1. A method for evaluating a semiconductor layer at least partially crystallized by exposure to a plurality of laser-radiation pulses having an energy density on the layer, the crystallization producing a first group of periodic surface features on the layer in a first direction, and a second group of periodic features in a second direction perpendicular to the first direction, the form of the first and second groups of periodic features depending on the energy density of the laser-radiation pulses to which the semiconductor layer has been exposed, the method comprising: illuminating an area of the crystallized semiconductor layer; recording a microscope image of the illuminated area in light diffracted from the illuminated area by the first and second groups of periodic features, the recorded image containing horizontal and vertical groups of periodic image-features corresponding to the first and second groups of periodic features in the illuminated area of the layer; and determining the energy density from a measure of the contrast of at least one of the horizontal and vertical groups of periodic image-features.