High-harmonic generation (HHG) is a signature optical phenomenon of strongly driven, nonlinear optical systems. Specifically, the understanding of the HHG process in rare gases has played a key role in the development of attosecond science1. Recently, HHG has also been reported in solids, providing novel opportunities such as controlling strong-field and attosecond processes in dense optical media down to the nanoscale2. Here, we report HHG from a low-loss, indium-doped cadmium oxide thin film by leveraging the epsilon-near-zero (ENZ) effect3,4,5,6,7,8, whereby the real part of the material’s permittivity in certain spectral ranges vanishes, as well as the associated large resonant enhancement of the driving laser field. We find that ENZ-assisted harmonics exhibit a pronounced spectral redshift as well as linewidth broadening, resulting from the photo induced electron heating and the consequent time-dependent ENZ wavelength of the material. Our results provide a new platform to study strong-field and ultrafast electron dynamics in ENZ materials, reveal new degrees of freedom for spectral and temporal control of HHG, and open up the possibilities of compact solid-state attosecond light sources.
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The data that support the plots within this paper and other findings of this study are available from the corresponding authors on reasonable request.
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This work started when Y.Y. was a postdoctoral researcher at Sandia National Laboratories. The work performed at Sandia National Laboratories was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, and performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the US DOE Office of Science. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, a wholly owned subsidiary of Honeywell International, for the US DOE’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in this article do not necessarily represent the views of the US DOE or the United States Government. The work performed at SLAC was primarily supported by the US DOE, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences Division through the Early Career Research Program. Y.Y. acknowledges support from the Youth Thousand Talent program of China. A.M. acknowledges the National Science Foundation (grant ECCS-1710697) and the UNM Center for Advanced Research Computing for providing high-performance computing resources. J.-P.M. acknowledges support from the National Science Foundation (grant CHE-1507947) and Army Research Office (grants W911NF16-1-0406 and W911NF-16-1-0037). S.G. thanks U. Thumm for stimulating discussions.
The authors declare no competing interests.
Peer review information: Nature Physics thanks Dmitry Turchinovich and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Nature Reviews Materials (2019)