A new graphene-based optical detector has been developed. The detector has a spectral range that spans from the visible to the TeraHertz region, a 40 picosecond response rate and fully functions at room temperature.
The external antenna on the detector captures long-wave infrared and terahertz radiation and funnels it to a graphene flake which is located in the center of the structure on a silicon carbide substrate. Foto: M. Mittendorff
The novel detector works at room temperature and shows rapid reactions to incident light over a broad range of wavelengths. The new detector can detect a spectral range that spans from visible light to infrared radiation and even upto the terahertz region, a feat that has never been achieved by a single detector until now.
The new graphene detector is already being used by HZDR scientists for the accurate synchronization of ltheir laser systems. The detector has few components; it consists of just a small flake of graphene on silicon carbide with an advanced antenna.
In contrast to other semiconductors like silicon or gallium arsenide, graphene can pick up light with a very large range of photon energies and convert it into electric signals. We only needed a broadband antenna and the right substrate to create the ideal conditions.
Dr. Stephan Winnerl - HZDR
The rays are absorbed by the graphene flake-antenna assembly which transfers the energy of the photons to electrons in graphenes 2D lattice. The energetic electrons increase the resitivity of the graphene detector, producing rapid electric signals that are easily observed. This effect is rapid that incident light is registered in 40 ps, i.e. one-trillionth of a second, by the detector.
Wide Spectral Range Achieved through Silicon Carbide Substrate
The most effective way of improving the graphene detector was by choosing an appropriate substrate.
The antenna also acts as a funnel for the effective capture of terahertz and long-wave infrared radiation. This design increased the spectral range capture by 90% when compared to previous models, which in turn, makes the longest detectable wavelength 1000 times bigger than the shortest. To put this into perspective red light, which has the longest wavelength in the visible region, has a wavelength only two times longer than violet light, which has the shortest visible wavelength.
Semiconductor substrates used in the past have always absorbed some wavelengths but silicon carbide remains passive in the spectral range
Dr. Stephan Winnerl - HZDR
The graphene 'universal optical detector' is being used to accurately synchronize two free-electron lasers with other lasers at the ELBE Center for High-Power Radiation Sources. The synchronization is critical for ‘pump probe’ experiments. In pump probe experiments one laser is used to excite a material, i.e. electrons are 'pumped' to a higher energy level in the material, and another laser of a different wavelength is used as a 'probe' to measure the excited state. The perfect synchronization of the two laser pulses is essential for these experiments to be accurate.
The graphene detector can be used like a stopwatch by the scientists, allowing them to detect when a laser pulse attains its goal. The large bandwidth of the detector also helps eliminate the need to change detectors during the course of an experiment, which is a common source of error. Unlike other detectors, the graphene detector functions well at room temperature so expensive and time-instensive helium/nitrogen cooling processes, as common with other detectors, are not nessecary.