How to Use Lasers for Imaging Attosecond Dynamics of Nuclear Processes

We identify a laser configuration in which attosecond electron wave packets are ionized, accelerated to multi-MeV energies, and refocused onto their parent ion. Magnetic focusing of the electron wave packet results in return currents comparable with large scale accelerator facilities. This technique opens an avenue towards imaging attosecond dynamics of nuclear processes.

Figure 1

Schematic of the laser setup consisting of two equal handed, circularly polarized, counterpropagating laser pulses with equal intensities. Electric and magnetic fields are parallel, point along the arrows, rotate in space along the propagation axis, and vary sinusoidal in time and $90°$ out of phase.

Figure 2

(a) Current of the returning electron versus time (full line). The arrows are associated with Fig. 3; kinetic energy of the returning electron versus time (dashed line). (b) Spectrum of the returning electron pulse. The parameters are laser peak intensity $I={10}^{21}\mathrm{W}/\mathrm{c}{\mathrm{m}}^{\mathrm{2}}$, wavelength $\lambda =800\mathrm{n}\mathrm{m}$. The laser electric field is described by a (plane wave) cos-carrier, i.e., is maximum at time $t=0$; hydrogenlike ion, $Z=15$, $I_p=3.1\mathrm{k}\mathrm{e}\mathrm{V}$.

Figure 3

Same parameters as in Fig. 2; the numbers refer to the numbers in Fig. 2. The full lines denote the $1/e$ width of the transversal electron wave packet at $t_r$. The three wave packets have birth times, $t_{b1}=7.3\mathrm{a}.\mathrm{u}.$, $t_{b2}=8.2\mathrm{a}.\mathrm{u}.$, and $t_{b3}=5.9\mathrm{a}.\mathrm{u}.$, and return times $t_{r1}=87\mathrm{a}.\mathrm{u}.$, $t_{r2}=84\mathrm{a}.\mathrm{u}.$, and $t_{r3}=92\mathrm{a}.\mathrm{u}.$

Figure 4

(a) Volume averaged electron current density and electron kinetic energy versus ion charge state $Z$; (b) laser peak intensity versus $Z$. Peak laser intensity in (b) was chosen to ionize $80\%$ of the ion; other parameters: super-Gaussian pulse shape with 40 fs FWHM duration, wavelength $\lambda =800\mathrm{n}\mathrm{m}$. The return energy and the peak current have been averaged over the interval $x=\pm 1\mu \mathrm{m}$, where recollision takes place. Note that the averaged current is smaller than the nonaveraged current depicted in Fig. 2a.