The imaginary part of the high-harmonic cutoff
arXiv:2003.00277 · doi:10.1088/2515-7647/ab8f1e
Abstract
High-harmonic generation - the emission of high-frequency radiation by the ionization and subsequent recombination of an atomic electron driven by a strong laser field - is widely understood using a quasiclassical trajectory formalism, derived from a saddle-point approximation, where each saddle corresponds to a complex-valued trajectory whose recombination contributes to the harmonic emission. However, the classification of these saddle-points into individual quantum orbits remains a high-friction part of the formalism. Here we present a scheme to classify these trajectories, based on a natural identification of the (complex) time that corresponds to the harmonic cutoff. This identification also provides a natural complex value for the cutoff energy, whose imaginary part controls the strength of quantum-path interference between the quantum orbits that meet at the cutoff. Our construction gives an efficient method to evaluate the location and brightness of the cutoff for a wide class of driver waveforms by solving a single saddle-point equation. It also allows us to explore the intricate topologies of the Riemann surfaces formed by the quantum orbits induced by nontrivial waveforms.
arXiv commentSupplementary Material is available at https://imaginary-harmonic-cutoff.github.io with a stable version at https://doi.org/10.5281/zenodo.3692562
References in corpus (18)
- Generation of phase-matched circularly-polarized extreme ultraviolet high harmonics for magnetic circular dichroism spectroscopy
- Symmetries and selection rules in Floquet systems: application to harmonic generation in nonlinear optics
- Symphony on Strong Field Approximation
- High-order above-threshold ionization: the uniform approximation and the effect of the binding potential
- It is all about phases: ultrafast holographic photoelectron imaging
- Spin conservation in high-order-harmonic generation using bicircular fields
- Bifurcations of Periodic Orbits and Uniform Approximations
- Probe of Multi-electron Dynamics in Xenon by Caustics in High Order Harmonic Generation
- Optimisation of Quantum Trajectories Driven by Strong-field Waveforms
- Control of attosecond light polarization in two-color bi-circular fields
- Laser-driven recollisions under the Coulomb barrier
- Slalom in complex time: emergence of low-energy structures in tunnel ionization via complex time contours
- Strong-field approximation in a rotating frame: High-order harmonic emission from p states in bicircular fields
- Pulse-shape control of two-color interference in high-order-harmonic generation
- Phase properties of the cut-off high-order harmonics
- Suppression of individual peaks in two-colour high harmonic generation
- Spectral caustic in two-color high harmonic generation: role of Coulomb effects
- Attosecond pulse shaping using partial phase matching