A method and system are presented for use in optical measurements on patterned structures. The method comprises performing a number of optical measurements on a structure with a measurement spot configured to provide detection of light reflected from an illuminating spot at least partially covering at least two different regions of the structure. The measurements include detection of light reflected from said at least part of the at least two different regions comprising interference of at least two complex electric fields reflected from said at least part of the at least two different regions, and being therefore indicative of a phase response of the structure, carrying information about properties of the structure.