Coherent excitation of rydberg states in the gas of cold $^{40}$Ca atoms

The spectra of highly excited $^{40}$Ca atoms prepared using a magneto-optical trap and an ultraviolet laser are experimentally studied. The dependence of the atomic density in the magneto-optical trap on the detuning frequency of cooling radiation and on the magnetic field gradient is determined. By using the technique based on the reduction of resonance fluorescence, the energy of the $76^1S_0$ Rydberg state for $^{40}$Ca atoms is determined. A new scheme for stabilization of the laser frequency to create highly excited Rydberg atoms is demonstrated. This scheme employs the saturated absorption spectrum in a cell with rubidium atomic gas.