Quantum theory of scattering of ultrashort electromagnetic field pulses by polyatomic structures

In the theoretical description of the scattering of ultrashort electromagnetic field pulses (USP), the semiclassical approach is usually used, where the electromagnetic field is classical and the atomic system is quantum. This article shows the need to take into account the quantum properties of scattered photons, it is that if we take into account the interaction of an USP with a system of atoms, then with the scattering of the pulse it is possible to generate a given number of n photons with a probability P _n. The main equations for the probability P _n of the production of n photons and their average energy E _n are found in an analytical form. It is shown that only for a certain number of atoms in the system can multiphoton scattering of ultrashort electromagnetic field pulses occur, where it is necessary to take into account the obtained basic equations for P _n and E _n. Various biomolecules, nanosystems and polyatomic structures can consist of such a number of atoms. This is especially important because experiments are currently being conducted with such structures at the present time using high-power ultrashort laser pulses. It is shown that the developed theory in limiting cases turns into well-known approaches of single-photon and multi-photon theories.