Using radio frequency pulses we connect the relatively unstructured re
sponse of a two level system to a half cycle pulse to the resonant res
ponse to a monochromatic wave. There is an obvious change from the non
resonant effect of a half cycle pulse to an interference pattern analo
gous to a Young's two slit interference pattern with two cycles. The a
nalog of illuminating more slits, adding progressively more cycles, le
ads to a gradual evolution of the interference maxima into sharp reson
ances. The structured response to EA cycles is implicit in the respons
e Co one cycle.