Quantum Electrodynamics of Multiphoton Processes: Laser Physics, Thermal Radiation and Astrophysics

Abstract

QED description of multiphoton processes (MPP) requires special account of densities j(ω) of incident photons fluxes. The reaction rate of N -photon process in laser field is expressed via (j/j 0) N , where j 0=1/σ(ω)τ(ω) is the density of reactions saturation and/or the threshold of opening new channel of reaction, σ(ω) and τ(ω) are the cross-section of elastic scattering and its duration. The calculations lead to the known plateau in spectra of higher harmonics generations. Processes of multiphoton ionization require also determination of the duration of momentum accumulation τ(p) and reaction rate depends on its conformity with τ(N ω). The method is generalized onto temperature fields. It allows to consider phase transition of the first kind as radiative transition between two levels (gas and condensate) and to determine their thresholds as the function of temperature and latent heat; it predicts a characteristic emission of allocated latent heat. The second rich field for the MPP theory is astrophysics, in which they can explain some singularities of spectra of stars and nebulae bursts: disappearance or suppression of low-frequency parts of spectra via energy pumping into higher frequencies, narrowing of lines, etc. MPP of higher harmonics generation and pairs birth are possible also on vacuum loops.