aluminum monochloride (AlCl). The theoretically predicted Franck-Condon factors of AlCl are excellent (>99%). In principle, one can scatter about 1,000 photons on AlCl before exciting the molecule vibrationally. The technically challenging part is the transition wavelength which is in the deep ultraviolet at 261nm. Our current approach to produce ultra-violet light around this wavelength is to use a frequency-tripled Ti:Saph laser system. Starting with an infrared beam at 783nm, we frequency-double this light in a second-harmonic generation enhancement cavity using a Lithium triborate crystal to 391.5nm. A second, sum-frequency generation process, then produces 261nm by focusing the fundamental and the blue light inside a Barium borate crystal.
We carried out the first detailed survey spectroscopy of AlCl using our self-built UV laser system. As shown in the plot, we observe the P, Q and R rotational branches of the X-A transition and we easily resolve the isotope shift of the two chlorine isotopes.
Since our laser system is very tunable, we were able to independently test our magneto-optical trap setup which is attached to the cryogenic beam source with atoms. We are happy to present our first trapped Ytterbium cloud, see photo on the right. The same tunability will allow us to explore new atomic species which have not been trapped before.
This project is a collaboration of groups at the University of California (UCB, UCLA, UCSB, UCR). We would like to acknowledge funding for this project through the UC Multicampus-National Lab Collaborative Research and Training Award.