Second Harmonic Generation Technique Research Articles

Switchable electric polarization and ferroelectric domains in a metal-organic-framework

AbstractMultiferroics and magnetoelectrics with coexisting and coupled multiple ferroic orders are materials promising new technological advances. While most studies have focused on single-phase or heterostructures of inorganic materials, a new class of materials called metal–organic frameworks (MOFs) has been recently proposed as candidate materials demonstrating interesting new routes for multiferroism and magnetoelectric coupling. Herein, we report on the origin of multiferroicity of (CH3)2NH2Mn(HCOO)3 via direct observation of ferroelectric domains using second-harmonic generation techniques. For the first time, we observe how these domains are organized (sized in micrometer range), and how they are mutually affected by applied electric and magnetic fields. Calculations provide an estimate of the electric polarization and give insights into its microscopic origin.

Single-frequency linear orthogonally polarized modes resulting in unidirectional traveling wave cavity green laser

A narrow linewidth (∼ 8 MHz , instrument limited) CW green laser at 532 nm is demonstrated in linear orthogonally polarized modes resulting in an unidirectional travelling wave cavity using intracavity second-harmonic generation technique with 250-mW output power.

High Second-Order NLO Response Exhibited by the First Example of Polymeric Film Incorporating a Diimine–Dithiolate Square-Planar Complex: The [Ni(o-phen)(bdt)

A novel square-planar diimine–dithiolate nonlinear optical (NLO) chromophore, the complex [Ni(o-phen)(bdt)] (1), is reported in this paper (o-phen = dianion of 1,2-phenylendiamina; bdt =1,2-benzenedithiolate). This compound has been fully characterized by single-crystal X-ray diffraction, UV–vis–NIR spectroscopy, cyclic voltammetry, DFT, and TD-DFT calculations. 1 crystallizes in the P21 space group and shows an almost planar molecule. The cyclic voltammetry measurements present an irreversible anodic peak at 0.87 V and reversible and quasi-reversible reduction waves at −0.35 and −1.13 V, respectively. A medium-intense (e = 1.91 × 104 mol–1 dm3 cm–1) absorption with a maximum at 728 nm appears in the UV–vis–NIR spectrum. The molecular second-order NLO properties of 1 have been measured by the electric field induced second-harmonic generation technique in DMF solution, giving values of −1000 × 10–48 esu for μβ1.907 and −356 × 10–48 esu for μβ0. Furthermore, remarkable solid-state responses have been measur...

Metal nanoparticles and IR laser applications in medicine for biotissue ablation and welding

We report the possibility of laser welding and ablation of biotissue by using metal and hybrid metal nanoparticles (NPs) and infrared laser irradiation spectrally located far from plasmon resonances. A nanosecond YAG:Nd laser of wavelength 1064 nm has been used for synthesis of metal NPs. The Ag, Au, Cu, Ti and Ni, as well as Au–Ag and Au–Cu hybrid metal colloidal NPs were formed in a liquid medium. The diagnostic technique of second harmonic generation (SHG) has been applied to determine the biotissue ablation area after IR laser irradiation. The effectiveness of biotissue ablation was 4–5 times larger in the case of a tissue sample colored with metal NPs than for an uncolored sample. IR laser welding has been demonstrated for deep-located biotissue layers colored by metal NPs.

Surface and interface states of Bi2Se3 thin films investigated by optical second-harmonic generation and terahertz emission

We investigate the surface and interface states of Bi2Se3 thin films by using the second-harmonic generation technique. Distinct from the surface of bulk crystals, the film surface and interface show the isotropic azimuth dependence of second-harmonic intensity, which is attributed to the formation of randomly oriented domains on the in-plane. Based on the nonlinear susceptibility deduced from the model fitting, we determine that the surface band bending induced in a space charge region occurs more strongly at the film interface facing the Al2O3 substrate or capping layer compared with the interface facing the air. We demonstrate that distinct behavior of the terahertz electric field emitted from the samples can provide further information about the surface electronic state of Bi2Se3.

Organic double layer element driven by triboelectric nanogenerator: Study of carrier behavior by non-contact optical method

By using optical electric-field-induced second-harmonic generation (EFISHG) technique, we studied carrier behavior caused by contact electrification (CE) in an organic double-layer element. This double-layer sample was half suspended in the open air, where one electrode (anode or cathode) was connected with a Cu foil for electrification while the other electrode was floated. Results showed two distinct carrier behaviors, depending on the (anode or cathode) connections to the Cu foil, and these carrier behaviors were analyzed based on the Maxwell–Wagner model. The double-layer sample works as a simple solar cell device. The photovoltaic effect and CE process have been proved to be two paralleled effects without strong interaction with each other, while photoconductivity changing in the sample can enhance the relaxation of CE induced charges. By probing the carrier behavior in this half-suspended device, the EFISHG technique has been demonstrated to be an effective non-contact method for clarifying the CE effect on related energy harvesting devices and electronics devices. Meanwhile, the related physical analysis in this letter is also useful for elucidating the fundamental characteristic of hybrid energy system based on solar cell and triboelectric nanogenerator.

Optical second-harmonic generation measurement for probing organic device operation.

We give a brief overview of the electric-field induced optical second-harmonic generation (EFISHG) technique that has been used to study the complex behaviors of organic-based devices. By analyzing EFISHG images of organic field-effect transistors, the in-plane two-dimensional distribution of the electric field in the channel can be evaluated. The susceptibility tensor of the organic semiconductor layer and the polarization of the incident light are considered to determine the electric field distribution. EFISHG imaging can effectively evaluate the distribution of the vectorial electric field in organic films by selecting a light polarization. With the time-resolved technique, measurement of the electric field originating from the injected carriers allows direct probing of the carrier motion under device operation, because the transient change of the electric field distribution reflects the carrier motion. Some applications of the EFISHG technique to organic electronic devices are reviewed.

Relationship between Dislocation Density in P91 Steel and Its Nonlinear Ultrasonic Parameter

P91 steel is an important bearing material used in nuclear power plants. The study of its mechanical degradation behavior is important for ensuring safe operation. The relationship between the dislocation density of P91 steel under different strains and the corresponding nonlinear ultrasonic parameter β was studied. The dislocation density of strained samples was estimated by X-ray diffraction. Nonlinear ultrasonic testing was conducted to evaluate β, showing that this value increased with increasing dislocation density induced by different tensile elongations. It was shown that the ultrasonic second-harmonic generation technique can effectively evaluate the degradation behavior of metallic materials, and the prediction of the residual life of bearing parts in service can be made based on β and the dislocation density.

Growth and characterization of nonlinear optical single crystals: bis(cyclohexylammonium) terephthalate and cyclohexylammonium para-methoxy benzoate

Bis(cyclohexylammonium) terephthalate (BCT) and cyclohexylammonium 4-methoxy benzoate (C4MB) single crystals were successfully grown by the slow evaporation solution growth technique. The harvested crystals were subjected to single-crystal X-ray diffraction, spectral, optical, thermal and mechanical studies in order to evaluate physiochemical properties. The Kurtz and Perry technique for second harmonic generation (SHG) study revealed that the powdered materials of BCT and C4MB exhibit SHG efficiency 0.2 times less and 1.3 times greater than that of standard reference material potassium dihydrogen phosphate. C4MB crystal exhibits high efficiency than BCT, because of methoxy group substituted in the para position of phenyl ring. With high SHG efficiency and thermal stability para substituted C4MB crystal will be a potential candidate for optical device fabrication.

Nonlinear optical diagnostics of local crystallization of lead zirconate titanate films using femtosecond laser radiation

Features of crystallization of microstructures to the perovskite-like phase in a lead zirconate titanate film are studied using multiple near-IR femtosecond laser pulse radiation. The kinetics of crystallization is in situ investigated using the second-harmonic generation technique. It is established that the crystallization is divided into high-temperature ultrafast (explosive) crystallization, which occurs right after the start of irradiation, and low-temperature slow (self-induced) crystallization, which starts after termination of irradiation of a strained multilayer structure. The advantages of the second-harmonic generation microscopy in studying annealed microstructures are demonstrated.

Charge injection and accumulation in organic light-emitting diode with PEDOT:PSS anode

Organic light-emitting diode (OLED) displays using flexible substrates have many attractive features. Since transparent conductive oxides do not fit the requirements of flexible devices, conductive polymer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) has been proposed as an alternative. The charge injection and accumulation in OLED devices with PEDOT:PSS anodes are investigated and compared with indium tin oxide anode devices. Higher current density and electroluminescence light intensity are achieved for the OLED device with a PEDOT:PSS anode. The electric field induced second-harmonic generation technique is used for direct observation of temporal evolution of electric fields. It is clearly demonstrated that the improvement in the device performance of the OLED device with a PEDOT:PSS anode is associated with the smooth charge injection and accumulation.

New Strategies for Cellular‐Scale Imaging of Bone and Cartilage

Confocal microscopy can be used to obtain detailed, 3D‐resolved images of cells inside bone and cartilage. However the high scattering coefficients of dense connective tissues often necessitate tissue sectioning for resolving cellular scale detail inside. Multiphoton microscopy enables clearer imaging and greater depth penetration into these tissues and the related technique of second harmonic generation enables acquisition of collagen images at the single‐fibril level in 3D and in some cases in vivo. New improvements in clearing technologies and optical methods such as light sheet microscopy continue to advance the depth in to which dense tissues can be imaged using highly‐specific fluorescent probes. Concurrently, improvements in X‐ray computed tomography, the standard method for 3D medical assessment of bone morphology and lesions, have led to resolutions rivaling those obtained with optical microscopy, in some cases with specifically targeted electron dense contrast agents. Different techniques excel for different specific questions to be addressed within this diverse and powerful imaging landscape.

Applications of second-harmonic generation imaging microscopy in ovarian and breast cancer.

In this perspective, we discuss how the nonlinear optical technique of second-harmonic generation (SHG) microscopy has been used to greatly enhance our understanding of the tumor microenvironment (TME) of breast and ovarian cancer. Striking changes in collagen architecture are associated with these epithelial cancers, and SHG can image these changes with great sensitivity and specificity with submicrometer resolution. This information has not historically been exploited by pathologists but has the potential to enhance diagnostic and prognostic capabilities. We summarize the utility of image processing tools that analyze fiber morphology in SHG images of breast and ovarian cancer in human tissues and animal models. We also describe methods that exploit the SHG physical underpinnings that are effective in delineating normal and malignant tissues. First we describe the use of polarization-resolved SHG that yields metrics related to macromolecular and supramolecular structures. The coherence and corresponding phase-matching process of SHG results in emission directionality (forward to backward), which is related to sub-resolution fibrillar assembly. These analyses are more general and more broadly applicable than purely morphology-based analyses; however, they are more computationally intensive. Intravital imaging techniques are also emerging that incorporate all of these quantitative analyses. Now, all these techniques can be coupled with rapidly advancing miniaturization of imaging systems to afford their use in clinical situations including enhancing pathology analysis and also in assisting in real-time surgical determination of tumor margins.

Quantitative evaluation of carbonation in concrete using nonlinear ultrasound

Abstract A new nonlinear ultrasonic technique for nondestructive evaluation of concrete components is developed and implemented to characterize the effects of carbonation on concrete. The physical principle of this method is the second harmonic generation (SHG) in propagating Rayleigh surface waves which are detected by a non-contact air-coupled transducer. The nonlinearity parameter, as an indicator of material properties, is experimentally obtained from measured Rayleigh wave signals and is used to quantitatively evaluate the progress of carbonation under accelerated conditions. The experimental results show that there is a significant decrease in the measured nonlinearity parameter, most likely originated from the deposit of the carbonation product, CaCO3, in pre-existing voids and microcracks. The sensitivity of the nonlinearity parameter is also verified by comparing with the measured Rayleigh wave velocity. The results in this paper demonstrate that the SHG technique using Rayleigh surface waves can be used to monitor carbonation in concrete.

Second Harmonic Generation Based on Strong Field Enhancement in Metallic Nanostructured Surface

Although absorption is still the primary optical property of interest, other spectroscopic techniques including optical second harmonic generation (SHG) are also used to understand anisotropic nature of nanomaterials. Benefit of SHG technique as compared with linear optical approach is that SH response is the most sensitive to surface potential changes and SH intensity mainly comes from surface/interface layers. This article reports that optical absorption spectra due to surface plasmon modes of metallic nanowires exhibit strong anisotropic absorption. Maxwell-Garnett simulation cannot fit with experimental results because of wire sizes much larger than wavelength of light, whereas finite-difference time-domain calculation can fit well with experimental findings in terms of position of photon energy of absorption peak with respect to polarization conditions. DOI: http://dx.doi.org/10.5755/j01.ms.20.4.6399

Review of Second Harmonic Generation Measurement Techniques for Material State Determination in Metals

This paper presents a comprehensive review of the current state of knowledge of second harmonic generation (SHG) measurements, a subset of nonlinear ultrasonic nondestructive evaluation techniques. These SHG techniques exploit the material nonlinearity of metals in order to measure the acoustic nonlinearity parameter, $$\beta $$ . In these measurements, a second harmonic wave is generated from a propagating monochromatic elastic wave, due to the anharmonicity of the crystal lattice, as well as the presence of microstructural features such as dislocations and precipitates. This article provides a summary of models that relate the different microstructural contributions to $$\beta $$ , and provides details of the different SHG measurement and analysis techniques available, focusing on longitudinal and Rayleigh wave methods. The main focus of this paper is a critical review of the literature that utilizes these SHG methods for the nondestructive evaluation of plasticity, fatigue, thermal aging, creep, and radiation damage in metals.

Time-, Energy-, and Phase-Resolved Second-Harmonic Generation at Semiconductor Interfaces

Interfacial charge transfer is ubiquitous in many chemical and physical processes and can occur on ultrafast time scales of femtoseconds to picoseconds. Probing dynamics on such time scales necessitates the use of ultrafast laser spectroscopies, but signatures of interfacial charge transfer can be overwhelmed by the signal from bulk materials. This problem may be alleviated in second-harmonic generation, which can be specifically sensitive to interfacial charge transfer if other bulk and interfacial contributions to the measured second-harmonic signal can be resolved. We report the development of a femtosecond spectral interferometry technique for second-harmonic generation with time, energy, and phase resolution. Using the model systems of a passivated GaAs(100) surface and copper phthalocyanine/GaAs(100) interface, we demonstrate the application of this technique in unveiling the rich dynamics of band renormalization, charge carrier motion, and interfacial charge transfer, all induced by across-bandgap ...

Air-coupled detection of nonlinear Rayleigh surface waves in concrete—Application to microcracking detection

This paper proposes a new technique for the application of the second harmonic generation (SHG) in Rayleigh surface waves to nondestructively quantify microstructural changes and microcracks in heterogeneous cement-based materials (mortar and concrete). The effect of shrinkage reducing admixture (SRA), as it influences microcrack formation in these materials, is considered as an example. A 50kHz wedge transmitter and a 100kHz air-coupled receiver are implemented for the generation and detection of nonlinear Rayleigh waves; the non-contact receiver has the advantage of eliminating the inconsistencies associated with coupling and can be used for inspections of in-service concrete components. The experimental results show that the SRA plays a crucial role in reducing shrinkage microcracks and the addition of the SRA to cement-based materials influences the material nonlinearity. These results demonstrate that the proposed SHG technique is capable of evaluating the relative nonlinearity parameter, βre and can be a reliable method to characterize microstructural changes in cement-based materials.

BODIPY-bridged push-pull chromophores for nonlinear optical applications.

A set of linear and dissymmetric BODIPY-bridged push-pull dyes are synthesized. The electron-donating substituents are anisole and dialkylanilino groups. The strongly electron-accepting moiety, a 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) group, is obtained by insertion of an electron-rich ethyne into tetracyanoethylene. A nonlinear push-pull system is developed with a donor at the 5-position of the BODIPY core and the acceptor at the 2-position. All dyes are fully characterized and their electrochemical, linear and nonlinear optical properties are discussed. The linear optical properties of dialkylamino compounds show strong solvatochromic behavior and undergo drastic changes upon protonation. The strong push-pull systems are non-fluorescent and the TCBD-BODIPY dyes show diverse photochemistry and electrochemistry, with several reversible reduction waves for the tetracyanobutadiene moiety. The hyperpolarizability μβ of selected compounds is evaluated using the electric-field-induced second-harmonic generation technique. Two of the TCBD-BODIPY dyes show particularly high μβ (1.907 μm) values of 2050 × 10(-48) and 5900 × 10(-48) esu. In addition, one of these dyes shows a high NLO contrast upon protonation-deprotonation of the donor residue.

Low coherence interferometric second harmonic generation microscopy for non-destructive material testing using a broadband 1550 nm fs-fiber laser

In this paper low coherence interferometric second harmonic generation (SHG) imaging is successfully demonstrated using a compact broadband fs-fiber laser operating around 1550 nm. In combination with linear optical coherence microscopy, this SHG technique is tailored for structural and functional investigations of surfaces and subsurface regions of non-biological samples, like corrosion sites formed on metals below organic coatings.