Abstract
The 5S 1/2 → 7S 1/2 two-photon transition of atomic rubidium, which is 100 times weaker than the 5S-5D transition, is observed with an extended-cavity diode laser and a vapor cell. Signals with a signal-to-noise ratio of 280 are obtained with a laser power of 10 mW, and the observed linewidth is 3 MHz. The laser wavelength is 760 nm and is locked on the transitions to a stability of 2 × 10 -11 . For the first time to our knowledge, the isotope shift of this transition is measured to be 130(4) MHz in atomic frequency. © 2004 Optical Society of America.