Phase-difference amplification using a Sagnac interferometer

In this paper, we describe a new method for achieving phase-difference ampl ification, which is quick and convenient, operates in real time, and requir es no photographic steps. Magnification factors of 2, 4 or 6 are achieved e asily in one step. Because the system operates in real time, phase stepping may be applied to extract the amplified phase distributions. Our method is a variation on longitudinally reversed shearing interferometry, using firs t- or higher-order diffraction from a grating (hologram) which is in fact t he interferogram of the wavefront under test. The grating is derived from a standard two-beam interferometer which is phase-stepped, and displayed in real time on a spatial light modulator in the phase-difference amplificatio n setup. It is illuminated by the two output beams from a Sagnac interferom eter, similar to the set up used by (Barnes et al. Barnes TH, Eiju T, Matsu da K. Appl Opt 1986; 25:1864). for spectral resolution enhancement, and a p hase-amplified fringe pattern is obtained by spatial filtering using a Four ier transform lens. We demonstrate operation of the phase amplifier and sho w amplified phase maps retrieved by phase-stepping. We believe this is the first time that real-time phase amplification without photographic steps an d with phase stepping has been demonstrated. (C) 2000 Elsevier Science Ltd. All rights reserved.