N-resonance characterization for compact atomic clocks

There is great current interest in developing small atomic clocks with low power consumption and fractional frequency stability of $10^{-12}/\sqrt{\tau/s}$ or better. N-resonances, all-optical three-photon-absorption resonances, offer a promising alternative to CPT-based clocks due to their high resonance contrast and the potential to cancel first-order light shifts. We present measurements of the N- resonance contrast, width and light-shift for $^{87}$Rb in a compact (1 mm long) vapor cell.