*Metalens Antennas in Microwave, Terahertz and Optical Domain Applications DOI: http://dx.doi.org/10.5772/intechopen.99034*

for the experimental and numerical results at the terahertz frequency of 0.3THz. The theoretical diffraction limit, k/(2NA), is 1.298 mm, which turns to be close to the experimental result of 1.3 mm. The numerical apertures (NA) of the experimental results at the frequencies of 0.6THz and 0.8THz are NA = 0.385, which matches the designed target as expected.

In general, this example shows that the resonant phase with the geometric phase could be combined to design a high-NA achromatic metalens with C-shaped or rectangular unit cells. The etching depth deviations and shape deformation effect are also considered in the simulation. The experimental results show that the achromatic lens is very close to design target and theoretical diffraction limit and also the durable robustness. The broadband achromatic terahertz metalens already shows the strong potential in some applications such as, hyperspectral imaging, terahertz microscopy.
