Illustration of (a) the raster scanning process of the focused beam, which is formed by phase-only grating patterns successively displayed on the SLM. Here, one grating pattern corresponds to one single focal spot in the target plane; (b) the beam is focused on the target, resulting in a wide-field distorted optical distribution around; (c) detection of the wide-field distribution in the target plane by applying FFT to the Fourier plane distribution followed by digital pinhole filtering.