System and method for measuring an optical property of a sub micrometer region of a sample including interacting a probe tip of a probe microscope with a region of the sample, illuminating the sample with a beam of light from a radiation source such that light is scattered from the probe-sample interaction region, interfering a reference beam with the scattered light wherein the reference beam has an adjustable optical phase, measuring with a detector at least a portion of the light scattered from probe-sample and background regions at a substantially constant reference phase, and constructing a signal indicative of the optical property of the sample wherein contributions from background scattered light are substantially suppressed.