Description
Monday poster session
A supercontinuum covering 480 to 930 nm was generated in seven thin fused silica plates with energy of 1.4 mJ at 1 kHz repetition rate, and the efficiency was close to 80%, supporting a sub-10-fs pulse duration.
1.9-fs deep ultraviolet pulses (150 nJ) are obtained from third-harmonic generation in argon using a laser micromachined gas cell. The source is synchronized with isolated attosecond XUV pulses offering new avenues in attosecond spectroscopy of bio-relevant molecules.
An approach is presented to directly probe the tunneling time, where the influence of Coulomb potential is avoided. A positive tunneling time is extracted, which is almost not influenced by the laser intensity in some range.
It has been shown that symmetric entangled coherent states of a many-mode optical radiation always result in completely locked Fourier superpositions for the expectation value of the electric field operator. Accordingly, in case of such entangled states, even an occasionally random distribution of the phases of the complex amplitudes cannot spoil the locking of the temporal Fourier components....
This works describes in detail the main photoelectron spectra features after excitation with several driven wavelengths under inhomegenous field conditions. Quantum and classical simulations are in good agreement showing an important cut-off enlargement and high photoelectrons yield.
We calculate the effect of intense laser fields on nuclear alpha decay process, using realistic and quantitative nuclear potentials. We show that alpha decay rates can indeed be modified by strong laser fields to some finite extent. We also predict that alpha decays with lower decay energies are relatively easier to be modified than those with higher decay energies, due to longer tunneling...
We investigate the anisotropic high-harmonic generation with laser fields from linear to circular polarization. To reveal the underlying microscopic dynamic, a real-space trajectory method with atom resolution is proposed.
We describe and illustrate a number of recent developments of the atomic and molecular ab initio R-matrix suites for both time-dependent calculations of ultrafast laser-induced dynamics and time-independent calculations of photoionization and electron scattering.
We developed an actively stabilized extreme ultraviolet (XUV) interferometer (stability: 7.8-as RMS over 12 hours) and thereby demonstrated the interferometric 1st-order autocorrelation of an isolated attosecond pulse with 100-as periodicity in the XUV region.
We investigate attosecond electron dynamics in metals with transient absorption spectroscopy supported by ab-initio calculations. We find that optical excitation of metallic titanium leads to an ultrafast electron localization and modifies electronic screening.
We suggest a new method of the attosecond pulse characterization using two-photon resonant Raman-type transitions via continuum. Similar technique can be used for measurement of the Wigner time delay for the Raman transitions.
Using transient absorption spectroscopy, we investigate laser-induced attosecond electron dynamics in III-V semiconductors. We find a complex interplay between intra- and inter-band transitions in the transient response. Our findings are supported by ab-initio calculations.
Tunneling ionization of atoms or molecules by a strong laser field generates an electron wavepacket. This electron wavepacket could reach the detector directly or undergoes rescattering by the parent ion, giving rising to the interference in the photoelectron momentum distribution (PEMD), referred as photoelectron holography in strong field tunneling ionization. We will first show how the...
We used fused silica thin plates to broaden the spectrum of femtosecond pulses. After careful group delay compensation, the 10 fs, 800 nm pulse was focused on Ar, and a train of 308 as pulses was detected.
We calculate photoionization cross section, asymmetry parameter and Wigner time delay for noble-gas and halogen atoms. We find that halogen atoms bear a strong resemblance to their noble-gas neighbors.
Trains of attosecond pulses are suitable tools to unveil the ultrafast dynamics of electrons. Here we report the results of photoionization time delays in atoms and small molecules resolved over angle and energy of emission.
Channel resolved electron emission from strong-field photoionization of H$_{2}$ molecules were measured using ultrashort laser pulses and a reaction microscope. An enhancement of the photoelectron yield in the low-energy region was observed for the case of bound ionization. This enhancement is understood as the population of autoionizing Rydberg states in the neutral molecule and subsequent...
We demonstrate broadband THz generation in organic crystals driven by mid-IR $3.9\,\mathrm{\mu m}$ pulses. Due to the suppression of multi-photon absorption, we record an order of magnitude increase in the damage and optical to THz conversion saturation thresholds as compared to conventional near-IR pump schemes.
We report a carrier-envelope phase stabilized kerr-lens mode locking (KLM) Yb:CYA laser with feed-forward methods. Signal-to-noise (SNR) of the out-of-loop carrier-envelope-offset (CEO) was measured to be 38 dB. Timing jitter of the stabilized CEO was 44 as.
We steer the LiH molecule towards a target dissociation channel by using few cycle CEP stabilized IR pulses and follow the dynamics using both time-resolved photoelectron spectroscopy and attosecond transient absorption spectroscopy.
We will demonstrate based on experimental results a direct correlation between measured EMP energy and the laser parameters such as laser energy and intensity. Finally numerical Finite Element Method simulations are performed of the laser target holder system showing good agreement with the experimental obtained results.
Using ab initio methods we identified a molecule in which charge migration dynamics survive long enough the dephasing by the nuclear motion to be observed and controlled. This represents an important step in the direction of accomplishing the dream of attochemistry.
Charges displaced by a laser pulse in solids can be useful for detection purposes. Our analytical approach reduces the computational costs, and give us an e?cient tool to investigate this phenomenon.
We study coherent hole dynamics triggered by attosecond laser pulse within the time-dependent multiconfiguration self-consistent field method. To evaluate coherence from the total wavefunction, we propose a new position-based reduced ionic density matrix.
We measured and stabilized the carrier-envelope phase by f-2f spectral interferometry with supercontinuum generated by sapphire bulk plate, hollow-core fiber and fused silica thin plates and calculated the coherence properties for each method theoretically.
We report a precision feed-forward locking between a 1064 nm continuous wave (CW) and an ultrastable optical frequency comb. The relative linewidth of the 1064 nm CW laser is narrowed to 1.14 mHz and the stability reaches 1.5×10$^{-17}$ at 1 s at the optical wavelength of 1064 nm.
We combine the simultaneous measurement of terahertz wave and high harmonic emission to resolve the coherent multichannel electron dynamics of aligned CO$_{2}$ molecules driven by two-color laser field. It provides a new tool for detecting and resolving these multi-electron phenomena.
We successfully combined an attosecond XUV pulse and a recoil-ion momentum spectroscopy into our home-built setup. The setup can complete the XUV-infrared pump-probe experiments, which provides attosecond pulse train and isolated attosecond pulse through high-order harmonic generation technology.
We show that high-harmonic generation conserves a nontrivial mixture of orbital and spin angular momentum, in which both the driving fields and the harmonic emission have novel field topologies and symmetries.
The control of high harmonic generation driven by time-delayed, few-cycle ω and 2ω counterrotating mid-IR pulses is analyzed. We show that the time delay between two pulses allows control yield and polarization properties of harmonics.
By exploiting machine learning in high-harmonic spectroscopy, we have reconstructed the molecular rotational dynamics with femtosecond resolution from the angular distributions of high-harmonics measured at various time delays of the probe pulse.
We propose a novel attosecond photoelectron interferometer, which is based on the interference of the direct and near-forward rescattering electron wave packets, to determine the time information characterizing the tunneling process.
Real-space picture of electron recollision with the parent ion guides our understanding of the highly nonlinear response of atoms and molecules to intense low-frequency laser fields. It is also among several leading contestants for the dominant mechanism of high harmonic generation (HHG) in solids, where it is typically viewed in the momentum space, as the recombination of the conduction band...
Double ionization of Neon in mid IR wavelengths is investigated. A new set of late rescattering trajectories connected to a specific regions of the transversal momentum space are described and the effect of the magnetic field discussed.
We construct the attosecond streak camera which adopts magnetic bottle time-of-flight spectrometer, and the flight tube of different lengths and diameters will be used to study photoelectron collection efficiency, noise and spectral resolution.
We developed a new unprecedented accurate algorithm to reconstruct photoelectron wavepackets. It significantly improves prior methods to resolve attosecond time delays in photoemission. Preliminary analysis of experimental data shows excellent agreement with prior results.
Single photon double ionization of helium at photon energies of 440 eV and 800 eV is numerically simulated beyond the dipole approximation. Distributions of ion momentum is in accordance with the experimental results. We also calculated the angular correlation spectrum in the coplanar geometer with equal energy sharing, in which interference between dipole and nondipole paths is included.
We designed a novel method to increase the high-order harmonic yield by introducing a spatial and transverse inhomogeneity into a mid-infrared laser field, which can be achieved by the illumination of plasmonic nanostructures with a short laser pulse.
In this study, we will control the photoelectrons by introducing the excited Dirac cones, and show their flip-effects induced by IR (Infrared)-pump.
Based on results of an ab-initio multi-scale simulation we present the build-up of high harmonics induced by strong and short laser pulses along the propagation direction inside a dielectric. We relate our findings to processes that need to be accounted for in realistic simulations.
In the present study, second harmonic generation (SHG) in thin ZnO crystal, pure MgO and Chromium (Cr) doped MgO crystals is investigated. We explore SHG dependence on the orientation angle between the crystal and laser polarization.
We present a high energy, mid-infrared laser source based on coherent beam combining using hollow core fiber. Through coupling two 4 μm lasers generated by optical parametric chirped pulse amplification (OPCPA) into the hollow-core fiber (HCF), we obtained a laser with 2.25 mJ and 22.9 fs.
Applying the double-pulse form to generate gas high-order harmonics, the appeared harmonics are narrower and more intense compared to the harmonics that generated by a regular Gaussian-shaped pulse. In this way, a practical method to generate intense, monochromatic pulses in the XUV region is proposed.
We report on a CEP-stable YDFA delivering 30 µJ, 100 kHz, 100 fs pulses at 1030 nm. The integrated CEP noise in the bandwidth [1 Hz; 50 kHz] is 325 mrad.
We demonstrate a hybrid dual-stage nonlinear compression scheme allowing to compress 330 fs-pulses generated from a high-energy ytterbium-doped fiber amplifier down to 6.8 fs pulse duration, with an overall transmission of 61%. This high transmission is obtained by using a first compression stage based on a gas-filled multipass cell, and a second stage based on a large-core gas-filled...
We generate a tunable mid-infrared (3 μm) to THz (15 THz) laser using a dual-chirped difference frequency generation (DC-DFG) scheme, which is energy scalable to generate mJ-class THz pulses.
Here we employ time-dependent density-functional theory to investigate how the electron dynamics resulting in high-harmonic emission in monolayer hexagonal boron nitride is affected by the presence of point defects.
At strong coupling, the scalar Schwinger effect is studied by the field-theoretic method of worldline instantons for dynamic fields of single-pulse and sinusoidal types.
We present our one dimensional models and simulation results of the hydrogen molecular ion and the helium atom that give strong field ionization dynamics quantitatively comparable to the true 3D case.
We investigate the possibilities to fully characterize the temporal profiles of photoemission processes, beyond the mere concept of delay, out of the associated complex spectral amplitudes.
Our theoretical and numerical results suggest that Thomson-backscattering of a NIR laser pulse on a suitable relativistic electron nanobunch creates an isolated XUV – soft X-ray pulse of ca. 20 asec length and uJ energy.
Micro-bunching instability (MBI) is considered as a critical obstacle for the realization of the isolated terawatt attosecond XFEL. To make high a peak current, the distribution of the electron beam in the phase space should be uniform. The micro-bunching instability will twist the distribution which results in very low peak current value. The effect by MBI has been investigated and a proposal...
A linear accelerator based waveform-controlled single-cycle attosecond source is investigated numerically. Pulses with 170 nJ energy and 80 attosecond duration are predicted at 20 nm wavelength.
We consider a spatially periodic (cosine) potential as a model for a crystalline solid that interacts with a harmonically oscillating external electric field. This problem is periodic both in space and time and can be solved analytically using the Kramers-Henneberger co-moving frame. By analyzing the stability of the closely related Mathieu-type differential equation, the electronic band...
The longitudinal tunnelling-exit momentum of the electron in strong-field tunnelling ionization is shown to be nonzero even in the static or the adiabatic limit. This nonzero momentum is a purely quantum mechanical effect determined by the shape of the wave function in the vicinity of the tunnelling-exit point. Nonadiabaticity or finite wavelength may increase this momentum substantially, and...
High-order harmonic generation in solids has attracted intensive investigations and many different features have been identified and interpreted. In this Letter, we find a distinct and clean interference pattern in the high-energy end of the spectrum by varying the maximum value of the vector potential of a driving pulse. This pattern can only be observed when the quasi-electron of the solid...
The complex behaviour of the harmonic yield radiated by a single noble gas atom via high-harmonic generation process is investigated as a function of the wavelength, as well as the peak intensity of the fundamental driving field.
We propose a theory of interferometric measurement of a normal Auger decay width in molecules and show analytically that it can be reconstructed from the relative ($\omega/2\omega$) phase scan of the Auger yield modulation.
We study photoionization of cold rubidium atoms in a strong infrared femtosecond laser field using a magneto-optical trap (MOT) recoil ion momentum spectrometer. The momentum distributions of Rb$^+$ created by absorption of two- or three-photon illuminate a dipole-like double-peak structure. The yielding momentum resolution of $0.12\pm0.03$ a.u. is achieved in comparison with calculations,...
By investigating the strong-field photoelectron holographic structure of the superposition state of the H_{2}^{+}, we find a bifurcation structure, from which the transient electron wave-packet can be read out.
We present an ab initio quantum study of below-threshold harmonic generation (BTHG) from H$_2^+$ molecules in the presence of an intense laser field by solving the time-dependent Schrödinger equation accurately in space and time. We find that multiple channels contribute to BTHG of H$_2^+$ molecules, which are related to the electron driven initially at specific time of the laser pulse from...
We obtain over 3.5 nJ water window soft x-rays by high-order harmonic generation (HHG), which is the strongest in ever reported results by HHG. X-ray absorption fine structure (XAFS) at Carbon k-edge is observed.
It is shown that excitation of the isomeric nuclear state $^{229m}$Th in the process of thorium atom irradiation by two-color field of Ti:Sa can be enhanced significantly with respect to other nucleus excitation processes.
An artificial neural network that is able to predict the total harmonic flux in a given spectral range is developed. The accuracy of the model and its prediction capabilities are demonstrated.
We simulate high harmonic generation (HHG) from few-cycle mid-infrared (MIR) lasers. We calculate optimum phase matching parameters for attosecond pulses at important soft X-ray edges for low energy driving lasers (< 0.5 mJ).
We report a novel metrology tool to characterize femtosecond pulses. It is free of phase matching, enabling to measure pulses with ultra-broadband spectra and very low energy at the limit of the spectrometer detection.
We show how the ultrafast photo-induced electron emission processes can reach the order of femtosecond timescale by suitable application of external ultrafast laser. Resulting evolution of the charge densities and emission currents are discussed. Our analysis is general and holds true for other class of two-dimensional materials as well.
In this first application of our newly developed molecular time-dependent R-matrix method we study two- and four-photon ionization cross sections for H$_{2}$ and study the effects of electron correlation and choice of one electron basis.
Chirp compensation of attosecond pulses by propagation in plasma after generation is numerically investigated. We analyze the contributions of plasma dispersion, spatial chirp, and propagation effects on the final pulse characteristics in experimentally feasible configurations.
Polarization of single-order circularly polarized high harmonic is characterized after the separation by a time-delay compensated monochromator. The ellipticity introduced by the anisotropy of the toroidal gratings in diffraction is evaluated for the compensation.
We explore the influence of elliptical polarization on the (non)sequential two-photon double ionization of atomic Helium with ultrashort extreme ultraviolet (XUV) light fields using time-dependent full ab initio simulations.
We show that the slope of a two-path interference pattern near the cutoff in above-threshold electron energy spectra obtained as a function of carrier-envelope phase is directly related to the shape of the atomic potential.
The molecular structure and ultrafast molecular processes can be decoded from the correlated electron-nuclear dynamics by measuring high-order harmonic generation and photoelectron momentum distributions. Subcycle time resolution can be achieved.
In this work, we report on the recent progresses in building an XUV comb at Wuhan Institute of Physics and Mathematics (WIPM).
In the present study, we focus on the ultrafast charge migration in the valence shell subsequent to Auger decay of a core-ionized/excited molecule. By using a two-color X-ray attosecond pump-probe scheme, we theoretically demonstrate that we can induce and measure charge migration at different sites of a molecule.
We investigate the [2+2]photo-cycloaddition of norbornadiene to quadricyclane by integrating the nuclear time-dependent Schrödinger equation for eight electronic states, coupled by nonadiabatic coupling and the interaction with an external electric field.
A new attosecond streaking scheme using crossed XUV and IR beams and delay-line detector was proposed to largely shorten the experimental time to realize quasi real time characterization of attosecond pulses.
We present a reconstruction algorithm for the temporal characterization method called as tunneling ionization with a perturbation for the time-domain observation of an electric-field (TIPTOE). The algorithm can be broadly applied for various laser pulses.
We present results of the theoretical and experimental study of the relativistic non-dipole effects in the strong field atomic ionization of Argon in the intensity range of $10^{14}$ -$10^{15}$ W/cm$^2$.
Plasmonically enhanced field exhibits a great potential to extend the energy-cutoff of the high-order harmonic generation (HHG). In addition, in recent years, circularly polarized harmonics were generated using bichromatic circularly polarized laser fields. In this work, we combine the two approaches and study the HHG process driven by plasmonically enhanced bichromatic circularly polarized...
We introduced an intra- and intercycle interference model in the $k$ space to reveal the yield modulations in high-order harmonic generation (HHG) processes in solid crystals.
We demonstrate a sensitive attosecond transient absorption scheme based on the balanced detection principle. We also find that the dominant noise source is the laser intensity fluctuation which causes a blueshift of the harmonic spectra.
We propose a method for single-shot imaging of electron band structure. The electron band structure is encoded in the carry-envelope-phase (CEP) dependent frequency-shift of high harmonic radiation generated by a few-cycle laser field. By analyzing the quantum trajectories, the relation between electron band structure and frequency of the emitted radiation is established with a temporal...
We present first soft X-ray absorption spectra of solvated organic molecules and inorganic salts recorded with a broadband high harmonic source delivering soft X-ray pulses in a photon energy range between 270 eV and 450 eV.
We report temporal soliton formation in a free-space enhancement cavity. Enabled by a spectrally tailored input coupler, a self-stabilizing 37-fs cavity soliton was driven by 350-fs laser pulses at a peak power enhancement of 3200.
In this contribution, we present a significant up-scaling of the average power of stretched hollow-core-fibers by spectrally broaden 5 mJ, 500 W, 280 fs pulses in a 4 m long, 450 $\mu$m inner-diameter fiber to a bandwidth supporting sub-17fs pulses.
We study high-order harmonic generation in a two-color configuration. Additionally to yield enhancement, cut-off extension and continuum generation, we report and explain a spectral shift of harmonic peaks controlled by the delay between the pulses.
We demonstrate the ability of intense few-cycle pulses to steer photochemical reactions by taking advantage of their ultrashort nature to dynamically tailor potential energy surfaces and to induce a radiative dumping in an ultrafast pump-dump scheme.
Using 100-mJ-class midinfrared laser pulses, that are generated by a dual-chirped optical parametric amplification (DC-OPA) system, for a multi-channel waveform synthesizer, strong ‘water window’ soft x-ray harmonics with 50-attosecond duration can be generated.
Our previous works reveal structure information, dynamics of valence electron, and tunneling ionization time can be encoded in the hologram in photoelectron momentum distribution (PEMD) and how to extract them. Recently, we study photoelectron holography in multicycle strong counter rotating laser fields by solving time dependent Schrodinger equation (TDSE).
We experimentally demonstrate that the strong-field momentum transfer in laser propagation direction from the field onto the photoelectrons is a time-dependent process within an optical cycle. The observation can mostly be explained with a classical model of a free electron in a laser field, extended by the parent ion interaction and an additional time-dependent initial momentum shift.
We applied attosecond transient absorption spectroscopy to probe aligned N$_{2}$ and O$_{2}$ molecules. The direction of the electronic transitions was determined and the symmetry of the final states was identified.
We present the development of a 0.7 mJ pulse energy, 188 fs pulse duration 7 µm OPCPA at 100 Hz and we show the generation of high harmonics in ZnSe covering all the visible and near-infrared regime.
The temporal characterization of a two-color laser field is performed using the tunneling ionization method. It is shown that the waveform of the laser field is successfully reconstructed from the modulation of the ionization yield.
We theoretically investigate the Terahertz emission from ZnO using the Semiconductor Bloch equations. The relation between the laser intensity and THz yield is unexpected, which is closely related to the band structure and Bloch oscillation.
The reflection and transmission of a few-cycle laser pulse impinging on two parallel thin metal layers have been analyzed. This study means a generalization of an earlier work, in which the role of the collective radiative back-reaction of one layer has been derived.
We derive an analytical expression for the complete three-dimensional carrier-envelope-phase (CEP) distribution in the focal volume of ultrashort pulsed beams. We show how to tailor the CEP map of mirror-focused and lens-focused few-cycle pulses practically.
Resonant high-harmonic generation (rHHG) offers an attractive way for increasing conversion efficiency at the resonant energy. In this work, we theoretically investigate the physical origin of resonant enhancement from atomic Mn and its cation and have found that the enhancement is attributable to a constructive interference between 3p-3d transition components.
With the recollisional imaging enabled by the above-threshold ionization process, we induce and study exchange interaction, temporally and spatially resolved.
Topological state is linked with dynamics, as manifested via chiral-edge currents. But is there an inherent timescale, associated with topology? We address this question using unique properties of primary electronic response to strong optical fields.
We use the two-color (400 nm + 800 nm) co-rotating circularly polarized laser fields to ionize argon atoms. In this double-hand attoclock, we introduce a spatially rotating temporal Young’s two-slit interferometer with the variable slit width, in which the oppositely modulated wave packets originating from consecutive laser cycles are dynamically prepared and interfered. Developing a...
We present a two-colour femtosecond field synthesiser deployed in attosecond streaking measurements at surfaces.
We present results from transient absorption spectroscopy measured with a HHG generated supercontinuum at the sulphur L$_{2,3}$-edge of poly(3-hexylthiophene) (P3HT) following single photon excitation at the $\pi - \pi^{*}$ resonance.
We study the ultrafast relaxation of excited carriers into the lowest lying excitonic state of monolayer MoS$_2$ after excitation with $\approx$ 20fs laser pulses with different carrier frequencies using a density-matrix-formalism including many-body effects and electron-phonon scattering from ab-initio calculations.
In this work, we report the first direct measurement of a short lived hole wavepacket migration (lifetime of ~15fs) in the isopropanol molecule (C$_{3}$H$_{8}$O) by means of an X-ray pump, X-ray probe scheme with a few femtosecond time resolution at the LCLS XFEL facility.
We demonstrate a universal feature on attosecond X-ray transient absorption spectra that emerges from the light-induced coherent intraband dynamics. This feature is linked to previous studies of light-induced Fano resonances in atomic systems.
We report on the amplification of XUV pulses in the frame of high-harmonic generation in argon. By synchronizing a strong IR femtosecond light pulse with a weak XUV attosecond pulse, our single-atom simulations explain the observed amplification in the 26 - 45 eV photon energy region.
High harmonic generation is analyzed in an intense IR- and weak XUV- fields. Multiple plateaus in harmonic spectra are discussed in terms of XUV-assisted multiphoton photorecombination cross section (PRCS). Multiphoton PRCS retrieving procedure is suggested.
