Demonstration of internal state laser cooling of molecular ions

This study demonstrates an all-optical internal state cooling scheme for HD
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molecular ions in the rovibrational ground state using a 5.484 mum cw-quantum cascade laser. Resonance-enhanced multi-photon dissociation is used to selectively remove the ground-state HD
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ions from the trap. The efficiency of the pumping scheme is investigated by comparing the corresponding changes in fluorescence with and without an optical pumping phase preceding the detection. An increase in the relative fluorescence decay by a factor of 3 is observed with optical pumping.