Influence of stimulated emission on the form of the signal emitted by a pulsed hydrogen maser

A calculation is reported of the influence of the stimulated emission of a system of hydrogen atoms on the response of a hydrogen maser to a short resonance-frequency pulse. It is shown that this emission produces two effects which result in a deviation of the form of the signal from the ideal curve exp(–t/T₂). The first increases effectively the decay time of the signal and it disappears even for I/I_th ≈ 0.3, when the atomic beam is interrupted during the observation time (I is the atomic flux and I_th is the threshold value of this flux). The second effect appears when the excitation pulse deviates from the 90° form and it lengthens the signal if ψ < π/2 and shortens it if ψ > π/2. The results of calculations are compared with the experimentally observed dependences.