Harmonic Efficiency Research Articles

Circularly Polarized High-Harmonic Beams Carrying Self-Torque or Time-Dependent Orbital Angular Momentum.

In the rapidly evolving field of structured light, self-torque has been recently defined as an intrinsic property of light beams carrying time-dependent orbital angular momentum. In particular, extreme-ultraviolet (EUV) beams with self-torque, exhibiting a topological charge that continuously varies on the subfemtosecond time scale, are naturally produced in high-order harmonic generation (HHG) when driven by two time-delayed intense infrared vortex beams with different topological charges. Until now, the polarization state of such EUV beams carrying self-torque has been restricted to linear states due to the drastic reduction in the harmonic up-conversion efficiency with increasing the ellipticity of the driving field. In this work, we theoretically demonstrate how to control the polarization state of EUV beams carrying self-torque, from linear to circular. The extremely high sensitivity of HHG to the properties of the driving beam allows us to propose two different driving schemes to circumvent the current limitations to manipulate the polarization state of EUV beams with self-torque. Our advanced numerical simulations are complemented with the derivation of selection rules of angular momentum conservation, which enable precise tunability over the angular momentum properties of the harmonics with self-torque. The resulting high-order harmonic emission, carrying time-dependent orbital angular momentum with a custom polarization state, can expand the applications of ultrafast light-matter interactions, particularly in areas where dichroic or chiral properties are crucial, such as magnetic materials or chiral molecules.

Enhanced high harmonic efficiency through phonon-assisted photodoping effect

High-harmonic generation (HHG) has emerged as a central technique in attosecond science and strong-field physics, providing a tool for investigating ultrafast dynamics. However, the microscopic mechanism of HHG in solids is still under debate, and it is unclear how it is modified in the ubiquitous presence of phonons. Here we theoretically investigate the role of collectively coherent vibrations in HHG in a wide range of solids (e.g., hBN, graphite, 2H-MoS2, and diamond). We predict that phonon-assisted high harmonic yields can be significantly enhanced, compared to the phonon-free case – up to a factor of ~20 for a transverse optical phonon in bulk hBN. We also show that the emitted harmonics strongly depend on the character of the pumped vibrational modes. Through state-of-the-art ab initio calculations, we elucidate the physical origin of the HHG yield enhancement – phonon-assisted photoinduced carrier doping, which plays a paramount role in both intraband and interband electron dynamics. Our research illuminates a clear pathway toward comprehending phonon-mediated nonlinear optical processes within materials, offering a powerful tool to deliberately engineer and govern solid-state high harmonics.

Enhancing second harmonic generation in lithium niobate metasurfaces through symmetric protection bound states in the continuum

In order to address the issue of high loss and low field effect in the generation process of traditional second harmonic, we employ lithium niobate (LN), a highly efficient nonlinear material. Our designed structure exhibits a symmetry-protected bound state in a continuum medium (BIC) when subjected to a y-polarized incident wave, resulting in an impressive second-harmonic conversion efficiency of 5.5 % at a pump strength of 0.4MW/cm2. Moreover, it also shows accidental BIC when subjected to an x-polarized incident wave, exhibiting a second harmonic conversion efficiency of 1.83 %. We conducted a Cartesian multipole analysis to investigate the underlying cause of BIC formation, and the results are in excellent agreement with the electromagnetic field map. Subsequently, we explored the correlation between asymmetry degree, Q value, and second harmonic conversion efficiency. Our study presents novel approaches for enhancing symmetry-protected BICs in second harmonic waves while providing simplified indicators for evaluating second harmonic transformation efficiency.

Role of blue-shift length in macroscopic properties of high-harmonic generation

The production of brighter coherent XUV radiation by intense laser pulses through the process of high-harmonic generation (HHG) is one of the central challenges in contemporary nonlinear optics. We study the generation and spatial propagation of high harmonics analytically and via ab initio simulations. We focus on the length scales defining the growth of the harmonic signal with propagation distance and show that the well-known coherence length limits HHG only for relatively low driving intensities. For higher intensities, the photoionisation of the medium, naturally accompanying HHG, leads to essentially transient phase matching and laser frequency blue shift. By systematically taking both of these factors into account, we demonstrate that the behaviour of the harmonic signal at higher intensities is defined by another length scale—the blue-shift length. In this generation regime the XUV intensity at a given frequency first grows quadratically and then saturates passing the blue-shift length, but the total harmonic efficiency continues growing linearly due to the linear increase of the harmonic line bandwidth. The changeover to this generation regime takes place for all harmonic orders roughly simultaneously. The rate of the efficiency growth is maximal if the atomic dispersion is compensated by photoelectrons near the centre of the laser pulse. Our theory offers a robust way to choose the generation conditions that optimise the growth of the harmonic signal with propagation.

Comprehensive Analysis of DC Link Capacitors Used in Cascaded H-Bridge Motor Driver

An essential part of inverter design is selecting direct current-Link Capacitors (DCLC) for Medium-Voltage Cascaded H-bridge motor Drivers (MV-CHBMD). This article analyzes capacitor configuration for MV-CHBMD to improve the quality of driver output and input current depending on an analysis of DCLC current effects. The techniques were employed with two-level converters to find the harmonics, and the root mean square (RMS) value of the capacitor current has been expanded to seven-level MV-CHBMD. Additionally, a novel mathematical technique has been recommended for determining the RMS current and voltage ripple of the DCLC. The proposed MATLAB simulation technique provides a comprehensive analysis of the outcome results. This allows for easy customization to other modulation methods and application to higher-level MV-CHBMD. Specifically, it calculates the worst-case scenario for the DC-link voltage in a 1000-horsepower and 3.3-kV system. The study also presents empirical evidence that specific system components endure excessive stress. This information is valuable for accurately specifying system components and ensuring optimal system design in the MV-CHBMD system. This article examines the potential impact of standard mode voltage on the bearings of medium-voltage motors. In addition, an optimal approach for selecting DCLCs in a multilevel cascaded H-bridge (CHB) motor driver strategy is proposed, effectively eliminating voltage stress on switching devices. The effectiveness of these systems is demonstrated by presenting simulation results. A comprehensive study analyzed the performance of various inverter levels, including total harmonic distortion (THD) and efficiency. The DC link was constructed using the MATLAB platform to conduct a thorough analysis. The proposed approach exhibits superior performance and lower costs compared to traditional methods. The experimental work and test confirm the simulation results. The test result showed that selecting DCLCs in a CHB provides a higher-quality output waveform into CHB, which supports the controlling structure and reduces the probability of malfunctions.

VSC-STATCOM Performance Under Different Fault Sensing using PSO Tuned Hybrid SMC

In this paper, we investigate the PSO-tuned hybrid SMC performance based VSC-STATCOM under different conditions of fault using hybrid renewable energy sources (HRES). A hybrid renewable energy resource system (HRES) consists of PV, wind power, and batteries. Here the Irradiance is the PV input and the wind energy is Wind Input. The storage of energy is used for battery. The battery is used for changing weather condition or the changing the condition of the environment. Hybrid VSC-STATCOM controller based on SMC to reduce power quality issues like sag, swell, harmonics etc. associated with HRES system mainly due to non-linear load conditions. The novelty of our proposed PSO-tuned hybrid Sliding Mode Controller (SMC) method lies in its integration of Particle Swarm Optimization (PSO) as a tuning mechanism within the SMC framework. The Harmonic reduction and efficiency improvement is verified by using the Simulation. Therefore, the proposed system performance is simulated and to optimize the terms are real and reactive power, Total Harmonic Distortion (THD) and Voltage Sag.

Critical Analysis of Active Filter for Harmonic Reduction under Varying Load

In this paper, we give the main focus on the proliferation of non-linear loads in power systems, the mitigation of harmonics has become a critical concern to ensure stable and efficient operation. This study presents an analysis of an advanced control active filter (ACAF) designed for harmonic reduction under varying load conditions. The ACAF is a sophisticated solution that employs advanced control algorithms to effectively suppress harmonics and maintain power quality. The research investigates the performance of the ACAF under varying load conditions, which represent real-world scenarios where power consumption fluctuates. A comprehensive analysis is conducted to evaluate the filter's ability to adapt and maintain harmonic suppression efficiency across different load profiles. The study considers various load scenarios, including steady-state operation, transient load changes, and dynamic load fluctuations. The findings of this research contribute to the understanding of advanced control active filters in practical power systems with non-linear loads and varying operating conditions. The analysis provides valuable insights into the design, optimization, and implementation of ACAFs for harmonic mitigation, ultimately improving power quality and system reliability in modern electrical networks. A classified list of 38 publications on this topic is also given for the quick reference.

Integration of electric vehicle into smart grid: a meta heuristic algorithm for energy management between V2G and G2V

Recently, Electric Vehicles (EV) have been providing fast response and substantial progress in the power generation model. Further, EVs are exploited as adaptable Energy Storage Systems (ESSs) and show a promising performance in ancillary service markets to increase the demand of Smart Grid (SG) integration. The expansion of Vehicle-to-Grid concept has created an extra power source when renewable energy sources are not available. Yet, numerous operational problems still are required to be considered for EV implementation to turn out to be extensive. Even the development of Photo-Voltaic (PV) technology creates a problem in SGs when used for EV charging. Because of this, the Energy Management System (EMS) is required to handle charging requirements and deal with the intermittent generation. Here, in this research, an Improved Honey Badger algorithm (IHBA) is proposed for integrating SGs with EV parking lot, solar panels, and dynamic loads at the Point of Common Coupling (PCC). The proposed IHBA uses a dynamic programming method to optimize the charging Grid-to-Vehicle (G2V) or discharging Vehicle-to-Grid (V2G) profiles of the EVs using the forecasts of PV generation. This algorithm considers user preferences while also lowering reliance on the grid and maximizing SG effectiveness. The study’s findings show that the Honey Badger method is efficient in resolving issues involving large search spaces. The developed method is used to optimize charging and discharging of EV which is tested in MATLAB to obtain a stable load profile. From the evaluation of obtained results, it is evident that the IHBA controller outperforms the WOA and EHO controllers in terms of total harmonic distortion voltage (3.12%), power loss (0.197 kW) and efficiency (98.47%).

Efficient control of three-phase cascaded multilevel Z-Source inverter using SHEPWM technique

This paper presents an enhanced control strategy for three-phase cascaded multilevel Z-source inverters, focusing on the implementation of Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) techniques to improve efficiency. Z-source inverters are gaining prominence in various applications due to their inherent advantages, such as increased voltage boost capability and inherent shoot-through protection. However, achieving optimal control in cascaded multilevel configurations poses challenges that this study seeks to address. The proposed control strategy optimizes the switching patterns of the inverter, thereby enhancing its overall performance. It allows for precise control over the output voltage and reduces harmonic distortion, ensuring the inverter operates efficiently across varying load conditions. The research methodology involves a comprehensive analysis of the proposed technique, including its mathematical modeling and simulation using advanced software tools. Performance metrics such as total harmonic distortion, efficiency, and transient response are evaluated to quantify the improvements achieved. The results obtained demonstrate the efficiency of the proposed control strategy. This method significantly reduces harmonic distortion in the output voltage, leading to improved power quality. Furthermore, the efficiency of the inverter is enhanced, making it suitable for applications demanding high-performance power conversion.

Enhancing second harmonic generation by Q-boosting lossless cavities beyond the time bandwidth limit

Abstract Nanostructures proved to be versatile platforms to control the electromagnetic field at subwavelength scale. Indeed, high-quality-factors nanocavities have been used to boost and control nonlinear frequency generation by increasing the light–matter interaction. However, nonlinear processes are triggered by high-intensities, which are provided by ultrashort laser pulses with large bandwidth, which cannot be fully exploited in such devices. Time-varying optical systems allow one to overcome the time-bandwidth limit by modulating the cavity external coupling. Here we present a general treatment, based on coupled mode theory, to describe second harmonic generation in a doubly resonant cavity for which the quality-factor at the fundamental frequency is modulated in time. We identify the initial quality factor maximizing second harmonic efficiency when performing Q-boosting and we predict a theoretical energy conversion efficiency close to unity. Our results have direct impact on the design of next generation time-dependent metasurfaces to boost nonlinear frequency conversion of ultrashort laser pulses.

Characterization of the Carrier Lensing Effect in a Second Harmonic Generator

This paper presents studies on the carrier lensing effect of a tapered amplifier in a compact cavity-enhanced second harmonic generator. When different injecting currents are applied, carriers in the tapered amplifier are depleted to different levels depending on the local optical field intensity, resulting in a spatial variation of the refractive index and creating an effective convex lens for the amplified laser beam. This can significantly reduce the mode matching between the pump beam and the cavity, leading to a degradation of the second harmonic generator efficiency. To characterize this effect and provide guidance for mode matching, the evolution of optical fields and carriers in the tapered amplifier is simulated numerically with Maxwell-Bloch equations. The effective focal length of the tapered amplifier is calculated theoretically and verified with experimental calibration. Based on these results, the coupling optics of the cavity can be properly designed so as to achieve a high coupling efficiency. Finally, a single-frequency continuous-wave laser at 461 nm is achieved, with an output power exceeding 500 mW and a conversion efficiency of 33%.

Robust energy storage system for stable in wind and solar

Energy storage systems (ESS) have become a conspicuous research hotspot since they store power and supply it during peak hours. Existing storage systems must be replaced by advanced energy storage with improved performance, energy management, and a control interface due to issues with size, dependability, and charging/discharging. The suggested robust energy retention system uses a battery and a super-capacitor to generate power from wind and solar energy. A Multiport DC converter with a buck-boost capacitor is used to properly discharge the stored energy to DC loads via a DC bus. The inverter is then delivered to a Power Flow Controller (PFC) and a Voltage Source Inverter (VSI). The Gravitational Search Algorithm (GSA) method optimizes the power controller settings based on the fluctuation of the system's active and reactive power. The optimization method ensures improved power flow while dealing with the least amount of power variance in imbalanced load situations. Based on the power variation, the proposed method generates appropriate control signals for the inverter system. The covers convert the inverter and reduce harmonics with a controller. Furthermore, the inverter AC supplied to the AC bus is converted into reactive power by an inductive load, and unwanted signals and harmonics are extracted using a Cascaded C-type filter. As a result, the described method has preserved total harmonic distortion, electrical efficiency, and finer transient stability.

A Review on the Non-Linear Optical Performance of Picric Acid based Crystals

This review delves into the nonlinear optical characteristics of crystals derived from picric acid, providing a comprehensive analysis of their unique properties and potential applications in the realm of nonlinear optics. Picric acid, with its distinctive molecular structure, has been widely explored for its nonlinear optical behaviour, making it a fascinating subject for research and development. The review begins by elucidating the fundamental need and significance of crystal growth. The summary of preparation, spectral analysis and nonlinear optical characteristics and the significance of picric acid as a promising material in this domain is also discussed. The interpretation of nonlinear behaviour in optical properties of various compounds of picric acid is reviewed and discussed. The structural data of aminoacidic picrate crystals in the field of non-linear applications are reviewed. The conceptual background of nonlinear optical properties is well deliberated and used in order to have a better knowledge of the optical behaviour of the picrate crystals. UV-VIS spectroscopy and Second harmonic efficiency of picric acid compounds are also briefly discussed. In conclusion, this review provides a comprehensive overview of the nonlinear optical performance of picric acid-based crystals, offering valuable insights for researchers, scientists, and engineers working in the field of nonlinear optics.

High-order harmonic generation of ZnO crystals in chirped and static electric fields

High harmonic generation in ZnO crystals under chirped single-color field and static electric field are investigated by solving the semiconductor Bloch equation (SBE). It is found that when the chirp pulse is introduced, the interference structure becomes obvious while the harmonic cutoff is not extended. Furthermore, the harmonic efficiency is improved when the static electric field is included. These phenomena are demonstrated by the classical recollision model in real space affected by the waveform of laser field and inversion symmetry. Specifically, the electron motion in k-space shows that the change of waveform and the destruction of the symmetry of the laser field lead to the incomplete X-structure of the crystal-momentum-resolved (k-resolved) inter-band harmonic spectrum. Furthermore, a pre-acceleration process in the solid four-step model is confirmed.

Control of high-harmonic generation from periodic asymmetric lattices

Periodic asymmetric lattices, viewed from one side to the other, have different spatial potential energies. This difference affects the electronic structure of valence electrons. Our work shows that pronounced even harmonic signals are observed from periodic asymmetric lattices driven by a multi-cycle pulse field. The phases of the odd and even harmonics driven by parallel and anti-parallel laser polarization directions are compared and show different dependences on laser polarization direction. Moreover, it is found that each burst in the synthesized attosecond pulse trains in a periodic asymmetric lattice shows the same carrier-envelope phase. We also show that the even-order harmonic efficiency in periodic asymmetric lattices can be enhanced (reduced) by using a multi-cycle driving laser in the presence of a weak terahertz pulse field.

Second Harmonic Emission From Dielectric Nanoresonators in the Absorption Regime

We study second harmonic generation in dielectric nanocylinders as a function of the wavelength of the incident field and geometrical dimensions. Uncommonly, we consider a spectral range in which the emitted nonlinear signal is partially absorbed by the dielectric. Surprisingly, we reveal that the second harmonic efficiency does not decrease as the imaginary part of the complex dielectric refractive index increases. Indeed, the presence of higher order multipoles supported by the resonators at the fundamental wavelength can significantly boost the generated second harmonic signal even in the dielectric absorption spectral region achieving nonlinear efficiency of the same order of magnitude with respect to the lossless case.

A Residential Miniboost Photovoltaic Inverter With Maximum Power Point Operation and Power Quality Compensation

Among the exiting multifunctional photovoltaic (PV) inverters (MPVIs), the main challenges are low efficiency, undesired harmonic emission, and weak compensation capability. In this paper, a theoretical study via rotating phasor to the PV curves is firstly proposed to figure out the undesired harmonic emission puzzle in different PV inverters as well as to provide the foundation for PV inverters to achieve multifunction ability under varying load conditions. On the other hand, a single-phase time-sharing miniboost MPVI with different operation modes is proposed and operated under varying PV and load conditions in order to improve its efficiency and compensation capability without undesired harmonic emission. Corresponding control strategy and stability analysis are given. Finally, a 1.5-kW prototype is presented, benchmarked against harmonic emission issues, compensation capability, and efficiency. Experimental results clearly indicate that the proposed topology and control method can perform the active power injection and power quality compensation with better efficiency and avoiding harmonic emission into the grid dynamically.

A 28 GHz fully integrated GaN enhanced single‐sideband time‐modulated MMIC for phased array system

AbstractThis paper presents a 28 GHz GaN enhanced single‐sideband time‐modulated phased array (ESTMPA), based on a monolithic microwave integrated circuit (MMIC), including both a time‐modulated circuit and an RF front‐end module (FEM). The time‐modulated circuit mainly consists of a numerically controlled attenuator to balance the amplitude, compact phase shifters to generate balanced signals, a reconfigurable power divider, and a quadrature power divider. The FEM mainly consists of a low noise amplifier and a power amplifier, featuring codesign of input/output networks. Based on the in‐phase/quadrature (I/Q) composite modulation technique, a stepped modulation waveform, realized by the time‐modulated circuit, is used to enable a weighted array of phases. This helps generate a scanned beam at the first positive sideband and eliminate the undesired sidebands. The final MMIC‐based four‐element ESTMPA shows a relative suppression level of −16 dB at the positive fifth sideband and −13 dB at the zeroth sideband, and a much higher level at the other undesired sidebands. As a result, a wider signal bandwidth and a higher harmonic efficiency are achieved. In addition, the ESTMPA shows a beam sweeping angle from −30° to 30° in far‐field measurement.

High-repetition-rate seeded free-electron laser enhanced by self-modulation

The spectroscopic methods for the ultrafast electronic and structural dynamics of materials require fully coherent extreme ultraviolet and soft X-ray radiation with high-average brightness. Seeded free-electron lasers (FELs) are ideal sources for delivering fully coherent soft X-ray pulses. However, due to state-of-the-art laser system limitations, it is challenging to meet the ultraviolet seed laser’s requirements of sufficient energy modulation and high repetition rates simultaneously. The self-modulation scheme has been proposed and recently demonstrated in a seeded FEL to relax the seed laser requirements. Using numerical simulations, we show that the required seed laser intensity in the self-modulation is ~3 orders of magnitude lower than that in the standard high-gain harmonic generation (HGHG). The harmonic self-modulation can launch a single-stage HGHG FEL lasing at the 30th harmonic of the seed laser. Moreover, the proof-of-principle experimental results confirm that the harmonic self-modulation can still amplify the laser-induced energy modulation. These achievements reveal that the self-modulation can not only remarkably reduce the requirements of the seed laser but also improve the harmonic upconversion efficiency, which paves the way for realizing high-repetition-rate and fully coherent soft X-ray FELs.

Study of the Crystal Architecture, Optoelectronic Characteristics, and Nonlinear Optical Properties of 4-Amino Antipyrine Schiff Bases.

Two Schiff bases, (E)-4-((2-chlorobenzylidene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (4AAPOCB) and (E)-4-((4-chlorobenzylidene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (4AAPPCB), have been synthesized and grown as single crystals. Single-crystal X-ray diffraction analysis was employed to determine the crystal structure of the compounds, and the results suggest that the compounds crystallized into an orthorhombic crystal system having P212121 and Pbca space groups, respectively. Further, the crystallinity of the compounds was analyzed by the PXRD technique. The UV-vis-NIR spectra of the compounds demonstrate excellent transmittance in the entire visible region. The lower cutoff wavelengths of the compounds were determined to be 338 and 333 nm, respectively; additionally, optical band gaps of the compounds found were 4.60 and 4.35 eV. FTIR and NMR (1H and 13C) spectral techniques were utilized to analyze the molecular structure of the compounds. The compounds emit photoluminescence with broad emission bands with centers at 401 and 418 nm. The thermal stability and phase transitions were assessed through thermogravimetric methods. The phase transition prior to melting was indicated by the endothermic event at around 190 °C in the DTA curves of both crystals, and the same was observed in the DSC curves. The second harmonic efficiencies of the powdered compounds I and II were found to be 3.52 and 1.13 times better than that of the standard reference KDP. The 4AAPOCB and 4AAPPCB compounds showed isotropic polarizability amplitudes of 46.02 × 10-24 and 46.52 × 10-24 esu, respectively. The calculation of linear polarizability and NLO second-order polarizability (β) along with other optical parameters was performed for optimized geometries. The nonzero amplitudes of the average β values for compounds 4AAPOCB and 4AAPPCB were found to be 14.74 × 10-30 and 8.10 × 10-30 esu, respectively, which show a decent potential of the synthesized molecules for NLO applications. The calculated β amplitudes were further explained based on calculated electronic parameters like molecular electrostatic potentials, frontier molecular orbitals, molecular orbital energies, transition energies, oscillator strengths, and unit spherical representation of NLO polarizability. The current analysis emphasizes the significance of synthesized compounds as prospective candidates for optical and NLO applications through the use of experiments and quantum computations.