| Since the laser was born in60’s of the20th century, the ultra-short laser pulse technology has been progressing towards two key aspects:the shorter and the more energetic, and playing a more and more important role in science and industry. The past decade has seen the development of numbers of ultrahigh-energy. ultrashort laser facilities driven by X-ray generation, electron acceleration, fast ignition application advances, such as PATAL, PHELIX, OMEGA-EP etc. Researchers find that the chromatic aberration of the lenses included in the spatial filters used by these laser facilities is of crucial importance in the pulse front distortion, which leads to severe spatio-temporal distortions and limits the peak power in the far field. Hence the measurement of pulse front distortion and the compensation of chromatic aberration are two most urgent problems remaining. In recent years, the measurement technique of ultra-short laser pulses extends the traditional one-dimension (temporal or spatial) to two-dimension spatio-temporal diagnostics, which makes it possible to extract the information of spatio-temporal coupling widely existing in ultra-short laser pulses. Unfortunately, there is no common language for characterization and evaluation of the pulse front distortion, which brings inconvenience to research and communion. In this paper, an expression of pulse front distortion based on spatio-temporal correlation coefficients is put forward starting from the definition of the pulse front. The chromatic aberration of refractive lens and Fresnel zone plate is analyzed, as well as the temporal effect of femto-second laser pulses focused by the Fresnel zone plate, which concludes that chromatic aberration is the key factor affecting the performace of large-aperture, short-pulse laser facilities, and diffractive-based chromatism correction using Fresnel zone plate is a promising solution of chromatism compensation in these laser systems. |
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