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Spatial and spectral variations of high-order harmonics generated in noble gases

We report on the spatial and spectral variation of high-order harmonics generation from noble gases when driven by high-repetition rate femtosecond laser with different peak intensity and polarization states. Ar, Xe, and Kr were chosen for the generation of coherent extreme ultraviolet radiation. We observe that increasing the intensity of the driving pulses (DPs) leads to disappearance of harmonics yield in the on-axis part of the spatial distribution of the harmonics in Xe target, contrary to Ar and Kr. This observation is attributed to the higher ionization potential of the latter gases. Spectral depletion of harmonics generated in Ar and Xe using radially and azimuthally polarized Gaussian–Laguerre two-color DPs is also observed. The significant depletion in the spectral distribution of harmonics is obtained when two-color pump (TCP) scheme is applied. We demonstrate how TCP scheme with azimuthally polarized DPs can be used as a tool to control the spectral distribution of harmonics generated from gas atoms during strong field by utilizing the presence of second harmonic electromagnetic field.