Split ring resonator based THz emitter and photo-imprinted THz diffraction gratings

摘要

Terahertz (THz) spectral band, from about 0.1 to 15 THz, is one of the least explored yet most technologically transformative spectral regions. A large number of interesting scientific phenomena are only accessible by THz photons and THz radiation also finds a lot of practical applications. However, for a long time, THz scientific research and technological development is greatly limited due to the technical difficulties in making efficient and compact THz emitters and detectors, and controlling THz waves has been proven to be more difficult. On the other hand, artificially subwavelength structured materials called metamaterials, have been actively pursued and developed, which enables people to tailor their optical responses or nonlinearities in THz region, setting them among the most promising candidates for the next generation optoelectronic devices to generate and manipulate THz waves. Here we present our design and study of (1) a novel split ring resonator (SRR) based high efficiency THz emitter and (2) all-optical photo-imprinted reconfigurable THz diffraction gratings. Firstly, the THz emitter is composed of a single layer of 40nm thick gold film with SRR lattice constant 382nm on a 1mm thick suprasil substrate. THz waves are generated by pumping the SRR magnetic dipole resonance at 1500 nm. The demonstrated second-order sheet nonlinear susceptibility is three orders of magnitude higher than those of conventional crystals and thin films. The emitter can be tailored to pump at any wavelength and can potentially generate THz spectrum covering the entire THz band. Secondly, the THz diffraction gratings are realized by projecting an optical image from a photo mask onto a GaAs substrate using femtosecond laser pulses. The resulting high contrast pattern of photoexcited carriers can therefore create diffractive elements to manipulate THz waves with reconfigurable functionalities.