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This paper introduces a new method for the simultaneous measurement of harmonic and supraharmonic distortion with improved robustness against amplitude and power frequency deviations. The proposed algorithm is based on wavelet analysis and it is designed to analyze a 10 cycles measurement interval, something crucial when implementing methods to measure harmonic and supraharmonic content according to the IEC 61000-4-7 standard. Discrete Fourier Transform (DFT)-based methods, instead, must analyze a fixed 200 ms interval in order to avoid apparent shifts of the supraharmonic frequency components. The results of the experimental measurements presented in the paper show that the DFT-based methodology suggested in the IEC 61000-4-7 standard produces results affected by the value of the power frequency and amplitude while the proposed method, instead, is insensitive to them. This feature also removes the need of a previous high pass filtering stage, required for the IEC method. Moreover, the proposed method has the additional advantage of working on the same measurement interval to calculate both harmonics and supraharmonics, which reduces the complexity of data handling by avoiding multithreaded Data Acquisition (DAQ) operations.

Ablation of LiF crystal by soft x-ray laser (XRL) pulses with wavelength λ=13.9 nm and duration TL=7 ps is studied experimentally and theoretically. It is found that a crater appears on a surface of LiF for XRL fluence, exceeding the ablation threshold Fa∼10.2 mJ/cm2 in one shot, or 5 mJ/cm2 in each of the three XRL shots. This is substantially below the ablation thresholds obtained with other lasers having longer pulse duration and/or longer wavelength. A mechanism of thermomechanical ablation in large bandgap dielectrics is proposed. The theory explains the low Fa via small attenuation depth, absence of light reflection, and electron heat conductivity.