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We theoretically investigate nonadiabatic effects in tunneling ionization of a hydrogen atom induced by a few-cycle elliptically polarized laser pulse. We find a deflection angle between the maximum of the photoelectron momentum distribution and the direction of the negative vector potential corresponding to the electric-field peak. This deflection angle mainly originates from the fact that the instant of the maximal ionization rate does not exactly correspond to the instant of the electric-field peak in the few-cycle elliptically polarized laser pulse, revealing an ionization time shift between those two instants. The ionization time shift is a result of the nonadiabatic effect induced by the envelope of the few-cycle elliptically polarized laser pulse, which disappears in a long-pulsed laser. Our study is useful for understanding attoclock experiments using few-cycle elliptically polarized laser pulses. [ABSTRACT FROM AUTHOR]

The elastic properties and thermal expansion behavior of lead-free halide double perovskite, Cs 2 AgBiBr 6 , were studied first with the aid of first principles calculations, which were followed by experimental characterization. The calculated full elastic constants enable the complete mapping of Young’s and shear moduli, and Poisson’s ratios of Cs 2 AgBiBr 6 along all crystallographic orientations. Results show that significant anisotropy in them despite the fact that Cs 2 AgBiBr 6 possesses cubic symmetry. Detailed structural analysis and a spring model were utilized to rationalize the observed anisotropy. Further, the theoretical results were validated by recourse to nanoindentation and high-pressure synchrotron powder X-ray diffraction experiments. The superior mechanical behavior of Cs 2 AgBiBr 6 over the hybrid bromide analogues, MAPbBr 3 (MA = CH 3 NH 3 + ), were attributed to the higher framework stiffness of the former, which is a result of the presence of relatively stronger Ag-Br and Bi-Br bonds in it. Variable temperature single crystal X-ray diffraction reveal linear and volumetric thermal expansion coefficients to be about 20% lower than those of MAPbBr 3 , again suggesting its higher framework rigidity. The superior stiffness, thermal expansion behavior, moisture stability, and nontoxicity of Cs 2 AgBiBr 6 make it a strong candidate for potential applications in optoelectronics and photovoltaics. [ABSTRACT FROM AUTHOR]

We report an unexplored observation of multi-orbital contribution in the below- and near-threshold harmonic generation of aligned molecules. A typical pump–probe configuration is used in our experiments. By scanning the time delay and crossing angle of polarization directions between the pump and probe pulses, we find that the harmonic yield in this region exhibits abnormal intensity-dependent modulation patterns. Further comparison and analysis show that this observation can be interpreted as due to the contribution of deeper-lying molecular orbitals, which are much more prominent than in the above-threshold region and can overall surpass the contribution of the highest occupied molecular orbital, leading to reversed modulation patterns. The particular importance of the deeper-lying orbitals in this regime is closely related to the multi-photon excitation pathways involved in the generation process. Our work will advance further investigations on the mechanism of below- and near-threshold harmonic generation. [ABSTRACT FROM AUTHOR]

The sensitivity of strong-field ionization to atomic orbital helicity has attracted much attention from physicists, due to its potential application in attosecond spectroscopy and spintronics. In order to intuitively observe the physical mechanisms of helicity-dependent ionization rates during photoionization, the concept of the Wigner phase can be used to characterize the different interactions between the rotating electrons and the Coulomb potential. Here, we find that in both one- and three-photon ionization schemes, the electrons liberated more easily by the circularly polarized laser field suffer less influence of the Coulomb potential during the propagation and then accumulate less Winger phase. This result indicates that the strength of the interaction between the rotating electrons and the Coulomb potential can explain the helicity-dependent ionization for different ionization mechanisms universally, which is also supported by our classical ensemble analysis. Our work provides an intuitive perspective towards the physics picture of ionization propensity rules. [ABSTRACT FROM AUTHOR]

We propose a quantitative polarization-resolved quantum trajectory approach to analyse the solid high-order harmonic generation (HHG). By using this approach, we can distinguish the ionization channels of different polarization components in HHG. We take the HHG in hBN under two counter-rotating circularly polarized fields as an example. We find that the right and left circular polarized high harmonics are contributed by the electron trajectories with the ionization channel around the high symmetry points K and K ′ respectively. Furthermore, the intensity of the right and left circular polarization harmonics is determined by the interference between these electron trajectories. Our work offers a quantitatively polarization-resolved analysis to understand the underlying mechanism in HHG in the view of electron reciprocal space trajectory. [ABSTRACT FROM AUTHOR]

Abstract: Single-phase La(Mg1/2Ti1/2)O3 has been prepared by ethylenediaminetetraacetic acid (EDTA) gel combustion synthesis process. The process starts with a pH adjusted aqueous solutions of La(NO3)3, Mg(NO3)2·6H2O, Ti(OC4H9)4, and EDTA. Combustion reactions occur when heating the gel to 250°C, which convert them to La(Mg1/2Ti1/2)O3 with traces of carbonaceous material directly. The derived powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, SEM and laser particle size distribution analysis. [Copyright &y& Elsevier]

Interferometry, a key technique in modern precision measurements, has been used for length measurement in engineering metrology and astronomy. An analogous time-domain interferometric technique would represent a significant complement to spatial domain applications and require the manipulation of interference on extreme time and energy scales. Here, we report an all-optical interferometer using laser-driven high order harmonics as attosecond temporal slits. By controlling the phase of the temporal slits with an external field, a time domain interferometer that preserves both attosecond temporal resolution and hundreds of meV energy resolution is implemented. We apply this exceptional temporal resolution to reconstruct the waveform of an arbitrarily polarized optical pulse, and utilize the provided energy resolution to interrogate the abnormal character of the transition dipole near the Cooper minimum in argon. This novel attosecond interferometry paves the way for high precision measurements in the time-energy domain using all-optical approaches. [ABSTRACT FROM AUTHOR]

Charge migration during light–matter interaction is one of the most fundamental processes which plays a key role in chemical and biological processes of molecule. The measurement of this process requires the extreme temporal and subatomic spatial resolutions. Here, we show that a scheme based on infrared pump and short extreme ultraviolet probe technique enables us to trace the laser-controlled electron motion with high spatiotemporal resolution. By numerically solving the time-dependent Schrödinger equation for combined with a simple double-slit model, we demonstrate that the laser-controlled charge migration can be directly reconstructed from the interference patterns of the photoelectron spectrum. [ABSTRACT FROM AUTHOR]

We theoretically investigate the high-order harmonic generation (HHG) driven by dual-pulse lasers. The first pulse of 800 nm can create plasma in the high-density gas target. Then, the second pulse of 1800 nm is spatiotemporally reshaped by the plasma and generates soft x-ray high-order harmonics in the overdriven regime. The simulation results show that adding the first pulse can promote the phase matching of HHG in the cutoff region. As a result, a cutoff-extended HHG is achieved, which is one order of magnitude more intense than that in one pulse scheme reported previously. In dual-pulse driving lasers, the harmonic yield and the cutoff photon energy can be optimized effectively by increasing the gas pressure inside the water window region. [ABSTRACT FROM AUTHOR]

We discuss the non-dipole effect in high-order harmonic generation from atoms driving by a linearly polarized vortex beam. Different from the selection rule under the dipole approximation, where only odd high harmonics are allowed, both even and odd harmonics are generated in the vortex beam. Moreover, the polarization states of the harmonics are modulated. Elliptically polarized high harmonics can be directly generated with a linearly polarized vortex beam. We show that these non-dipole effects arise from the orbital angular momentum and spin angular momentum of the vortex beam. [ABSTRACT FROM AUTHOR]

By numerically solving the three-dimensional time-dependent Schrödinger equation, we theoretically investigate the dynamic interference of the hydrogen atom in intense arbitrarily polarized high-frequency XUV pulses with and without the non-dipole correction included. Our results show a clear shift of the dynamic-interference peaks in the photoelectron spectra from the linearly and circularly polarized XUV pulses, which can be attributed to the different AC Stark shifts of the ground state. The non-dipole correction for the electron–light interaction produces a similar peak shift along the propagation direction in the photoelectron momentum spectra for the linear and circular pulses. But no obvious non-dipole effect for the AC Stark shift of the ground state is identified for the light pulse with intensity around 1019 W cm−2. [ABSTRACT FROM AUTHOR]

We propose a new method to improve the energy resolution of photoions with an aplanatic velocity map imaging spectrometer. Building on the traditional VMI spectrometer with three aperture electrodes, we apply a stepped voltage on the extractor electrode of the spectrometer to reduce the spherical aberration effect of the electrostatic lens. This stepped voltage acts as a diverging electrostatic lens in ion optics. A combination of the converging electrostatic lens and the subsequent diverging electrostatic lens constitutes an aplanatic electrostatic lens. With precisely controlling the moment of the voltage, we suppress the spherical aberration effect induced by the converging electrostatic lens in the traditional VMI spectrometer. Both simulated and experimental results demonstrate that the energy resolution is significantly improved using this aplanatic-lens VMI spectrometer. [ABSTRACT FROM AUTHOR]

Abstract: Carbonyl iron fibers were fabricated by magnetic-field-induced thermally decomposition of polymetallic carbonyl. Their fibrous morphology and magnetic properties were investigated by scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) at room temperature respectively. The microwave characterizations of carbonyl iron fiber-filled foam composites were evaluated through arch test based on a network analyzer. The diameter and aspect ratio of the fibers have great influence on reflection loss. It was also found that carbonyl iron fiber-filled foam composites with small thinness and lightweight exhibit good microwave absorbing properties in the frequency of 8–18GHz, 26–40GHz and 75–110GHz. [Copyright &y& Elsevier]

The second-harmonic generation (SHG) in gallium doped ZnO (GZO) nanofilms was studied. The Ga doping in GZO nanofilms influenced the crystal structure of the films, which affected SHG characteristics of the nanofilms. In our experiments, a strong SHG response was obtained in GZO nanofilms, which was excited by 790 nm femtosecond laser. It was observed that the Ga doping concentrations affected, not only the intensity, but also the polarimetric pattern of SHG in GZO nanofilms. For 5.0% doped GZO films, the SHG intensity increased about 70%. The intensity ratio of SHG between the incident light polarization angle of 90° and 0°changed with the Ga doping concentrations. It showed the most significant increase for 7.3% doped GZO films, with an increased ratio of c/a crystal constants. This result was attributed to the differences of the ratios of d33/d31 (the second-order nonlinear susceptibility components) induced by the crystal distortion. The results are helpful to investigate nanofilms doping levels and crystal distortion by SHG microscopy, which is a non-destructive and sensitive method. [ABSTRACT FROM AUTHOR]

The partition of the photon energy into the subsystems of molecules determines many photon-induced chemical and physical dynamics in laser-molecule interactions. The electron-nuclear energy sharing from multiphoton ionization of molecules has been used to uncover the correlated dynamics of the electron and fragments. However, most previous studies focus on symmetric molecules. Here we study the electron-nuclear energy sharing in strong-field photoionization of HeH2+ by solving the one-dimensional time-dependent Schrödinger equation (TDSE). Compared with symmetric molecules, the joint electron-nuclear energy spectrum (JES) of HeH2+ reveals an anomalous energy shift at certain nuclear energies, while it disappears at higher and lower nuclear energies. Through tracing the time evolution of the wavepacket of bound states, we identify that this energy shift originates from the joint effect of the Stark shift, associated with the permanent dipole, and the Autler-Townes effect due to the coupling of the 2pσ and 2sσ states in strong fields. The energy shift in the JES appears at certain nuclear distances only when both Stark effect and Autler-Townes effect play important roles. We further demonstrate that the electron-nuclei energy sharing can be controlled by varying laser intensity for asymmetric molecules, providing alternative approaches to manipulate photochemical reactions for more complex molecules. [ABSTRACT FROM AUTHOR]