A small part of a focused laser beam in a Mach–Zehnder arrangement is used for the detection of high‐frequency pressure waves. The interferometer is stabilized on an interference slope by means of a simple electro‐optical feedback system. The method introduces only little perturbation to the pressure field and yields the true pressure historyp(t) with a submicrosecond time resolution. Several examples of registrations show the capability of this ideal microphone.