arXiv subjects

André Staudte

Publications and source records attributed to André Staudte.

14 recordsLinked to original sources

arXiv2026

Sub-cycle metrology of bright quantum light

In quantum optics, quantization of the electromagnetic field typically occurs in a finite volume - a cavity - which results in discrete frequency modes where photons are created, annihilated and exchanged between such modes. As a result, evolution of quantum optical states is periodic in the carrier wave of the field, measurement protocols return cycle-averaged information, and any sub-cycle evolution that is foundational to many light-matter interactions, especially at high field strengths, remains hidden. Adapting an attosecond technique, here we capture the electric-field evolution of a quantum optical state, femtosecond bright squeezed vacuum, with sub-cycle precision. We find that it consists of many stochastic, time-localized bursts within each pump pulse whose phase randomly switches between two values. We exploit the random phase flips to generate quantum random bit sequences with a generation rate that can reach petahertz frequencies. In addition, the sub-cycle resolution allows us to measure coherence functions of the waveforms between any two times, which we explain with a superposition of time-limited modes. These results bridge attosecond metrology and quantum optics and pave the way to measuring quantum light-matter interactions as they evolve on a few-femtosecond time scale, and integrate quantum randomness in petahertz electronics.

quant-ph↗

arXiv2026

Phonon-driven decoherence of high-harmonic generation in the solid-state

High-harmonic generation in solids has emerged as a powerful probe of ultrafast electron dynamics and lattice motion, and recent theoretical work has suggested that thermally driven lattice fluctuations can act as an effective source of decoherence in the harmonic-generation process. However, a direct experimental link between high-harmonic emission and temperature-driven incoherent phonons has remained unclear. Here, we investigate the temperature dependence of high-harmonic generation in ultrapure silicon using reflection-geometry measurements over a wide temperature range. We observe that the harmonic yield increases significantly with decreasing temperature. To interpret these results, we introduce a one-dimensional atomic-chain model in which finite temperature is represented by random lattice displacements that mimic incoherent phonon fluctuations. The simulations reproduce the magnitude of temperature-dependent change of the harmonic signal and support a picture in which thermally induced lattice disorder enhances electron-hole decoherence, thereby reducing high-harmonic emission. Our results establish incoherent phonons as an important source of decoherence in solid-state high-harmonic generation.

cond-mat.mes-hall↗

arXiv2025

High Harmonic Generation from a Noble Metal

High-harmonic generation (HHG) in solids has typically been explored in transparent dielectrics and semiconductors. Metals have long been dismissed due to their strong reflectivity at infrared wavelengths. Here, we demonstrate HHG from silver - a noble metal - using few-cycle near-infrared laser pulses at near-normal incidence. Our results show that sub-cycle electron dynamics within the material's penetration depth can drive high-order harmonics, challenging the prevailing notion that metals are unsuited for infrared-driven strong-field processes. Despite silver's high reflectivity and large free-electron density, we observe nonperturbative harmonics extending into the extreme ultraviolet (up to 20 eV). Moreover, silver's multi-shot damage threshold proves surprisingly high (30 TW/cm^2) - comparable to large-bandgap dielectrics like magnesium oxide - thereby enabling intense strong-field processes in a metallic environment. Measuring the orientation dependence of the emitted harmonics reveals that the process arises from coherent electron dynamics in the crystal lattice, rather than from a plasma-driven mechanism. Time-dependent density-matrix simulations based on maximally localized Wannier functions show that low-order harmonics predominantly originate from conduction electrons near the Fermi surface (s- and p-type orbitals), whereas higher harmonics rely on bound d-electron excitations. These findings establish metals - long thought unfavorable for HHG - as a promising platform for ultrafast strong-field physics, extending high-harmonic spectroscopy to regimes in which lattice order and plasma formation directly intersect. This work expands the frontier of solid-state HHG to all-metallic attosecond pulse generation and underscores the potential of metals as robust XUV sources for advanced attosecond metrology.

physics.optics↗

arXiv2024

Towards simultaneous imaging of ultrafast nuclear and electronic dynamics in small molecules

When a chemical bond is broken, the molecular structure undergoes a transformation. An ideal experiment should probe the change in the electronic and nuclear structure simultaneously. Here, we present a method for the simultaneous time-resolved imaging of nuclear and electron dynamics by combining Coulomb explosion imaging with strong-field photoelectron momentum imaging. The simplest chemical reaction, H$_2^+$ $\rightarrow$ H$^+ +$ H, is probed experimentally for the delay-dependent kinetic energy release, and numerically for the transient change in the photoelectron spectra during the dissociation process. The three-dimensional Schrödinger equation is solved in the fixed-nuclei approximation numerically and the results are compared to those from a simple imaging model. The numerical results reflect the evolution in the electron density in the molecular ion as its bond is first stretched and then brakes apart. Our work shows how simple gas-phase chemical dynamics can be captured in complete molecular movies.

physics.atom-ph↗

arXiv2023

Imaging molecular orbitals with laser-induced electron tunneling spectroscopy

Photoelectron spectroscopy in intense laser fields has proven to be a powerful tool for providing detailed insights into molecular structure. The ionizing molecular orbital, however, has not been reconstructed from the photoelectron spectra, mainly due to the fact that its phase information can be hardly extracted. In this work, we propose a method to retrieve the phase information of the ionizing molecular orbital with laser-induced electron tunneling spectroscopy. By analyzing the interference pattern in the photoelectron spectrum, the weighted coefficients and the relative phases of the constituent atomic orbitals for a molecular orbital can be extracted. With this information we reconstruct the highest occupied molecular orbital of N$_2$. Our work provides a reliable and general approach for imaging of molecular orbitals with the photoelectron spectroscopy.

physics.atom-ph↗

arXiv2022

Observation and dynamic control of a new pathway of H$_3^+$ formation

We propose and experimentally demonstrate that the trihydrogen cation (H$_3^+$) can be produced via single photoionization of the molecular hydrogen dimer (H$_4$). Using near-infrared, femtosecond laser pulses and coincidence momentum imaging, we find that the dominant channel after single ionization of the dimer is the ejection of a hydrogen atom within a few hundred femtoseconds, leaving an H3+ cation behind. The formation mechanism is supported and well reproduced by an ab-initio molecular dynamics simulation. This is a new pathway of H$_3^+$ formation from ultracold hydrogen gas that may help explain the unexpected high abundance of H$_3^+$ in the interstellar medium in the universe.

physics.atm-clus↗

arXiv2021

Chiral high-harmonic generation and spectroscopy on solid surfaces using polarization-tailored strong fields

Strong-field methods in solids enable new strategies for ultrafast nonlinear spectroscopy and provide all-optical insights into the electronic properties of condensed matter in reciprocal and real space. Additionally, solid-state media offers unprecedented possibilities to control high-harmonic generation using modified targets or tailored excitation fields. Here we merge these important points and demonstrate circularly-polarized high-harmonic generation with polarization-matched excitation fields for spectroscopy of chiral electronic properties at surfaces. The sensitivity of our approach is demonstrated for structural helicity and termination-mediated ferromagnetic order at the surface of silicon-dioxide and magnesium oxide, respectively. Circularly polarized radiation emanating from a solid sample now allows to add basic symmetry properties as chirality to the arsenal of strong-field spectroscopy in solids. Together with its inherent temporal (femtosecond) resolution and non-resonant broadband spectrum, the polarization control of high harmonics from condensed matter can illuminate ultrafast and strong field dynamics of surfaces, buried layers or thin films.

physics.optics↗

arXiv2020

Signatures of magnetic field effects in non-sequential double ionization manifesting as back-scattering for molecules versus forward-scattering for atoms

For two-electron diatomic molecules, we investigate magnetic field effects in non-sequential double ionization where recollisions prevail. We do so by formulating a three-dimensional semi-classical model that fully accounts for the Coulomb singularities and for magnetic field effects during time propagation. Using this model, we identify a prominent signature of non-dipole effects. Namely, we demonstrate that the recolliding electron back-scatters along the direction of light propagation. Hence, this electron escapes opposite to the direction of change in momentum due to the magnetic field. This is in striking contrast to strongly-driven atoms where the recolliding electron forward-scatters along the direction of light propagation. We attribute these distinct signatures to the different gate that the magnetic field creates jointly with a soft recollision in molecules compared to a hard recollision in atoms. These two different gates give rise, shortly before recollision, to different momenta and positions of the recolliding electron along the direction of light propagation. As a result, we show that the Coulomb forces from the nuclei act to back-scatter the recolliding electron in molecules and forward-scatter it in atoms along the direction of light propagation.

physics.atom-ph↗

arXiv2019

Experimental Separation of Sub-Cycle Ionization Bursts in Strong-Field Double Ionization of H$_2$

We report on the unambiguous observation of the sub-cycle ionization bursts in sequential strong-field double ionization of H$_2$ and their disentanglement in molecular frame photoelectron angular distributions. This observation was made possible by the use of few-cycle laser pulses with a known carrier-envelope phase in combination with multi-particle coincidence momentum imaging. The approach demonstrated here will allow sampling of the intramolecular electron dynamics and the investigation of charge-state specific Coulomb-distortions on emitted electrons in polyatomic molecules.

physics.chem-ph↗

arXiv2019

Sub-femtosecond tracing of molecular dynamics during strong-field interaction

We introduce and experimentally demonstrate a method, where the two intrinsic time scales of a molecule, the slow nuclear motion and the fast electronic motion, are simultaneously measured in a photo-electron photo-ion coincidence experiment. In our experiment, elliptically polarized, 750~nm, 4.5~fs laser pulses were focused to an intensity of $9\times10^{14}\mathrm{W/cm}^2$ onto H$_2$. Using coincidence imaging, we directly observe the nuclear wavepacket evolving on the \ssg{} state of H$_2^+$ during its first roundtrip with attosecond temporal and picometer spatial resolution. The demonstrated method should enable insight into the first few femtoseconds of the vibronic dynamics of ionization-induced unimolecular reactions of larger molecules.

physics.chem-ph↗

arXiv2019

Streaking strong-field double ionization

Double ionization in intense laser fields can comprise electron correlations, which manifest in the non-independent emission of two electrons from an atom or molecule. However, experimental methods that directly access the electron emission times have been scarce. Here, we explore the application of an all-optical streaking technique to strong-field double ionization both theoretically and experimentally. We show that both sequential and non-sequential double ionization processes lead to streaking delays that are distinct from each other and single ionization. Moreover, coincidence detection of ions and electrons provides access to the emission time difference, which is encoded in the two-electron momentum distributions. The experimental data agree very well with simulations of sequential double ionization. We further test and discuss the application of this method to non-sequential double ionization, which is strongly affected by the presence of the streaking field.

physics.atom-ph↗

arXiv2019

Spatiotemporal imaging of valence electron motion

Electron motion on the (sub-)femtosecond time scale constitutes the fastest response in many natural phenomena such as light-induced phase transitions and chemical reactions. Whereas static electron densities in single molecules can be imaged in real-space using scanning tunnelling and atomic force microscopy, probing real-time electron motion inside molecules requires ultrafast laser pulses. Here, we demonstrate an all-optical approach to imaging an ultrafast valence electron wave packet in real-time with a time-resolution of a few femtoseconds. We employ a pump-probe-deflect scheme that allows us to prepare an ultrafast wave packet \textit{via} strong-field ionization and directly image the resulting charge oscillations in the residual ion. This approach extends and overcomes limitations in laser-induced orbital imaging and may enable the real-time imaging of electron dynamics following photoionization such as charge migration and charge transfer processes.

physics.atom-ph↗

arXiv2017

Disentangling intra-cycle interferences in photoelectron momentum distributions using orthogonal two-colour laser fields

We use orthogonally polarized two-colour (OTC) laser pulses to separate quantum paths in multiphoton ionization of Ar atoms. Our OTC pulses consist of 400~nm and 800~nm light at a relative intensity ratio of 10:1. We find a hitherto unobserved interference in the photoelectron momentum distribution, which exhibits a strong dependence on the relative phase of the OTC pulse. Analysis of model calculations reveal that the interference is caused by quantum pathways from non-adjacent quarter cycles.

physics.atom-ph↗

arXiv2014

Laser-sub-cycle two-dimensional electron momentum mapping using orthogonal two-color fields

The two-dimensional sub-cycle-time to electron momentum mapping provided by orthogonal two-color laser fields is applied to photoelectron spectroscopy. Using neon as the example we gain experimental access to the dynamics of emitted electron wave packets in electron momenta spectra measured by coincidence momentum imaging. We demonstrate the opportunities provided by this time-to-momentum mapping by investigating the influence of the parent ion on the emitted electrons on laser-sub-cycle times. It is found that depending on their sub-cycle birth time the trajectories of photoelectrons are affected differently by the ion's Coulomb field.

physics.atom-ph↗