Figure 1

(a) (Color) Drift motion of a classical free electron subjected to a six-cycle cosine laser pulse (black curve). The electron was initially at rest. The red and the green curves show the trajectory of the classical electron if a static magnetic field of $30\mathrm{T}$ directed out of the $x\text{−}y$ plane and into it, respectively, is added to the laser pulse. (b) Wiggly electron motion along the laser propagation direction as a result of the interplay between the drift and the attraction of the nucleus. The electron is initially in the ground state of ${\mathrm{He}}^{+}$ and is subjected to a $1\text{−}4\text{−}1\text{−}\text{cycle}$ trapezoidal laser pulse of $780\mathrm{nm}$. The peak intensity of the pulse is $5.48\times {10}^{14}\mathrm{W}∕{\mathrm{cm}}^2$. The expectation value of the electronic wave function is shown vs the time of interaction. (c) Harmonic spectrum arising from the electron motion in (b).Reuse & Permissions

Figure 2

(Color) (a) Impact of a static magnetic field on the HHG spectrum shown in Fig. 1c. The black line represents the HHG spectrum in the case of vanishing static magnetic field, whereas the red and the green lines display the spectrum which occurs in the presence of a $30\text{−}\mathrm{T}$ magnetic field pointing out of the $x\text{−}y$ plane and into it, respectively. The orientation of the static magnetic field turns out to be crucial. (b) depicts a cutout of (a) focusing on the range of frequencies around $25.7{\omega }_L$, whereas ${\omega }_L$ denotes the laser angular frequency. (c) takes a closer look at the cutoff region of the HHG spectrum in (a).Reuse & Permissions

Figure 3

(Color) Center-of-mass motion of the electronic wave packet in the presence of an additional static magnetic field. The black line represents the electron motion for vanishing static magnetic field, as already depicted in Fig. 1b. The red and green curves show the cases, in which a static magnetic field of $30\mathrm{T}$ is added pointing out of the $x\text{−}y$ plane and into it, respectively.Reuse & Permissions

Figure 4

(Color) (a) Dipole acceleration and time profiles. The black, red, and green lines represent the dipole acceleration during interaction with the laser pulse, black, no static magnetic field; red, static magnetic field of $30\mathrm{T}$ pointing out of the $x\text{−}y$ plane; green, static magnetic field of $30\mathrm{T}$ directed into the $x\text{−}y$ plane. These dipole accelerations belong to the wiggly center-of-mass motion of the electronic wave packet depicted in Fig. 3. The blue and pink curves represent scaled time profiles of the frequency ranges centered at $25.7{\omega }_L$ and $99.3{\omega }_L$, respectively. For clarity, only time profiles in the case of vanishing static magnetic field are depicted. The peaks of the time profiles indicate the times when radiation of the corresponding frequency range is emitted. (b) Cutout of (a) focusing on dipole acceleration in the time interval at $195\mathrm{a.u.}$ (c) Cutout of (a) for dipole accelerations in the time interval at $160\mathrm{a.u.}$Reuse & Permissions

Figure 5

Dependence of the harmonic signal on the strength of the applied static magnetic field: (a) for the harmonic signal at a frequency of $25.7{\omega }_L$; (b) for the harmonic signal at a frequency of $99.3{\omega }_L$.Reuse & Permissions