The development of laser driven plasma accelerators with high average power in solids requires simple and robust autofocus systems to determine, with accuracy, the focal position with respect to a rapidly refreshing target. Trial-and-error processes used in single shot experiment are not useful in this scenario. In this work we present a passive pre-alignment procedure to calibrate an autofocus setup, for fast refreshing solid target system, based on an astigmatic optical system. The calibration technique uses a hard aperture and a photodetector, located at the target position, to find the focal point with an experimental error, standard deviation, of less than 5 μm, which represents our translation stage resolution, achieved for a Rayleigh length of 35 μm. A geometrical analysis and numerical simulation have been done to demonstrate the effectiveness of the calibration technique and the accuracy of the astigmatic autofocus system. System accuracy can be improved with a better resolution of the translation stage.
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