A Rydberg-Atom Based Detector for Terahertz Sources
Final Report Abstract
Rydberg atoms have unique properties such as long lifetimes, strong dipole interaction, large polarizability, resulting in an exaggerated response to magnetic and electric fields because they can couple strongly to electric dipole transitions driven by electromagnetic fields, behaving as extreme sensitive antennas. Under this project we built a new experimental setup to develop a Rydberg atom-based detector to sensor and characterize a quantum cascade laser as THz source emitter. For the optical detector to function, the external THz field needed to be coupled to the Rydberg atoms inside an atomic vapor cell. For high-THz range, covered by a quantum cascade laser (QCL) THz source for our experiment, standard glass vapor cells could not be used due to their large index of refraction. This causes internal standing waves leading to power losses which can significantly reduce the optical detection. We successfully fabricated a new hybrid Si-glass anodically bonding rubidium vapor cell compatible for both visible and near IR lasers (780, 480nm) and THz radiation above 1 THz [A]. The cell was implemented in an EIT scheme where the probe and coupling lasers were a combination of co-propagating and counter-propagating configuration and it was demonstrated by obtaining the EIT signal. Developments in the use a special AR coating for the vapor cell based in organic Parylene to increase the transmission of THz was started and it was reported for the first that rubidium reacts with parylene coating (never documented before). Working with THz light was surprising harder than expected: from operating the QCL in the cryostat to alignment blindly to bring the light into the vapor cell and align with the probe and coupling laser beams. Unfortunately, during the project, we never observed a dip in the EIT peak due to AT splitting, meaning the THz field from the QCL did not couple to the Rydberg state. This could have been caused due to the broadened QCL's effective linewidth, not on resonant due to be off the frequency range, the QCL current injection was too noisy or the QCL was only on resonant for a very short time due to drift in the bath temperature and the applied current of the QCL. Further improvements in the experimental setup such a low noise current driver for pulsing the current of the QCL, as well as frequency-current calibration will be needed to continue with further measurements.
Publications
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A Rydberg Gas Terahertz Sensor. Optical Sensors and Sensing Congress 2022 (AIS, LACSEA, Sensors, ES), SM3C.3. Optica Publishing Group.
Torralbo-Campo, Lara; Dorsch, Eric; Battran, Felix; Lue, Xiang; Grahn, Holger T.; Koelle, Dieter; Kleiner, Reinhold & Fortágh, Jozsef
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A practical guide to terahertz imaging using thermal atomic vapour. New Journal of Physics, 25(3), 035002.
Downes, Lucy A.; Torralbo-Campo, Lara & Weatherill, Kevin J.
