Harmonic Emission Research Articles

Generation of an intense single harmonic emission event and attosecond pulse from hydrogen molecular ion and its isotopic molecular ions with the assistance of half-cycle unipolar pulse

Through controlling the charge resonance enhanced ionization process of the isotope molecules of hydrogen molecular ion, deuterium molecular ion and tritium molecular ion, the intense single harmonic emission event has been produced, which is beneficial to generate the single attosecond pulse. Moreover, the optimal laser parameter combinations for producing the intense harmonic spectra and attosecond pulses have been shown from 4 × 1014 W/cm2 to 7 × 1014 W/cm2. Further, by properly adding a half-cycle unipolar pulse, the selected single harmonic emission event can be further extended, which can support the shorter attosecond pulse with higher photon energy. Finally, by superposing these harmonics, a number of intense attosecond pulses shorter than 40 as can be obtained.

Robust control of the minima of high-order harmonics by fine-tuning the alignment of CO2 molecules for shaping attosecond pulses and probing molecular alignment

In a recent paper [C. Jin, S.-J. Wang, X. Zhao, S.-F. Zhao, and C. D. Lin, Phys. Rev. A 101, 013429 (2020)], we reported that the position and depth of the minima in the harmonic spectra of ${\mathrm{CO}}_{2}$ molecules can be dramatically manipulated by a slight change of the degree of alignment, thus providing a convenient method of shaping attosecond pulses which could lead to the splitting of a typical single attosecond burst into two. Here, we demonstrate that harmonic minima can also be dramatically controlled by changing the pump-probe angles to shape attosecond pulses. In the meanwhile, since the pump-probe angle-dependent harmonic spectra are very sensitive to the degree of alignment, harmonic spectra can also be used to calibrate the alignment distribution of molecules. We identify such robust control of harmonic generation is due to the optical property of ${\mathrm{CO}}_{2}$ and the coherent harmonic emission from the oriented molecules. The photoionization transition dipoles (PITDs) of ${\mathrm{CO}}_{2}$ exhibit deep minima that change rapidly with molecular orientations accompanied by large phase changes of $\ensuremath{\pi}$ in PITDs, thus leading to strong interference when the dipoles are added up coherently.

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.

Interferometric imaging with LOFAR remote baselines of the fine structures of a solar type-IIIb radio burst

Context. Solar radio bursts originate mainly from high energy electrons accelerated in solar eruptions like solar flares, jets, and coronal mass ejections. A sub-category of solar radio bursts with short time duration may be used as a proxy to understand wave generation and propagation within the corona. Aims. Complete case studies of the source size, position, and kinematics of short term bursts are very rare due to instrumental limitations. A comprehensive multi-frequency spectroscopic and imaging study was carried out of a clear example of a solar type IIIb-III pair. Methods. In this work, the source of the radio burst was imaged with the interferometric mode, using the remote baselines of the LOw Frequency ARray (LOFAR). A detailed analysis of the fine structures in the spectrum and of the radio source motion with imaging was conducted. Results. The study shows how the fundamental and harmonic components have a significantly different source motion. The apparent source of the fundamental emission at 26.56 MHz displaces away from the solar disk center at about four times the speed of light, while the apparent source of the harmonic emission at the same frequency shows a speed of < 0.02 c. The source size of the harmonic emission observed in this case is smaller than that in previous studies, indicating the importance of the use of remote baselines.

The imaginary part of the high-harmonic cutoff

High-harmonic generation—the emission of high-frequency radiation by the ionization and subsequent recombination of an atomic electron driven by a strong laser field—is widely understood using a quasiclassical trajectory formalism, derived from a saddle-point approximation, where each saddle corresponds to a complex-valued trajectory whose recombination contributes to the harmonic emission. However, the classification of these saddle points into individual quantum orbits remains a high-friction part of the formalism. Here we present a scheme to classify these trajectories, based on a natural identification of the (complex) time that corresponds to the harmonic cutoff. This identification also provides a natural complex value for the cutoff energy, whose imaginary part controls the strength of quantum-path interference between the quantum orbits that meet at the cutoff. Our construction gives an efficient method to evaluate the location and brightness of the cutoff for a wide class of driver waveforms by solving a single saddle-point equation. It also allows us to explore the intricate topologies of the Riemann surfaces formed by the quantum orbits induced by nontrivial waveforms.

Improving energy indicators of the charging station for electric vehicles based on a three-level active rectifier

A new structure of the charging station for electric vehicles has been proposed, which was developed on the basis of a three-phase transformer and a three-level active four-quadrant rectifier with the power factor correction. This paper describes the parameters of the proposed structure of the charging station and gives the parameters for the replacement circuit of the battery compartment in the electric car TESLA, model S, which was reduced to a single equivalent battery. We have described a method for fast charging the battery with constant current and constant voltage CC-CV, which ensures a greater number of battery charge-discharge cycles. The mathematical formulae have been given for calculating the power losses components and the efficiency of the proposed structure of the charging station over a full interval of the battery charge. We have outlined a system of automated control over the charge current and voltage, which is based on the pulse-width modulation of the second order and an integrated regulator. The simulation model of the proposed structure of the charging station, built in the MATLAB/Simulink programming environment, has been presented, as well as the simulation results: the oscillograms of input and output currents and voltages, the dynamics of the charge current regulator operation. The polynomial approximation of the IGBT-modules energy characteristics aimed at calculating the static and dynamic losses in the power switches of an active rectifier has enabled the construction of a loss counter model. It has been shown that increasing the value of a charge current under the CC mode decreases the resultant integrated value of the charge process efficiency, but, at the same time, the power factor increases and the emission of higher harmonics decreases. We have performed the optimization of power losses in the proposed system of the charging station based on the parameters of the minimal charge current and the modulation frequency in PWM. Our analysis of the components of energy losses in the proposed structure has confirmed its energy efficiency in comparison with other existing structures. The advantage of the proposed structure is that it enables improved efficiency and power factor while lowering the emission of current higher harmonics. The following system indicators have been obtained: the integrated efficiency value of the electric car full charging process using a CC-CV method is 95.6 %, the power factor is 0.99, the total harmonic distortion coefficient of the input current is 2.5 %

Origin of strong-field-induced low-order harmonic generation in amorphous quartz

Kerr-type nonlinearities form the basis for our physical understanding of nonlinear optical phenomena in condensed matter, such as self-focusing, solitary waves and wave mixing1–3. In strong fields, they are complemented by higher-order nonlinearities that enable high-harmonic generation, which is currently understood as the interplay of light-driven intraband charge dynamics and interband recombination4–6. Remarkably, the nonlinear response emerging from the subcycle injection dynamics of electrons into the conduction band, that is from ionization, has been almost completely overlooked in solids and only partially considered in the gas phase7–10. Here, we reveal this strong-field-induced nonlinearity in a-SiO2 as a typical wide-bandgap dielectric by means of time-resolved, low-order wave-mixing experiments, and show that, close to the material damage threshold, the so far unexplored injection current provides the leading contribution. The sensitivity of the harmonic emission to the subcycle ionization dynamics offers an original approach to characterize the evolution of laser-induced plasma formation in optical microprocessing. Strong-field-induced nonlinearities from the injection of electrons into the conduction band contribute to harmonic generation in amorphous quartz. Close to the damage threshold, they dominate over intraband and interband contributions.

Stochastic Assessment of Harmonic Propagation and Amplification in Power Systems Under Uncertainty

The time-varying harmonics in power systems are not only caused by the stochastic harmonic emissions from different types of harmonic sources, but also the uncertain harmonic response of the system. This paper aims to reveal the impact of the latter and presents a stochastic assessment technique to study the harmonic propagation and amplifications in power systems. To achieve this, systematic indices are defined to quantify the harmonic propagation and amplification characteristics of the system. Potential system uncertainties are then categorized using aleatory and epistemic uncertainties. As a result, both the time-varying and epistemic randomness can be characterized. Finally, the stochastic behavior of the harmonic propagation and amplification is studied using the Monte Carlo simulation technique. Moreover, the impact of load modelling method on the randomness of harmonic propagation and amplification has been investigated, raising awareness to the importance of careful selection and validation of the load modelling on harmonic studies. Extensive case studies confirm the usefulness and effectiveness of the proposed method.

Topological light fields for highly non-linear charge quantum dynamics and high harmonic generation.

We study theoretically the electron quantum dynamics in atoms driven by intense IR laser pulses that are phase and/or polarization structured. The extremely non-linear electron dynamics causes high harmonic emission, which we calculate, analyze, and characterize. Results are presented for three different types of structured lasers: radially polarized and azimuthally polarized beams and optical skyrmions. We identify a topological index that is inherent to the driving pulse topology and is taken over by the high harmonics. All harmonics are found to have the same topological index. For vector IR pulses as driving fields, the far-field emitted beam tightens with a higher topological order and remains unchanged when the atom is driven by an optical skyrmion.

Quantum Ring in a Magnetic Field: High Harmonic Generation and NOT Logic Gate

AbstractThe effect of a static magnetic field on the high harmonic generation (HHG) from a quantum ring driven by one laser polarized along the x‐axis is studied. The spin polarization and the temporal emission of the harmonics are studied by varying the intensity of the magnetic field and it is shown how these results have a significant technological impact in computer technology; in fact a boolean algebra can be implemented by assigning 0 and 1 values to low and high pulse intensities of the emitted harmonics and logic gates like the NOT can be created.

Approach to determine harmonic contributions in distribution networks using underdetermined blind source separation and form similarity distance

This study proposes a new approach to determine harmonic contributions in distribution networks. The approach effectively combines underdetermined blind source separation (UBSS) and form similarity distance (FSD), and it aims to minimise the negative impacts of harmonic source coupling and background harmonic fluctuations. Considering the underdetermined measurement, UBSS is introduced to estimate the harmonic emission current in the light of the sparsity of source signals. Through analysing the form variation features of harmonic time series, FSD is applied to identify the relatively stable background harmonics for utility equivalent harmonic impedance calculation. Furthermore, a complete procedure of harmonic contribution assessment is presented. To verify the high performance of the proposed approach, the simulation study and field test are both conducted, and a detailed comparative analysis of different approaches is carried out. The results show that the proposed approach is able to more accurately determine harmonic contributions than the existing methods, and has better robustness against significant harmonic source coupling and drastic background harmonic fluctuations.

Multielectron Effect for High-Order Harmonic Generation From Molecule Irradiated by Bichromatic Counter-Rotating Circularly Polarized Laser Pulses

We investigated high-order harmonic generation in molecules N2 and C6H6 irradiated by bichromatic counter-rotating circularly polarized laser pulses by using time-dependent density-functional theory methods. It is found that $3N$ ( $N$ is an integer) order harmonics in C6H6 disappear. Whereas, $N$ order harmonics are obtained in N2. Analysis of the high harmonic generated from individual electronic orbital of the molecule, shows that, the characteristics of harmonic spectra are determined by the spatial distribution of electronic orbits. Moreover, effects of molecular orientation on harmonic emission are also presented.

Role of potential on high-order harmonic generation from atoms irradiated by bichromatic counter-rotating circularly polarized laser fields**Project supported by the National Key Research and Development Program of China (Grant Nos. 2019YFA0307700 and 2017YFA0403300), the National Natural Science Foundation of China (Grant Nos. 11627807, 11774175, 11534004, 11774129, 11975012, and 11604119), the Fundamental Research Funds for the Central Universities of China (Grant

We investigate high-order harmonic generation from atoms irradiated by bichromatic counter-rotating circularly polarized laser pulses by numerically solving the time-dependent Schrödinger equation. It is found that the minimum energy position of the harmonic spectrum and the non-integer order optical radiation are greatly discrepant for different atomic potentials. By analyzing the quantum trajectory of the harmonic emission, discrepancies among the harmonic spectra from different potentials can be attributed to the action of the potential on the ionized electrons. In addition, based on the influence of the driving light intensity on the overall intensity and ellipticity of higher order harmonics, the physical conditions for generating a high-intensity circularly polarized harmonic can be obtained.

A Modular Power Converter With Active Front-End System to Mitigate Harmonics in Distribution Networks

Power quality improvement of power electronics systems in many applications such as adjustable speed drive (ASD) is vital due to the high penetration of grid-connected converters in distribution networks. Conventional diode bridge rectifiers are widely utilized in three-phase systems due to their cost-effectiveness, simplicity, and reliability. To improve their harmonic behavior, in this article, a three-phase bridge rectifier with harmonic mitigation function using an electronic inductor is proposed. The proposed system can mitigate current harmonics caused by other conventional rectifiers connected at the same point of common coupling (PCC). Based on the proposed harmonic reduction technique, a combination of three-phase rectifiers can comply with low-order harmonic emission limits according to IEC 61000-3-12 standard. Simulation and practical measurements are performed to validate the proposed method.

A theoretical model of high-harmonic generation from two-color relativistic circularly polarized laser pulse interacting with over-dense plasmas

In this article, we set up a theoretical model to investigate the physical mechanism of circularly polarized (CP) high-harmonic generation (HHG) by two-color relativistic driving lasers (with one at fundamental and the other at second harmonic). The compression effect of the electron density profile and the boundary oscillating are responsible for the harmonic emission. Based on this model, the scaling law between the intensity of the 4th harmonic and that of the fundamental driving laser can be successfully acquired. Our theoretical model holds only when the second-harmonic laser is much weaker than the fundamental laser. For more general cases, particle-in-cell (PIC) simulations are performed to demonstrate that the HHG efficiency. The intensity of higher order harmonics can be effectively tuned by gradually enhancing the intensity of the second-harmonic driving laser.

Novelty method for the utility harmonic impedance estimation based on Gaussian mixed model

The accurate estimation of harmonic impedance on the utility side of a point of common coupling (PCC) is much important to harmonic control, harmonic emission level, and harmonic responsibility analysis. In this study, a novel estimation method for the utility harmonic impedance is proposed, which employs the Gaussian mixed model (GMM) to fit the measured data at a PCC, because the authors find that the statistical distribution of the measured data at a PCC is close to the Gaussian distribution. Also, in theory, GMM can approach the probability distribution of any data. In this method, the Norton equivalent circuit model at a PCC is first expressed as a GMM, and the utility harmonic impedance in the GMM is estimated by expectation maximisation iterative method. Compared to the existing estimation methods, an outstanding advantage of this method is that it is less affected by background harmonics; therefore, higher accuracy can be acquired in this method. The effectiveness and accuracy of this method are verified by simulation experiments and field data.

Analysis and Rectification of Power Line Conducted Emission Test Exceeding Standards

The power transmission emission test (CE102) is the key to electromagnetic compatibility (EMC) testing. The device exceeded the limit at multiple frequencies in the CE102 test. The analysis was performed to locate the curve. The filter was selected based on the frequency characteristics of the filter components and the DC-DC conversion was performed. The harmonic emission of the switching frequency of the converter was analyzed and effectively suppressed. The filter module circuit was set according to the characteristics of the interference source, the key parameters of the filter module was calculated, the rectification method was formulated, and CE102 test was performed again to determine the accuracy of the rectification plan.

Методи боротьби з кондуктивною завадоемісією у зворотноходових перетворювачах

Pulsed power supplies of various topologies (return running, forward running, half-bridge and full-bridge converters) generate high-frequency common-mode noise through their high-frequency mode of pulse-width modulation. Electrical and electronic equipment is known to comply with electromagnetic compatibility standards such as CISPR, IEC, EN, FCC. If necessary, to reduce the converter mass, the pulse-width modulation frequency will increase. As a result, the electromagnetic noise of the power source also becomes larger. Therefore, electromagnetic compatibility problems become one of the most difficult to design power supplies.The article presents methods for reducing conducted noise emission, namely the suppression of common-mode noise in switching power supplies. In particular, schematic methods and methods with constructive changes, physical harmonics compensation methods (interleaving), and methods based on special control methods are presented. The structural and compensation approach allows achieving significant results in reducing the level of common-mode noise. The structural approach includes grounding and shielding. The compensation approach includes three methods: the first is the method of mutual compensation of noise sources; the second is the method of quasicompensation of noise sources; the third is the method of active compensation. The conducted simulation confirmed the decrease in the emission of higher harmonics of the input current in the power network.

Multipolar, polarization-shaped high-order harmonic generation by intense vector beams

High harmonic generation (HHG) is a manifestation of the strongly nonlinear response of matter to intense laser fields and has, as the basis for coherent XUV sources a variety of applications. Recently, HHG from atoms in a phase and polarization structured laser was demonstrated and interpreted based on the transverse electric field component of the driving pulse. Here we point out that as dictated by Maxwell equations, such fields have a longitudinal component which in general has a fundamental influence on the charge dynamics. For instance, its interplay with the transversal field component enables endowing the emitted radiation locally with circular polarization and a defined polarity. It is shown that the time-dependent Stokes parameters defining the polarization state of HHG can be tuned by varying the waist of the driving field which in turn, changes the ratio between the longitudinal and transverse electric-field components of the driving laser. In addition, employing a multipole expansion of the produced harmonics exposes the specific multipolar character and the relation to the spatial structure of the driving field polarization states. The scheme proposed here allows a full polarization control of the emitted harmonics by only one driving laser. A tighter focusing of the driving pulse renders possible the emission of harmonics with both even and odd spatial symmetry. The underlying mechanism is due to the fundamental interplay between the transverse and longitudinal components of the laser's electromagnetic vector potential. The ratio between those components is controllable by just focusing the laser spot, pointing to an accessible tool for polarization and polarity control of the high harmonics.

Selection of intense spectral region and attosecond pulse from X2+ by using chirp-delay effect

A potential scheme to obtain intense harmonic spectra from X[Formula: see text] ([Formula: see text] and T) has been studied by using chirped-delay effect and half-cycle pulse. First, for the shorter pulse duration case, the main contributions of harmonic spectra of H[Formula: see text] and T[Formula: see text] are both coming from the falling part of laser field. While, for the longer pulse duration case, the rising and falling parts of laser field play the main role in harmonic spectra of H[Formula: see text] and T[Formula: see text], respectively. Second, according to the changed law of harmonic yields of H[Formula: see text] and T[Formula: see text] and by properly introducing the chirp-delay effect at some specific timing, the intense harmonic emission peak (HEP) can be obtained from both H[Formula: see text] and T[Formula: see text]. Third, with the help of the half-cycle pulse, the selected HEP can be further extended, showing the intense and broad spectral continua. Finally, by Fourier transformation of some harmonics on the spectral continua, the intense attosecond pulses with durations of 35 as can be produced.