Dual-Band Negative Index Metamaterial: Double-Negative at 813 nm and   Single-Negative at 772 nm
  This work is concerned with the experimental demonstration of a dual-band negative index metamaterial. The sample is double-negative (showing both a negative effective permeability and a negative effective permittivity) for wavelengths between 799 and 818 nm of linearly polarized light with a real part of refractive index of about -1.0 at 813 nm; the ratio -Re(n)/Im(n) is close to 1.3 at that wavelength. For an orthogonal polarization, the same sample also exhibits a negative refractive index in the visible (at 772 nm). The spectroscopic measurements of the material are in good agreement with the results obtained from a finite element electromagnetic solver for the actual geometry of the fabricated sample at both polarizations. 
Uday K. Chettiar, Alexander V. Kildishev, Hsiao-Kuan Yuan, Wenshan   Cai, Shumin Xiao, Vladimir P. Drachev, and Vladimir M. ...