Design Of The Imaging System Of Terahertz Radiation Using A Rydberg Atom Photocathode

THz technology has great scientific value and broad application prospects in objectimaging, environmental monitoring, medical diagnostics, radio astronomy, broadbandmobile communications, especially in satellite communications and military radar, etc. Ascompared to microwave, X-ray and magnetic resonance imaging, THz imaging can notonly give the density information of the object, but also give information of physicalproperties, such as dielectric constant, refractive index and absorption coefficient. Thus,THz imaging technology has become an important aspect of THz applications.Rydberg atoms in the outermost layer of the alkali metal only have one electron, whenthe only electron is excited to higher quantum states, the electron binding energy of thenucleus become smaller. The electron can be ionized when the electron absord THz photonenergy, and the photoelectric conversion can be achieved. In this thesis, we report on theimaging system of terahertz radiation which using a Rydberg atom photocathode. When theatoms through the electric field, the Stark effect will happen, resulting in level splitting.When Rydberg atoms in a particular quantum state receive THz radiation, due to havinglarger atomic photoionization cross section, atoms in a weakly bound Rydberg state can beionized by THz photon. By controlling the movement of ions which are ionized, coupledwith the ion optics system and subsequent image processing system, we can achieve THzimaging.First of all, we analyse Rydberg atoms in the theoretical level to understand theircharacteristics in electric field and THz field, in this way to improve the efficiency andaccuracy of the preparation and ionization of Rydberg atoms. Secondly, experiments areconducted to verify the impact of field parameters on ionization process and to understandthe impact of atom density, degree of vacuum, intensity of the electric field and otherconditions on the ionizing process. Finally, based on the working principle of the imagingsystem, the active region, the vacuum chamber, the receiving circuit and the ion opticalsystem are designed and built.The thesis provides a new methodt for THz radiation detection using Rydberg atoms,and report on a new THz imaging system. Compared to the existing imaging technology,the new imaging system has its advantages: working with both continuous wave and pulsedwave, imaging at a high speed, wavelength-selective, etc. Therefore the new THz imagingsystem has important theoretical and practical value.