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Generally, driven by a specific laser waveform, a single-order harmonic from the atomic harmonic spectrum can be enhanced, caused by the multiple acceleration-recombination processes. However, in t...

—Harmonic levels in distribution power systems are expected to rise in the future. Understanding the consumer load composition of each individual circuit and maximum harmonic limits can help utilities plan and mitigate power quality issues. This paper presents a sensitivity analysis approach of IEEE Standard 519 total harmonic distortion (THD) current limits on an actual utility model. A new dynamic harmonic index method for characterizing distribution power circuits is proposed, which utilizes the short circuit ratio (SCR) as the main parameter. OpenDSS is used as a modeling platform to study the THD of the voltage (THDv), while increasing the harmonic spectrum of random consumer load points. The main goals are to: (1) identify voltage behavior in power utility networks when an increasing number of consumers operate at the Std. 519 limits, and (2) categorize utility circuits using available information. The short circuit at the point of common coupling, maximum demand load currents, and the circu...

A new method for the high-order harmonic generation on the quantum dots is proposed. Interaction of the kicking laser field with a single-electron cylindrical quantum dot without and in the presence of an external magnetic field is considered. The finite hard wall model and heterostructured semiconductor quantum dot are assumed in order to provide relation to real system which could be studied in an experiment. In particular, GaAs/AlxGa1-xAs quantum dot is examined throughout the paper. Harmonics to a very high-order are obtained which is significant for the attosecond pulse generation. This result can be explained on the basis of the quantum-confined Stark effect. During the kick, the electron energy is increased and it is associated with the pronounced quantum-confined Stark effect in the energy spectrum. The electron transitions to the inner shells give such harmonic emission as a result. It is shown that the range of the harmonic spectrum is strongly dependent on the pulse duration. The influence of a realistic form of kick present in experiments, as the Gaussian approximation for delta function, to the harmonic emission is examined.

High-order harmonic generation from the asymmetric helium hydrogen molecular ion exposed to a few-cycle chirped laser field is theoretically investigated by numerically solving the reduced one-dimension non-Born–Oppenheimer time dependent Schrodinger equation. The numerical results show that the plateau of the high-order harmonic spectrum is dramatically broadened and smoother with the introduction of the chirp. Further study presents that only the short quantum path contributes to harmonic emission and the long quantum path disappears in the chirped laser. In addition, an 80-as isolated attosecond pulse is obtained by superposing the harmonics from the 100th to the 130th order in the chirped field. The time-frequency distributions and the electronic probability distributions are presented to explain the underlying physical mechanism.

An improved polarization gating scheme on attosecond X-ray pulse generation from high-order harmonic generation has been investigated. It is found that by properly adding a linearly polarized pulse to the circularly polarized pulse, the harmonic spectrum is remarkably enhanced and controlled, leading to an efficient generation of the ultra-broadband supercontinuum covered by the spectrum range from ultraviolet to X-ray. Classical and the quantum time–frequency analyses have been shown to explain the harmonic emission process. Moreover, from analyzing the harmonic phases, we see that the phases of the generated harmonics are almost linear, which is beneficial to the attosecond pulse generation. As a result, a series of phase-steady and wavelength-tunable sub-50 as X-ray pulses can be obtained.

We theoretically investigate the high-order harmonic generation from the helium ion in a two-color spatially inhomogeneous laser field. The numerical calculations show that this spatiotemporally synthesized laser field can not only significantly extend the harmonic cut-off, but also generate an ultrabroad extreme ultraviolet supercontinuum with a 1737 eV bandwidth. In addition, the spatiotemporal combination can eliminate the long quantum path and select the short one, and then an ultrashort isolated 12.3 as pulse with a bandwidth of 310.2 eV is obtained directly. Further, the dependences of the harmonic spectrum on the parameters including spatial inhomogeneity, time delay, carrier-envelope phase, and intensity are further discussed.

—A new controller is developed for a single-phase inverter based on the dynamic evolution control method. The non-linear model equations and algorithm of the approach is derived and presented. The simulation is conducted based on the proposed method by MATLAB/Simulink to test the performance of the controller for large load variations. The system was also tested experimentally to show the feasibility of the proposed method applied to a single-phase inverter. Results show that the proposed approach is suitable for applications with large load variations. Practical results show that the controller can successfully handle a 40 times load change in less than 2 ms. It also has good output in the harmonic spectrum compared with the IEEE 519 harmonic standard during no-load and full-load conditions.

A promising method to both extend the harmonic energy and enhance the harmonic intensity is presented when a He atom is exposed to the combination of a two-color chirped pulse and an ultrashort ultraviolet pulse. It is found that: (1) with the introduction of the two chirps, the harmonic energy has been remarkably extended; (2) by properly adding an ultrashort ultraviolet pulse to this synthesized two-color chirped pulse, the harmonic yield is enhanced by 3 orders of magnitude compared with the two-color chirped case; (3) the harmonic spectrum higher than the 96th order shows an ultrabroad supercontinuum with a 395 eV bandwidth, and the proper superposition over the harmonics directly produced a series of intense 40 as pulses which is 3 orders of magnitude higher than that in the two-color chirped case.

In this paper, we theoretically investigate high-order harmonic generation (HHG) from a helium atom prepared in a coherent superposition state in a two-color laser field. Numerical results show that the emission efficiency of the harmonic spectrum in a coherent superposition state is enhanced by approximately eight orders of magnitude compared with the case of the ground state. In addition, the effect of the initial population of the excited state on the HHG is presented to reveal the physical origin of the enhancement of HHG. By adjusting the laser parameters of the driving pulse, such as the chirping parameter, the relative phase, and the intensity of the driving pulse, an ultrabroad continuum with a width of 275 eV can be observed. Finally, an isolated 12-as pulse is generated after phase compensation.

By numerically solving the time-dependent Schrodinger equation for helium gas in a special two-color laser field, which is synthesized by a long (9 fs) driving pulse and a short (6 fs) controlling pulse, we discuss the influence of the carrier-envelope phase, frequency, and the intensity of the controlling pulse on the generation of harmonic spectra and isolated attosecond pluses. In the cutoff region, two or three plateaus can be controlled by optimizing these laser parameters, and an ultrabroad supercontinuum harmonic spectrum with a bandwidth of 800 eV can be produced, which can support an ultrashort isolated 4.5 as pulse generation by Fourier transformation. Furthermore, using classical ionizing and returning energy maps, time–frequency analyses are presented to explain the underlying physical mechanisms.

An efficient method to enhance the harmonic efficiency and generate an isolated attosecond pulse is proposed by preparing the initial state as a coherent superposition of the ground state and a Rydberg state in a two-color laser field. By numerically solving the time-dependent Schrodinger equation, we found that for the superposition state with the optimal Rydberg state, not only is the harmonic efficiency enhanced significantly, but also the width of the continuous spectrum is extended. The ionization probability and the time-frequency distribution of the harmonic spectrum are also calculated to understand the physical origin of the enhancement of the harmonic spectrum. In addition, by adjusting the parameter of the laser pulse, a supercontinuum with both higher conversion efficiency and slighter modulation can be observed. As a result, an isolated 7-as pulse with a bandwidth of 495 eV can be obtained after phase compensation.

We make a detailed assessment of which form of the dipole operator to use in calculating high order harmonic generation within the framework of the strong field approximation, and look specifically at the role the form plays in the inclusion of multielectron effects perturbatively with regard to the contributions of the highest occupied molecular orbital. We focus on how these corrections affect the high-order harmonic spectra from aligned homonuclear and heteronuclear molecules, exemplified by $\mathrm{N}_2$ and CO, respectively, which are isoelectronic. We find that the velocity form incorrectly finds zero static dipole moment in heteronuclear molecules. In contrast, the length form of the dipole operator leads to the physically expected non-vanishing expectation value for the dipole operator in this case. Furthermore, the so called "overlap" integrals, in which the dipole matrix element is computed using wavefunctions at different centers in the molecule, are prominent in the first-order multielectron corrections for the velocity form, and should not be ignored. Finally, inclusion of the multielectron corrections has very little effect on the spectrum. This suggests that relaxation, excitation and the dynamic motion of the core are important in order to describe multielectron effects in molecular high-order high harmonic generation., Figures 2 and 4 have been simplified in order to fulfil the size requirements of arXiv; in the new version references have been added

We propose a new scheme for the generation of single zeptosecond pulses by using a one-dimensional muonic hydrogen atom model. Owing to the large mass of the muon, the muonic atoms can survive much stronger fields, which causes a very broad plateau in the high-order harmonic spectrum. By solving a one-dimensional time-dependent Schrodinger equation, the high-order harmonic spectrum of the muonic atom in super-intense nonlinear chirped laser pulses is obtained. It is found that the harmonic spectrum is greatly affected by the chirp rate parameters of the laser field. By adjusting the chirp rate parameters, an ultra-broad super-continuum spectrum could be obtained, from which a single zeptosecond pulse could be generated without phase compensation.

We have created a reintonation system that minimizes measured roughness of parallel sonorities as they are produced. Intonation adjustments are performed by finding, within a user-defined vicinity, a combination of fundamental frequencies that yields minimal roughness. The vicinity imposition limits pitch drift and eases real-time computation. Prior knowledge of the tones played and timbres used is not used for execution of the algorithm. We test a proof of concept prototype by adjusting equal temperament intervals rendered with a harmonic spectrum towards pure intervals in real-time. This prototype exemplifies musical and auditory characteristics of roughness minimization by adaptive techniques. We discuss the results obtained, limitations, possible improvements, and future work.

Although a hysteresis current control technique is a simple and a reliable modulation scheme in switching control systems, its harmonic spectrum around the switching side band may not distribute properly. Random pulse width modulation technique is an effective scheme that distributes the harmonic spectrum of the load current, and it can reduce the acoustic noise and the mechanical vibration of inverter-fed motor drives. This paper presents a new method for hysteresis current control based on random band control for a better spreading of the harmonic spectrum of the load current. In this paper, the effect of the random-band hysteresis current control is analysed to determine the best hysteresis band variation and the results have been compared with the traditional hysteresis current control. Theoretical analysis and simulations have been performed to describe the method.

We analyse S-matrix-type approaches to strong-field ionization by an intense few-cycle laser pulse. We derive simple modifications of approximate S-matrix-type approaches that either neglect the effect of the ionic potential after ionization, or treat this potential perturbatively. We show how these modifications eliminate some crucial problems and artefacts, such as the 'curse of the displaced atom', associated with the choice of gauge in the strong field approximation. We then discuss how these approximate S-matrix-type approaches should be applied to dissociating molecules using the example of H [image omitted]. We show that suppression of electron tunnelling between the two fragments of the molecular ion introduces dramatic changes in the spectrum of high harmonic emission generated by an intense laser pulse that probes the molecular dissociation. For large internuclear distances and even when the active electron is fully delocalized between the two fragments, the high harmonic spectrum loses all traces of the conventional interference pattern associated with a two-centre molecular structure.

The purpose of this article is to analyze the harmonic spectrum of the three-phase PWM inverter drives used in a power system. The analytical methods are based on a 3-D modulation model and double Fourier series (DFS). In this article, with Matlab, we analyzed the harmonic model created by DFS, and used time-domain simulation tools, Pspice and Simulink, to construct the model and simulation of the three-phase DC to AC PWM inverter found in the system. Results show that the harmonics generated by the simulator tools and that generated by DFS method are almost identical, and that the harmonic model constructed by means of the 3-D modulation model proposed is highly accurate.

Results are presented on the generation of high harmonics due to the scattering of relativistic electrons from high-intensity laser light. The experiments are carried out with a Nd:glass laser system with a peak intensity of 1019 W cm-2 in underdense He, N2 and Ar plasma. It is shown that, at high intensities when the normalized electric field approaches unity, in addition to the conventional atomic harmonics from bound electrons, there is significant contribution to the harmonic spectrum from free electrons. The characteristic signatures of this are found to be the emission of even-order harmonics, a linear dependence on the electron density, a significant amount of harmonics even with circular polarization and a much smaller spatial region over which these harmonics are produced as compared to the atomic case. Imaging of the harmonic beam shows that it is emitted in a narrow cone with a divergence of 2-3°. The measured spatial profile of the harmonics is shown to be in excellent agreement with calculati...

Robust random switching control for a three-phase hysteresis current-controlled PWM inverter to promote its ability in servo driving control is studied in this paper. After observing the effect of varying band on the output harmonic distribution characteristic of a hysteresis current-controlled PWM inverter, a random switching hysteresis PWM scheme is developed. A robust spectrum shaping technique is devised such that the randomized inverter output harmonic spectrum is further shaped to the desired pattern. In the resulted frequency spectrum, the magnitudes of lower-frequency harmonics are reduced significantly. This makes the hysteresis PWM inverter suitable to serve as a driving source for position servo motor drives. The effect of AC motor neutral point isolation on the random switching performance is observed. The developed random switching inverter is used to power a linear permanent magnet synchronous motor-driven magnetic suspended positioning stage, and the resulted position control performance is...

This paper presents the assessment and comparison of power quality problems created by common electronic loads. T1he key issues covered are reactive kVA drawn, harmonic spectrum, total harmonic distortion, power factor and displacement factor. The different loads considered in this study are commonly used electronic gadgets as personal computer, printer and fluorescent tube. The results highlight the extent of damage being caused by these loads in polluting the utility grid. Improvement in quality of power attained by the use of constant voltage transformer is also presented. Use of active filters for Improvement of power factor of such electronic loads is suggested.

We consider the transmission of an intense short light pulse through a solid insulator undergoing tunnel ionization sufficiently high to change the sign of the plasma dielectric function from positive to negative. This may cause a strong reflection of the incident wave from the insulator surface. The ionization process also involves harmonic generation due to a sharp change in ionized electron density. We describe a theoretical scheme based on the Floquet expansion that provides a qualitative analysis of both self-reflection and the harmonic spectrum. Comparison of the exact numerical solution with the slow envelope of the fundamental harmonic shows that the Floquet expansion approach fails at the limit of strong reflection. We calculate the harmonic spectrum using the exact wave equation and study its peculiar features when reflection increases.

We discuss, through classical simulations, some general properties of the response of anharmonic oscillators to an intense external oscillating force. We address in particular the question of the presence of hyper-Raman or ‘atomic’ components in the harmonic spectrum.

The harmonic spectrum emitted by a two-level atom driven by a resonant laser field is calculated. The spectrum is seen to depend on the shape of the pulse. In the case of an asymmetric pulse profile, harmonic emission is present also at a relatively low intensity field.

Computer synthesis of sound offers varied and precise controls and is therefore more versatile than synthesis with ordinary electronic equipment. To use it efficiently, one needs a convenient program to describe the physical structure of a wide variety of sounds and a user who provides such a description. New “musical” possibilities are opened in regard to the frequency, amplitude, harmonic spectrum and phase of waveform. The computer storage and editing facilities permit us to drive multiple sound sources (speakers), to change the physical capacity of our hearing, and give us new ideas to represent a “musical” universe. In this paper, the author presents the continuum of sound from the past, the computer sound synthesis system MIDIM, and different aspects of the use of a flexible electroacoustic system (storage/transfer/diffusion).

A novel PPM scheme, namely the three level complementary slope elementary PPM (3-L CS-E-PPM) is proposed in this paper. It is shown that this scheme possesses a number of significant features which makes it suitable for variable frequency inverter drive applications, ( a) It has a strong fundamental component (especially for low values of the modulation index, A, which is linearly controlled by the pulse width τ.( b) Its operation is uniform throughout the whole frequency range avoiding thus undesirable transitional stages; this is a significant advantage over PWM schemes, (c) The minimum time interval between successive choppings is held sufficiently long so that safe commutation of switching elements is guaranteed, ( d) Appropriate values of (A, τ) parameters can be chosen in such a way that the desired fundamental component is achieved while the higher harmonic spectrum is sufficiently low. Moreover, the pulsating torques developed due to voltage harmonics can be ‘optimized’. This is possible due to th...

The paper presents a study of the problem of quantization which is linked with the numerical control voltage of a three-phase cycloconverter controlled by a microprocessor. The study makes a compromise between either using a large number of quantizing steps of the desired control voltage, which requires an Increase in microprocessor memory size, or using small number of steps, which leads to a high degree of harmonic presence in load current. In order to carry out such a study, a complete digital simulation of the whole system (source, cycloconverter, load and control devices) is used. Two types of numerical control-voltage are compared subject to the harmonic spectrum of the load current. Calculation is given for the optimum number of steps and the type of the numerical control-voltage

Pulse-width modulation (PWM) technique can be applied for reduction or elimination of any M-line current harmonic components in ac/ac and ac/dc converters. PWM technique shifts the line-side harmonic spectrum to higher frequencies. Hance, filter size and cost are considerably reduced. The existing methods are compared with the proposed PWM technique. A new power circuit suitable for PWM technique is presented. The proposed schemes are experimentally verified and the results are discussed.