Researchers have found a way to dramatically improve the sensitivity of microwave bolometers, devices used for sensing microwave radiation. The new bolometer uses monolayer graphene to achieve 100,000 times greater sensitivity than current commercial devices.
Bolometers sense electromagnetic radiation via temperature changes. The more radiation power is incident upon the bolometer, the hotter it gets, and the temperature can be correlated to the amount of radiation.
Graphene’s electrical and thermal properties have long made it a promising material for bolometry. It can efficiently absorb photons of many different frequencies, and its electron-electron scattering time is short. At its charge-neutrality point, graphene has a vanishing density of states, which results in a small heat capacity and an electron-to-phonon thermal conductance.
The researchers developed the thin bolometric sensor with a graphene-based Josephson junction, a quantum mechanical device composed of two superconducting electrodes separated by a barrier.
“The microwave bolometer developed under this project is so sensitive that it is capable of detecting a single microwave photon, which is the smallest amount of energy in nature,” said Joe Qiu of the Army Research Office, which funded the research. “This technology will potentially enable new capabilities for applications such as quantum sensing and radar, and ensure the U.S. Army maintains spectral dominance in the foreseeable future.”
Attempts at utilizing the bolometric response of graphene in other bolometers were stymied by the degradation in the thermometer sensitivity when electron temperatures rose during the photon-absorption stage of the measuring process. This severely stunted the possible applications of those designs, and showed that there was more work to be done in order to improve on this technology.
The new design overcomes this challenge by adopting a measuring technique in which the monolayer graphene is simultaneously integrated into the microwave resonator and the Josephson junction.
The bolometer can operate at nearly 105 times faster than standard nanowire bolometers.