A method for carrying out a plasma deposition process including the steps of providing a substrate tube, supplying dopant-containing glass-forming gases to the substrate including a main gas flow and one or more secondary gas flows, inducing a plasma in the substrate tube, moving a reaction zone back and forth in strokes between a reversal point near the supply side and a reversal point near the discharge side, and interrupting the secondary gas flow during a portion of each stroke, each interruption having a start point and an end point within the same stroke.