Description
Wednesday poster session
In solids, the separation of the nonlinear current into intraband and interband parts is essential to understanding, but was recently shown to be gauge-dependent in its usual formulation. Here, we propose a new, gauge-invariant formulation.
We develop the theory of photoelectron circular dichroism from a geometric perspective, uncover its connection to Berry-curvature effects in solids, and provide formulas for aligned and anti-aligned molecular ensembles.
We theoretically investigate high-harmonic generation in a 1D crystal in the natural real-space basis for periodic systems, the Wannier states. A full quantum simulation confirms our semi-classical model and its interpretation.
We extend the gauge-including projector augmented wave method to the case of time-dependent electric fields of arbitrary strength and present its implementation in the VASP code. Interaction with an environment is described within the stochastic approach.
I will present an overview of the Intense XUV Beamline at the Lund Laser Centre including the specifications and experimental possibilities, as well as a general outlook about ongoing developments. In addition, I will give insights into experimental results of photo-dissociation of the simplest diamondoid adamantane (C$_{10}$H$_{16}$, m=136 u), which plays a role in astrophysics and biology.
Using the R-matrix method, we systematically analyze the photoionization time delay of Ne. Photoionization time delay between 2p and 2s shell at 106 eV photon energy is 24.75 as, which agree well with the experimental result $21\pm5$ as.
Utilizing a 1.3 mJ, 100 kHz light source, angle-resolved RABBITT measurements investigate the variation of photoionization delays as a function of photoemission direction in noble gases and molecules.
The RABBITT method dressed by a 2$\omega$ field provides a similar information as the original RABBITT method. An attosecond pulse train is measured and macroscopic effects around the 1s3p resonance of Helium are highlighted.
We theoretically explore the contribution of radial and angular electron correlation terms in the two-photon single ionization of helium, by a full dimensional numerical solution of the time dependent Schrödinger equation, over a wide photon energy range.
We present XUV Coherence Tomography (XCT) driven by a high-harmonic light source. Using a novel One-dimensional phase retrieval algorithm, XCT enables non-destructive, artifact-free, nanoscale, cross-sectional imaging of silicon based samples, e.g., semiconductor devices.
We theoretically study the photoelectron momentum distributions (PMDs) of H$_2^+$ in elliptically polarized laser fields. Depending on the internuclear distance of H$_2^+$ by numerically solving the time-dependent Schördinger equation (TDSE), the PMDs reveal different asymmetries with respect to the major and minor axes of the laser ellipse.
After a technical description of the beamline, the first two experimental campaigns achieved in 2018, and preliminary results, will be briefly presented.
We present designs and specifications of the Artemis ultrashort extreme ultraviolet laser facility upgrade consisting of a boosted Ti:sapphire chirped pulse amplifier, 100 kHz optical parametric chirped pulse amplifier and an additional high harmonic beam line.
We present a CEP-stabilized, sub-20fs Ti:Sa laser delivering 1 TW peak power pulses at 1 kHz and 20 W average power at 10 kHz. Its output wavelength is tunable within a 90 nm range around 800 nm.
In this work, a detailed description on the characterization of attosecond light pulses using the RABBITT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions) technique along with frequency chirp of attosecond pulses is presented.
We report that the spatial profile of an extreme-ultraviolet emission generated through frustrated tunneling ionization can be coherently controlled by manipulating the quantum paths of electron wavepackets in a strong laser field.
Interaction of intense femtosecond laser pulses with solid surface provides a promising opportunity to reach ultrashort radiation in XUV region of the spectrum efficiently. A comprehensive insight into this direction is provided.
In the present study we employ two computational approaches of R-matrix technique to investigate the appearance of the Cooper minimum (CM) in singly ionized argon in both the photoionization cross-section (PICS) and high-harmonic generation (HHG) spectrum.
Attosecond Transient Absorption Spectroscopy (ATAS) of core-excited states provides the opportunity to study these induced dipoles on their natural timescale from the local perspective of a reporter atom. We show how Singular Value Decomposition (SVD) can be used to separate and decompose signals from different phenomena in ATA.
We propose and demonstrate a novel scheme to detect the nonadiabatic behavior of tunnel ionization studied in an attoclock configuration, without counting on the laser intensity calibration or the modeling of the Coulomb effect.
We present soft x-ray attosecond spectroscopy for simultaneous observation of electronic and lattice dynamics.
We present a variation of the self-diffraction dispersion-scan technique and apply it in the simultaneous characterization of two pulses derived from an inhomogeneous near-UV beam.
A high harmonics source is used to probe the dynamics of laser-induced ultrafast demagnetization with respect to the wavelength of the pump beam. Longer pump wavelengths are found to increase the initial quenching levels.
In this work we overview considerations aiming to optimize high harmonic generation (HHG) for the ever growing laser powers through the examples of two gas HHG beamlines of ELI-ALPS.
We develop and explore, theoretically and experimentally, a high harmonic spectroscopy technique for the interlocking of attosecond pulse trains (APTs). We produce a pair of intertwined APTs by driving HHG with cross-linear $\omega$-2$\omega$ fields and then modify their properties by introducing slight ellipticities to the drivers. Most importantly, we developed an analytic formula that maps...
We report on the enhancement of high harmonics by field confinement in zinc oxide nanostructured cones and the generation of high harmonics carrying an orbital angular momentum using two different approaches.
Enhancement of high harmonics generation (HHG) in transmission by using spatial modulated targets is considered. We observed a dependence of HHG enhancement upon SPPs arose via the coupling of laser to grating in two-dimension simulations.
The detection of the first train of attosecond light pulses in the ELI-ALPS facility is reported in this work. Both the XUV spectrum and the temporal profile of the generated high harmonics are discussed.
The platform dedicated to studies of extreme ultraviolet (EUV) laser on atom/molecule has been established recently at the Institute of Modern Physics, CAS, Lanzhou. The platform consists of an EUV laser system and a reaction microscope. Testing experiment on single ionization of helium atom by EUV photon of about 37.5 eV was conducted. Photoelectron angular distributions are obtained and...
Ultrahigh-order wave mixing is observed in quartz using non-collinear two-color interferometric measurements. Using this methodology, we can initiate, control, follow, and reconstruct phonon dynamics of quartz in real-time with high fidelity.
During the first experimental campaign in 2017, we demonstrated the PCA principle using subps KrF lasers with high (5.1 eV) photon energies. In 2018 we continued the experiments with Large Aperture Photoconductice Antennas (LAPCAs), fabricated from the previously measured best candidates (4H-SiC and 6H-SiC).
By triggering the dissociation of H$_2^+$ with an isolated attosecond pulse, we manipulate the dissociation process using laser pulses with different wavelengths. The bond hardening and angle-resolved dissociation are observed.
Photoionization of noble gaseous atoms via HHG have been studied with the reaction microscope recently established in Lanzhou. Simultaneous excitation and photoionization of Ar is investigated where asymmetric parameters for the photoelectron angular distributions are obtained.
We present a tapered photonic crystal fiber using for octave spanning continuum generation. With an input of 300 pJ pulse, a robust and low noise fceo signal was measured to be 35 dB, which supports easy stabilization.
We present currently installed user stations that exploit the secondary source of extreme ultraviolet (XUV) radiation produced via high harmonic generation (HHG) in gases at ELI Beamlines facility.
Results of the model calculation and first experiments are presented on custom designed gas cell prototypes for high order harmonic generation fit to the high repetition laser based secondary sources in ELI-ALPS.
We present recent results on high harmonic generation in graphene and we study the dependence of the generation process on the band structure of 2D materials and bulk crystals through polarization spectroscopy.
The ellipticity dependence of HHG from noble gas clusters was measured for different cluster sizes. Results show that electrons recombine with the parent ion only and the charge does not become delocalized in the cluster.
High harmonic generation driven with 16 mJ /35 fs Ti:sapphire laser was studied. By optimizing the media length, gas pressure and the position of the gas cell, we obtained collimated XUV radiation at the same time with enhanced energy.
High order harmonic generation (HHG) driven by a combination of two or more femtosecond laser fields has lately been thoroughly investigated for its capability to impart specific properties to the outgoing XUV spectrum. Although HHG is a strong field process, the observations were mainly interpreted in terms of photon conservation. Here, we will present a complementary approach based on the...
We demonstrated 1 TW Ti:sapphire laser system at 1 kHz, which uses a cavity-mode-adjustable regenerative cavity as pre-amplifier for adjustable beam waist to match the beam mode in subsequent multi-pass amplifier. The compressed pulses with power of 25 mJ in 27.1 fs, which corresponds to 0.92 TW, were realized under the pump power of 108 W with cryogenically cooling. The result will pave a way...
Attosecond coincidence spectroscopy is a powerful tool to study ultrafast phenomena in molecules. Here, we present an attosecond pulse source working between 50 and 100 kHz which we are currently developing for photoelectron/-ion coincidence spectroscopy.
We present a new design and characterization of a velocity-map-imaging electron spectrometer combined with a reflectron mass spectrometer. Together with attosecond and femtosecond pump-probe methods it will enable studies of ultrafast dynamics in large molecules.
We present a high-energy mid-IR OPA tunable between 2.8 and 3.8 $\mu$m for strong-field applications. HHG driven by two-colour pulses was studied in atoms and molecules using this source.
Here, we extend the study of high-order harmonic generation in graphene, simulating through DFT methods its electronic structure when the crystalline material is brought in extreme conditions, namely when is exposed to local ultrahigh pressure. By solving the time-dependent Schrödinger equation in the density matrix formalism, we have access to the current in the time-domain and a Fourier...
The interaction of matter with a quantized electromagnetic mode is considered. Using Neumann-lattice coherent states, we present a transparent phase-space picture describing the back-action of the material sample on the exciting mode.
Our current work indicates that solids with vacancy-defect are potential band-gap materials for generation of high-energy radiation in XUV and soft x-ray energy regime. HHG from solids with vacancy-defect will be fascinating avenues for future work.
We study the optimal switching of relativistic high harmonic generation mechanisms and show that careful experiments can be designed by choosing appropriate parameter space where one can generate intense attosecond pulses from laser-plasmas.
Irradiating a strong laser field on a hydrogen atom forms a Kramers-Henneberger atom, whose photoelectron presents double-slit interference characters if it is exposed to another strong laser pulse.
Isotope effects on the ionization of hydrogen molecular ions in strong laser fields are studied systematically for single-photon, multiphoton and tunneling ionization. We also propose a potential technique to image diatomic molecules.
Here, we introduce Homodyne Attosecond Streaking (HAS) to characterize the temporal properties of the nonlinear photoemission from nanostructure materials. Our work opens new pathways for exploring the interaction of light and matter, the advancement of light-based electronics, and lays the groundwork for attosecond electron diffraction studies.
Three-dimensional momentum distributions of Ar$^{n+}$ (n=1,2,3,4) are measured. The longitudinal and lateral momenta reveal the multiple ionization dynamics as well as the interaction of the ionized electrons with parent ion in strong laser fields.
We present NewStock, a time-dependent program to compute the photoionization of polyelectronic atoms by arbitrary light pulses. The program expands the capabilities of the Stock B-spline close-coupling structure code to the time-dependent domain.
We performed nonlinear Fourier-transform spectroscopic measurements of C$_2$H$_2$ using intense attosecond pulse trains and an interferometer with sub-100-as accuracy, and revealed that the C-C dissociation proceeds via the resonant transition of C$_2$H$_2^+$ at ~11 eV.
We investigated the dissociative ionization of O$_2$ by pump-probe measurements using extreme-ultraviolet attosecond pulse trains, and revealed that an electron-nuclear wave packet composed of O$_2^+$($B^2 \Sigma_g^−$) and O$_2^+$($3^2 \Pi_u$) is created by the pump pulse train.
Proposing a theoretical model enabling nonperturbative treatment of core-level photoemission of metallic systems, we could properly account for extrinsic plasmon losses and determine the corresponding photoemission delays. This is the first-time exploration of inelastic photoemission delays of higher order plasmon satellites beyond the lowest order and then gives a route to manipulate the...
By using the frequency-domain theory, we investigate the nonsequential double ionization (NSDI) process of helium in IR+XUV two-color laser fields, where we found the two lasers play different roles in the NSDI processes.
Photoionization delays are measured and calculated for CO$_2$. Comparison of theory to experiment shows that inter-channel coupling and electronic energy exchanges are present in the data. Time-domain observations of channel coupling effects are reported.
Based on the soft-photon approximation, a 3D Monte-Carlo trajectory method is developed to simulate attosecond interferences (RABBITT) experiments of liquid water. The method is presented and it is explained how it can help to understand the experimentally measured delays.
We propose a mechanism that explains the population inversion between the $B^2\Sigma^+_u$ state and the $X^2Σ^+_g$ state and is based on the combined effect of several processes.
We investigated the strong-field induced nonlinear optical response of solid dielectrics emerging from the sub-cycle injection dynamics of electrons into the conduction band by low-order wave mixing experiments and corresponding simulations.
In this contribution we investigate the effect, commonly known as interference stabilization, in the time-domain by employing an effective Hamiltonian, which describes a two-level system coupled to an arbitrary number of continua.
The photodissociation of LiF is usually described on the nonadiabatically coupled lowest two $\Sigma$ electronic states considering only the vibrational motion of the molecule. In the present work we highlight the importance of both the lowest $\Pi$ state and the molecular rotation.
The interference of electronic wave packets created during ionization leaves a characteristic mark on the momentum distribution of the photoelectrons which is interpreted as the hologram of the target. We report our findings on the sensitivity of these holographic structures on the atomic species of the target.
We measure the variation of the photoemission time delay as a function of XUV photon energy in Xe 4d$_{5/2}$ and 4d$_{3/2}$ shells and investigate the post collision interaction between the photoelectrons and the Auger electrons.
The thermodynamical properties of the photon-plasma system had been studied using statistical physics approach. It is demonstrated that the presence of the plasma medium enables the photon gas to undergo a Bose-Einstein condensation by adjusting the relevant parameters to criticality. Planck’s law of blackbody radiation is also modified with the appearance of a gap below the plasma frequency...
We investigate the polarization states of high-harmonics generated from different semiconductors. We find significant deviations from the driving pulses’ polarization and circularly polarized harmonics from elliptically polarized pulses.
The combination of Yb amplifier with a stretched, hollow-core fiber, results in the generation and post-compression of laser pulses to reach 25 fs at the energy record of 40 mJ, corresponding to 1.6 TW peak power.
Molecular photoemission delay includes contributions from electron birth process and its subsequent propagation within the molecular environment. Here attosecond streaking spectroscopy enabled disentangling these contributions facilitating to understand the influence of molecular environment on it.
We discuss how a new two-dimensional mass spectrometry can maximise the structural information derived from molecules fragmented using ultra-short laser pulses, and achieve closed-loop quantum control over the dissociation of specific bonds in biomolecules.
Based on a time-gated ion microscopy self-referenced technique, we report evidence of electron quantum path interferences in the harmonics generated by field-free aligned N$_2$ molecules and measure their phase dependence on molecular orientation.
We experimentally show the compression of a radially polarized vector beam to the few-cycle regime with the conventional method that we compress Gaussian beams, without distorting their radially polarized nature.
Based on phase space analysis of tunnel ionization, we propose a new method to retrieve the exit momentum and the time instant of the electrons’s emergence at the exit of the tunnel, from measured data.
In this presentation, we will show how to easily probe magnetization dynamic with linearly polarized EUV or soft X-ray light with a versatility similar to XMCD by exploiting the Faraday effect.
In this work, we study the effect of linearly polarized electric fields on the dynamics of oriented chiral molecules. We aim at understanding the conditions required to break chirality by bringing enantiomers out-of-equilibrium.
We formulate a general theory for selection rules in HHG that accounts for both microscopic and macroscopic symmetries of the light-matter interaction. We demonstrate experimentally selection rules of new symmetries, including elliptic and multi-scale.
In the present work we theoretically investigate several geometrical arrangements between the polarization vectors and the emission direction, that lead to selective sideband orders in the ionization spectrum.
In this work we review two techniques that are able to perform spatio-temporal pulse characterization of few-cycle pulses without the need for a separate reference pulse.
We present an f-to-2f interferometry method to simultaneously measure and control the delay and carrier-envelope phase (CEP) of a near single-cycle waveforms. Long-term stabilization of the phase-locking system results in a CEP stability of 280 mrad and a delay stability of 28 attosecond over 8 hours at 1 kHz repetition rate.
We demonstrate single-image measurement of an isolated attosecond pulse. By imaging X-rays on a detector, the amplitude and phase of the attosecond pulse are measured from a single image, showing a duration of 190 as.
We characterize and minimize spatio-temporal distortions originating from noncollinear optical parametric amplification in an OPCPA laser source with the help of the dispersion-scan technique and 3D Fourier transform spectrometry.
We present an experimental scheme capable of revealing complete spatio-temporal dynamics of a femtosecond filament. Our findings may help exploit the full potential of filamentation for supercontinuum generation.
The spatial influence of the intensity-dependent dipole phase is incorporated into a Gaussian optics model in order to study chromatic aberration of broadband XUV attosecond pulses. This effect may lead to spatiotemporal coupling when refocusing the beam.
We present a study of dependencies of the HHG conversion efficiency and the spectral shift of the harmonics on the driving laser intensity in a loose focusing configuration and long generation medium.
Strong field dynamics of ultrashort laser pulses with hyper-Gaussian temporal profiles in cascade three-level system under two-photon resonant condition is studied here.
We report on time-resolved soft X-ray absorption spectroscopy of nitric oxide at the nitrogen K-edge (400 eV). Dynamics of electron and nucleus under strong electric field has been observed with electronic-state specificity.
On-axis and off-axis components dominates XUV radiation near cut-off frequency and within the plateau respectively. Hence, phase-matching condition need to be evaluated along both axial and lateral direction to obtain global optimal HHG flux.
Sub-cycle electron localization from interference of $1s\sigma_g$ and $2p\sigma_u$ states of H$_2$ in a multicycle laser pulse is tracked, which can be assigned to the dynamics correlation between ionization and dissociation process.
The generation of the below threshold harmonics (BTHs) under different driving laser intensities is investigated. The linearly shifting of photon energy and resonantly enhancement of photon yield of the harmonics from 23rd (H23) to 27th (H27) are found by changing the laser intensity around 18.6 TW/cm$^{2}$.
We study the subcycle transfer of photon momentum in tunnel ionization beyond the dipole approximation using the attoclock setup. We separate the momentum transfer during tunneling and propagation in continuum using the backpropagation method.
Here we present recent results on Surface High-order Harmonic Generation (SHHG) by using the Jeti200 laser system using long focal length f/12 system, with a peak intensity of >10$^{19}$ W/cm$^{2}$ (<3J, 25fs, single plasma mirror). The experiment examines the ROM harmonic emission efficiency in a multi parametric scan of pulse duration (GVD), laser energy and spatial intensity distribution.
Strong modulation in the spectral density of neon’s high harmonic spectra are experimentally observed, being driven by strongly shaped two-colour laser fields. They reveal intricate interference features that are not observed in the existing literature.
It is shown that polarization of many-electron atoms in an intense laser pulse may lead a screening of the laser field, which results the suppression of atom depletion and thereby enhances the high-order harmonic generation yield.
We demonstrated that femtosecond chiral dynamics in fenchone can be probed using core level spectroscopy with circularly polarized XUV light provided by the free-electron laser FERMI.
Here, we report the development of a table-top transient absorption setup, based on high-harmonic generation to generate broadband continua covering the water window (284-538 eV).
Intra-cavity based harmonic sources have enabled the generation of extreme ultraviolet frequency combs and are attracting increasing attention as attosecond sources. We here discuss recent advances and our efforts towards a high power attosecond source.
A waveform-synthesized field obtained by frequency mixing of a Ti:S laser with a 1257-nm OPA is used to drive high harmonic generation. The measured and simulated spectra as a function of delay show similar features.
In some solids, ultrafast nonlinear excitation of valence electrons to conduction bands creates population inversion and, with it, optical gain at frequencies within the transparency region of the unperturbed solid.
We demonstrate two-color interferometric measurements of high-order harmonic generation (HHG) of liquids. The relative phase of the modulations of odd and even harmonics is independent of the intensity, but shows a strong photon-energy dependence above the bandgap.
We propose and theoretically explore an all-optical technique for detecting atomic, molecular, or solid ring-currents based on high harmonic generation, where ring current-carrying media emit elliptically polarized high harmonics, whereas current-free media emit strictly linearly polarized harmonics.
We have experimentally studied the three-body dissociation dynamics of (OCS)$_{2}^{(3,4)+}$ based on the coincidence measurement. Two indirect and one direct channels are resolved and the influences of neighbor ions in the dimer have been discussed.
Taking into account electronic band structure of multilayer graphene, and using a semi-classical approach, we address the mechanisms of high harmonic generation in graphene, and identify strong contributions towards HHG.
Ultrafast electron emission dynamics in the interaction of relativistic intensity laser pulses with solid density plasma have been investigated by analyzing temporal profile of the emitted THz field which are recorded in single-shot electro-optic measurement.
The electronic decay of O2s vacancy in fluorinated cumulenones has been investigated using ab initio methods. In all studied cases this state decays non-locally by emitting an electron from the remote fluorines.
Electron transfer between the organic dye to semiconducting substrate in Dye Sensitized Solar Cells (DSSC) plays a crucial role in determining the efficiency of the solar cells. We discuss how the photoexcited charge transfers in such molecules and the overall photoabsorption can be further tuned under suitable laser field.
A universal pulse characterization method that can be applied for a multi-octave wavelength range from UV to IR without having a duration limit is presented. The validity of the method is verified theoretically and experimentally.
XUV transient absorption spectroscopy has been performed on small gaseous molecules with few femtosecond time resolutions using a strong field IR/VIS pump and high harmonic probe. Rydberg/cationic excited state nuclear dynamics have been observed.
