Production of large numbers of atoms in a selected excited state by laser optical pumping: calcium

An experiment is described in which large numbers ( approximately 10¹⁶) of calcium atoms are placed in the 4s4p ³P metastable level by optical pumping with a tunable dye laser and then studied spectroscopically. Equations governing the degree of excitation by the laser are derived. Predictions of the theory are shown to be in good agreement with experimental results. In particular, at low optical depths produced by 10¹⁵ ground state atoms cm^-2 the dye laser raises approximately 50% of the calcium atoms into the metastable state. At higher optical depths associated with 10¹⁷ ground state atoms cm^-2 the number of excited states is limited only by the laser energy and line width. For the dye laser used the largest number of metastables produced was approximately 10¹⁶. The absorption spectra of the 4s4p ²P level is seen out to 4s4p ³P to 4s22d ³D. The relaxation rate between the excited state fine structure is studied directly with an optically delayed dye laser continuum. Other applications of this technique of producing large numbers of excited states are briefly discussed.