There is much interest in employing terahertz (THz) radiation across a range of imaging applications, but so far, technologies have struggled to achieve the necessary frame rates. Here, we demonstrate a THz imaging system based upon efficient THz-to-optical conversion in atomic vapor, where full-field images can be collected at ultrahigh speeds using conventional optical camera technology. For a 0.55-THz field, we show an effective $1\text{−}{\mathrm{cm}}^2$ sensor with near diffraction-limited spatial resolution and a minimum detectable power of $(190\pm 30)\mathrm{fW}{\mathrm{s}}^{-1/2}$ per $(40\times 40)\mu {\mathrm{m}}^2$ pixel capable of video capture at 3000 frames per second. This combination of speed and sensitivity represents a step change in the state of the art of THz imaging and will likely lead to its uptake in wider industrial settings.

This tutorial aims to provide details on the underlying principles and methodologies of atom-based terahertz imaging techniques. Terahertz imaging is a growing field of research which can provide complementary information to techniques using other regions of the electromagnetic spectrum. Unlike infrared, visible and ultraviolet radiation, terahertz passes through many everyday materials, such as plastics, cloth and card. Compared with images formed using lower frequencies, terahertz images have superior spatial resolution due to the shorter wavelength, while compared to x-rays and gamma rays, terahertz radiation is non-ionising and safe to use. The tutorial begins with the basic principles of terahertz to optical conversion in alkali atoms before discussing how to construct a model to predict the fluorescent spectra of the atoms, on which the imaging method depends. We discuss the practical aspects of constructing an imaging system, including the subsystem specifications. We then review the typical characteristics of the imaging system including spatial resolution, sensitivity and bandwidth. We conclude with a brief discussion of some potential applications.

Understanding the interactions between atoms and light is at the heart of atomic physics. Being able to ‘experiment’ with various system parameters, produce plots of the results and interpret these is very useful, especially for those new to the field. This tutorial aims to provide an introduction to the equations governing near-resonant atom-light interactions and present examples of setting up and solving these equations in Python. Emphasis is placed on clarity and understanding by showing code snippets alongside relevant equations, and as such it is suitable for those without an excellent working knowledge of Python or the underlying physics. Hopefully the methods presented here can form the foundations on which more complex models and simulations can be built. All functions presented here and example codes can be found on GitHub.

We demonstrate the rapid readout of terahertz orbital angular momentum (OAM) beams using an atomic-vapor-based imaging technique. OAM modes with both azimuthal and radial indices are created using phase-only transmission plates. The beams undergo terahertz-to-optical conversion in an atomic vapor, before being imaged in the far field using an optical CCD camera. In addition to the spatial intensity profile, we also observe the self-interferogram of the beams by imaging through a tilted lens, allowing the sign and magnitude of the azimuthal index to be read out directly. Using this technique, we can reliably read out the OAM mode of low-intensity beams with high fidelity in 10 ms. Such a demonstration is expected to have far-reaching consequences for proposed applications of terahertz OAM beams in communications and microscopy.

We demonstrate far-field super-resolution imaging in the terahertz (THz) frequency band by using a structured illumination via the virtually structured detection (VSD) method. Leveraging our previously reported high-speed, high-sensitivity atomic-based THz imager, we achieve a resolution enhancement of (74 3)% at 0.55 THz, without the aid of deconvolution methods. We show a high-speed THz imaging system is compatible with the use of advanced optical techniques, with potential disruptive effects on applications requiring both high speed and high spatial resolution imaging in the THz range.

We present new measurements of quantum defects and core polarizabilities in cesium ( Cs 133 ), based on transition frequency measurements between Rydberg states ( 14 ≤ n ≤ 38 ) obtained through THz and radio-frequency spectroscopy in a thermal atomic vapor. We perform a global fitting of our measurements to extract quantum defects of the s 1 / 2 , p 1 / 2 , p 3 / 2 , d 3 / 2 , d 5 / 2 , f 5 / 2 , f 7 / 2 , g 7 / 2 , and g 9 / 2 electronic states. Transitions between high angular momentum states ( 4 ≤ ℓ ≤ 8 ) were measured to extract the Cs + dipole and quadrupole polarizabilities. We find α d = 15.729 ( 18 ) a 0 3 and α q = 76.3 ( 1.9 ) a 0 5 respectively. Using these results, and accounting for the covariances between parameters in the global fit, the energies for n ℓ j Rydberg states can be estimated to a precision of a few MHz or less.