A method to generate an optical metasurface is developed. In our experimental setup, we use a pump-probe technique,
where the pump beam is used to project patterns of v-shaped antennas on the surface of a silicon substrate. In the areas
illuminated with the images of v-shaped antennas electron-hole pairs are created. Therefore, the antenna structures on
silicon will have metallic-like properties, we classify this structure as a metasurface. The THz beam probes refraction
and reflection on the metasurface generated on the silicon substrate. The dynamic change of these patterns of
metasurface causes the beam steering effects of THz radiation.
An innovative method of examining properties of metasurfaces is presented. A pump-probe technique is used to create a metasurface composed of conductive shapes on a silicon surface. A wave-front of intense pulse of 82 fs from Ti:Sa laser with wavelength of 800 nm is shaped by a spatial light modulator and then focused into a preprogrammed array of vshaped features on a high purity float zone silicon substrate. The laser pulse generates electron-hole pairs on the silicon substrate, thus a metasurface consisting of an array of metal-like v-shaped antennas is inscribed on the silicon substrate. The lifetime of v-shaped antennas is in millisecond time range. In the meantime, the second, less intense pulse, also of wavelength 800 nm is converted to a pulse of terahertz radiation with a peak-power at wavelength approximately 800 μm and used to probe the metasurface inscribed in the silicon. Tracing the position of the refracted terahertz beam is achieved with a specially designed INO video camera for terahertz radiation.
Optical metasurfaces demonstrate outstanding capabilities of optical parameters modifications by changes in the structural architecture at the nano-scale level. We demonstrate results of electrophoretic experiments that modify the structure of a metasurface by using diamond nanoparticles with sizes much smaller than the wavelength of light; the nanoparticles are suspended in an aqueous solution and a uniform electric field is applied. The electric field controls the concentration of nanoparticles inside the sub-wavelength apertures and on the top plane of the metasurface. The higher concentration of diamond nanoparticles increases the refractive index of the suspension as well as increasing scattering and absorption. Results of optical material parameter characterization for a wavelength of 512 nm are provided for different concentrations of the diamond nanoparticles dispersions.