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All-angle negative refraction and active flat lensing of ultraviolet light



Decades ago, Veselago1 predicted that a material with simultaneously negative electric and magnetic polarization responses would yield a ‘left-handed’ medium in which light propagates with opposite phase and energy velocities—a condition described by a negative refractive index. He proposed that a flat slab of left-handed material possessing an isotropic refractive index of −1 could act like an imaging lens in free space. Left-handed materials do not occur naturally, and it has only recently become possible to achieve a left-handed response using metamaterials, that is, electromagnetic structures engineered on subwavelength scales to elicit tailored polarization responses. So far, left-handed responses have typically been implemented using resonant metamaterials composed of periodic arrays of unit cells containing inductive–capacitive resonators and conductive wires. Negative refractive indices that are isotropic in two2 or three3 dimensions at microwave frequencies have been achieved in resonant metamaterials with centimetre-scale features. Scaling the left-handed response to higher frequencies, such as infrared or visible, has been done by shrinking critical dimensions to submicrometre scales by means of top-down nanofabrication4. This miniaturization has, however, so far been achieved at the cost of reduced unit-cell symmetry, yielding a refractive index that is negative along only one axis. Moreover, lithographic scaling limits have so far precluded the fabrication of resonant metamaterials with left-handed responses at frequencies beyond the visible5. Here we report the experimental implementation of a bulk metamaterial with a left-handed response to ultraviolet light. The structure, based on stacked plasmonic waveguides6, yields an omnidirectional left-handed response for transverse magnetic polarization characterized by a negative refractive index. By engineering the structure to have a refractive index close to −1 over a broad angular range, we achieve Veselago flat lensing, in free space, of arbitrarily shaped, two-dimensional objects beyond the near field. We further demonstrate active, all-optical modulation of the image transferred by the flat lens.

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Figure 1: Ultraviolet bulk metamaterial.
Figure 2: Experimental and simulated results for refraction of power and phase.
Figure 3: Ultraviolet flat lensing.


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We thank A. Liddle, K. Srinivasan, R. McMichael, A. Nahata and S. Blair for discussions. We also thank the staff from CNST NanoFab for technical support. T.X. and M.A. acknowledge support under the Cooperative Research Agreement between the University of Maryland and the National Institute of Standards and Technology Center for Nanoscale Science and Technology, award number 70NANB10H193, through the University of Maryland.

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The experiments were designed and performed by T.X., A.A., M.A. and H.J.L. Simulations were performed by T.X., M.A. and K.J.C. with further analysis by A.A. and H.J.L. All authors contributed to the interpretation of results and participated in manuscript preparation.

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Correspondence to Henri J. Lezec.

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The authors declare no competing financial interests.

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Xu, T., Agrawal, A., Abashin, M. et al. All-angle negative refraction and active flat lensing of ultraviolet light. Nature 497, 470–474 (2013).

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