The Ashby–Jephcott interferometer is used to measure the temporal variations in electron densities in plasmas. A double‐ended HeNe laser is used as part of an interferometer to make these measurements. In the present work, the experimental setup of the original method has been modified to prevent the drift in the temporal fringe patterns that are observed. This allows for more precise measurements of electron densities in plasmas. Further, the modification allows for commercially available HeNe lasers to be used to measure electron densities. The fringe patterns observed in aZ‐pinch discharge using the original Ashby–Jephcott method and the modified method are shown. The differences in the temporal variation of the electron density measurements using the two methods are discussed.