Free electron model

About: Free electron model is a research topic. Over the lifetime, 4678 publications have been published within this topic receiving 103535 citations.

Sub-cycle time resolution of multi-photon momentum transfer in strong-field ionization

Abstract: During multi-photon ionization of an atom it is well understood how the involved photons transfer their energy to the ion and the photoelectron. However, the transfer of the photon linear momentum is still not fully understood. Here, we present a time-resolved measurement of linear momentum transfer along the laser pulse propagation direction. Beyond the limit of the electric dipole approximation we observe a time-dependent momentum transfer. We can show that the time-averaged photon radiation pressure picture is not generally applicable and the linear momentum transfer to the photoelectron depends on the ionization time within the electromagnetic wave cycle using the attoclock technique. We can mostly explain the measured linear momentum transfer within a classical model for a free electron in a laser field. However, corrections are required due to the interaction of the outgoing photoelectron with the parent ion and due to the initial momentum when the electron appears in the continuum. The parent ion interaction induces a measurable negative attosecond time delay between the appearance in the continuum of the electron with minimal linear momentum transfer and the point in time with maximum ionization rate.

g Value in Alkali-Metal Conduction-Electron Spin Resonance

Abstract: A method for examining the convergence of expansions of wave functions for nearly free electrons is presented. It is shown that Bardeen-type expansions of alkali-metal conduction-electron wave functions converge sufficiently slowly so that it is necessary, when calculating the value of a physical quantity to any given power of k, to include all terms of all orders in $u(\mathrm{k},\phantom{\rule{0ex}{0ex}}\mathrm{r})$ which contribute to that power. Consequently, wave-function expansions to third order in k which include the effects of spin-orbit interaction to first order are derived, in the spherical approximation, for these metals. Using these wave functions in Yafet's equation, the $g$ shift, to second order in|k| is expressed in terms of radial wave functions. The radial functions are evaluated numerically using the quantum defect nethod under four different approximations: (i) With and without the so-called "polarization correction" and (ii) with and without a term in the potential corresponding to an approximate self-consistent Hartree field due to the presence of other conduction electrons within the Wigner-Seitz sphere. The best agreement with experiment is obtained when the "polarization correction" is neglected and the Hartree term included. In this approximation the effective mass ratio, $\frac{m}{{m,}^{*}}$ is considerably closer to unity in the heavier alkali metals than was predicted by earlier calculations. The "polarization correction" is examined in detail in an unsuccessful effort to determine why it leads to a considerable decrease in the agreement with experiment.

Method of obtaining a medium having a negative absorption coefficient in the x-ray and ultraviolet spectral range and a laser for practical application of said method

Abstract: A plasma is formed from a material in which the ions possess discrete metastable energy states interacting with the energy states of the continuum which are populated by the free electrons of the plasma. Population inversion is achieved between a number of these metastable states and states of lower energy, negative absorption being then produced for the transition which couples the metastable states with said states of lower energy.

Electrically excited flowing gas laser and method of operation

Abstract: A method of and apparatus for producing spatially uniform discharges including producing laser action in a flowing gas by electrical means using first means to create electrons and second means to maintain the optimum electron environment to produce lasing action. Apparatus for and a method of producing spatially uniform discharges substantially throughout a large volume of gaseous medium by generating in an enclosure a substantially uniform density of free electrons in the medium and controlling the electron temperature of the free electrons to increase their average energy without substantially increasing their density that at a predetermined level and uniformity of both the density and temperature of the medium, a stable and uniform discharge is produced in the medium suitable for the intended use of the medium such as the generation and amplification of light waves by means of devices including gaseous media in which stimulated emission of radiation is provided by electrical means to create free electrons and maintain the optimum electron environment to produce lasing action, there being a particular relationship between the density of free electrons, gas pressure and gas velocity.