Phase Shifts in the Molecular Beam Method of Separated Oscillating Fields

The effects of phase differences between the two oscillating fields in the separated oscillating fields method for molecular beam radiofrequency spectroscopy is discussed theoretically. It is shown that measurements in which the relative phase is changed from 0° to 180° effectively double the intensity of the signal and hence increase the sensitivity of the apparatus. Phase shifts of $\frac{\pi }{2}$ radians give resonances in the form of dispersion curves. Consequently, measurements in which the phase is changed from $+\delta$ to $-\delta$, where $\delta$ is near 90°, give particularly sensitive means of determining the resonance frequency.