Lateral Shearing Interferometry key features

Distortions of a grid of points can be measured in several ways. The simplest method consists in calculating the centroid of each point in given cells to determine its position. However, this technique does not take into account crosstalk between points, and cell size must be large enough to get an accurate statistical sampling.
To increase transverse high resolution, an advanced analysis method is required. It is described above. The Fourier analysis is definitely well adapted for periodical signal processing. Moreover, the sinus shape of interference fringes allows to be very close to the Nyquist frequency, 2x2 pixel² per fringe. In our case, for dynamic purposes, we chose to use 4x4 pixel² per fringe. Thus with a standard 512x512 CCD camera, we can obtain 128x128 pixels² phase (and intensity) maps.

Classical interferometer pitch is strongly dependent on wavelength. In our case, thanks to the use of a diffraction grating, multi-wave lateral shearing interferometers are achromatic : the chromaticity of the grating is exactly compensated by the interference chromaticity. The interferogram pitch is exactly equal to the grating pitch.
Therefore a SID4 wavefront sensor is the perfect device for short pulse laser characterization.