Software for focal spot optimization
Phase Retrieval algorihm PhaRAO is also available in WaveTune as an optional module. With the help of a simple CCD camera, PharAO enables users to control and optimize the focal spot directly in the interaction chamber.
The phase retrieval algorithm processes the acquired data and calculates the differential aberrations between the wavefront sensor and the focal spot diagnostic camera. The result of these calculations is the differential aberrations of the system, i.e. aberrations that are present either on the wavefront sensor path or on the main laser path up, but not on both path (as those were corrected in the first step). Results are crossed checked by doing recalculation of the focal spot of calculated differential aberrations and checking that they are indeed similar to the acquired images of the focal spot. The phase retrieval algorithm has been optimized in terms of calculation speed. It can take several minutes for the usual algorithm to calculate a single wavelength. The optimized algorithm takes only a few seconds. This increase of speed is necessary in order to get the full correction within a few minutes even if several iterations of steps 2, 3 and 4 are necessary to get the perfect focus beam.