Ablative Rayleigh–Taylor instabilities are analyzed in terms of an incompressible fluid model. A generalized surface wave dispersion relation can be derived for arbitrary step-profiles with ablative mass and heat flow. A systematic overview on different regimes of ablative stabilization and growth reduction is given. Convective stabilization by the incoming and outcoming flows are found included as upper and lower limits on the instability growth. Applications for self-consistent steady-state conditions are discussed and a comparison is made with previous numerical work.
An incompressible fluid model of the ablative Rayleigh–Taylor instability [Phys. Fluids 29, 2067 (1986)] is generalized to include self-consistent diffuse boundaries. With diffuse boundaries the incompressible model is found to be in excellent agreement with a number of previous stability studies of laser ablation. The present theory can predict the scaling of the instability cutoff over an extended parameter range and its dependence on the heat conduction law. It is found that more favorable stability behavior can be obtained both for weak and strong thermal diffusion. Furthermore a strong dependence of the stabilization mechanism on the functional form of the heat conductivity is indicated. Representative conditions for laser ablation are identified and discussed in detail.
The electron–ion collision frequency in a strong laser field is calculated in the framework of the quantum Vlasov theory in first-order Born approximation. Using a Wigner representation of the density matrix, the collision frequency can be expressed in terms of the Lindhard dielectric function and a close correspondence between classical and quantum-mechanical approaches can be obtained. Asymptotic formulas for the high-frequency collision frequency in weak and strong electric fields are obtained and compared with complete numerical calculations. The basic strong-field behavior can be explained in terms of the cold plasma model.
Radiation conditions are introduced as an exact method to truncate numerical solutions of the timedependent Schrödinger-equation at the boundaries of the numerical grid. A rigorous derivation of radiation conditions is given by the Green-function method for one-and three-dimensional regions. An accurate finitedifference representation is obtained for a one-dimensional region. The method is applied to calculations of strong-field photoionization. The calculation of ionization probabilities and energy spectra by the truncated solution is illustrated. ͓S1050-2947͑97͒06107-6͔PACS number͑s͒: 32.80.Rm, 31.15.Ϫp
A relativistic treatment of strong-field photoionization based on the phase-space-averaging method is presented. A procedure is described for preparing a relativistic microcanonical ensemble of the atomic ground state and for calculating the final compensated energies for relativistic electrons. The method is applied to over-the-barrier ionization of hydrogen with ultrashort laser pulses. Ionization probabilities and electron energy spectra have been obtained for laser pulse amplitudes near and well above the atomic unit. The results are in excellent agreement with previous experiments under similar conditions. In sufficiently strong fields, saturation of ionization is shown to limit the attainable electron energies.
Electron-ion collisions in the presence of a strong laser field lead to a distribution of fast electrons with maximum energy Emax=(k0+2v0)2∕2(a.u.), where k0 is the impact and v0 the quiver velocity of the electron. The energy spectrum is calculated by two approaches: (1) The time-dependent Schrödinger equation is numerically solved for wave packet scattering from a one-dimensional softcore Coulomb potential. Multiphoton energy spectra are obtained demonstrating a separation of the energy spectrum into an exponential distribution for transmission and a plateau distribution for reflection. (2) The energy spectrum is analytically calculated in the framework of classical instantaneous Coulomb collisions with random impact parameters and random phases of the laser field. An exact solution for the energy spectrum is obtained from which the fraction of fast electrons in the plateau region can be estimated.
Collective absorption of intense laser pulses by atomic clusters is studied by PIC simulations. The cluster is modeled in two-dimensional calculations as a cylindrical plasma column with a diameter of D ϭ 6.4 nm and an initial electron density of n e0 ϭ 10 23 cm Ϫ3 . The frequency and intensity dependence of absorption is discussed. It is found that nonresonant absorption by electron emission increases as a power law with the laser intensity. The absorbed energy per electron reaches a maximum of about W max ϭ mv p 2 D 2~v p : plasma frequency, m: electron mass! at the intensity where ionization saturates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.