Tunable Tesla-Scale Magnetic Attosecond Pulses through Ring-Current Gating

Abstract

Coherent control over electron dynamics in atoms and molecules using high-intensity circularly polarized laser pulses gives rise to current loops, resulting in the emission of magnetic fields. We propose, and demonstrate with ab initio calculations, "current-gating" schemes to generate direct or alternating-current magnetic pulses in the infrared spectral region, with highly tunable waveform and frequency, and showing femtosecond-to-attosecond pulse duration. In optimal conditions, the magnetic pulse can be highly isolated from the driving laser and exhibits a high flux density (∼1 T at a few hundred nanometers from the source, with a pulse duration of 787 attoseconds) for application in forefront experiments of ultrafast spectroscopy. Our work paves the way toward the generation of attosecond magnetic fields to probe ultrafast magnetization, chiral responses, and spin dynamics.

Figure 1

(a) Scheme of a circularly polarized electric pulse inducing a long-lived stationary azimuthal current, whose origin is associated with a different electron population in the p₊ and p_– valence orbitals. The resulting magnetic field is static and linearly polarized along the longitudinal axis, and it persists after the laser pulse. (b) Dependence of the long-lived current amplitude on the driving peak intensity for different incident central wavelengths (267 nm is displayed in purple, 400 nm in blue, and 800 nm in orange). (c) The ultrafast buildup of the ring current (black dashed line) and the magnetic field (blue solid line) at the center of the current loop for a driving wavelength of 267 nm and peak intensity of 1.4 PW/cm². We also depict in panel c the temporal profile of the incoming circularly polarized electric pulse (green line in an arbitrary vertical axis).

Figure 2

Current-gating schemes for waveform control of ultrashort magnetic pulses. (a) The synthesis of two time-delayed counter-rotating circularly polarized temporally gates the emission of a DC magnetic pulse by limiting the temporal window of the ring current. (c) The duration of the magnetic burst can be tuned by the time delay t_d. The inset shows the linear relation of the full-width at half-maximum (fwhm) intensity of the magnetic field with the time delay, with the shortest pulse corresponding to 787 attoseconds. By adding a third gating pulse in panel (b), we synthesize in panel (d) the profile of a single-cycle magnetic pulse, whose wavelength can be tuned with the time delay between the pulses.

Figure 3

Illustration of (a) a single ring-current producing a magnetic field B₀ at the center and (b) a macroscopic distribution. (c) Decay of the magnetic field (relative to the field at the origin) along the longitudinal axis for a single loop (cyan), a 2D loop distribution of 401 × 401 nm² (yellow), and a 3D target of 401 × 401 × 101 nm³, which is experimentally accesible (green). (d) Magnetic flux at 100 nm from the edge of the 2D distribution as a function of the number of loops for different average separation distances ⟨d⟩.