Low-Noise Quadrature Phase-Shifting Interferometry

We propose and demonstrate a modified implementation of two-step phase-shifting interferometry (holography) in which the amplitude and phase of the signal are determined directly from phase-shifted measurements, rather than using the real and imaginary parts. This leads to measurements that are more accurate and less prone to noise, which we demonstrate with colinearly-referenced measurements of various Laguerre-Gaussian modes and structured images.