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. 2019 Apr 16;10:1778. doi: 10.1038/s41467-019-09811-9

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — Terahertz emission from uniform nonlinear metasurfaces (NLMS). a Experimental set-up. Ti:Sapp amplified titanium sapphire laser, OPA optical parametric amplifier, PTFE teflon filter, DL delay line. ZnTe 0.5 mm ZnTe (110-cut) crystal, λ/4 quarter wave plate, WP Wollaston prism, BPD balanced photodiode. b Time domain spectroscopy (TDS) signal of terahertz (THz) pulse emitted from an NLMS (red line) and from a 0.1 mm ZnTe (110-cut) crystal under the same excitation conditions (blue line). The ripples following the single-cycle pulse emitted from the ZnTe are due to phonon absorption in the ZnTe crystal. c Emission spectrum from a uniform NLMS and ZnTe. d Spatiotemporal measurement of THz pulse emitted from NLMS, plotted in the time domain. The temporal cross-section at the center of the beam is shown in red. e Frequency domain representation of the measurement in d. The dashed lines mark the expected frequency-dependent diffraction profile of a beam emitted from a 1 mm wide emitter