A study of the transients in resonance fluorescence following a step or a pulse of magnetic field

Following (i) a sharp step or (ii) a pulse of applied magnetic field, the resonance fluorescence of an atomic vapour exposed to steady linearly polarized resonance radiation undergoes transient behaviour until a new steady state is reached; the form of the transient will be (i) modulation of the intensity with an exponential envelope, or (ii) simple exponential decay. From the modulation period the gJ value of the excited state is obtained. From the exponential decay the lifetime for the relaxation of atomic alignment is obtained directly. The technique, applied to the 63P1 state of mercury, gives 117.4+or-1.0 ns for the natural mean life.