Coherent detection of terahertz radiation with graphene

Despite that significant efforts have been made in the development of time-integrated graphene-based detectors operating in vis/IR/THz ranges, little is known about coherent detection of THz pulses with graphene. To date only a few time resolved studies with on-chip detection schemes, which significantly limit the spectral range naturally provided by the gapless band structure of graphene, are known. Here we demonstrate free-space room-temperature detection of THz radiation in a wide spectral range with optically gated graphene. The detection principle is based on registration of the time-domain waveform of the THz field by measuring the hot-carrier photocurrent under THz pulse exposure in optically excited graphene using a pump probe scheme. The applied method is simple and robust, while the sensitivity and working range of the developed graphene-based detector are comparable and in some aspects outperform materials conventionally used for terahertz time domain spectroscopy based on electro-optic sampling and photoconductive antennas. In addition, we demonstrate that efficient coherent detection of terahertz radiation in a wide range to above 2 THz does not require highly crystalline, single-layer graphene but can be also realized with ultrathin graphite film, which is synthesized directly on an arbitrary dielectric substrate. Employment of such a material for fabrication of ultrafast terahertz detectors creates a versatile platform for the scalable production of wide-aperture photoconductive detectors applicable in spatially resolved time-domain terahertz spectrometers and visualizers.