  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 andbandwidth. We conclude with
a brief discussion of some potential applications
