We present THz ultrashort pulse detection by a photoconductive antenna array consisting of 16 photoconductive antennas. The efficient excitation of the photoconductive antennas has been realized by a microlens array which generates 16 single spots from the exciting fs-laser beam. This combination of optoelectronics and microoptics improves the detection efficiency by an order of magnitude in comparison to an excitation by a line focus.
The ability of subwavelength structures to create an artificial effective index opens up new perspectives in designing highly efficient diffractive optical elements. We demonstrate a design approach for binary multi-phase level computer generated holograms based on the effective medium approach. The phase pattern is formed by various subwavelength structures that cause a certain phase delay to an incident light wave. This binary structure approach leads to a significant cost reduction by simplifying the fabrication process. For demonstration, a three-phase level element, operating in the visible range, is fabricated and experimentally evaluated.
Recent research revealed that using the effective medium approach to generate arbitrary multi-phase level computer-generated holograms is a promising alternative to the conventional multi-height level approach. Although this method reduces the fabrication effort using one-step binary lithography, the subwavelength patterning process remains a huge challenge, particularly for large-scale applications. To reduce the writing time on variable shaped electron beam writing systems, an optimized strategy based on an appropriate reshaping of the binary subwavelength structures is illustrated. This strategy was applied to fabricate a three-phase level CGH in the visible range, showing promising experimental results.
Subwavelength structures open up the possibility to create an artificial index material which enables the realization of high-efficient diffractive structures. This can be used to generate optical elements with nearly arbitrary phase profiles. We demonstrate the realization of computer-generated holograms based on this effective medium approach. High diffraction efficiencies can be realized by multi-phase-level modulation based on two-dimensional binary nanostructures. The fabrication is performed by one lithographical step using a high-speed e-beam writer which allows high-resolution patterning even on large areas. A diffractive element in the visible range is experimentally demonstrated using the presented effective index approach
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