This thesis investigates the interaction between Rydberg atoms and THz radiation and details development of an atom-based imaging system for THz frequency fields. Room temperature caesium atoms are excited to a Rydberg state using resonant infrared lasers and the response of these atoms to THz radiation is studied in multiple ways. We look at the absorption of the initial excitation laser and show how the observed lineshape changes in response to an applied THz field. We use this to measure the power of a THz field across a range of 350 GHz. These measurements also lead us to determine values for the quantum defects in caesium without reliance on data from any other sources. These values agree within error with those previously reported in literature. We study the optical fluorescence emitted by the laser-excited \nvapour and develop a model to predict this emission. We highlight deviations from this model and suggest possible mechanisms for this discrepancy. We show how this model can be used to determine the optimum transition for atom-based THz imaging within our experimental parameters. We demonstrate a high-speed THz imaging system using Rydberg atoms and show that it has near diffraction-limited \nspatial resolution and is able to capture images at kHz framerates. We measure the minimum THz power that the system can detect and show how it compares to other technologies. This system is then used to perform some proof-of-principle experiments to highlight its usefulness in commercial settings. Using optical elements \ndesigned and produced in-house we create and characterise THz vortex beams with both radial and azimuthal phase. We show how these beams are similar to Laguerre-Gauss modes and highlight some important differences.
This thesis investigates the interaction between Rydberg atoms and THz radiation and details development of an atom-based imaging system for THz frequency fields. Room temperature caesium atoms are excited to a Rydberg state using resonant infrared lasers and the response of these atoms to THz radiation is studied in multiple ways. We look at the absorption of the initial excitation laser and show how the observed lineshape changes in response to an applied THz field. We use this to measure the power of a THz field across a range of 350 GHz. These measurements also lead us to determine values for the quantum defects in caesium without reliance on data from any other sources. These values agree within error with those previously reported in literature. We study the optical fluorescence emitted by the laser-excited \nvapour and develop a model to predict this emission. We highlight deviations from this model and suggest possible mechanisms for this discrepancy. We show how this model can be used to determine the optimum transition for atom-based THz imaging within our experimental parameters. We demonstrate a high-speed THz imaging system using Rydberg atoms and show that it has near diffraction-limited \nspatial resolution and is able to capture images at kHz framerates. We measure the minimum THz power that the system can detect and show how it compares to other technologies. This system is then used to perform some proof-of-principle experiments to highlight its usefulness in commercial settings. Using optical elements \ndesigned and produced in-house we create and characterise THz vortex beams with both radial and azimuthal phase. We show how these beams are similar to Laguerre-Gauss modes and highlight some important differences.
This thesis studies the response of the interaction between Rydberg atomic vapour and a THz frequency field. When Caesium atoms at room temperature are excited to a Rydberg state using three infrared lasers and a 0.55 THz field resonant with the 14P3/2 → 13D5/2 transition is applied, the atoms respond by emitting a green optical fluorescence corresponding to the 13D5/2 → 6P3/2 decay. This response is exploited to investigate the absorption coefficient for different polymer materials that transmit well in the THz frequency range using the Beer–Lambert law. We calibrate the system to obtain a measure of THz intensity. As the THz imaging system is highly sensitive to environmental changes, and to show that our results are consistent, we provide a comparison of results between our atomic detection method and a commercial thermal power meter. Additionally, we measure the absorption coefficient of the same materials at a frequency of 1.1 THz, and the results are compared with those measured at 0.55 THz. The THz imaging system is also used to perform some experiments in order to demonstrate its effectiveness in real-world applications. The system provides an interesting image contrast in the case of a sample containing two different polymer materials measured at two THz frequencies. The result is a proof-of-concept that multispectral THz imaging can provide additional information and is motivation to improve our THz imaging system by introducing a dual-species THz imager. We also investigate the polarisation spectroscopy of an excited-state transition of rubidium vapour at room temperature as a step towards a rubidium THz imaging system. The narrow dispersive signal produced by this spectroscopy technique is ideal for laser frequency stabilisation of excited-state transitions.
Terahertz imaging has become increasingly important across various fields and practical production applications. Achieving both high sensitivity and high speed remains a primary challenge for most current THz imaging technologies. In this work, we present an imaging system based on Rydberg atomic vapor operating at frequencies exceeding 1 THz. By utilizing Cesium 133 atoms coupled with THz waves, de-excitation radiation generated after atomic excitation to Rydberg states converts invisible THz waves into visible light, enabling the acquisition of spatial information and intensity distributions of THz fields. The system achieves a minimum detectable power of 330 fW /s 1/2 per (2.4×2.4) μm 2 , an imaging resolution of approximately 1.7 mm, and an imaging bandwidth of 8.6 MHz. Additionally, the theoretical imaging rate can exceed 1 MHz. The Rydberg-atom-based THz imaging system exhibits a simple structure and is amenable to miniaturization. This THz imaging method holds promise for advancing applications in THz nondestructive testing, biomedical imaging, and concealed object detection.
Abstract Rydberg-atom–based Terahertz (THz) reflection imaging provides ultra-high sensitivity and, in principle, the potential for MHz-level imaging speed, overcoming the limitations of THz transmission imaging for strongly absorbing samples. Here, we experimentally demonstrate a Rydberg-atom THz reflection imaging system, converting reflected THz fields into visible fluorescence using a cesium vapor cell along the 14 P 3/2 → 13 D 5/2 → 6 P 3/2 pathway, and sequentially imaging the fluorescence with a sCMOS camera. The system achieves clear reflection images with a minimum resolvable line-pair period of approximately 1.26 mm, and a minimum detectable power of 2.41 fW·s -1/2 per (6.5×6.5) μ m 2 pixel. Representative applications include reflection imaging of metallic samples, discrimination of Polar Liquids, and non-contact visualization of superficial human vasculature and finger motion. This system offers a promising route toward high-frame-rate, room-temperature, full-field THz imaging for both industrial and scientific applications.
Atomic sensing and measurement of millimeterwave (mmW) and THz electric fields using quantum-optical EIT spectroscopy of Rydberg states in atomic vapors has garnered significant interest in recent years towards the development of atomic electric-field standards and sensor technologies. Here we describe recent work employing small atomic vapor cell sensing elements for near-field imaging of the radiation pattern of a Ku- band horn antenna at 13.49 GHz. We image fields at a spatial resolution of λ/10 and measure over a 72 to 240 V/m field range using off-resonance AC-Stark shifts of a Rydberg resonance. The same atomic sensing element is used to measure sub-THz electric fields at 255 GHz, an increase in mmW-frequency by more than one order of magnitude. The sub-THz field is measured over a continuous ±100 MHz frequency band using a near-resonant mmW atomic transition.
We provide theoretical demonstration of a quantum antenna based on Rydberg atoms for detection of THz field. We investigate optical properties of Rydberg cesium atoms based on electromagnetically induced transparency (EIT) for four-level excitation scheme. In this quantum system, probe and coupling fields applied between levels 6S1/2→6P3/2 (D2 transition of 133Cs) and 6P3/2→20D5/2, respectively. One E-field at THz frequency (1.026THz) drives the 20D5/2→22P3/2 Rydberg transition of caesium atoms. We study effect of intensity of the coupling and THz fields on the optical properties of the probe light. We find that the absorption of the probe light through the atomic vapour cell efficiently affected by the intensity of the THz and coupling fields. Moreover, the effect of the incoherent pumping field on the EIT resonance in the presence of the THz field is also investigated. The proposed model is of major significance for THz detection based on Rydberg atoms – based quantum antenna via incoherent pumping field. In this paper, different technology based on incoherent pumping field is presented to enhance the detection accuracy and efficiency, hoping to inspire more possibilities in the improvement of metrics of Rydberg atom-based electric field sensing and broadness of application scenarios.
We present a millimeter-wave imaging system based on fluorescence induced by Autler-Townes splitting in a four-level atomic Rydberg system. By employing counter-propagating probe and coupling beams, we create a plane of atoms in a dark state that is sensitive to incident mmWaves at 91.4 GHz. Objects placed in the mmWave beam path diffract the beam which, when imaged onto the cell using a PTFE lens, induce AT splitting in regions of higher intensity, increasing 780 nm fluorescence at 780 nm. Imaging this fluorescence with an optical camera effectively images the incident mmWave field. The system demonstrates a temporal response time of 16.41 µs, corresponding to a maximum frame rate exceeding 60 kHz, and achieves diffraction-limited spatial resolution. Additionally, we show the ability to image vortex modes generated by 3D-printed phase plates, further demonstrating the system’s versatility. This approach provides a pathway for high-speed and highresolution mmWave imaging, with potential applications in security, communications, and scientific research.