Electric Field-induced Second Harmonic Generation Research Articles

Synthesis and DFT calculations of linear and nonlinear optical responses of novel 2-thioxo-3-N,(4-methylphenyl) thiazolidine-4 one

ABSTRACTThe aim of this work is to present results of both experimental and theoretical studies of 2–thioxo–3–N, (4–methylphenyl) thiazolidine–4–one. In this paper, we present the chemical synthesis of 2–thioxo–3–N, (4–methylphenyl) thiazolidine 4–one followed by spectroscopy study. The applying of 1H and 13C nuclear magnetic resonance (NMR), ultraviolet–visible (UV–vis) spectroscopy, performed its structural characterization. UV–vis measurements showed absorption between 250 and 350 nm. The optical gap energy is calculated using the Tauc method, which comes out to be around 3.91 eV. Density functional theory (DFT) computations were adopted for the geometry optimization of this compound and to evaluate their static polarizability (the mean polarizability and the polarizability anisotropy ) and static first hyperpolarizability (the electric field–induced second harmonic generation (EFISHG) and the hyper–Rayleigh scattering (HRS) ) using several functionals. These static electrical properties are studied in detail. An inverse relation between the first hyperpolarizability and the HOMO–LUMO gap has been obtained for the 2–thioxo–3–N, (4–methylphenyl) thiazolidine–4–one. Based on these results, we can conclude that the synthesized molecule is considered as a good candidate for optoelectronic device applications.

Experimental and numerical studies on electric field distribution of a premixed stagnation flame under DC power supply

In this work, we achieve a sub-breakdown electric field measurement in a premixed stagnation flame by electric-field-induced second-harmonic generation (ESHG) using a nanosecond laser. Under the application of a DC voltage, the premixed flame can transit from a flat substrate-stabilized mode to a conical nozzle-stabilized mode due to the two-way interaction between the electric and hydrodynamic responses of the flame. The average electric fields along the laser pathway for these two flame modes are measured at different heights above the burner. Combining the measurement and the numerical simulation of a charge transport model, we further elucidate that the flame affects the electric field distribution in two different ways. For the flat flame mode, the electric field strength is shielded at the flame front and then quickly increases both upstream and downstream, reaching the maximum at the electrodes. The charge transport model reveals that the electrostatic shielding effect of the flame front can be attributed to the charge redistribution in the chemi-ionized conductive layer. For the conical flame mode, the electric field strength has a large gradient near the conical tip and remains almost zero downstream. The conical flame front then serves as a conductive layer to guide the charge transport under the application of the electric field. The positive and negative charges are separated at different radial positions because of the inclined asymmetric flame front. Thus, the largest electric field gradient is generated upstream of the flame conical tip, where the net charge and the electric body force maximize and create a virtual flame stabilization mode.

Structural, spectroscopic and nonlinear optical properties of sulfonamide derivatives; experimental and theoretical study

Abstract Nonlinear optical (NLO) materials have broad range applications in the field of optoelectronic devices. Nowadays great interest has been developed for synthesizing the compounds having high NLO response. Herein we are reporting the structural, spectroscopic and NLO properties of two, structurally simple sulfonamide derivatives. Both compounds are synthesized in respectable yields, characterized by using NMR (1H and 13C), FT-IR and UV–vis spectroscopic techniques. X-ray diffraction analysis confirmed the final structures. Density functional theory (DFT) at B3LYP/6-31G(d,p) method are performed for validation of experimental data (X-ray as well as spectroscopic data). Absorption studies of both compounds are performed by using TD-DFT method. Coefficients of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of both compounds reflect the high stability. First hyperpolarizability (βo), polarizability (αo) and dipole moment (μ) analyses calculated at LC-BLYP method revealed that both derivatives have reasonable nonlinear optical (NLO) response. The static, dc-Kerr effect and electric field-induced second harmonic generation (ESHG) hyperpolarizability co-efficient are also studied for refractive index (n2) calculation of both sulfonamides, to further observe their NLO response.

Field-Induced Nonlinearities in Silicon Waveguides Embedded in Lateral p-n Junctions

Silicon waveguides embedded in lateral p-n junctions show field-induced optical nonlinearities. By properly polarizing the junction, these can be used to achieve electro-optic modulation through the Direct Current Kerr effect. In addition, these enable second-order nonlinear processes such as the electric-field-induced second harmonic generation (EFISHG). In this work, we study in detail electro-optic effects in integrated silicon microresonators and demonstrate experimentally a field-induced resonance wavelength shift. This process is due to both the DC Kerr effect and the plasma-dispersion effect. By means of finite element method simulations, these effects are properly modeled and their contributions are accurately disentangled. The strength of the equivalent second-order nonlinear coefficient that would have provided the same electro-optic effect is about 16 pm/V. This result is comparable with that of materials possessing an intrinsic second order nonlinearity, and is one order of magnitude stronger than the most recent measurements of strain-induced Pockels effect in silicon.

First theoretical study of linear and nonlinear optical properties of diphenyl ferrocenyl butene derivatives

In this work, structure, linear and nonlinear optical (NLO) properties, as well structure–property relationships of fourteen diphenyl ferrocenyl butene compounds (DFB compounds 1–7 (E and Z isomers) have been investigated by ab initio methods and density functional theory (DFT) to evaluate the effects of the basis sets, functionals and electron correlation at the MP2 level. For the linear optical properties, we have been interested on the mean polarizability 〈α〉 and the polarizability anisotropy Δα. For the NLO properties, electric field-induced second harmonic generation (EFISHG) β//(−2ω;ω,ω) and hyper-Rayleigh scattering (HRS) βHRS(−2ω;ω,ω) were investigated. Close structures have been obtained with some DFT functionals for compound 2. NLO calculations reveal that compounds 1 and 2 for both E and Z isomers are a remarkably large βHRS. The results reached from the traditional functionals are in good accordance with those obtained by the corrected functionals. Inverse relationships between the gaps of HOMO–LUMO orbitals and first hyperpolarizabilities have been obtained. Using strong acceptor groups, the results will provide into the electronic properties of this important class of compounds with a promising future.

On the possibility of simultaneous temperature, species, and electric field measurements by coupled hybrid fs/ps CARS and EFISHG.

Optical signals of gas temperature, species concentration, and electric field are monitored in simple mixtures at room temperature and in the fuel-rich region of a hydrogen diffusion flame. A two-beam pure-rotational coherent anti-Stokes Raman scattering (CARS) approach was utilized for the temperature and species detection, where the combined pump/Stokes pulse doubled as the electric field induced second harmonic generation (EFISHG) pump for the electric field detection. Time-averaged EFISHG signals in environments with argon, nitrogen, oxygen, hydrogen, and air were found to match the relative hyperpolarizabilities of the molecules tabulated in literature. Measurements in a dynamic H2-air environment represented the ability to monitor the signal dependence of species on a single-shot basis. Time-averaged EFISHG signals in different thermal environments showed the expected ∝1T2 EFISHG signal dependence when also correcting for relative H2/N2 concentrations. Finally, measurements in a flame showed the ability to monitor the EFISHG signal dependence on the gas temperature on a single-shot basis in a plasma discharge environment.

Optical second harmonic generation in a ferromagnetic liquid crystal.

A comparative experimental investigation of the dependence of second harmonic generation (SHG) on an applied external voltage between a standard nematic liquid crystalline material and an analogue ferromagnetic nematic liquid crystalline material was performed by using a fundamental optical beam at an 800 nm wavelength. For the ferromagnetic material, the dependence of SHG on an applied magnetic field was also examined. Three different polarization combinations of the fundamental and the second harmonic radiation were analysed. The SHG signal observed in the former material is attributed to a combination of electric field-induced SHG (EFISHG) and flexoelectric deformation-induced SHG, while the SHG signal observed in the latter material is attributed solely to flexoelectric deformation-induced SHG. The obtained dependences of the SHG signal on the associated optical retardation show that, in the most favourable polarization combination, the two contributions generate about the same effective nonlinear optical susceptibility.

Stability in 3D and 2D/3D hybrid perovskite solar cells studied by EFISHG and IS techniques under light and heat soaking

Abstract We investigate the effect of temperature and light soaking on the stability and charge carrier behavior in triple cation 3-Dimensional (3D) and 2-Dimensional (2D)/3-Dimensional perovskite solar cells (PSCs) using electric field induced second harmonic generation (EFISHG) and impedance spectroscopy (IS) techniques. To prepare the 2D/3D perovskite structures, a layer-by-layer deposition method was employed. Spiro-OMeTAD based hole transport layer was deposited on the top of the perovskite layer using a spin coating procedure. The average power conversion efficiency (PCE) of the fresh fabricated cells was ∼18%. The electric fields in the PSCs were selectively probed by the EFISHG measurements, using the fundamental laser beam wavelength of 960 nm. The results show that the EFISHG technique could be potentially used to identify the degradation mechanism in the PSCs. Also, the IS technique was performed to investigate the electrical parameters affected under light and heat soaking environment. The 2D/3D hybrid PSCs show relatively good stability and better efficiency as compared to 3D PSCs.

Gauge-origin independent calculations of electric-field-induced second-harmonic generation circular intensity difference using London atomic orbitals

ABSTRACTWe present the first gauge-origin independent calculations of the circular intensity difference (CID) in electric-field-induced second-harmonic generation (EFISHG), including all contributions up to the electric-quadrupole–magnetic-dipole level. A recursive, open-ended response theory framework in combination with the use of London atomic orbitals allows us to ensure gauge-origin independent results. We apply this approach to study EFISHG-CID in a collection of chiral amino acids. We demonstrate that diffuse polarising basis functions are critical in order to obtain accurate CIDs, and that a basis set of at least aug-cc-pVTZ quality is needed in order to obtain results close to the basis-set limit. The use of London orbitals does not lead to significantly faster basis set convergence, although the improved basis set convergence allows the aug-cc-pVDZ basis set to be used with some confidence for larger molecules.

Investigation of Electric Field–Induced Structural Changes at Fe-Doped SrTiO3 Anode Interfaces by Second Harmonic Generation

We report on the detection of electric field–induced second harmonic generation (EFISHG) from the anode interfaces of reduced and oxidized Fe-doped SrTiO3 (Fe:STO) single crystals. For the reduced crystal, we observe steady enhancements of the susceptibility components as the imposed dc-voltage increases. The enhancements are attributed to a field-stabilized electrostriction, leading to Fe:Ti-O bond stretching and bending in Fe:Ti-O6 octahedra. For the oxidized crystal, no obvious structural changes are observed below 16 kV/cm. Above 16 kV/cm, a sharp enhancement of the susceptibilities occurs due to local electrostrictive deformations in response to oxygen vacancy migrations away from the anode. Differences between the reduced and oxidized crystals are explained by their relative oxygen vacancy and free carrier concentrations which alter internal electric fields present at the Pt/Fe:STO interfaces. Our results show that the optical SHG technique is a powerful tool for detecting structural changes near perovskite-based oxide interfaces due to field-driven oxygen vacancy migration.

Nonlinear-optical study of magnetoelectric interactions in multilayer structures

ABSTRACTTemperature dependences of electric field-induced and magnetic field-induced optical second harmonic generation (SHG) were used to study La0.7Ca0.25MnO3/BaTiO3 (LCMO/BTO) superlattice. Ferroic properties of the superlattice are reveal by magnetic field-induced and electric field-induced SHG hysteresis loops (“magnetic” and “electric” SHG loops). However, direct modifications of the SHG hysteresis loops by the other field (electric field for the “magnetic loop” and vice versa) were not found. Strong modifications of the “electric” SHG hysteresis loops occur at temperatures close to the paramagnetic-ferromagnetic and the insulator-metal phase transitions in LCMO. In this way, the magnetoelectric interaction in an LCMO/BTO superlattice was established indirectly.

Electric-field-induced optical second-harmonic generation in doped graphene

Abstract A graphene layer interacting with an incident electromagnetic wave of frequency ω will produce dipole radiation at frequency 2 ω in the presence of an in-plane electric field breaking the spatial inversion symmetry of the graphene. Here, we develop a theory that describes such electric-field-induced second-harmonic generation (EFISHG) from doped graphene. We derive an analytic expression for the relevant third-order nonlinear optical (NLO) susceptibility χ ( 3 ) ( − 2 ω ; ω , ω , 0 ) and numerically evaluate the absolute magnitude of the χ ( 3 ) for various values of the system's parameters. We find that the | χ ( 3 ) | spectrum is dominated by the resonant peak structure located at the incident photon energy ℏ ω equal to the Fermi energy E F of charge carriers in the doped graphene. We also show that the possibility to tune the doping level of graphene by an external gate voltage allows one to maximize the radiated EFISHG power at ℏ ω = E F , which may be of practical interest for the designs of the NLO devices based on employing a SHG-signal.

Coupled cluster evaluation of the frequency dispersion of the first and second hyperpolarizabilities of water, methanol, and dimethyl ether.

The static and dynamic first (β‖) and second (γ‖) hyperpolarizabilities of water, methanol, and dimethyl ether have been evaluated within the response function approach using a hierarchy of coupled cluster levels of approximation and doubly augmented correlation consistent atomic basis sets. For the three compounds, the electronic β‖ and γ‖ values calculated at the CCSD and CC3 levels are in good agreement with gas phase electric field-induced second harmonic generation (EFISHG) measurements. In addition, for dimethyl ether, the frequency dispersion of both properties follows closely recent experimental values [V. W. Couling and D. P. Shelton, J. Chem. Phys. 143, 224307 (2015)] demonstrating the reliability of these methods and levels of approximation. This also suggests that the vibrational contributions to the EFISHG responses of these molecules are small.

Background-free electric field-induced second harmonic generation with interdigitated combs of electrodes.

The electric field-induced second harmonic (EFISH) generation is a powerful tool for the investigation of optical nonlinearities, material polarization, internal electric fields, and other properties of photonic materials and devices. A conventional generation of the second harmonics (SH) in materials with the disturbed centrosymmetry causes a field-independent background to EFISH and limits its applications. Here we suggest and analyze the application of the interdigitated combs of electrodes for EFISH generation in thin films. Interdigitated electrodes form an optical transmission amplitude diffraction grating. Phase matching of the EFISH radiation creates unusual diffraction fringes with the zero intensity along the zeroth order direction and with the diffraction angles different from diffraction angles of incident fundamental laser radiation and its second harmonics. It enables a simple geometrical separation of the EFISH signal from a conventional SH background, simplifies the sample preparation, and provides additional experimental possibilities. We demonstrate applicability of the suggested technique for characterization of submicrometer thickness organic films of transparent and resonantly interacting polymers and of their mixtures.

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.

Direct probing of contact electrification by using optical second harmonic generation technique.

Contact electrification between two different materials is one of the oldest fields of study in solid-state physics. Here, we introduced an innovative system based on optical electric-field-induced second harmonic generation (EFI-SHG) technique that can directly monitor the dynamic performance of the contact electrification on the surface of polyimide film. After the contact, the EFI-SHG system visualized briefly three relaxations of the tribo-induced charges on the surface of a polyimide film, a fast relaxation within 3 min followed by two much slower relaxations, which were possibly related to different charge diffusion routes. The contact electrification under several special experimental conditions (wind, water and steam) was studied to demonstrate the high flexibility and material selectivity of the EFI-SHG. The EFI-SHG studies confirmed the motion of the water can remove the surface charge, while the appearance and the evaporation of a thin water layer cannot enhance the charge diffusion. We anticipate that this experimental technique will find a variety of applications in the field of contact electrification and the development of the recently invented triboelectric nano generator.

T‐Shaped (Donor–π–)2Acceptor–π–Donor Push–Pull Systems Based on Indan‐1,3‐dione

AbstractSixteen model (donor–π–)2acceptor–π–donor [(D–π–)2A–π–D] molecules with an extraordinary T‐shaped arrangement were designed and synthesized. Indan‐1,3‐dione was employed as a central acceptor with electron donors linked at the C‐2, C‐4, and C‐7 positions. These push–pull molecules represent a first systematic modification of an indan‐1,3‐dione‐fused benzene ring. The structures and properties of all target molecules were investigated by X‐ray analysis, electrochemistry, UV/Vis absorption spectroscopy, differential scanning calorimetry, electric‐field‐induced second‐harmonic generation (EFISHG) studies, and DFT calculations. A thorough evaluation of all of the gathered data has been performed, and structure–property relationships were evaluated. Electron donors attached at the C‐2 position through π systems of various lengths affect the studied properties most significantly. The side donors at C‐4 and C‐7 can be described as auxiliary and do not dominate the observed properties. However, thiophene is a more efficient donor than N,N‐dimethylaniline in this respect. Hence, indan‐1,3‐dione bearing a piperidylthiophene donor connected through a propenylidene spacer at C‐2 completed with two side thiophen‐2‐ylethynyl branches at C‐4 and C‐7 showed the highest figure of merit among the studied properties.

Intramolecular Cooperative Effects in Multichromophoric Cavitands Exhibiting Nonlinear Optical Properties

We report on the design, synthesis, and characterization of a new class of multichromophoric cavitands based on resorcin[4]arenes. The novel compounds have exhibited high values of second-order nonlinear optical (NLO) properties, as evidenced by electric-field-induced second harmonic generation (EFISHG) measurements. Theoretical calculations indicate the presence of edge-to-face T-shaped interactions between the aromatic building blocks within these multichromophoric systems, which is further supported by the detection of hypsochromic shifts in UV-vis and upfield aromatic chemical shifts in 1H NMR. We proved for the first time that the gain in the quadratic hyperpolarizabilities of multichromophoric NLO macrocycles, originating from the near parallel orientations of the subchromophores, can be partially suppressed if the distance between the dipolar subunits falls into a specific range, where intramolecular cooperative and/or collective effects are operative. Our finding will contribute to the better understanding of the phenomenon of cooperativity in new molecular materials with promising NLO properties. (Figure Presented). © 2015 American Chemical Society.

Second-order nonlinear optical properties of dithienophenazine and TTF derivatives: A butterfly effect of dimalononitrile substitutions

Using density functional theory (DFT) methods, the nonlinear optical (NLO) properties have been calculated with strong donor-π-conjugation-acceptor configurations. The static first hyperpolarizability (β0) and dynamic (frequency dependent) electric field induced second harmonic generation (EFISHG) first hyperpolarizability (μβ) are calculated for all designed systems. Our DFT calculations show dithienophenazine merged TTF (2) holds larger β0 amplitudes (β0=21.04×103a.u.) as compared to its corresponding compounds of TTF merged-difurophenazine (1), dicyclopentaphenazine (3) and dipyrrolophenazine (4) derivatives having β0 amplitudes of 16.25×103, 12.69×103, and 18.38×103a.u., respectively. Furthermore, substitution of dimalononitrile [C(CN)2]2 groups at acceptor end of these compounds results in new derivatives 1a–4a, respectively. Interestingly, a butterfly effect on first hyperpolarizability of all systems 1a–4a has been spotted, which not only results in their robustly larger β0 amplitudes but also changes the increasing order of β0 amplitudes from systems 3<1<4<2 to 1a<2a<3a<4a at both PBE0/6-31G* and CAM-B3LYP/6-31+G* levels of theory. For example, the increase in β0 amplitudes of systems 1a, 2a, 3a and 4a are 3, 3, 5, and 19 times as compared with their corresponding non dimalononitrile derivatives at PBE0/6-31G* level of theory, respectively. Remarkably, unlike the static first hyperpolarizability, the dynamic EFISHG hyperpolarizability (μβω) has the largest value for system 4a with its amplitudes of 1378.59×10−46 and 1349.40×10−46esu, at PBE0/6-31G* and CAM-B3LYP/6-31+G* levels of theory, respectively. TD-DFT calculations have been performed to trace the origin of first hyperpolarizability. It has been found that the lower transition energy and higher oscillator strengths cause robustly large amplitudes especially in systems 3a and 4a, which consequently stems in strong donor-π-conjugation-acceptor configuration of these systems. Thus the present results intrigue the butterfly effect of a two-step substitution on NLO properties of TTF merged dithienophenazine compounds that can be used as an efficient NLO material.

Imaging local electric fields produced upon synchrotron X-ray exposure

Electron-hole separation following hard X-ray absorption during diffraction analysis of soft materials under cryogenic conditions produces substantial local electric fields visualizable by second harmonic generation (SHG) microscopy. Monte Carlo simulations of X-ray photoelectron trajectories suggest the formation of substantial local electric fields in the regions adjacent to those exposed to X-rays, indicating a possible electric-field-induced SHG (EFISH) mechanism for generating the observed signal. In studies of amorphous vitreous solvents, analysis of the SHG spatial profiles following X-ray microbeam exposure was consistent with an EFISH mechanism. Within protein crystals, exposure to 12-keV (1.033-Å) X-rays resulted in increased SHG in the region extending ∼ 3 μm beyond the borders of the X-ray beam. Moderate X-ray exposures typical of those used for crystal centering by raster scanning through an X-ray beam were sufficient to produce static electric fields easily detectable by SHG. The X-ray-induced SHG activity was observed with no measurable loss for longer than 2 wk while maintained under cryogenic conditions, but disappeared if annealed to room temperature for a few seconds. These results provide direct experimental observables capable of validating simulations of X-ray-induced damage within soft materials. In addition, X-ray-induced local fields may potentially impact diffraction resolution through localized piezoelectric distortions of the lattice.