A metrology system includes a radiation source, first, second, and third optical systems, and a processor. The first optical system splits the radiation into first and second beams of radiation and imparts one or more phase differences between the first and second beams. The second optical system directs the first and second beams toward a target structure to produce first and second scattered beams of radiation. The third optical system interferes the first and second scattered beams at an imaging detector. The imaging detector generates a detection signal based on the interfered first and second scattered beams. The metrology system modulates one or more phase differences of the first and second scattered beams based on the imparted one or more phase differences. The processor analyzes the detection signal to determine a property of the target structure based on at least the modulated one or more phase differences.