A system is described, for use in optical measurement of a sample. The system comprising: an illumination unit configured for providing coherent illumination of one or more selected wavelength ranges and directing it onto one or more selected inspection regions of the sample, a collection unit configured for collecting light returning from the inspection region and generating output data comprising a sequence of image data pieces indicative of secondary speckle patterns formed at an intermediate plane in optical path of light collection, a depth resolving module configured for affecting at least one of the illumination unit and the collection unit for determining an association between collected secondary speckle patterns and depth layers of the sample; and a control unit being connectable to said depth resolving module and configured for operating said depth resolving module and for receiving said sequence of image data pieces from the collection unit and processing said sequence of image data pieces by determining correlation functions between at least portions of said secondary speckle patterns associated with corresponding depth layers of the sample, thereby determining one or more parameter variations along depth of the sample.