Performance of small-scale frequency references

We consider theoretically the expected performance of ultra-small vapor-cell frequency references with cell volumes below 1 mm/sup 3/. The short-term stability is found to degrade as the size is reduced. The amount of degradation depends on whether a buffer gas or wall coating is used for the atomic confinement. Preliminary experimental results with all-optical excitation indicate that the atomic Q-factor behaves as expected.