Germany develops new graphene optical detector

Scientists at the HZDR Research Center in Helmsholt, Germany, have developed a new optical detector by adding a tiny flake graphene plus antenna to SiC. The new detector is said to quickly reflect incident light at all different wavelengths and can operate at room temperature. This is the first time a single detector has been implemented to monitor the spectral range from visible to infrared radiation and up to terahertz radiation.

Scientists at the HZDR Center have begun using new graphene detectors for precise synchronization of laser systems. According to physicist Stephan Winnerl of the HZDR Institute of Physics and Materials, compared to other semiconductors, such as silicon or gallium arsenide, graphene can carry light with a very large range of photon energy and convert it into an electrical signal, requiring only one broadband and appropriate substrates.

The graphene sheets and antenna assembly absorb light and transfer the energy of the photons into the electrons of the graphene. These "hot electrons" increase the resistance of the detector and produce a fast electrical signal that completes the incident light injection in as little as 40 picoseconds.

The choice of substrate is the key to improving the light collector. The semiconductor substrate used in the past absorbs some wavelengths of light, but silicon carbide does not actively absorb light in the spectral range. In addition, the antenna acts like a funnel, capturing long-wave infrared and terahertz radiation. At present, scientists have been able to increase the spectral range to 90 times that of previous models, and the shortest wavelength that can be detected is 1000 times smaller than the longest. In visible light, the red wavelength is the longest, the violet wavelength is the shortest, and the red wavelength is only twice that of violet.

The optical detector has been adopted by the HZDR Center for precise synchronization of two free electron lasers in the center of the Elbe. This precise synchronization is especially important for "pump probe" experiments where the researchers use one of the lasers to excite the material and then use another laser with a different wavelength for the measurement. In this experiment, the laser pulses must be precisely synchronized. Therefore, scientists use graphene detectors as if they use a stopwatch. A precisely synchronized detector can show when the laser pulse reaches the target, and a large bandwidth helps prevent the detector from becoming a potential source of error. Another advantage of this type of detector is that all measurements can be taken at room temperature, avoiding the expensive and time consuming nitrogen or helium cooling process required by other detectors.

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