Continuous sign change crossing zero of the light refraction observed at the Au/air interface

Light transmission at the Au/air interface was measured for wedge-shaped Au film samples. Light refraction continuously changing its sign from positive to negative at the Au/air interface in the spectrum range of 470-700 nm was observed with a zero refraction occurred at about 525 nm. The results indicate that the effective refraction index ne of samples are not correlated with wedge angles, implying that ne can be considered an intrinsic characteristic of the metal material. The positive and negative refractions observed in the experiment can be attributed to the dispersive feature of the dielectric function of Au with qualitative explanation according to the mechanisms of electron transition and the boundary conditions restricted at the interface.