Reverse flow of light energy at the focus

As early as 424 BC In the play of the ancient Greek poet, Aristophanes "Cloud" mentioned that fire can be mined by focusing sunlight. From then to this day, the study of light behavior in focus is of interest to optics. In the focus, light converges from different areas of space, which has different amplitude, phase and state of polarization. In order to adequately describe the light in focus, all six projections of the vectors of the tension of the electric and magnetic fields should be used.
In 1959, B. Richards and E. Wolf created an analytical theory of strictly description of light near an acute focus, which is still used. Today, it is possible to check its correctness using a different solution of the Maxwell equations system within one of many commercial software products. The numerical method of solving the Maxwell equations (FDTD method) was developed by A. Taflov and M.I. Bodevin in 1975
One of the interesting optical effects, which takes place in the acute focus of light fields, is the effect of the reverse flow of energy, which was first mentioned in 1920 by V.S. Ignatovsky. In this book, the effect of the reverse flow of energy in the focus of laser light is studied theoretically on the basis of Richards-Wolf"s formalism, numerically on the basis of a different solution of Maxwell’s equations and experimentally. The nature of this effect and the conditions under which it arises.
The book is intended for a wide range of scientists, engineers working in the field of optics, photonics, laser physics, optical technologies, and optical instrumentation. It can also be useful bachelors and master in specialties "Applied Mathematics and Physics", "Applied Mathematics and Informatics", "Optics" and graduate students specializing in these areas