Cancellation of light shifts in an N-resonance clock.

We demonstrate that first-order light shifts can be canceled for an all-optical, three-photon-absorption resonance (N-resonance) on the D, transition of Rb-87. This light-shift cancellation facilitates improved frequency stability for an N-resonance clock. For example, by using a tabletop apparatus designed for N-resonance spectroscopy, we measured a short-term fractional frequency stability (Allan deviation) of similar or equal to 1.5 x 10(-11) (tau)-1/2 for observation times of 1 s <= tau <= 50 s. Further improvements in frequency stability should be possible with an apparatus designed as a dedicated N-resonance clock. (c) 2006 Optical Society of America.