Harmonic Generation Method Research Articles

Multifunctional Organometallic Compounds: An Interesting Luminescent NLO‐Active Alkynylplatinum (II) Complex

AbstractReaction of 4‐methylphenylacetylide with the known chlorido platinum(II) complex bearing the cyclometalated 1,3‐bis(pyridin‐2‐yl)‐4,6‐difluoro‐benzene ligand afforded a novel alkynyl platinum(II) complex, 1, that was fully characterized by elemental analysis, NMR and UV‐visible spectroscopies, by photoluminescence measurements, and by computational modelling. Its structure was determined by X‐ray diffraction studies on a single crystal whereas its second‐order nonlinear optical (NLO) properties were determined in solution by the Electric‐Field Induced Second Harmonic generation method. The novel multifunctional complex 1 is characterized by good luminescence properties, like the related chlorido Pt(II) complex, but by a much higher second‐order NLO response.

Nonlinear guided wave mixing in weld joints for detection of material nonlinearity

The remarkable sensitivity of ultrasonic waves to detect the early stages of material degradation stems from their inherent nonlinear nature. However, distinguishing the nonlinearity induced by the measurement system from that of the weak materials remains a persistent challenge in second harmonic generation methods. Ultrasonic wave mixing has emerged as a feasible solution for isolating nonlinearities originating from the measurement system. While bulk waves, surface waves, and guided waves have undergone extensive study in wave mixing, the potential of feature-guided wave (FGW) mixing remains largely unexplored. This paper investigates the mutual interaction of FGWs to generate second-order mixed harmonic waves, focusing specifically on weld joints. Acoustic energy trapped along structural features such as weld joints exhibits reduced decay compared to uniform plates, making them ideal for nonlinear characterization. We investigate the effectiveness of FGW mixing for characterizing material nonlinearities in welded joints, utilizing phase velocity matching and resonance criteria to enhance the generation of mixed harmonic components. Through three-dimensional numerical simulations and experimental tests, we showcase the generation of mixed harmonics induced by the mixing of FGWs. Our findings underscore the potential of FGW mixing as a novel approach for enhancing nonlinear-based damage detection techniques in welded joints.

Study of ultrasonic parameters for quality monitoring of plate heat exchanger

Abstract Heat exchangers are crucial heat transfer devices widely used in energy industries such as power generation, oil production, and engine cooling. The plate heat exchanger is one of the most economical and efficient types of exchangers. It transfers heat using metal plates and has a high heat transfer efficiency because the fluid is exposed to a higher plate surface area. However, due to the presence of dissolved or suspended particles in the heat-exchanging fluids, a layer of deposit (fouling layer) is formed on the heat exchanger plates. It results in reduced efficiency of the device. Thus, a common cleaning method, such as chemical-based or manual methods, is employed. However, it always poses a risk of over-cleaning or removal of the protective oxide layer. Thus, an efficient mechanism to monitor the onset of the fouling layer would greatly help to achieve increased efficiency and cost reduction in the cleaning of the plates. Recent advances show ultrasound as one of the promising non-destructive inspection techniques to monitor the growth of the fouling layer. However, the variation in heat-exchanging fluid temperature affects the investigated acoustical parameter measurement. Thus, this research aims to study the linear and nonlinear ultrasonic parameters incorporating temperature-dependent effects from the fluid to provide an accurate real-time monitoring tool. The nonlinear acoustics analysis is experimentally employed in the research using the Second harmonic generation method (SHGM). The proposed research will help design ultrasound-assisted plate heat exchangers for maximum heat transfer efficiency.

Second harmonic generation in structures with inhomogeneous magnetization distribution

The study of the interaction of laser radiation with ferromagnetic materials is not only an inexhaustible source of new effects, but also provides an opportunity to study magnetic media at the micro- and macroscale. This is especially important for the development of modern technologies to produce structures with fundamentally new magnetic and optical properties that can’t be observed in natural materials. The review presents the results of studies of nonlinear optical effects in ferromagnetic nano- and microstructures, as well as films of different compositions. The unique capabilities of nonlinear-optical diagnostics of anisotropic, vortex, exchange-biased magnetic structures, visualization of the micromagnetic structure of the surface layers of ferrite garnets, based both on the high sensitivity of the optical second harmonic generation method to the magnetic state of nanostructures and interfaces, and on the symmetry properties of high-order magnetizationinduced susceptibility tensor have been demonstrated.

Growth and improved properties of single crystal α-LiIO3 doped with amino acids

In this study, the effect of doping the amino acids L-arginine and L-nitroarginine on α-LiIO3 single crystal were presented. Bulk crystals were grown both from solutions doped with L-arginine and L-nitroarginine and from pure solution of α-LiIO3.When doped with L-arginine and L-nitroarginine the optical quality of the crystals was improved and growth rate was increased. These grown crystals were studied by single-crystal X-ray diffraction, IR and UV–Vis spectroscopy, Vickers microhardness, diffuse reflection, and second harmonic generation methods. Studies of microhardness and nonlinear optical activity showed that the properties of α-LiIO3 crystals were improved in the presence of L-arginine and L-nitroarginine. UV–Vis transmittance was improved in the presence of L-arginine (range 370–800 nm) and L-nitroarginine (range 290–370 nm). The second harmonic generation activity of the crystals α-LiIO3 grown with L-arginine (1.16 times) and L-nitroarginine (1.18 times) dopants is higher than that of pure α-LiIO3. The energy of the band gap increases by 1.2 times in the case of arginine dopants, and it decreases by 1.37 times in the case of the nitroarginine dopants, compared to that for the pure α-LiIO3.

Molecular Structure, Computational Studies and Nonlinear Optical properties of a New Organic Chalcone Crystal

A new conjugated chalcone compound (Z)-2-(1-(1-(2,4-dimethylphenyl)-3-oxo-3-phenylprop-1-en-2-yl)pyridin-2(1H)ylidene) malononitrile was prepared and structurally analyzed using single-crystal X-ray diffraction. This new compound's quadratic and cubic susceptibilities at 1064 nm were analyzed and evaluated using the second and third harmonic generation methods after deposition in PMMA polymer thin films. These films have been used for the induced second harmonic generation measurements achieved using the corona poling technique. Complementary information on electric dipole moment, static dipole polarizability, and initial hyperpolarizability of this compound were obtained from the density functional theory (DFT) calculation performed at the DFT/B3LYP/6-311G++ (d, p) and Gaussian 09 software. The findings demonstrate that when compared to previous chalcone NLO crystals that have been published, the synthesized crystals had greater crystal transparency, polarizability, and π-conjugation. In particular, the (Z)-2-(1-(1-(2,4-dimethylphenyl)-3-oxo-3-phenylprop-1-en-2-yl)pyridin-2(1H)ylidene) malononitrile crystal's SHG and THG susceptibility are 0. 243 [pmV−1] and 41.13 10−22 [m2V−2], respectively. The combined findings demonstrate that the NLO properties depend only on the steric hindrance and the chemical structure, that is, the system of π-conjugated electrons.

Coexistence of Bloch and Parametric Mechanisms of High-Frequency Gain in Doped Superlattices

The detailed theoretical study of high-frequency signal gain, when a probe microwave signal is comparable to the AC pump electric field in a semiconductor superlattice, is presented. We identified conditions under which a doped superlattice biased by both DC and AC fields can generate or amplify high-frequency radiation composed of harmonics, half-harmonics, and fractional harmonics. Physical mechanisms behind the effects are discussed. It is revealed that in a general case, the amplification mechanism in superlattices is determined by the coexistence of both the phase-independent Bloch and phase-dependent parametric gain mechanisms. The interplay and contribution of these gain mechanisms can be adjusted by the sweeping AC pump strength and leveraging a proper phase between the pump and strong probe electric fields. Notably, a transition from the Bloch gain to the parametric gain, often naturally occurring as the amplitude of the amplified signal field grows, can facilitate an effective method of fractional harmonic generation in DC–AC-driven superlattices. The study also uncovers that the pure parametric generation of the fractional harmonics can be initiated via their ignition by switching the DC pump electric field. The findings open a promising avenue for the advancement of new miniature GHz–THz frequency generators, amplifiers, and dividers operating at room temperature.

НОВЫЕ ДАННЫЕ ОБ ОСОБЕННОСТЯХ ЛОКАЛЬНОЙ СТРУКТУРЫ ТВЕРДОГО РАСТВОРА Ca9La(PO4)7(1-x)(VO4)7x:Eu3+(1 %)

Solid solutions of phosphate-vanadates Ca9La(PO4)7(1–x)(VO4)7x:Eu3+(1 %) with the structure -Ca3(PO4)2 activated by europium were synthesized by the standard solid-phase method. It is shown that a continuous series of solid solutions is formed upon substitution P5+ → V5+. At the same time, the study by the second harmonic generation method showed that a symmetry inhomogeneity is observed in the series. When studying the luminescent properties, standard transitions of the europium cation with the dominant electric dipole transition 5D0 → 7F2 were found. The most intense emission was demonstrated by compositions with a centrosymmetric structure.

Nonlinear acoustic characterization of heterogeneous plasticity in bent aluminium samples

Knowledge of the state of plastic deformation in metallic structures is vital to prevent failure. This is why non-destructive acoustic tests based on the measurement of first order elastic constants have been developed and intensively used. However, plastic deformations, which are usually heterogeneous in space, may be invisible to these methods if the variation of the elastic constants is too small. In recent years, digital image correlation techniques, based on measurements carried out at the surface of a sample, have been successfully used in conjunction with finite element modeling to gain information about plastic deformation in the sample interior. Acoustic waves can penetrate deep into a sample and offer the possibility of probing into the bulk of a plastically deformed material. Previously, we have demonstrated that nonlinear acoustic methods are far more sensitive to changes in dislocation density than linear ones. Here, we show that the nonlinear Second Harmonic Generation method (SHG) is sensitive enough to detect different zones of von Mises stress as well as effective plastic strain in centimeter-size aluminium pieces. This is achieved by way of ultrasonic measurements on a sample that has undergone a three-point bending test. Because of the relatively low stress and small deformations, the sample undergoes plastic deformation by dislocation proliferation. Thus, we conclude that the nonlinear parameter measured by SHG is also sensitive to dislocation density. Our experimental results agree with numerical results obtained by Finite Element Method (FEM) modeling. We also support the acoustic results by X-ray Diffraction measurements (XRD). Although intrusive and less accurate, they also agree with the acoustic measurements and plastic deformations in finite element simulations.

Biophysical studies of peptoid interactions with phospholipids.

Using second harmonic generation and fluorescence anisotropy methods, we monitored adsorption of water-soluble peptoids to phospholipid bilayers at varying pH conditions and temperatures. We compared equilibrium binding constants and relative surface coverages of different peptoids sequences as we varied the cholesterol content, head group charge and physical phase of the lipids. We also collected pressure-area isotherms of lipid monolayers in the presence and absence of peptoids to gain insight into the physical principles that govern how peptoid sequence and membrane composition alter peptoid-lipid interactions.

Wave theory-based fourth harmonic generation of Bessel–Gauss beam by total internal reflection-quasi phase matching in a rectangular slab of beta barium borate

This work presents a theoretical approach to a highly multimode-guided wave-based fourth harmonic (FH) generation method by exploiting a zero-order Bessel–Gauss beam through the total internal reflection quasi phase-matching technique. An anisotropic crystal featuring a rectangular structure of beta barium borate has been used to carry out this analysis. In contrast to the conventional frequency conversion scheme using a Gaussian beam, the projected scheme yields a maximum six times superior efficiency of 6.9547% in a crystal length of nearly 6.3 mm, corresponding to a 266-nm FH wavelength. The analysis has also taken into account optical losses, such as absorption, Goos–Hänchen-shift, surface roughness, and the effect of the nonlinear law of reflection. Finally, a systematic study has been performed to describe the influence of parametric modification, such as variations in slab length and thickness, to provide a more comprehensive picture of the overall analysis.

Nonlinear Ultrasonic Inspection of the Effect of Contaminants on Material Properties of Epoxy-Adhesive

Adhesive joints have been an effective alternative to conventional mechanical fasteners for joining materials in the aerospace and automotive industries. Although adhesive joints have various advantages, including uniform stress distribution, lower weight, improved corrosion tolerance, and design flexibility, there can be various defects in adhesive joints, which have limited wider application. This paper investigates the effect of a contaminant on the chemical and mechanical properties of the epoxy-adhesive and seeks to determine if a second harmonic generation method can reliably detect and characterize the degree of contamination in the epoxy-adhesive. A contact based ultrasonic through-transmission method was used to measure nonlinearity and then the nonlinearity parameter was calculated using the measured fundamental and second harmonic frequency components in the signals. It was found that there is higher sensitivity to contaminant concentration, up to 1.5%, of the nonlinearity parameter than that for the sound velocity. These data were also found to correlate with changes in the mechanical hardness, which was measured by the Rockwell hardness testing, with different four levels of contamination. Differential scanning calorimetry (DSC) and the thermogravimetric analysis (TGA) were also conducted to assess the effect of the contaminant on thermal properties of the epoxy-adhesive. The DSC and TGA techniques were used to evaluate the curing reaction and the thermal stability of the epoxy-adhesive respectively.

Multiple Synchronous Rotating Frame Transformation-Based 12th Current Harmonic Suppression Method for an IPMSM

In order to solve the problem that the three-phase current of the interior permanent magnet synchronous motor (IPMSM) contains the 11th and 13th current harmonics, a multiple synchronous rotating frame transformation (MSRFT)-based current harmonic suppression method is established. Firstly, the influencing factors of current harmonics in IPMSM vector control are analyzed, and the influence mechanism of the inverter’s dead-time effect and the permanent magnet flux linkage harmonics on the current harmonics is described. Secondly, a simple current harmonic extraction method is proposed by optimizing the traditional current harmonic extraction method based on MSRFTs. The proposed method achieves the accurate extraction of the current harmonic components. Thirdly, a harmonic voltage generation method is established and is combined with the proposed current harmonic extraction method to form a current harmonic suppression strategy. Finally, the feasibility and effectiveness of the proposed method are verified via MATLAB/Simulink simulations and experiments. The simulation and experimental results show that the proposed current harmonic extraction method can extract the current harmonic components accurately, and the proposed current harmonic suppression strategy can suppress the 11th and 13th current harmonics effectively.

A novel combined Fuzzy-M5P model tree control applied to grid-tied PV system with power quality consideration

ABSTRACT A novel control strategy based on an effective combination of the fuzzy logic controller and the M5P decision tree algorithm (Fuzzy-M5P) for a grid-interfaced solar energy system is proposed in this paper. The aim is to benefit from fuzzy logic advantages using its resulting datasets along with the fast model tree functionality. This mixed control has the ability to cope effectively with the large computation time and complexity of fuzzy logic controllers especially when embedded systems or real-time implementation are considered. Using a photovoltaic (PV) inverter with active filtering capability, the primary objective is to provide a grid-solar topology with a maximum PV energy extraction and power quality enhancement. For the inverter control, the M5P model was tested in the indirect current technique. This harmonic generation method is very efficient and its performances are entirely dependent on the chosen dc-link controller. Moreover, a novel maximum power point tracking technique (MPPT) based on the M5P model tree is performed in which data inputs are collected from fuzzy logic-based MPPT. WEKA and MATLAB software are used to translate the model by formulating a simple hierarchical program structure. To validate the effectiveness of the proposed control, simulation, and experimental tests are done under steady and dynamic conditions. The final developed algorithm based on simple IF-ELSE rules shows promising results, it can reduce harmonic distortions to 2.77%, perfectly compensates reactive power with almost unity power factor, and enhances dynamic performances with fast transient response.

Spatiotemporally resolved measurements of electric field around a piezoelectric transformer using electric-field induced second harmonic (E-FISH) generation

When a piezoelectric transformer (PT) is actuated at its second harmonic frequency by a low input voltage, the generated electric field at the distal end can be sufficient to breakdown the surrounding gas, making them attractive power sources for non-equilibrium plasma generation. Understanding the potential and electric field produced in the surrounding medium by the PT is important for effectively designing and using PT plasma devices. In this work, the spatiotemporally resolved characteristics of the electric field generated by a PT operating in open air have been investigated using the femtosecond electric field-induced second harmonic generation (E-FISH) method. Electric field components were determined by simultaneously conducting E-FISH measurements with the incident laser polarized in two orthogonal directions relative to the PT crystal. Results of this work demonstrate the spatial distribution of electric field around the PT’s output distal end and how it evolves as a function of time. Notably, the strongest electric field appears on the face of the PT’s distal surface, near the top and bottom edges and decreases by approximately 70% over 3 mm. The time delay between the PT’s input voltage and measured electric field indicates that there is an about 0.45π phase difference between the PT’s input voltage and output signal.

Characterization of delamination features of orthotropic CFRP laminates using higher harmonic generation technique: Experimental and numerical studies

In this work, the key delamination features of orthotropic CFRP laminates are investigated by the higher harmonic generation (HHG) method based on experimental and numerical approaches. A laser scanning vibrometer (LSV) is adopted for the non-contact experimental setup and an explicit 3D FEM model is proposed to facilitate the numerical simulations of underlying mechanism of HHG in CFRP. The 2D contour images are established to identify the delamination existence and the maximum response amplitude (MRA) is proposed to quantify the delamination condition. The effect of key features of delamination including the size, depth and relative orientation respect to the wave front on the nonlinear response is subsequently studied and found that the approximate location of delamination can be identified by the HHG approach and the MRA of higher harmonics is highly sensitive to the variation of delamination features. In addition, the effect of delamination features on MRA variation is briefly analyzed from the perspective of physical origin of nonlinear response. The work will enhance the detection of damage in composite structures and demonstrates the applicability of HHG technique for decoding the causality and complexity of nonlinear elasticity in delaminated composites and its potential for the comparative evaluation in defect information.

Study of the Crystalline State of MBE (013)HgCdTe/CdTe/ZnTe/GaAs Heterostructure Layers by the Second Harmonic Generation Method

The crystal perfection of HgCdTe layers of heterostructures grown on (013)GaAs substrates with ZnTe and CdTe buffer layers and orientation rotation in the plane(angle φ) and perpendicular to the growth direction (angle theta) were studied by the method of second harmonic generation. A change in the angle φ for CdTe layers was observed depending on the GaAs substrate orientation and its non-monotonic change throughout thickness in the MCT layer of constant composition and graded widegap layers at its boundaries. An increase in the angle theta was observed when growing the upper graded widegap MCT layer. The absolute value of the angle theta can be used for a qualitative assessment of the crystalline perfection of the HgCdTe layers. Keywords: crystals of the sphalerite class, second harmonic, azimuthal angular dependencies, crystal perfection, CdxHg1-xTe heterostructures.

Evaluating the cross-membrane dynamics of a charged molecule on lipid films with different surface curvature

Does the curvature of a phospholipid membrane influence the permeability of the lipid bilayers? This is a question of great importance yet hard to answer. In this work the permeability of a positively charged rod like probing molecule (D289 dye) on the bilayers of DOPG lipid vesicles was investigated using angle resolved second harmonic generation method. It was revealed that the permeability of D289 on the surface of small vesicles with ∼ 100 nm diameter was notably lower than that on giant vesicles with ∼ 1000 nm diameter. With the increasing of temperature or the introducing of dimethyl sulfoxide (DMSO) in the solutions, the D289 permeability of the lipid bilayers was notably enhanced as expected, on both the small and the giant vesicles. Still, the D289 permeability of the lipid film with more curvature is lower than the relatively flat film in all these cases. This work demonstrated a general protocol for the investigating of surface permeability of lipid films with various curvature.

Assessment of cortical bone fatigue using coded nonlinear ultrasound* *Project supported by the China Postdoctoral Science Foundation (Grant No. 2021M690709), the National Natural Science Foundation of China (Grant Nos. 11827808, 11874289, 11804056, and 12034005), the Program of Shanghai Academic Research Leader (Grant No. 19XD1400500), and the Project of Shanghai Science and Technology Innovation Plan (Grant No. 19441903400).

Bone fatigue accumulation is a factor leading to bone fracture, which is a progressive process of microdamage deteriorating under long-term and repeated stress. Since the microdamage of the early stage in bone is difficult to be investigated by linear ultrasound, the second harmonic generation method in nonlinear ultrasound technique is employed in this paper, which is proved to be more sensitive to microdamage. To solve the deficiency that the second harmonic component is easily submerged by noise in traditional nonlinear measurement, a weighted chirp coded sinusoidal signal was applied as the ultrasonic excitation, while pulse inversion is implemented at the receiving side. The effectiveness of this combination to improve the signal-to-noise ratio has been demonstrated by in vitro experiment. Progressive fatigue loading experiments were conducted on the cortical bone plate in vitro for microdamage generation. There was a significant increase in the slope of the acoustic nonlinearity parameter with the propagation distance (increased by 8% and 24% respectively) when the bone specimen was at a progressive level of microdamage. These results indicate that the coded nonlinear ultrasonic method might have the potential in diagnosing bone fatigue.

Vibrational CARS measurements in a near-atmospheric pressure plasma jet in nitrogen: I. Measurement procedure and results

The non-equilibrium ro-vibrational distribution functions of molecules in a plasma can heavily influence the discharge operation and the plasma-chemistry. A convenient method for measuring the distribution function is coherent anti-Stokes Raman scattering (CARS). CARS spectra are measured in a ns-pulsed plasma between two parallel, 1 mm spaced molybdenum electrodes in nitrogen at 200 mbar with pulse durations of 200 ns/250 ns and a repetition rate of 1 kHz. The CARS spectra are analyzed by a fitting routine to extract information about the vibrational excitation of the nitrogen molecules in the plasma. It is found that during the discharge the vibrational distribution for can be described by a vibrational two-temperature distribution function. Additionally, the electric field is measured by the electric field induced second harmonic generation method during the discharge pulse. It is found to be constant in time after the initial ionization wave with values close to 81 Td for the investigated conditions. During the afterglow between two discharge pulses a more general fitting approach is used to obtain the population differences of two neighboring vibrational states. This allows to capture the more complex vibrational dynamics in that time period. The measurement results are discussed in more detail and compared to simple plasma models in a companion paper Kuhfeld et al (2021 J. Phys. D: Appl. Phys. 54 305205).