  We demonstrate that first-order light-shifts can be cancelled for an
all-optical, three-photon-absorption resonance ("N-resonance") on the D1
transition of Rb87. This light-shift cancellation enables improved frequency
stability for an N-resonance clock. For example, using a table-top apparatus
designed for N-resonance spectroscopy, we measured a short-term fractional
frequency stability (Allan deviation) 1.5e-11 tau^(-1/2) for observation times
1s< tau < 50s. Further improvements in frequency stability should be possible
with an apparatus designed as a dedicated N-resonance clock.
