Harmonic Emission Spectrum Research Articles

Spectroscopic clarifications, topological insights, Hirshfeld interactions, and quantum chemical computational analysis of antibacterial agent benzimidazolium picrate

The distribution of density at the B3LYP level with a 6–311++G(d,p) basis set for Benzoimidazolium Picrate was presumably assessed to comprehend additional information regarding its molecular shape, harmonic emission, and complex kinetic spectra. Leveraging VEDA software, spectral investigations were conducted for each system which enabled us to gain both qualitative and quantitative assessments of the Raman and IR spectra. Simulations were additionally implemented for net Mulliken charge, Fukui inquiry, RDG review, and intact coupling orbital analyses. The likelihood of shifting charges in the molecule's structure is foretold by the FMO potential gap of 3.9719 eV. Conceptual and feasible computations were employed to evaluate the UV–vis optical properties of BP. The dimensions, design, charge concentration dispersion, and the chemical activity region of the components were established with the electrostatic potential layer (ESP). The morphological attributes of BP were further depicted via ELF and LOL charts. The hyperpolarizability ratings of the drug demonstrate an appropriate level of reliability, and found to be 24 times than urea. To identify the target molecule's appropriate bonding energy with amino acids, a docking virtual reality was conducted.

Effect of the interference between interband currents on the crystal harmonic spectra

By numerically solving the semiconductor Bloch equation, we study the high-order harmonic emission spectrum of a MgO crystal under the interaction of a linearly polarized laser pulse. Based on two-band and three-band models, by comparing the variation of the harmonic spectrum with the laser peak intensity, it is found that when the laser intensity is lower, the harmonic spectra from both cases are generally consistent above the minimum band gap. However, some harmonic intensities in the three-band model are significantly enhanced or weakened compared to the two-band case when the laser intensity is higher. By analysis of the electron population and the harmonic phase, it is demonstrated that the harmonic enhancement or reduction is caused by the interference between two interband polarization sources, one of which originates from the current between the first conduction band and the valence band and the other of which is from the polarization between the second and the first conduction band. The harmonic interference between different interband currents contains rich dynamic information and has a significant impact on the harmonic structure and yield, which is helpful for further understanding the generation mechanism of crystal harmonics.

Detecting Majorana Zero Modes via Strong Field Dynamics.

We propose a protocol to detect topological phase transitions of one-dimensional p-wave superconductors from their harmonic emission spectra in strong fields. Specifically, we identify spectral features due to radiating edge modes, which characterize the spectrum and the density of states in the topological phase and are absent in the trivial phase. These features allow us to define a measurable signature, obtained from emission measurements, that unambiguously differentiates between the two phases. Local probing provides insight into the localized and topologically protected nature of the modes. The presented results establish that high-harmonic spectroscopy can be used as an all-optical tool for the detection of Majorana zero modes.

Probing ultrafast electron correlations in high harmonic generation

This paper develops an optical method to probe ultrafast electron correlations, based on bielliptical high harmonic generation. The authors use ab-initio numerical results to show that, with this approach, correlations are imprinted on the harmonic emission spectra, appear in a wide energy range, and persist far from any material resonant behavior.

Atomic even-harmonic generation due to symmetry-breaking effects induced by spatially inhomogeneous field**Project supported by the National Natural Science Foundation of China (Grant Nos. 91850114, 11774131, 11604119, and 11627807).

We ab initio investigate the interaction between the hydrogen atom and the inhomogeneous field which is induced by resonant plasmons within a metal nanostructure. Same as normal laser pulse (homogeneous field), only odd-harmonic generation occurs when the bow-tie nanostructure is utilized. For the single nanotip case, the even-harmonic generation can be distinctly found in the harmonic emission spectrum. By investigating the symmetry and trajectories of different inhomogeneous fields, we demonstrate that the breaking symmetry of system can enable even high harmonic generations.

Spontaneous and stimulated emissions of a preformed quantum free-electron wave function

Do the wavepacket-size of free-electron wavefunction and its history have physical effect in its interaction with light? Here we answer this problem by analyzing a QED model, considering both spontaneous and stimulated emission of quantized radiation field. For coherent radiation (Glauber state), we confirm that stimulated emission/absorption of photons has a dependence on wavepacket size that decays when it exceeds the interacting radiation wavelength, consistently and complementarily with Schrodinger equation analysis of wavepacket acceleration in classical electromagnetic field. Furthermore, the stimulated emission of modulated electron wavepacket with coherently-bunched profiles has characteristic harmonic emission spectrum that is also wavepacket size dependent but beyond the frequency cut-off. In either case, there is no wavepacket dependent emission of Fock state radiation, and particularly the vacuum state spontaneous emission is wavepacket-independent. The transition of radiation emission from the classical point-particle limit to the quantum electron wavefunction limit is demonstrated in electron wavepacket representation. It indicates a way for measuring the wavepacket size of single electron wavefunction, and suggests a new direction for exploring light-matter interaction fundamentally.

Methods for Modifications of Harmonic Spectra from Laser-Produced Plasmas

We review the studies of the modifications of harmonic spectra from laser-produced plasmas. The substantial spectral broadening and blue shift of the harmonics generating in the laser plasma during transformation of the spectrum of the laser radiation formed the filaments upon passage of femtosecond pulses through the argon gas is analyzed. We also discuss the studies of harmonic spectra variations that occur as a result of the passage of the laser pulses through the carbon- and metal-containing plasmas at the variable density of ablated species and intensity of driving pulse. To show other type of modulation of harmonic emission spectra, the plasmas containing the small molecules of silver produced during ablation of the bulk silver and silver nanoparticles at the conditions suitable for efficient harmonic generation of the ultrashort pulses propagating through the laser-produced plasmas were analyzed. The time-of-flight mass-spectroscopy studies of plasmas confirmed the presence of these species in plasmas.

XUV pulse effect on harmonic emission spectra and attosecond pulse generation

The generation of the high-order harmonic and the attosecond pulse from He atom driven by the near-infrared (NIR) field combined with the XUV pulse has been theoretically investigated by solving the three-dimensional time-dependent Schrödinger equation. The results show that by properly adding the XUV pulse into the NIR field, (i) not only the harmonic yield is enhanced, caused by the laser-induced excited state effect; but also the multi-cutoff extension of the harmonics can be found, caused by the absorption of the extra XUV photons during its recombination process. (ii) With the introduction of the XUV pulse, the frequency modulation of the high-order harmonic generation (HHG) can be found and controlled. (iii) By directly superposing the harmonics in the cutoff region, two isolated XUV pulses with the durations of 150 as can be obtained.

Harmonic emission spectra and attosecond pulse generation from helium atom driven by the mid-infrared nonhomogeneous field

ABSTRACTThe generations of the high-order harmonics and the attosecond pulses from helium atom driven by the mid-infrared symmetric and asymmetric nonhomogeneous field have been theoretically investigated. It is found that (i) due to the surface plasmon polaritons in the metallic nanostructure, the extensions of the harmonics from the positive and the negative laser amplitudes, or only from the positive laser amplitude can be found for the cases of symmetric and asymmetric nonhomogeneous fields, respectively. (ii) The wavelength scalings of the harmonic cutoff and the harmonic yield show that the harmonic cutoff and the harmonic yield can be extended and decreased with the increase in laser wavelength, respectively. However, due to the limit of the gap size of the nanostructure, the threshold value of the harmonic cutoff can be achieved for a given gap size of the nanostructure. (iii) By adding a weak terahertz field to the mid-infrared fundamental field with the asymmetric nonhomogeneous effect, the intensity of the harmonic plateau can be enhanced by one order of magnitude, showing a 1280 eV supercontinuum with the single quantum trajectory contribution. Finally, by properly superposing the harmonics, some attosecond X-ray pulses shorter than 35 as can be produced.

Identifying spatially asymmetric high-order harmonic emission in the falling edge of an intense laser pulse

Two different induced effects of a laser falling edge on high-order harmonic generation (HHG) are resolved by numerically solving the full-dimensional electronic time-dependent Schrödinger equation beyond the Born–Oppenheimer approximation. The harmonic spectrum of and isotopes are compared to see the effects of a four-cycle falling edge of a 800 nm, 15-cycle trapezoidal laser pulse of I = 3 W cm−2 intensity on harmonic emission spectrum. The harmonic emission at the laser falling part is negligible for due to ionization suppression, but considerable for . The falling edge of the laser pulse induces two effects on the HHG in . The first well-known effect is non-adiabatic frequency redshift of generated odd-order harmonics. The second unknown one is spatially asymmetric harmonic emission, which appears as even harmonic orders. In order to clarify this new effect, spatial distribution of HHG and resolving HHG into different components are demonstrated. Asymmetric emission appears for both atoms and molecules as long as the harmonic emission of either the rising or falling edge of an intense trapezoidal or non-trapezoidal laser pulse is dominant.

Nuclear signature effect on spatial distribution of molecular harmonic in the presence of spatial inhomogeneous field

Spatial distribution of the molecular harmonic spectra from in the presence of inhomogeneous field has been theoretically investigated. It shows that (i) the harmonic intensities from the negative-H nucleus play the dominating role in harmonic emission spectra. (ii) Through the investigations of the nuclear signature effect on the spatial distribution of the molecular harmonic spectra, the differences of the harmonic intensities between the negative-H nucleus and the positive-H nucleus can be enhanced and reduced with the introduction of the higher vibrational state and the heavy nucleus (i.e. ), respectively. The time-frequency analyses of the harmonic spectra, the time-dependent wave function and the electron localization have been shown to explain the harmonic spatial distribution and the electron motion. (iii) Due to the plasmon-resonance-enhancement near the metallic nanostructure, the harmonic cutoff can be remarkably enhanced as the spatial position of the inhomogeneous field moving away from the gap center. The ionization probabilities have been shown to explain the harmonic cutoff extension.

Role of quantum trajectory in high-order harmonic generation in the Keldysh multiphoton regime.

We present a systematic study of spectral and temporal structure of high-order harmonic generation (HHG) by solving accurately the time-dependent Schrödinger equation for a hydrogen atom in the multiphoton regime where the Keldysh parameter is greater unity. Combining with a time-frequency transform and an extended semiclassical analysis, we explore the role of quantum trajectory in HHG. We find that the time-frequency spectra of the HHG plateau near cutoff exhibit a decrease in intensity associated with the short- and long-trajectories when the ionization process is pushed from the multiphoton regime into the tunneling regime. This implies that the harmonic emission spectra in the region of the HHG plateau near and before the cutoff are suppressed. To see the generality of this prediction, we also present a time-dependent density-functional theoretical study of the effect of correlated multi-electron responses on the spectral and temporal structure of the HHG plateau of the Ar atom.

Influence of atomic potential on the generation of high harmonic generation from the atoms irradiated by mid-infrared laser pulses

By numerically solving the time dependent Schrodinger equation, the harmonic spectra generated from the atoms are obtained. The atomic potentials are modeled by a short-range potential and a long-range soft Coulomb potential, respectively. It is found that using the same laser parameters, the intensity of harmonic spectrum from the short-range atom is lower than the one from the long-range atom. However, in a high energy (near the cutoff) region of harmonic spectra, their conversion efficiencies are almost the same. The differences in emission intensity among harmonic spectra decrease as the harmonic energy increases. We calculate the time dependent probabilities of the ground state and ionization. It is found that the ionization probability of the long-range potential is larger than that of the short-range potential. There is no large difference in ground probability between the potentials of two models. The high harmonic generation is a stimulated process, and its intensity is proportional to the product between the amplitude for ground state and the amplitude of the continuum state. Thus the product of the long-range atom is larger than that of the short-range atom, and the emission spectrum presents a similar character. In order to analyze the mechanism of the intensity difference between two models, we perform a time-frequency analysis of the harmonic emission spectrum. The analysis is selected of the wavelet of the time dependent dipole moment. From the emission profile of the harmonic analysis, we find that the harmonic generated from long orbit plays a dominant role for the short-range atom. The amplitudes of electric field are large for the long orbit harmonic emission, thus the ionization mechanism of the atom is the tunnel ionization. For the short orbit, the instant field for the ionization is weak. Thus the short orbit plays a small role in the harmonic emission from the short-range atom. Using this feature of the short-range atom, we generate an isolated attosecond pulse. The short model atom is widely used to study the ionization of the plasma. Thus this work will contribute to the research on the high-order harmonic generation from the plasma.

Sub‐cycle Dynamics of High Harmonic Generation of Ne Atoms Excited by Attosecond Pulses and Driven by Near‐infrared Laser Fields: A Self‐Interaction‐Free TDDFT Approach

AbstractIn the framework of the self‐interaction‐free time‐dependent density‐functional theory (TDDFT), we have performed three‐dimensional ab initio calculations of Ne atoms in near‐infrared (NIR) laser fields subject to excitation by a single extreme ultraviolet (XUV) attosecond pulse (SAP). The TDDFT equations are solved accurately and efficiently by means of the time‐dependent generalized pseudo spectral (TDGPS) method. We have explored the transient dynamical behavior of the sub‐cycle high harmonic generation (HHG) for transitions from the excited states to the ground state and found oscillation structures with respect to the time delay between the SAP and NIR fields. We investigate the harmonic emission spectrum from singly excited state 2p3s, 2p4s, 2p3d, 2p5s, 2p4d and 2p6s, 2p5d and the virtual states 2p3p‐, 2p4f‐ and 2p4p+ as the function of time delay. We explore the sub‐cycle Stark shift phenomenon in NIR fields and its influence on the photon emission process. Our analysis reveals several novel features of the sub‐cycle transient HHG dynamics and spectra, the quantum interference pattern between different multiphoton excitation pathways, and we identify the mechanisms responsible for the observed peak splitting in the photon emission spectra.

Attosecond pulse generation from two-electron harmonic emission spectrum**Project supported by the Scientific Research Fund of Liaoning Provincial Education Department, China (No. L2014242) and the Scientific Research Fund of Liaoning University of Technology, China (Grant Nos. X201319 and X201312).

In this paper, we theoretically investigate the high-order harmonic generation and attosecond pulse generation when a two-electron He atom is exposed to the intense laser pulse. It shows that due to the two-electron double recombination mechanism, an extended plateau beyond the classical single-electron harmonic has been obtained on the two-electron harmonic spectrum. Further by using this two-electron harmonic extension scheme combined with the two-color field, two supercontinuum bandwidths with 200 eV have been obtained. As a result, a series of sub-60 as extreme ultraviolet (XUV) pulses have been directly generated.

Subcycle dynamics of high-harmonic generation in valence-shell and virtual states of Ar atoms: A self-interaction-free time-dependent density-functional-theory approach

We perform an ab initio all-electron study of the subcycle structure, dynamics, and spectra of high harmonic generation (HHG) processes of Ar atoms in the presence of extreme ultraviolet (XUV) attosecond pulses and near-infrared (NIR) laser fields by means of the self-interaction-free time-dependent density functional theory (TDDFT). The TDDFT equations are solved accurately and efficiently via the time-dependent generalized pseudospectral (TDGPS) method. We focus on the subcycle (with respect to NIR field) temporal behavior of the level shift of the excited energy levels and related dynamics of harmonic photon emission. We observe and identify the subcycle shifts in the harmonic emission spectrum as a function of the time delay between the XUV and NIR pulses. In the region where the two pulses overlap, the photon emission peaks have an oscillatory structure with a period of $\ensuremath{\sim}1.3$ fs, which is half of the NIR laser optical cycle. We present and analyze the harmonic emission spectra from $3sn{p}_{0},3{p}_{0}ns,3{p}_{1}n{d}_{1},3{p}_{1}n{p}_{1},3{p}_{0}n{d}_{0},3{p}_{0}n{p}_{0}$, and $3{p}_{0}ns$ excited states and the $3{p}_{0}4{p}_{0}^{\ensuremath{-}}$ virtual state as functions of the time delay. In addition, we explore the subcycle a.c. Stark shift phenomenon in NIR fields and its influence on the harmonic emission process. Our analysis reveals several features of the subcycle HHG dynamics and spectra as well as a temporal energy level shift.

Photon and photoelectron emission of the atom under the action of high-frequency laser pulse

By numerically solving the time-dependent Schrdinger equation, we investigate the ionization probability, photoelectron spectrum, and harmonic emission spectrum of the atom under the action of high-frequency laser pulses. It is found that with the increase of incident laser pulse intensity, the ionization probability of the atom first increases to a maximum value gradually and then decreases, and in this process, both the photoelectron spectrum and high-order harmonic generation spectrum change from a single-peak structure to a multi-peak one. Through the time-frequency analysis of the harmonic emission spectrum, we also find that the harmonic emission is suppressed around the pulse peak, and it occurs at the rising edge and the falling edge, which interfere with each other, thus forming the multi-peak structure. Utilizing the laws of the changes of photoelectron and harmonic spectra with incident laser pulse intensity, we can diagnose the laser intensity at which the atomic ionization suppression occurs.

Low Frequency Conducted Emissions of Grid Connected Static Converters

Pulse-width modulated rectifiers are nowadays commonly used for AC to DC power conversion. PWM rectification technology is very effective and allows for bidirectional power flow with the possibility of power factor improvement and low-order harmonic emission limitation. Unfortunately, employed PWM boost topology results with generation of input current harmonic distortions in a frequency range tightly correlated to modulation frequency. PWM carrier frequency and its harmonic components in typical applications are usually located in frequency range from single kHz up to hundreds of kHz. Increase of harmonic emission in this particular frequency range can be disturbing for other sensitive systems, therefore can cause lack of electromagnetic compatibility. Interferences in low frequency range are increasingly frequent EMC issue because of extensive use of low power PWM rectifiers and significant increase of rated power of individual converters, which already reach several MW. Presented comparison of current harmonic emission spectra of PWM rectifiers with relation to classic diode rectifiers is focused on frequency range of 2 to 9 kHz, for which emission limitation rules are currently under development. New class of EMC problems arising in low frequency range in power system are underlined as a result of increased harmonic emission in frequency range of 2 to 9 kHz.

Attosecond-resolution two-electron harmonic emission

• A two-electron time-dependent Schrödinger equation analysis. • Harmonic emission spectrum from the neutral He atom in intense laser field. • An extended harmonic plateau with many new harmonic cutoffs. • A propose model of double recombination arising from electron correlation effect. • A general characteristic of double recombination in the two-electron system. Two-electron harmonic emission from the He atom has been investigated by solving the two-electron time-dependent Schrödinger equation (TDSE), which exhibits an extended plateau and many new harmonic cutoffs beyond the classical single-electron harmonic cutoff. Theoretical analyses show that these extended new cutoffs are caused by the sequential double recombination and the nonsequential double recombination of the two electrons, which is a general characteristic for the two-electron harmonic emission and which is revealed through the investigation on laser parameter effects. Moreover, from analyzing the time-dependent wave functions, the motions of the two electrons and the single and double ionization time have been described.

Investigation of the generation of high-order harmonics through Bohmian trajectories

We theoretically investigated the generation progress of high-order harmonics utilizing Bohmian trajectories, which are calculated from the accurate numerical wave function. It is found that the harmonic emission spectrum from atoms in an intense laser field calculated by Bohmian trajectories agrees well with that found by numerically solving the time-dependent Schr\odinger equation. Through the analysis of the dynamic behavior of Bohmian trajectories, we investigated the ionization process, the acceleration of the ionized electron in the laser field, and its recollision with the parent ion in the progress. Furthermore, the individual behavior and the coherent contribution of these trajectories to the harmonic emission are discussed.