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Laser Cooling of Atoms with an Optical Frequency Comb

Despite the prominent role of laser cooling in modern atomic physics, with applications ranging from quantum sensors to high-precision spectroscopy and ultracold chemistry, laser cooling techniques are still limited to atoms with simple energy level structure and closed transitions that are accessible by currently available continuous wave (cw) laser sources. Two main obstacles prevent the extension of laser cooling techniques to a variety of atomic species and molecules. The first is associated with technical difficulties in creating cw laser light in the vacuum ultraviolet (VUV) spectral range — the absence of those laser sources prevents laser cooling of simple atoms such as hydrogen, deuterium, and antihydrogen. The second obstacle is associated with complex energy level structure of many atoms and almost all molecules — it permits decay of an excited state into a number of lower-lying states that can be widely separated in energy, which makes laser cooling of such species inefficient and experimentally very challenging.