Production and detection of rovibrationally cold molecular ions usinga cryogenic liear ion trap

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We have developed a compact cryogenic linear ion trap to producerovibrationally cold molecular ions embeded in an ion Coulomb crystal. First, the compact cryogeniclinear ion trap with double radiation shields was newly developed and was connected to a 10 Kcryocooler. Then, we performed laser cooling experiments of trapped Ca+ions. We have successfullygenerated Ca+Coulomb crystals containing more than a few thousands ions under low-temperatureenvironments of about 50 K. We also succeeded in producing cold CaH+ions, which are generated bylaser-induced reactions between Ca+*(2P1/2) and H2 molecules. A few thousands of cold CaH+ions aremaintained over one hour under the low-temperature environments. The results imply that thepopulation of the rotational ground state (J = 0) of CaH+is increased to 13%, while the roomtemperature population is only 2%. It is noted that in this condition the sum of J = 0-3 populationreaches to 90% and the vibrational ground state is attained (the vibrational constant is about 0.18 eV).This is an important achievement to perform rovibrational spectroscopy of CaH+.