Distributed cavity phase shifts & microwave photon recoils

We examine cylindrical TE₀₁₁ microwave cavities and find large phase shifts of the microwave field near the edges of the cut-off waveguide apertures, where there are nodes in the field. The phase shifts lead to a potential distributed cavity phase shift for atomic clocks. Using an additional larger diameter cut-off waveguide section can effectively exclude the nodes and the large phase shifts from the atomic trajectories. It has been suggested that recoils from the absorption of microwave photons lead to frequency shift and also a loss of fringe contrast. We present measurements of the contrast for up to 2 19π/2 pulses and find no loss of contrast beyond that expected from measuring microwave field inhomogeneities with up to 19π Rabi pulses.