Transient response following frequency or amplitude switching in a cesium beam tube

The transient responses of an optically pumped cesium beam tube to square w ave frequency and amplitude modulation is considered. The frequency transie nt is computed assuming a phase difference phi of either 0 or pi between th e two oscillatory fields. We present theoretical and experimental data show ing that, contrary to the frequency transient, the amplitude transient depe nds on the direction of switching. The knowledge of this property is useful for the design of the servo-loop controlling the amplitude of the microwav e signal applied to the atomic resonator. A justification of this asymmetri cal behavior is given. Experimental results confirm the theoretical predict ions in the case phi = pi.