Generating high-harmonic array beams

The demand for spatially structured ultrashort beams at shorter wavelengths is high, and their adaptability in potential applications such as imaging, metrology, and attosecond science is undeniable. In this work, we present the generation of high-harmonic array beams. We utilize ultrashort structured array beams in the near-infrared wavelength as the pump source to reliably generate extreme-ultraviolet array beams at the tenth harmonic of the pump wavelength. The pump array beams showed shape-invariant free space propagation and exhibited a self-healing ability against adverse spatial effects introduced by aberrations. Moreover, we found that the spatial profile of these array beams remained unchanged for any polarization state, a unique feature that enhances their versatility. The interaction of shape-invariant array beams with an argon gas jet in a two-color pump configuration generated high harmonics consisting of both weak odd and even orders, a suppression of odd harmonics from the 13th to the 17th order when driven by two-color laser fields, but a strong 10th order harmonic appeared in the extreme-ultraviolet. This 10th harmonic unveiled a spatial distribution, including a unique string structure that is a hallmark of array beams. This extreme nonlinear optical process of structured high-harmonic generation is a significant advancement that offers a new degree of freedom for generating diverse structured harmonics in extreme ultraviolet and soft x-ray regimes.