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- 2019
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- anharmonic Bloch oscillations
- coupled mode method
- array of waveguides
- active harmonic filter
- Multifunctional VSC
- unity power factor operation
- power quality improvement
- grid-connected SPV system
- renewable energy sources
- Optoelectronic Information Science and Engineering
- Electrical Engineering and Automation
- Shevchenko Pridnestrovskii State University
- Malaviya National Institute of Technology
- Academy of Sciences of Moldova
- IIITD&M Kancheepuram
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Electron excitation dynamics in a molecule modeled by valence-bond coupled localized electron wave packets; ????-?????μ?????±???¨é???-??3￠????????????????-????é???-???±èμ·?????¤????????ˉ??1;
摘要： A simple model of localized electron wave packets, floating and breathing Gaussians with non-orthogonal valence-bond spin-coupling, is demonstrated to produce an accurate high-harmonic generation (HHG) spectrum from an LiH molecule induced by an intense laser pulse. In contrast with the conventional molecular orbital picture in which the Li 2s and H 1s atomic orbitals are strongly mixed in the valence σ bonding orbital, the present calculation indicates that a superposition of independent responses of the electrons reproduces the spectrum in which the contribution of the H 1s electron dominates the characteristic plateau and cut-off of HHG.
关键词： High-harmonic generation,Electron dynamics,Valence-bond theory,Localized wave-packets
更新于2025-09-23 15:19:57
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Photo-induced meta-stable polar conformations in polystyrene microspheres revealed by time-resolved SHG microscopy
摘要： Photo-induced second harmonic generation (SHG) was observed in centrosymmetric polystyrene (PS) microspheres using 1064 nm, sub-nanosecond laser-pulse irradiation. The SHG signal gradually increased upon stationary laser-pulse irradiation. After stopping the irradiation, the increased SHG signal disappeared in approximately 30 min. When the PS bead was irradiated by laser pulses again, the SHG signal reappeared with similar temporal behavior, which was attributed to the probable growth and contraction of meta-stable polar conformations of PS chain segments under periodic photo-thermal stimuli.
关键词： second harmonic generation,photo-induced,polystyrene microspheres,time-resolved SHG microscopy
更新于2025-09-23 15:19:57
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Simultaneous effects of pressure, temperature, impurity location, SOI and magnetic field on THG of a pyramid quantum dot
摘要： We have investigated simultaneous effects of pressure, temperature, impurity location, Rashba and Dresselhaus spin–orbit interaction and magnetic field on THG of realized GaAs/Al0.5Ga0.5As pyramid quantum dot with considering the wet layer. For this purpose, we have calculated the energy levels and wave function of one electron that is confined in constant potential, in presence of impurity, magnetic field, Rashba and Dresselhous SOI in various temperatures, pressure and impurity location in effective mass approximation by FEM. In the following, we have presented the effect of magnetic field, Rashba and Dresselhous SOI, temperature, pressure and impurity location on THG in various conditions. Results show that: (1) THG increases by increasing the magnetic field and the distance between the peaks decrease. Also, the peak corresponding to the E21 transition has a blue shift and the peaks corresponding to the E31/2 and E41/3 transitions have a red shift. (2) THG decreases and shifts to higher energies and has a small blue shift by augment of temperature. (3) THG enhances and all of peaks have a red shift by increment of pressure. (4) THG has a minimum around z0 = 4 nm in all magnetic field, temperature and pressure cases. Also, all of peaks have a blue shift by augment of z0 until z0 = 4 nm and then have a red shit by increasing the z0.
关键词： Pyramid quantum dot,Spin orbit interaction,Third harmonic generation
更新于2025-09-23 15:19:57
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Structural, spectral and nonlinear optical analysis of Bis(2-methyllactato)borate tetrahydrate: a new nonlinear optical crystal for laser applications
摘要： A new nonlinear optical crystal, ‘Bis(2-methyllactato)borate tetrahydrate’ (BMBT) has been crystallized by slowly evaporating the solvent. It crystallizes in the space group P21212. Sharp peaks present in powder XRD profile reveals the good crystallinity. Its transmission bandwidth (220 nm – 1100 nm) suggest that it can be used to generate UV radiation upto 220 nm and also in optoelectronic applications. Vibrations of functional groups (B-O, CH3, CO) associated with the crystal structure have been identified through FTIR and FT-Raman spectral studies. OH stretching vibrations have been observed near 3000 cm-1 clearly endorses the existence of water molecule in the BMBT structure. The chemical shifts observed in 1H and 13C NMR spectral results establishes the molecular structure of BMBT crystal. Second harmonic generation (SHG) efficiency is obtained as 0.9 times of KDP. The third order nonlinear susceptibility (χ3), nonlinear refractive index (n2) and nonlinear absorption co-efficient (β) were found using Z-scan technique. χ3 of title crystal is found to be 4.16 X10-5 esu. The existence of SHG efficiency and the enhanced χ3 value are due to the hydrogen bonded intermolecular interactions present in the BMBT crystal structure. The observed results suggest that BMBT can be used in Q-switching, mode locking and optical sensors like night vision devices.
关键词： Crystal structure,Z-scan analysis,crystal growth,NMR spectroscopy,second harmonic generation
更新于2025-09-23 15:19:57
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Reconstruction of attosecond pulses in the presence of interfering dressing fields using a 100 kHz laser system at ELI-ALPS
摘要： Attosecond Pulse Trains (APT) generated by high-harmonic generation (HHG) of high-intensity near-infrared (IR) laser pulses have proven valuable for studying the electronic dynamics of atomic and molecular species. However, the high intensities required for high-photon-energy, high-flux HHG usually limit the class of adequate laser systems to repetition rates below 10 kHz. Here, APT’s generated from the 100 kHz, 160 W, 40 fs laser system (HR-1) currently under commissioning at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS) are reconstructed using the Reconstruction of Attosecond Beating By Interference of two-photon Transitions (RABBIT) technique. These experiments constitute the first attosecond time-resolved photoelectron spectroscopy measurements with attosecond pulses performed at 100 kHz repetition rate and one of the first experiments performed at ELI-ALPS in the framework of projects commissioning its newly installed technologies. These RABBIT measurements were taken with an additional IR field temporally locked to the extreme-ultraviolet APT, resulting in an atypical ω beating. We show that the phase of the 2ω beating recorded under these conditions is strictly identical to that observed in standard RABBIT measurements within second-order perturbation theory. This work highlights an experimental simplification for future experiments based on attosecond interferometry (or RABBIT), which is particularly useful when lasers with high average powers are used.
关键词： photoelectron spectroscopy,High-harmonic generation,attosecond,RABBIT
更新于2025-09-23 15:19:57
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610-GHz Fourth Harmonic Signal Reactively Generated in a CMOS Voltage Controlled Oscillator Using Differentially Pumped Varactors
摘要： A fourth harmonic signal reactively generated in a voltage controlled oscillator (VCO) using differentially pumped varactors is used to demonstrate a compact 610-GHz source in 65-nm CMOS. The nonlinear C?V characteristics of accumulation mode varactor pair are used to generate the harmonic power. The circuit also utilizes a technique to boost the varactor Q and dynamic cut-off frequency to increase the harmonic power. The source delivers a peak radiating power of ?25.2 dBm, with a frequency tuning range of 604.5–618.6 GHz (2.3%), a 3-dB tuning bandwidth of 607.1–614.3 GHz (1.2%), and a dc-THz ef?ciency of 0.01% (0.013% excluding the power consumption in the current source). The chip core area is 0.62 mm × 0.39 mm excluding the area for bond pads.
关键词： Nonlinear,reactive harmonic generation,varactor,voltage controlled oscillator (VCO)
更新于2025-09-23 15:19:57
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Spectral splitting and phase matching of the macroscopic high-order harmonic generation in intense laser fields
摘要： We theoretically investigate the macroscopic high-order harmonic generation in argon gaseous medium by numerically solving the three-dimensional macroscopic propagation equation, and the results show that the harmonic spectral and spatial profiles of harmonics are gradually splitting with the increasing of the driving laser intensity. This splitting is mainly due to the distortions which the driving field suffers during propagation and the consequence is also on phase matching. To illustrate the physical mechanisms of harmonic splitting, a theoretical analysis of the phase matching is presented. The harmonic spectra from different focus positions reveal that the split is dependent on the focus-gas-jet relative position. Moreover, we demonstrate that the spectral splitting of high harmonics can hardly be observed for neon gas jet due to the high ionization energy.
关键词： phase matching,high-order harmonic generation,intense laser fields,macroscopic propagation,spectral splitting
更新于2025-09-23 15:19:57
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Nonlinear optics with resonant metasurfaces
摘要： The field of nonlinear optics is a well-established discipline that relies on macroscopic media and employs propagation distances longer than a wavelength of light. Recent progress with electromagnetic metamaterials has allowed for the expansion of this field into new directions of new phenomena and novel functionalities. In particular, nonlinear effects in thin, artificially structured materials such as metasurfaces do not rely on phase-matching conditions and symmetry-related selection rules of natural materials; they may be substantially enhanced by strong local and collective resonances of fields inside the metasurface nanostructures. Consequently, nonlinear processes may extend beyond simple harmonic generation and spectral broadening due to electronic nonlinearities. This article provides a brief review of basic concepts and recent results in the field of nonlinear optical metasurfaces.
关键词： frequency conversion,high-harmonic generation,resonances,metasurfaces,nonlinear optics
更新于2025-09-23 15:19:57
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Microcavity Nonlinear Optics with an Organically Functionalized Surface
摘要： We report enhanced optical nonlinear effects at the surface of an ultrahigh-Q silica microcavity functionalized by a thin layer of organic molecules. The maximal conversion efficiency of third harmonic generation reaches ～1680%=W2 and an absolute efficiency of 0.0144% at pump power of ～2.90 mW, which is approximately 4 orders of magnitude higher than that in a reported silica microcavity. Further analysis clarifies the elusive dependence of the third harmonic signal on the pump power in previous literature. Molecule-functionalized microcavities may find promising applications in high-efficiency broadband optical frequency conversion and offer potential in sensitive surface analysis.
关键词： Nonlinear Optics,Microcavity,Third Harmonic Generation,Surface Functionalization,Organic Molecules
更新于2025-09-23 15:19:57
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Periodically Poled MgO:LiNbO <sub/>3</sub> , MgO:LiTaO <sub/>3</sub> and KTiOPO <sub/>4</sub> Crystals for Laser Light Frequency Conversion
摘要： We present the recent achievements in periodical poling in MgO doped single crystals of lithium niobate (LN), lithium tantalate (LT) and potassium titanyl phosphate (KTP) based on the experimental study of the domain structure evolution by the complementary high-resolution domain visualization methods [1]. The crystals with tailored periodically poled domain structures (PPLN and PPLT) produced with nano-scale period reproducibility have been used for Second Harmonic Generation (SHG) and Optical Parametric Oscillation (OPO) based on quasi-phase-matched nonlinear optical wavelength conversion. The periodical poling techniques were based on the deep experimental and theoretical study of the mechanisms of domain growth and domain wall motion in these crystals. The wide range of wall velocities with two orders of magnitude difference was observed for switching in a uniform electric field [2,3]. The kinetic maps allowed analyzing the spatial distribution of the wall motion velocities and classifying the walls by velocity ranges. The distinguished slow, fast, and superfast types of domain walls in KTP differed by their orientation. The revealed increase in the wall velocity with deviation from low-index crystallographic planes for slow and fast walls was considered in terms of determined step generation and anisotropic kink motion. It was shown that the polarization reversal in KTP with artificial surface dielectric layer leads to formation and growth of the large number of narrow domain streamers oriented strictly along [010] direction with about ten times higher velocity (6-60 mm/s) than the domain walls (2-5.5 mm/s). Study of the static domain structures demonstrated that the streamers are formed by [100] and [010]-oriented domain walls. The streamer width was about 500 nm and the distance between the neighboring streamers – about 100 nm. The global domain kinetics during the poling process at elevated temperatures has been studied by in situ optical observation which allowed us to reveal the main characteristics of the poling process at elevated temperatures. It has been shown that the periodically poled area propagates from the edges to the middle of the electrode pattern. The interfering effect of essential increasing of the bulk conductivity during poling has been studied and several ways to overcome this problem have been proposed. The static domain images revealed by chemical etching were visualized by optical and scanning probe microscopy. The influence of the spatially nonuniform electric field on the domain kinetics has been studied for finite-size electrodes of various shapes. The key role of the field anomalies at the electrode corners, ends, and edges in the nucleation process has been revealed by computer simulations and confirmed experimentally. Essential acceleration of the switching at the boundaries of the electrode patterns (so called “pattern effect”) has been explained. The optimized design of the electrode pattern was based on experimental results and computer simulation. The fan-out periodical domain structures created in 3-mm-thick MgO:LN wafers allowed us to realize the widely tunable OPO generation with the signal wave from 2.5 to 4.5 μm using the 1.053 μm pump. The possibility of producing the elements with thickness up to 10 mm for high-power application has been discussed. The peridical domain struture with period of 40 μm was created in KTP single crystals for OPO generation at 2.4 μm using the 1.053 μm pump. The abilities and perspectives of producing the elements with submicron periods has been discussed. The optimized periodical poling techniques have been used for creation of ridge waveguides in periodically poled MgOLN single crystals. The high-index contrast of obtained multi-mode waveguides allowed tuning of the SHG wavelength from 510 to 570 nm using the 1.064 μm pump. The deep knowledge of the domain structure evolution at elevated temperatures and relaxation of the high bulk conductivity along the charged domain walls MgO:LN and MgO:LT allowed us to optimize the periodical poling technique and to produce high-fidelity domain patterns.
关键词： domain structure evolution,MgO:LiTaO3,KTiOPO4,Second Harmonic Generation,Optical Parametric Oscillation,MgO:LiNbO3,Periodically Poled
更新于2025-09-23 15:19:57