A team of researchers from Germany and the US have developed a graphene-based light detector that is able to monitor the entire spectral range from visible light, to infrared radiation and right through to terahertz radiation.
Jointly developed by scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the University of Maryland the detector, claimed to be the first of its kind, could be used to improve the accuracy of so called pump probe experiments that use lasers to precisely monitor dynamic processes like chemical reactions.
The device consists of a tiny flake of graphene on silicon carbide and a futuristic-looking antenna. The graphene flake and antenna assembly absorbs the rays, thereby transferring the energy of the photons to the electrons in the graphene. These “hot electrons” increase the electrical resistance of the detector and generate rapid electric signals. The detector can register incident light in just 40 picoseconds.
“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.” explained HZDR physicist Dr. Stephan Winnerl.
By using the antenna to capture long-wave infrared and terahertz radiation the scientists have therefore been able to increase the spectral range by a factor of 90 in comparison with the previous model, making the shortest detectable wavelength 1000 times smaller than the longest.
This detector is already being used at the HZDR for the exact synchronisation of the two free-electron lasers at the ELBE Centre for High-Power Radiation Sources with other lasers. This alignment is particularly important for “pump probe” experiments where researchers use one laser to excite a material and a second laser with a different wavelength to probe the material.
The laser pulses must be exactly synchronised for such experiments. So the scientists are using the graphene detector like a stopwatch. It tells them when the laser pulses reach their goal, and the large bandwidth helps to prevent a change of detector from being a potential source of error.