Second Harmonic Generation Method Research Articles

Characterization of cracking-healing cycle of asphalt mixture based on air-coupled second harmonic measurement using Duffing-van der pol oscillator

Second harmonic generation (SHG) technique using Rayleigh surface wave has been successfully attempted for the non-destruction evaluation of asphalt mixture during the self-healing process. The air-coupled transducer placement is desirable for the convenient implementation of SHG for the large-scale detection. Nevertheless, the pronounced attenuation of ultrasonic wave by air-coupled propagation will cause the second harmonic induced by microcracks to be barely detectable, particularly under the influence of inevitable noise. In this study, a novel approach by combining Duffing oscillator and van der pol equation is developed to identify and quantify the second harmonic in noise-contained signals based on the phase trajectory and periodic trajectory area exponent. The multi-physics finite element model is first established to simulate the air-asphalt propagation of Rayleigh waves, and proof-of-concept numerical simulations are carried out to estimate the second harmonic amplitude of noise-contaminated signals. The air-coupled SHG experiments are conducted, and the approach of the Duffing-van der pol oscillator is applied to extract the second harmonic in experimental data, and the self-healing behavior of asphalt mixture is analyzed through the variation of the nonlinear parameter of SHG measurements. The results indicate that the contactless SHG method combined with the Duffing-van der pol oscillator can effectively realize the convenient and reliable estimation of the nonlinear ultrasonic signal during the cycle of asphalt deterioration and healing, which is important for the property characterization of asphalt mixture considering its high attenuation to the ultrasonic waves.

Measurement of inhomogeneous electric field based on electric field-induced second-harmonic generation

The electric field-induced second-harmonic generation (E-FISH) method can offer high spatiotemporal resolution in electric field measurement, but faces challenge in reconstructing the inhomogeneous electric field along the probing laser. This paper presents an inversion method to reconstruct the electric field profile by using E-FISH signals measured from multiple points along the probing laser. The relationship between the condition number of the inversion coefficient matrix and the parameters of E-FISH measurement system is clarified. The inversion method is validated through experimental investigations conducted in three different electrode configurations, namely the plate-to-plate gap, the rod-to-rod gap, and the rod-plate gap. With the inhomogeneity coefficient varies from 1 to 10.7, the maximum deviation between the measured electric field and the finite element simulation is less than 6%. This method does not rely on priori assumptions and electrode configurations, and exhibits good robustness in resisting the effect of measurement noise on the inversion accuracy.

Influence of wavelength, linewidth, and temperature on second harmonic generation of a superfluorescent fiber source.

Low-coherence tunable visible light sources have a wide range of applications in imaging, spectroscopy, medicine, and so on. Second harmonic generation (SHG) based on a superfluorescent fiber source (SFS) can produce high-brightness visible light while retaining most of the characteristics of superfluorescent sources, such as low coherence, low intensity noise and flexible tunability. However, due to the limitations in phase matching conditions, SHG based on SFS is difficult to reach an equilibrium between high efficiency and robustness of phase matching to temperature variation. In this paper, based on a spectral tunable SFS, we provide a comprehensive analysis, both experimental and theoretical, of the impact of wavelength, linewidth, and temperature on the output performance of SHG. Our findings indicate that broader linewidths adversely affect conversion efficiency, yet they enhance the capacity to withstand temperature variations and central wavelength detuning, which is an advantage that traditional SHG methods do not possess. This work may pave the way for utilizing low-coherence visible light in domains and extreme environments where robust output stability becomes imperative.

Monitoring the response of a model protocell to dye and surfactant molecules through second harmonic generation and fluorescence imaging.

Probing the interaction between molecules and protocells is crucial for understanding the passive transport of functional molecules in and out of artificial and real cells. Second-harmonic generation (SHG) has been proven to be a powerful method for analyzing the adsorption and cross-membrane transport of molecules on lipid bilayers. In this study, we used SHG and two-photon fluorescence (TPF) imaging to study the interaction of charged dye molecules (D289) with a lipid vesicle. Unexpectedly, it was observed that the transport of D289 at a relatively high concentration is not as efficient as that at a lower dye concentration. Periodic shrinking of the model protocell and discharging of D289 out from the vesicle were revealed by combined analyses of SHG and TPF images. The response of the vesicle to a surfactant was also analyzed with D289 as a probe. This work demonstrates that the combined SHG and TPF imaging method is a unique approach that can provide detailed information on the interaction of molecules and lipids (both morphology and molecular kinetics). Determining these subtle interfacial kinetics in molecules is important for understanding the mechanism of many biophysical processes occurring on lipids.

Experimental study on nonlinear ultrasonic characterization of concrete during crack propagation

Damage and failure of concrete structures are essentially caused by crack initialization and expansion. Conventional ultrasonic tests cannot detect changes in the micro-cracks in concrete. Second harmonic generation (SHG) is effective at characterizing the micro-damage. However, research on the influence of micro-cracks on the nonlinear parameter β is still insufficient. Three cubic concrete specimens 150 mm × 150 mm× 150 mm were fabricated, and the design and average compressive strength were 30 MPa and 39.24 MPa, respectively. Before compressive loading, the integrity of concrete specimens was verified using scanning electron microscopy. The load rate is set to 0.6 kN/s during the test. A simultaneous test system for stress σ, strain ε, and nonlinear parameter β was designed, and the regularity of the nonlinear parameter β during compressive loading was investigated. The nonlinear parameter β increases significantly at the beginning of the compressive load. As the load continues to increase, the nonlinear parameter β decreases rapidly and then fluctuates during the subsequent loading. Furthermore, attenuation was also analyzed in this experiment based on the head-wave amplitudes. At the beginning of the compressive loading, the attenuation is weak as no obvious damage exist in concrete. The non-linear parameter β is less affected by the attenuation when the integrity of the concrete specimens is good. When the cracks expand and penetrate, strong attenuation can be observed at the fundamental and second harmonic waves. The results of the experiment have considerable importance with respect to the method of SHG for micro- and macro-scale damage in concrete.

Mn2+ Luminescence in Ca9Zn1-xMnxNa(PO4)7 Solid Solution, 0 ≤ x ≤ 1.

The solid solution Ca9Zn1-xMnxNa(PO4)7 (0 ≤ x ≤ 1.0) was obtained by solid-phase reactions under the control of a reducing atmosphere. It was demonstrated that Mn2+-doped phosphors can be obtained using activated carbon in a closed chamber, which is a simple and robust method. The crystal structure of Ca9Zn1-xMnxNa(PO4)7 corresponds to the non-centrosymmetric β-Ca3(PO4)2 type (space group R3c), as confirmed by powder X-ray diffraction (PXRD) and optical second-harmonic generation methods. The luminescence spectra in visible area consist of a broad red emission peak centered at 650 nm under 406 nm of excitation. This band is attributed to the 4T1 → 6A1 electron transition of Mn2+ ions in the β-Ca3(PO4)2-type host. The absence of transitions corresponding to Mn4+ ions confirms the success of the reduction synthesis. The intensity of the Mn2+ emission band in Ca9Zn1-xMnxNa(PO4)7 rising linearly with increasing of x at 0.05 ≤ x ≤ 0.5. However, a negative deviation of the luminescence intensity was observed at x = 0.7. This trend is associated with the beginning of a concentration quenching. At higher x values, the intensity of luminescence continues to increase but at a slower rate. PXRD analysis of the samples with x = 0.2 and x = 0.5 showed that Mn2+ and Zn2+ ions replace calcium in the M5 (octahedral) sites in the β-Ca3(PO4)2 crystal structure. According to Rietveld refinement, Mn2+ and Zn2+ ions jointly occupy the M5 site, which remains the only one for all manganese atoms within the range of 0.05 ≤ x ≤ 0.5. The deviation of the mean interatomic distance (∆l) was calculated and the strongest bond length asymmetry, ∆l = 0.393 Å, corresponds to x = 1.0. The large average interatomic distances between Mn2+ ions in the neighboring M5 sites are responsible for the lack of concentration quenching of luminescence below x = 0.5.

New Series of Red-Light Phosphor Ca9-xZnxGd0.9(PO4)7:0.1Eu3+ (x = 0-1).

In this study, a new series of phosphors, Ca9−xZnxGd0.9(PO4)7:0.1Eu3+ (x = 0.00−1.00, step dx 0.05), was synthesized, consisting of centro- and non-centrosymmetric phases with β-Ca3(PO4)2-type structure. Crystal structures with space groups R3c (0.00 ≤ x < 0.35) and R3¯c (x > 0.8) were determined using X-ray powder diffraction and the method of optical second harmonic generation. In the region 0.35 ≤ x ≤ 0.75, phases R3c and R3¯c were present simultaneously. Refinement of the Ca8ZnGd(PO4)7 crystal structure with the Rietveld method showed that 71% of Gd3+ ions are in M3 sites and 29% are in M1 sites. A luminescent spectroscopy study of Ca9−xZnxGd0.9(PO4)7:0.1Eu3+ indicated the energy transfer from the crystalline host to the Gd3+ and Eu3+ luminescent centers. The maximum Eu3+ luminescence intensity corresponds to the composition with x = 1.

Optimization of beam shaping and error quantification of calibration approach using E-FISHG based electric field measurements

Electric-field measurement based on the electric-field-induced second-harmonic generation (E-FISHG) method is a promising tool for a noncontact field measurement in plasmas and gases. For the E-FISHG method, a probing laser beam is focused at the measurement target by a lens, and the signals integrated along the laser path are acquired. Although the signal is frequently calibrated under uniform electric fields, the yielded value is erroneous if one does not consider the difference in the electric-field-profiles between the calibration and measurement. In this paper, we review the calibration and measurement targets of relevant studies, assess the error in the conventional method for the streamer discharge measurement, and give guidelines on which calibration approach to use depending on the electric field profile to be measured. Our approach uses cylindrical-to-cylindrical electrodes and multipoint measurement corresponding to the target length along the optical path, gas, and pressure.

Ultrasonic methods for the characterization of additively manufactured 316L stainless steel

This research utilizes linear and nonlinear ultrasonic techniques to establish a linkage between microstructure and macroscale mechanical properties of additively manufactured (AM) stainless steel 316L samples. The specimens are manufactured using two methods: laser-powder bed fusion and traditional wrought manufacturing. Using the nonlinear ultrasonic method of second harmonic generation, the acoustic nonlinearity parameter is estimated in samples with different heat treatment levels intended to alter microstructural and mechanical properties. Linear ultrasonic parameters including wave speed and resonant frequency are additionally measured. Mechanical properties are obtained through tensile testing of coupons corresponding to the test samples. Microstructural information for the samples is obtained using electron backscatter diffraction to help elucidate the relationships between microstructure, mechanical properties, and ultrasonic response. Results indicate correlations between the nonlinearity parameter and both ultimate tensile strength and yield strength, where nonlinearity generally decreases as sample strength increases, particularly in the AM samples. We hypothesize that microstructural evolution of grain characteristics across different heat treatments influences trends in measured nonlinearity, as well as substructures at smaller scales such as dislocations. These results show promising evidence for the feasibility of AM parts qualification using nondestructive nonlinear ultrasonic testing.

Optical second harmonic generation: role of symmetry and local resonances (review)

We report some results of studying optical second-harmonic generation (SHG) on surfaces and at interfaces of centrosymmetric media, in resonant nano- and microstructures, and in ferroelectric materials. The research was carried out at the Department of Quantum Electronics of the Lomonosov Moscow State University under the supervision of Professor O.A. Aktsipetrov, and subsequently developed by his disciples. As examples that clearly demonstrate the possibilities of the SHG method for examining nonstandard objects of nonlinear optics, we discuss the behaviour of the nonlinear optical response of single-crystal silicon and germanium surfaces and their interfaces with oxides, as well as nonlinear electroreflection. Optical interferometry and its possibilities are briefly described using the example of these systems. Unique sensitivity of SHG to the symmetry and resonance properties of nanostructures, including magnetic ones, is shown, which determines the efficiency of this method for investigating such systems. Finally, we demonstrate that the SHG effect is a unique remote and sensitive method for studying ferroelectric structures.

Gain‐Associated Nonlinear Phenomenon in Single‐Conductor Odd‐Mode Plasmonic Metamaterials

AbstractNonlinear phenomena such as second‐harmonic generation (SHG) play an important role in both optical and microwave technologies. To achieve high second‐harmonic (SH) conversion efficiency and single‐conductor system adaptability simultaneously, a gain‐associated SHG method based on odd‐mode spoof surface plasmon polaritons (SSPPs) is proposed. Field analysis indicates that the odd‐mode SSPPs can support internal electric potential difference on the cross sections of single‐conductor transmission structures to feed active semiconductor chips, which is hardly achieved by the even modes of single‐conductor structures. Measured results demonstrate the realization of SHG with a gain of 4.93 dB at 9 GHz based on the odd‐mode SSPPs, accompanied by the third‐harmonic suppression and backward SH isolation as a result of the customized passband of odd‐mode SSPPs. The ingenious detachable chip carrier can easily be disassembled, replaced and repaired, bringing big convenience and adaptability to practical applications. Moreover, the proposed single‐conductor active integration method can be extended to other single‐conductor devices, which has great potentials in the flexible systems and wearable devices.

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.

Исследование кристаллического состояния слоев молекулярно-лучевой эпитаксии гетероструктур (013)HgCdTe/CdTe/ZnTe/GaAs методом генерации второй гармоники

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 θ) were studied by the method of second harmonic generation. A change in the angle φ for CdTe layers was observed depending on the orientationof the GaAs substrate 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 θ was observed when growing the upper graded widegap MCT layer. The absolute value of the angle θ can be used for a qualitative assessment of the crystalline perfection of the HgCdTe layers

Monitoring of stress variation of strands in prestressed concrete by second harmonic generation measurements based on piezoelectric sensors

The stress loss of prestressed concrete may cause the ultimate failure of structures and the monitoring of stress variation of prestressed structures is therefore important to ensure the service safety. This paper developed a nondestructive evaluation method of nonlinear ultrasonic second harmonic generation (SHG) based on piezoelectric (PZT) sensors and applied for the distinction of different stress level of post-tensioned steel strands in concrete. The nonlinear ultrasonic behavior of both free strand and embedded strand having different length is studied with the developed SHG technique and a defined nonlinear parameter is introduced in SHG experiments to correlate with the tension stress in the strand. It is found that the nonlinear parameter has a negative correlation with the increasing stress of strand in both free and embedded case, indicating the nonlinear ultrasonic behavior is getting weak corresponding to the increasing contact force among strand wires. In addition, the decreasing ratio of nonlinear parameter is very close to each other regardless of the length of steel strand, indicating the possibility of replacing the large-scale on-site testing with scaled down samples in laboratory. The experimental results of this research demonstrate that the SHG technique based on PZT sensors could be useful for the stress monitoring of prestressed reinforced concrete with consideration of the relatively high sensitivity of nonlinear parameter to the variation of contact force of strand wires.

Phase-matching properties of AgGa0.86In0.14S2 for three-wave interactions in the 0.615−10.5910 µm spectral range

We report new experimental results on the phase-matching properties of AgGa0.86In0.14S2 for second-harmonic generation (SHG) and sum-frequency generation (SFG) of a Nd:YAG laser-pumped KTiOPO4 (KTP), AgGaS2 optical parametric oscillators (OPOs), and a CO2 laser in the 0.615−10.5910 µm spectral range. In addition, we present Sellmeier equations that provide a good reproduction of the present experimental results and the value of the nonlinear optical constant d36(AgGa0.86In0.14S2) = 13.4 pm/V measured by SHG method.

Estimation of second harmonic generation intensity-noise in random periodically poled lithium niobate

Periodically poled lithium niobate (PPLN) predominantly has a random duty-cycle error (RDE), latent in them by virtue of poling mechanism. This error needs to be quantitatively predicted to abstain from parasitic harmonic generation. In this paper, we have calculated the influence of the RDEs degenerate noise in second-harmonic generation (SHG) consisting of PPLN. Here, we propose a method for calculating the random domain-wall distribution statistics by the SHG. We explored the equivalence between the statistics of random domain distribution by SHG and far-field diffraction pattern method.

Second-order NLO response in chiral ferroelectric liquid crystals: Molecular and bulk consideration

Nonlinear optical (NLO) properties of three chiral smectic liquid crystals were investigated by Hyper-Rayleigh Scattering (HRS) and the Second-Harmonic Generation (SHG) methods. The HRS measurements of two compounds (MHPOBC and D16), with the biphenyl unit in their center, in solution demonstrate the quadratic NLO activity. The third compound (D17), having three isolated phenyl rings in the core, does not exhibit the NLO activity. The NLO properties in smectic phases of all investigated compounds have been also studied by wide-field second-harmonic and two-photon fluorescence microscopy confirming noncentrosymmetry for compounds with biphenyl π coupling (MHPOBC and D16).

Recursive transfer-matrix method for second-harmonic generation in a one-dimensional nonlinear photonic crystal at arbitrary incidence angle

In this paper, we derive a recursive transfer-matrix method (RTMM) and use the method to analyse the problem of second-harmonic generation (SHG) in a one-dimensional nonlinear photonic crystal (1D-NPC) under oblique incidence of fundamental-frequency (FF) wave and nondepleted pump approximation. This method is very simple and useful for determining SHG conversion efficiency at various incident angles of FF wave and thicknesses of nonlinear layer. The RTMM calculation results show that a maximum SHG conversion efficiency can be produced by the strong local FF field confinement in 1D-NPC due to optimal incidence angle and nonlinear layer thickness.

The analysis of amplified spontaneous emission and luminescence enhancement of BUBD-1 based on host-guest system

The lowest amplified spontaneous emission (ASE) threshold (1.51 μJ/pulse) of CBP: 2 wt%BUBD-1 blend films was about 6 times lower than that of BUBD-1 neat film (9.25 μJ/pulse). The OLEDs with blend film as the emission layer (EML) exhibited an excellent photoelectric performance. In this regard, a series of theoretical analysis were carried out to explain the enhancement of ASE and luminescence performance of BUBD-1 in different aspects. Except for the reducing concentration quenching, a higher Stokes shift, energy transfer efficiency and radiation attenuation rate (kr) happened in the blend films. Moreover, the molecular dipole orientation of EML films at the interface and in thin films were analyzed based on the second-harmonic generation (SHG) method and angle-dependent PL spectra analysis. We find that not only the molecular dipole orientation angle alters in the blend film relative to the neat film, but also the angle is different when the films deposited with different methods. Based on the calculated molecular dipole orientation angle, we propose that the varied dipole angle in the blend film contributed to the device properties too. Our works provide a theory insight into the enhancement of ASE and luminescence properties based on host-guest system.

Second Harmonic Generation Imaging of Collagen in Chronically Implantable Electrodes in Brain Tissue.

Advances in neural engineering have brought about a number of implantable devices for improved brain stimulation and recording. Unfortunately, many of these micro-implants have not been adopted due to issues of signal loss, deterioration, and host response to the device. While glial scar characterization is critical to better understand the mechanisms that affect device functionality or tissue viability, analysis is frequently hindered by immunohistochemical tissue processing methods that result in device shattering and tissue tearing artifacts. Devices are commonly removed prior to sectioning, which can itself disturb the quality of the study. In this methods implementation study, we use the label free, optical sectioning method of second harmonic generation (SHG) to examine brain slices of various implanted intracortical electrodes and demonstrate collagen fiber distribution not found in normal brain tissue. SHG can easily be used in conjunction with multiphoton microscopy to allow direct intrinsic visualization of collagen-containing glial scars on the surface of cortically implanted electrode probes without imposing the physical strain of tissue sectioning methods required for other high resolution light microscopy modalities. Identification and future measurements of these collagen fibers may be useful in predicting host immune response and device signal fidelity.