Robust enhancement of extreme ultraviolet radiation via transient electrostatic field induced by electron nanobunches from double nanofoils

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Electronic dynamics at relativistic laser intensities have aroused extensive attention, and meanwhile, the enhancement of extreme-ultraviolet high-order harmonic generation (XUV-HHG) intensities has also been pursued. Here we propose, for the first time, a new scheme that involves the construction of a transient electrostatic field induced by electron nanobunches from relativistic intensity laser-irradiated double nanofoils, which then results in robust enhancement of XUV radiation in the transmitted direction, and experimentally demonstrate it. This scheme does not require purposely optimizing the laser contrast and pulse duration, and significant enhancement of harmonic radiation by more than one order of magnitude can be achieved as long as the laser is focused between the two foils. Our work offers novel insights into plasma-induced electronic dynamics at relativistic laser intensities and also proposes a robust scheme to realize significant enhancement of XUV-HHG at relativistic laser intensities, which promotes the application of XUV-HHG in atomic physics, ultrafast dynamics, and other fields.