Ultrashort-pulse laser plasmas: Fraction of hot electrons escaping from the target and electron spectra in planar and spherical geometry

Abstract

Hot electrons generated upon interaction of ultrashort, intense laser pulses with solid targets have many applications in various fields of physics. In this paper a simple theory is developed which allows calculation of the fraction of electrons which escape from the target and the altered electron energy distribution at a distance from the target. The theory is worked out in planar and spherical geometry. It is exact if the electrons are instantaneously generated. In planar geometry all particles eventually return to the target. In spherical geometry, however, a fraction of the electrons are found to escape and, moreover, the electron energy spectrum at large distances approaches an asymptotical one. Two examples of initial electron distributions are treated in detail, viz., an exponential and a Lorentzian distribution.

Laser-Driven Ultrafast Field Propagation on Solid Surfaces

“…where r c ¼ 2:82 Â 10 À15 m is the classical electron radius [17,18]. The main source of error in the calculation of 1 comes from the choice for r 0 .…”

Picosecond imaging of low-density plasmas by electron deflectometry

“…On the basis of the model described above we have carried out simulations coupling the result of a hydrodynamic plasma code [18] (which solves the equations of motion of the electrons in Lagrangian coordinates) to the general particle tracer code for calculating electron-beam propagation [19]. The temporal evolution of the peak intensity of the focused line is presented in Fig.…”

Highly intensified emission of laser-accelerated electrons from a foil target through an additional rear laser plasma

“…However, most laser-accelerated electrons cannot escape from the laser plasma because they are trapped by a strong quasistatic electric field, called the sheath field, produced around the steep density gradient boundary between the solid/plasma and the vacuum [19,20]. Furthermore, theoretical work shows that the fraction of fast electrons escaping from the laser plasma decreases as the initial target size decreases because the fast electrons are trapped by their own potential [21]. Almost all electrons are bound within the solid target, and only about 1% of the hot electrons can escape [10,22].…”

“…They also observed that suppressing the sheath field increased the number of escaping electrons. For the fast electrons to reach far enough from the target as escaping electrons and not return to the laser plasma and reach the detectors, however, the potential produced by fast electrons must also be decreased [21]. It was predicted that the potential depends on the number of accelerated electrons, temperature, and initial target size.…”

“…4 with the scale length. To explain the dependence of the number of escaping electrons on time delay, we apply a simple model proposed by Fill [21] and used by Quinn et al [22]. When Maxwellian electrons are released from an initially neutral sphere of radius r 0 , the fraction of electrons, ξ ∞ , that can escape from the potential they produce may be estimated by…”