Foundations of Physics, Vol. 34, No. 12, December 2004 (© 2004) DOI: 10.1007/s10701-004-1631-4 Interferometry with Phase Conjugate Mirrors and Measure of One-Way Velocity of Light Augusto Garuccio 1 Received September 27, 2004 A Michelson interferometer with a phase-conjugate mirror (PCM) is described and discussed. The behavior of phase conjugate mirrors is discussed and the result of an experiment with a Michelson interferometer with a phase-conjugate mirror is described and commented. This interferometer has been proposed to be used to test the intrinsic non-locality of quantum mechanics. In this paper a new experimental setup to study the one-way velocity of light is proposed, which uses this new interesting device. KEY WORDS: interferometry; phase conjugate mirror. 1. INTRODUCTION The experimental measure of the one-way velocity of light is, up to now, an open problem of modern physics. Most physicists are convinced that this velocity is not measurable as a matter of principle. For example, in 1898 Poincar´ e claimed (1) that “This is a postulate without which it would be impossible to start any measurement of this velocity: It will always be impossible to verify experimentally the said postulate”. In general all the researchers in this field agree at lest that the constancy of velocity of light is an useful conventional assumption. In this paper we will discuss a new approach to measure the one-way velocity of light based on a modified Michelson interferometer in which one metallic mirror is substituted for a phase conjugate mirror. The inter- ference produced on reflection at phase-conjugate mirror has been studied in detail both from a classical and quantum point of view theoretically, 1 Dipartimento Interateneo di Fisica and I.N.F.N. Sezione di Bari Via Amendola, 173-70126 Bari, Italy; email: Garuccio@fisica.uniba.it 1983 0015-9018/04/1200-1983/0 © 2004 Springer Science+Business Media, Inc.