Determination of lifetimes and hyperfine structures of the 8, 9 and 10 ²D_3/2 states of ¹³³Cs by quantum-beat spectroscopy

The states were studied by selective detection of the fluorescence generated in atoms of the vapour by stepwise excitation, using as sources a conventional caesium lamp for the first step from the ground state and a pulsed, tunable laser for the second. The techniques of delayed coincidence counting were applied to measure the time distribution of intensity of the fluorescent light. The observed modulation, representing in each case a superposition of the hyperfine intervals showed a characteristic period which was interpreted as the reciprocal of the magnetic interaction constant a for the states in question. The relative simplicity of the modulation patterns is a consequence of the negligibly small quadrupole interaction in ¹³³Cs. With the polarizer oriented at cos^-1 3^-1/2 to the analyzer the modulation was suppressed, leaving a simple exponential decay from which the lifetime of the population tau , could be determined.