Harmonic Generation Effect Research Articles

Laser stimulated second and third harmonic optical effects in F: SnO2 nanostructures grown via chemical synthetic route

Laser stimulated second and third harmonic generation effects in Fluorine doped tin oxide (F:SnO2) nanostructures versus the fluorine content is presented. The F:SnO2 nanostructures have been fabricated at various fluorine doping concentrations by spray pyrolysis technique. The films exhibit polycrystalline nature with a preferential growth orientation along (1 1 0) diffraction plane as evident from x-ray diffraction studies. The optical transmittance of the F:SnO2 films has increased from 68% to 80%. Photoluminescence studies revealed that strong violet emission peak corresponds to ∼400 nm and relatively weak red emission peak at about ∼675 nm was observed for all the F:SnO2 films. Increase in theβeff value upon fluorine incorporation supports the applicability of the deposited films in passive optical limiting applications. The principal origin of second harmonic generation signals (SHG) for this type of nanostructures is played by the space charge density acentricity due to the F doping. The enhanced second and third harmonic generation signals observed on F:SnO2 nanostructures endorses the credibility of these materials in various nonlinear optical trigger device applications.

Self-assembling amyloid-like peptides as exogenous second harmonic probes for bioimaging applications.

Amyloid-like peptides are an ideal model for the mechanistic study of amyloidosis, which may lead to many human diseases, such as Alzheimer disease. This study reports a strong second harmonic generation (SHG) effect of amyloid-like peptides, having a signal equivalent to or even higher than those of endogenous collagen fibers. Several amyloid-like peptides (both synthetic and natural) were examined under SHG microscopy and shown they are SHG-active. These peptides can also be observed inside cells (in vitro). This interesting property can make these amyloid-like peptides second harmonic probes for bioimaging applications. Furthermore, SHG microscopy can provide a simple and label-free approach to detect amyloidosis. Lattice corneal dystrophy was chosen as a model disease of amyloidosis. Morphological difference between normal and diseased human corneal biopsy samples can be easily recognized, proving that SHG can be a useful tool for disease diagnosis.

Large Second Harmonic Generation (SHG) Effect and High Laser‐Induced Damage Threshold (LIDT) Observed Coexisting in Gallium Selenide

AbstractA big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced damage threshold (LIDT). Herein we report the preparation of a new Ga2Se3 phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS2 (AGS), respectively. In addition, its IR transparent window ca. 0.59–25 μm is also significantly wider than that of AGS (ca. 0.48–≈11.4 μm). The occurrence of the strong SHG responses and good phase‐matching indicate that the structure of the new Ga2Se3 phase can only be non‐centrosymmetric and have a lower symmetry than the cubic γ‐phase. The observed excellent SHG and phase‐matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.

Large Second Harmonic Generation (SHG) Effect and High Laser-Induced Damage Threshold (LIDT) Observed Coexisting in Gallium Selenide.

A big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced damage threshold (LIDT). Herein we report the preparation of a new Ga2 Se3 phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS2 (AGS), respectively. In addition, its IR transparent window ca. 0.59-25 μm is also significantly wider than that of AGS (ca. 0.48-≈11.4 μm). The occurrence of the strong SHG responses and good phase-matching indicate that the structure of the new Ga2 Se3 phase can only be non-centrosymmetric and have a lower symmetry than the cubic γ-phase. The observed excellent SHG and phase-matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.

Phase Identification and Strong Second Harmonic Generation in Pure ε-InSe and Its Alloys.

Two-dimensional material indium selenide (InSe) has offered a new platform for fundamental research in virtue of its emerging fascinating properties. Unlike 2H-phase transition-metal dichalcogenides (TMDs), ε phase InSe with a hexagonal unit cell possesses broken inversion symmetry in all the layer numbers, and predicted to have a strong second harmonic generation (SHG) effect. In this work, we find that the as-prepared pure InSe, alloyed InSe1- xTe x and InSe1- xS x ( x = 0.1 and 0.2) are ε phase structures and exhibit excellent SHG performance from few-layer to bulk-like dimension. This high SHG efficiency is attributed to the noncentrosymmetric crystal structure of the ε-InSe system, which has been clearly verified by aberration-corrected scanning transmission electron microscopy (STEM) images. The experimental results show that the SHG intensities from multilayer pure ε-InSe and alloyed InSe0.9Te0.1 and InSe1- xS x ( x = 0.1 and 0.2) are around 1-2 orders of magnitude higher than that of the monolayer TMD systems and even superior to that of GaSe with the same thickness. The estimated nonlinear susceptibility χ(2) of ε-InSe is larger than that of ε-GaSe and monolayer TMDs. Our study provides first-hand information about the phase identification of ε-InSe and indicates an excellent candidate for nonlinear optical (NLO) applications as well as the possibility of engineering SHG response by alloying.

Rational design of a new chalcogenide with good infrared nonlinear optical performance: SrZnSnS4

The new nonlinear optical material SrZnSnS4 is a two-dimensional layer structure with a large band gap (3.37 eV). The orderly arrangement of [ZnS4]6− and [SnS4]4− groups mainly contribute to the second harmonic generation effect (∼LiGaS2).

Studies of Er(iii)–W(v) compounds showing nonlinear optical activity and single-molecule magnetic properties

Studies of {[Er(dma)5][W(CN)8]}n (1) showing nonlinear optical effect of second harmonic generation, and [Er(dma)5(H2O)2]·[W(CN)8]·dma·H2O (2) and [Er(dma)4(H2O)3]·[W(CN)8]·dma·3H2O (3) revealing field-induced single molecule magnet behavior.

Модифицированная модель Друде-Лоренца, позволяющая учесть топологические характеристики среды

The Drude-Lorentz model, which allows to describe nonlinear response of dielectric or conduc-tor, could be used for describing nonlinear non resonant responses of some exotic media, such as the topological insulators, the Weyl semimetals and the Dirac metals. Generalized Drude-Lorentz model and its simplified version, where the topological effects are taken into account in the minimal order, are presented in paper. A nonlinear conductance of the second order corre-sponding to second harmonic generation and optical rectification effect is obtained in paper as an example of use of the simplified model. It is shown that the ratio of the topological conductance to the ordinary linear conductance contains the constant value that is proportional to the fine structure constant and axion field gradient.

Cascade random-quasi-phase-matched harmonic generation in polycrystalline ZnSe

We experimentally and numerically investigated the cascade random-quasi-phase-matched harmonic generation in polycrystalline zinc selenide with tightly focused mid-infrared nanosecond laser pulses. We observed a sharp transition between two distinct intensity scaling regimes as a function of pump energy from sub IN to super IN, where I is the pump intensity and N is the harmonic order. To gain an understanding of the observations of this complex nonlinear process, we carried out simulations of the coupled three-wave mixing equations with random grain sizes and orientations. We found a grain size dependence of the effective phase-matching condition, suggesting that manipulation of grain size can be an effective pathway to phase-matching optimization. This approach may provide a framework for effectively enhancing high harmonic generation and other wave mixing effects in polycrystalline materials.

Y2(CO3)3·H2O and (NH4)2Ca2Y4(CO3)9·H2O: Partial Aliovalent Cation Substitution Enabling Evolution from Centrosymmetry to Noncentrosymmetry for Nonlinear Optical Response

An effective approach, the partial aliovalent cation substitution (PACS), was successfully employed to develop nonlinear optical (NLO) material. Two novel rare earth carbonates, Y2(CO3)3·H2O (YC) and (NH4)2Ca2Y4(CO3)9·H2O (CYC), were synthesized, which feature the same honeycomb-like framework structure. From YC to CYC, the partial substitution of Y3+ with Ca2+ led to the evolution of space group from centrosymmetric P63/mcm to noncentrosymmetric P63mc. The CYC exhibited a second harmonic generation (SHG) effect of 2.1 × KH2PO4 (KDP) and a deep-UV cutoff edge (<200 nm). It was concluded that the SHG effect originates from the ordered arrangement of (CO3)2– groups and the dipole polarization enhancement of [Ca0.33Y0.67O9] polyhedra. Specifically, the long-range ordered electric field of channels induced the ordered arrangement of (CO3)2– groups. This synthetic approach and SHG-activated induction mechanism may afford new strategies for the design and synthesis of NLO materials.

Nonlinear Optical Properties of CdS Semiconductor nanowires

In this work, we report on the nonlinear optical properties in single Cadmium sulfide nanowires (CdS NWs). The high qulity growth of CdS semiconductor nanowires were synthesized by chemical vapor deposition (CVD) method. The as-obtained products were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and the energy dispersive X-ray spectrom (EDS) was used to determine the specific elemental distribution and show purity of the CdS semiconductor nanowires . The excitation of femtosecond laser(800 nm, 50 fs, 80 MHz) was used to study the nonlinear optical properties of CdS nanowires, such as the Second Harmonic Generation(SHG) and optical waveguide effect. CdS NW has a second harmonic generation with a blue emission bands at a wavelength of 400 nm . Finally, based on the dark field image of the CCD taken and combined with the spectrum, it is proved that CdS NW has an optical waveguide effect.

Cyano-Based Materials with Giant Optical Anisotropy and Second Harmonic-Generation Effect

It is a huge challenge to achieve giant optical anisotropy (e.g., birefringence) over a wide region from infrared (IR) to ultraviolet (UV) spectroscopy. This is mainly due to the lack of ideal optical motifs, which should have giant structural anisotropy with a wide transparent range. Especially in the field of nonlinear optical (NLO) materials, polar motifs with giant optical anisotropy are extremely scarce, but they are favorable to exhibit strong second harmonic generation (SHG) effect and phase-matching capacity. On the basis of analysis of microstructure and macro optical property, in this study, we focus on one-dimensional chained cyano (CN) motif and surprisingly find that it can exhibit sufficiently large optical anisotropy and SHG effect from IR to UV regions. Therefore, it is reasonable to believe that the CN motif can be considered as a novel NLO material gene, which was totally ignored in the previous studies. Interestingly, the CN-gene can be integrated into various coordination structures, such as metal cyanides, cyanogen halides, and cyanogen chalcogenides, to promote these materials to exhibit tunable NLO capabilities from IR to UV and deep-UV regions. Remarkably, the chained acentric CNI structure, which has already been obtained in the experiment, can achieve the IR and UV frequency conversion with a sufficiently large SHG effect (∼17 pm/V) and a giant optical birefringence (∼0.7 at 1064 nm). Therefore, the cyano-based compounds proposed in this article can not only enrich the structural chemistry of NLO materials, but also potentially advance the development of optical material genome project.

Nonlinear propagation effects in high harmonic generation in reflection and transmission from gallium arsenide.

High harmonic spectroscopy in solids is emerging as a new tool to investigate ultrafast electron dynamics in the presence of strong optical fields. However, the observed high harmonic spectra do not usually reflect the microscopic origin of high harmonic generation (HHG) because of nonlinear and/or linear propagation effects. Here, we systematically investigate the HHG in reflection and transmission from gallium arsenide exposed to intense mid-infrared optical pulses. In transmission geometry, we find that the properties of high harmonics are drastically changed by nonlinear effects during the propagation of even tens of micrometers. Especially, the nonlinear absorption and/or nonlinearly induced ellipticity of the drive pulses as well as a cascade nonlinear mixing significantly alter the high harmonic signals in the case of the transmission geometry, making an extraction of the microscopic electron dynamics of gallium arsenide difficult. On the contrary, in reflection geometry, we obtain HHG spectra that are free from propagation effects, opening a general approach for high harmonic spectroscopy.

Gaussian beam focusing in metamaterial with the second harmonic generation effect as a perfect lens using paraxial group transformation

In this paper, propagation of the Gaussian beam in two structures of the perfect lens with the ability of the second harmonic generation is investigated by using paraxial group transformation method. For this purpose, at first the concept of perfect lens, the second harmonic generation, and paraxial group transformation method are introduced. Then, generation and propagation of the second harmonic beam in two structures of perfect lens are simulated. Results show that the image quality can be increased by these structures.

Density Functional Theory Prediction of the Second Harmonic Generation and Linear Pockels Effect in Trigonal BaZnO2

Polycrystalline powder of trigonal BaZnO2 has been synthesized and characterized by X-ray diffraction, dielectric measurements, and vibrational spectroscopy (infrared and Raman). These properties have been also calculated using the density functional theory and compared with the experimental ones. The experimental phonon modes have been assigned, and we have revisited the previous theoretical assignment reported in the literature combining the calculated and the experimental data. The dielectric constant has been analyzed by decoupling it into three contributions (electronic, phonon, and strain). The second-order nonlinear susceptibility and the electro-optic response have been predicted as no theoretical or experimental investigations of these optical properties have been previously reported in the literature. The second-order nonlinear optical susceptibility and the electro-optic coefficients of BaZnO2 are predicted to be significantly higher than those reported in α-quartz or α-GeO2. Thus, considering ...

Cumulative plasma effects in cavity-enhanced high-order harmonic generation in gases

Modern ultrafast laser architectures enable high-order harmonic generation (HHG) in gases at (multi-) MHz repetition rates, where each atom interacts with multiple pulses before leaving the HHG volume. This raises the question of cumulative plasma effects on the nonlinear conversion. Utilizing a femtosecond enhancement cavity with HHG in argon and on-axis geometric extreme-ultraviolet (XUV) output coupling, we experimentally compare the single-pulse case with a double-pulse HHG regime in which each gas atom is hit by two pulses while traversing the interaction volume. By varying the pulse repetition rate (18.4 and 36.8 MHz) in an 18.4-MHz roundtrip-frequency cavity with a finesse of 187, and leaving all other pulse parameters identical (35-fs, 0.6-μJ input pulses), we observe a dramatic decrease in the overall conversion efficiency (output-coupled power divided by the input power) in the double-pulse regime. The plateau harmonics (25–50 eV) exhibit very similar flux despite the twofold difference in repetition rate and average power. We attribute this to a spatially inhomogeneous plasma distribution that reduces the HHG volume, decreasing the generated XUV flux and/or affecting the spatial XUV beam profile, which reduces the efficiency of output coupling through the pierced mirror. These findings demonstrate the importance of cumulative plasma effects for power scaling of high-repetition-rate HHG in general and for applications in XUV frequency comb spectroscopy and in attosecond metrology in particular.

Two Novel Deep‐Ultraviolet Nonlinear Optical Crystals with Shorter Phase‐Matching Second Harmonic Generation than KBe2BO3F2: A First‐Principles Prediction

In this work, we propose a strategy to design new deep‐ultraviolet (deep‐UV) nonlinear optical (NLO) materials through the combination of borate and phosphate NLO material genome. Accordingly, a series of borophosphates are predicted with very large energy bandgaps, strong second harmonic generation (SHG) effects, and moderate birefringence in the deep‐UV region. In particular, two novel fluoride borophosphates, PBO3F2 and PB3O6F2, are able to achieve the deep‐UV SHG laser output with shorter phase‐matching wavelengths (≈155 and 137 nm) than that of KBe2BO3F2 (KBBF, ≈161 nm). Further calculations show that these two structures are dynamically and thermodynamically stable, thus triggering possible synthesis, growth, and applications of them. The results attest that the proposed strategy is instructive and pave a comprehensive road map for us to discover new NLO crystals, especially in the borophosphate catalog with excellent deep‐UV phase‐matching capabilities beyond KBBF.

Frontispiece: Co‐Crystals of 2‐Amino‐5‐Nitropyridine Barbital with Extreme Birefringence and Large Second Harmonic Generation Effect

Frontispiece: Co‐Crystals of 2‐Amino‐5‐Nitropyridine Barbital with Extreme Birefringence and Large Second Harmonic Generation Effect

Co-Crystals of 2-Amino-5-Nitropyridine Barbital with Extreme Birefringence and Large Second Harmonic Generation Effect.

Technological innovation enforces a revolutionized approach towards materials chemistry. In this paper a new methodology towards crystal engineering of polar materials for possible applications in linear or non-linear optics (NLO), as well as ferroelectric, pyroelectric or piezoelectric crystals is presented. The necessity to fulfil several criteria concerning symmetry, electron properties of the building blocks, and also mechanical and optical stability was achieved by fusion of a pharmaceutical molecule and an NLO-phore. Co-crystals of 2-amino-5-nitropyridine barbital, presented in this manuscript, show cutting-edge optical performance. Large second harmonic generation (SHG) efficiency (40 times better than potassium dihydrogen phosphate, KDP), extreme birefringence (2.7 times higher than for calcite), simplicity in preparation, and optical and mechanical stability of the product proves that in fact a new generation of smart materials was obtained.

Wavelength and intensity dependence of recollision-enhanced multielectron effects in high-order harmonic generation

Using a model molecular system (${A}_{2}$) with two active electrons restricted to one dimension, we examine high-order harmonic generation (HHG) enhanced by rescattering. Our results show that even at intensities well below the single ionization saturation, harmonics generated from the cation (${A}_{2}{}^{+}$) can be significantly enhanced due to the rescattering of the electron that is initially ionized. This two-electron effect is manifested by the appearance of a secondary plateau and cutoff in the HHG spectrum, extending beyond the predicted cutoff in the single active electron approximation. We use our molecular model to investigate the wavelength dependence of rescattering enhanced HHG, which was first reported in a model atomic system [I. Tikhomirov, T. Sato, and K. L. Ishikawa, Phys. Rev. Lett. 118, 203202 (2017)]. We demonstrate that the HHG yield in the secondary cutoff is highly sensitive to the available electron rescattering energies as indicated by a dramatic scaling with respect to driving wavelength.