Ya. I. Khanin **. **Lectures on quantum radiophysics.

Theoretical fundamentals of quantum radiophysics are stated. Quantum mechanics is formulated in terms of density matrix: quantum theory of an electromagnetic field, quantum theory of radiation and absorption of electromagnetic waves by a substance including elements of nonlinear optics and quantum theory of relaxation are considered. A stationary response of a two-level quantum system to an assigned electromagnetic field is thoroughly examined, basic non-stationary effects of laser optics (nutation, self-induced transmittance, optical echo, etc.) are described. Operation principles of lasers are presented, most commonly used types of lasers are reviewed. Conversion to an equivalent two-level description for three- and four-level active media is considered. A semi-classical self-consistent set of equations for a laser is given, its simplification in the balance approximation is discussed, and dynamic characteristics of single-mode lasers are studied.

The book is intended for students and post-graduated of radiophysics and optical specialities, as well as for experts in the field of quantum electronics and laser physics.