Depositions at rates higher than 1 nm/s show differences in properties when one deposits with a vapor stream that is modulated against those that are deposited with a steady vapor stream. For carrying out investigations along these lines, it was necessary to develop a real‐time, noninvasive, and sensitive technique for determining the nature and extent of flux variations in atomic streams close to the deposition plate. A pulsed laser based resonant photoionization technique is proposed for meeting these requirements. The paper describes the method and its application to a case where modulation is caused by residual ripple in high voltage accelerating supply used in the electron gun of the evaporator. The proposed technique overcomes the limitation on sensitivity due to background pressure experienced in the nonresonant approach. Other attractive features are the use of much lower laser intensities for a given sensitivity and the employment of a simpler ion detection system.