Scattering of ultrashort laser pulses on “ion‐sphere” in dense plasmas

Abstract

Scattering of ultrashort electromagnetic pulses on the dense strongly coupled plasma is under consideration in the frame of hard ion sphere model. The electron distribution inside the ion sphere is obtained from self-consistent solution of the Shrodinger equation for bound electrons and the Poisson equation for free electrons. The electron density distribution is determined by plasma electron temperatures. The ion density of Al plasmas under consideration is of the order of 10 20 -10 22 cm −3 , the electron temperature changes between 54 and 816 eV. Dynamical polarizability of the hard sphere determining the scattering cross sections is calculated using the modified local plasma frequency approximation. The spectrum of scattering cross section has maxima in the vicinity of the mean plasma frequency. Dependencies of scattering probability on carrier frequency and pulse duration are analysed in detail. The transition of the total scattering probabilities from nonlinear time dependence at small times to standard linear ones with the increase of pulse duration is demonstrated. KEYWORDSdynamical polarizability, ion sphere, local plasma frequency, scattering cross section, scattering probability, ultrashort laser pulse INTRODUCTIONModern progress in generation of ultrashort laser pulses (USPs) [1,2] requires the development of adequate methods for the description of the interaction of such pulses with different targets. The conventional approach based on the concepts of probability per unit time and intensity of the radiation used for long quasi-monochromatic pulses appears to be insufficient in the case of USP. [3] In fact, probability per unit time arises in quantum mechanical consideration as a limit when the pulse duration tends to infinity. [4] In such an approach, it is assumed that the timescale of the target internal motion is much smaller than the pulse duration. The last assumption becomes incorrect for sufficiently short pulses. Then, one should describe the photoprocess in terms of total probability during the entire time of the pulse action and electric field strength in the pulse instead of probability per unit time and pulse intensity. [5] The conditional consideration of radiation scattering in ideal plasmas is based on the account of free electron density fluctuations and fluctuations of screened electron density near ions. These two contributions to scattering probabilities are the sum of Thomson scattering on free electrons and transition scattering on the Debye screening sphere. [6] In contrast with ideal plasmas, the electron structure in strongly coupled plasmas is determined by strong ion-ion correlations resulting in the formation of a plasma structure in the form of isolated hard ion spheres (the so called "ion sphere model," see ref.[7]). Ion spheres are separated by ion's sphere radii of the order of interion distances and contain both bound and free electrons that are distributed strongly nonuniformly. The last makes it actual to look for light scattering on such structures.

X-ray diffraction analysis of matter taking into account the second harmonic in the scattering of powerful ultrashort pulses of an electromagnetic field

“…The theoretical basis for carrying out this kind of research is rather poorly developed and often does not take into account the aspects of scattered USPs 14,16,[23][24][25][26][27][28] , which is why theoretical studies of the aspects of USPs in their scattering by various polyatomic systems are currently being carried out. In spite of this, the magnetic component of such USPs is usually not taken into account.…”

Diagnostics of Nanosystems with the Use of Ultrashort X-Ray Pulses: Theory and Experiment (Brief Review)

“…To determine spectra of the scattering of USPs by any structures using any quantum theory, it is first necessary to evaluate the wavefunction of an atomic electron in the field of a pulse. The problem of the determination of this wavefunction is fundamental and exists not only in the scattering theory [73][74][75][76][77][78][79] but also in many other fields of physics, e.g., the theory of ionization in intense USPs [80]. X-ray USPs are spatially inhomogeneous; consequently, their theoretical description is complicated because the dipole approximation is inapplicable.…”

Scattering of X-ray Ultrashort Pulses by Complex Polyatomic Structures

“…The theory of X-ray diffraction is typically constructed in the approximation of plane wave scattering of infinite time duration [ 15 ]. The scattering processes of femto- and particularly attosecond pulses on such structures have not been sufficiently studied and are actively developed in our time [ 6 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Usually such theories consider simple systems, such as atoms, simple molecules, model systems, systems of one-part atoms, etc.…”