Understanding the Role of Slant Angle in Oblique Slit Arrays Made of Metal at Terahertz Frequencies

Analytical expressions are given for zeroth-order diffraction efficiencies of metallic gratings with slanted and straight slit arrays at microwave and terahertz frequencies when the slit width is small enough to ensure that non-principal eigenmodes supported by the slit remain below cut-off. These expressions show that at lower normalized frequencies when the grating is zeroth order and all off-specular diffraction orders are evanescent, metallic slit arrays with slanted and straight walls could become identical to each other whenever certain relation is held between the geometrical parameters of the two structures. A noteworthy advantage of juxtaposing slanted and slit arrays is that it shows slant angle in slanted structures is tantamount to decreasing the slit width and increasing the slit thickness in slit arrays with straight walls. This particular finding suggests that metamaterials with high index of refraction and smaller thickness can be realized by increasing the slant angle instead of decreasing the slit width.