Infrared and Millimeter Waves, Volume 16: Electromagnetic Waves in Matter, Part III deals with electromagnetic devices based on infrared and millimeter waves. This book covers infrared optoacoustics; freestanding fine-wire grids for use in millimeter- and submillimeter-wave spectroscopy; and population inversion and far-infrared (FIR) emission of hot electrons in semiconductors. The theory on distributed feedback lasers with weak and strong modulations is also considered. This monograph is comprised of six chapters and begins with a discussion on the optoacoustic effect in the infrared, with emphasis on where optoacoustics and infrared physics combine in the areas of Fourier spectroscopy, optically pumped FIR lasers, and photothermal non-destructive remote material evaluation. The next chapter presents the basic principles of the theory on distributed feedback lasers with weak and strong modulations, together with results of analytical and numerical calculations. The following chapters focus on the construction of freestanding fine-wire grids for use in millimeter- and submillimeter-wave spectroscopy; general equations for the mean distance between impurity ions in solid-state devices, signal vectors in communication theory, and stars in the solar neighborhood; and prospects for hot-carrier systems in active FIR solid-state devices. The final chapter is devoted to quenched germanium and its FIR optical properties. This text will be a valuable resource for physicists and electronics and electrical engineers.