Published in Physica Scripta, Vol. 52, 271-276, 1995.
We report on spectroscopic measurements of the Rb 5D5/2 state performed using two-photon excitation with a resonant intermediate state. With the two beams (5S1/2 -> 5P3/2 at 780 nm and 5P3/2 -> 5D5/2 at 776 nm) counter-propagating, the spectra are Doppler-free and the signals are very robust, even in a room temperature vapor. This is due to the near match of the transition wavelengths. The 5D3/2 hyperfine constants have been measured and compared to previous determinations. We have also performed the excitation in a sample of laser-cooled atoms and compare these results to those obtained at room temperature. The fact that the 5P3/2 -> 5D5/2 transition is narrow, robust, diode-laser accessible, and relatively immune to AC-Stark shifts, may make it a promising candidate for a frequency reference at 776 nm.