Half-Cycle Microwave Excitation of Rubidium Rydberg Atoms

Excitation from $\mathrm{ns}$, $\mathrm{np}$, and $\mathrm{nd}$ Rydberg states of rubidium to the adjacent manifolds by electrical pulses of 140 and 9 ns duration up to 200 V/cm is studied. These pulses correspond to half cycles of microwave fields of 2.6 GHz and 40 MHz. The observed population transfer (up to 40%) is not monotonically increasing with the field strength. For the 140 ps pulse local minima are found due to the absence of avoided crossings of appropriate size at the peak of the pulse. For the long pulses Stueckelberg oscillations are observed in the transfer yield.