Doppler-free optical-optical triple-resonance (DF-OOTR) spectra of Rydberg levels in sodium molecules and the widths and lineshifts of these energy levels

The DF-OOTR excitation fluorescence spectra for a series of Rydberg energy levels in sodium molecules were reported for the first time here, and their linewidths and lineshifts were measured under the variations of both temperature and foreign buffer-gas pressure. The results demonstrate that the natural widths (including homogeneous broadening) of these Rydberg energy levels (n=5-8) are between 60-130MHz, and mainly depend on the principal quantum number n. All these levels are in the red line-shifts with the increase of atomic density (the increase of temperature) or foreign buffer-gas (Ar) pressure, but with different shift rates within 100MHz/��.