Scatterometry is a non-destructive metrology method, allowing measurement of material and geometrical properties of micro and nano systems. The experimental setup is quite simple since no imaging system is involved. A target is illuminated by a light source and the scattered field is measured by a detector in dependence on the direction.
Since the measured light carries no direct information about the measured system, inverse techniques have to be used to reconstruct parameters of the system. Therefore, simulations for different configurations of the systems are performed and the best matching results to the experimental measurement are determined.
An example can be found here.