The physics of miniature atomic clocks: 0-0 versus "end" resonances

We consider advantages of the "end" resonances for the miniaturized alkali vapor-cell atomic clock, namely a higher signal-to-noise ratio (SNR) and a narrower linewidth at high vapor densities. We report our preliminary observations of the unusual phenomenon of light narrowing, in which the rubidium end-resonance linewidth is substantially reduced and the SNR greatly improved as the laser light intensity is increased. Contributions to the total linewidth from other broadening mechanisms are discussed.