A method for use in optical measurements on patterned structures, the method including 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 including detecting light reflected from the at least part of the at least two different regions within the measurement spot, the detected light including interference of at least two complex electric fields reflected from the 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.