Nonlinear Optical Response Research Articles

Simultaneous Achievement of Enhanced Nonlinear Optical Absorption and Nonlinear Refraction in Highly Crystalline 2D Covalent Organic Frameworks Ultrathin Films.

Large enhancement of nonlinear absorption and nonlinear refraction are achieved simultaneously in highly ordered two dimensional (2D) covalent organic framework (COF) films prepared by solidliquid interface one-step method to overcome the weakness of COF powders in solubility. In the intrinsic nonlinear optical response obtained at 532 nm with 5 ns pulse, the nonlinear absorption coefficients (β) of two COF films are -4.87 × 10-5and -1.29 × 10-5mW-1, respectively. Simultaneously, the fitted closed-aperture curves also show large nonlinear refractive indexes (n2), -5.62 × 10-12 m2W-1 and -0.76 × 10-12 m2W-1. The 4f coherent imaging performed at the same condition with a single-shot pulse further verifies the outstanding nonlinear optical response without any damage probably experienced in the Z-scan technique. Moreover, the differences in framework electronic structure and photoexcited states between two COF films are compared to explain the difference in nonlinear optical response. All the results indicate that two COF crystalline films with intrinsic giant nonlinear optical response can be capable of modulating both amplitude and phase of light, providing huge potential in all-optical manipulating and switching at the nanoscale as outstanding nonlinear optical materials.

Generation of Massively Entangled Bright States of Light during Harmonic Generation in Resonant Media

At the fundamental level, full description of light-matter interaction requires quantum treatment of both matter and light. However, for standard light sources generating intense laser pulses carrying quadrillions of photons in a coherent state, the classical description of light during intense laser-matter interaction has been expected to be adequate. Here, we show how nonlinear optical response of matter can be controlled to generate dramatic deviations from this standard picture, including generation of several squeezed and entangled harmonics of the incident laser light. In particular, such nontrivial quantum states of harmonics are generated as soon as one of the harmonics induces a transition between different laser-dressed states of the material system. Such transitions generate an entangled light-matter wave function, which can generate quantum states of harmonics even in the absence of a quantum driving field or material correlations. In turn, entanglement of the material system with a single harmonic generates and controls entanglement between different harmonics. Hence, nonlinear media that are near resonant with at least one of the harmonics appear to be quite attractive for controlled generation of massively entangled quantum states of light. Our analysis opens remarkable opportunities at the interface of attosecond physics and quantum optics, with implications for quantum information science. Published by the American Physical Society 2025

Effect of alkaline earth metal ions R2+ (R = Mg, Ca, Sr, and Ba) on the properties of LiNbO3 glass ceramics

AbstractAs a functional crystal, LiNbO3 plays a significant role in nonlinear optics, optical storage, illumination, and three‐dimensional display. Recent investigations have suggested that the precipitation of LiNbO3 in a nonequilibrium system shows unique crystallite geometry and orientation, leading to fascinating nonlinear optical properties. This work focuses on the effect of alkaline earth metal ions on the properties of Li2O–Nb2O5–SiO2 glass ceramics. The results demonstrate that within the Li2O–Nb2O5–SiO2 glass matrix, irregularly shaped crystals of approximately 5 µm in size precipitate through volume crystallization. Upon incorporation of Mg2+, the glass ceramic remains in volume crystallization while LiNbO3 crystals grow to 10 µm and become spherical. In contrast, the compositions containing Ca2+, Sr2+, and Ba2+ change to surface crystallization, producing submicron or even nano‐sized crystals. Besides, the nonlinear optical response can be improved after the hybridization of alkaline earth metal oxides. This research offers insights into the crystallization behavior of LiNbO3 crystals from the nonequilibrium environment.

Exploring the thermal-induced optical nonlinearity of crude oil via spatial self-phase modulation technique

This study aims to investigate the nonlinear optical (NLO) characteristics of diluted crude oil samples from the Ramshir, Rag-e-Sefid, and Ahwaz-20 reservoir fields in the southwest region of Iran. Utilizing spatial self-phase modulation (SSPM) techniques, we measured the nonlinear refractive index () by observing the intensity-dependent number of diffraction rings with continuous-wave laser beams at and wavelengths. This study focused on examining the ratios of different sample concentrations to identify the role of thermal effects in the observed NLO responses. Our findings indicate a direct correlation between the concentration of crude oil in the samples and their NLO properties, with thermal effects significantly influencing the changes in NLO responses. In the thermal region, the nonlinear refractive index was approximately determined to be . Additionally, the study explores the collapse of diffraction rings to further understand how the relative nonlinear refractive index varies with the sample concentration and incident intensity at both wavelengths. The results suggest that crude oil possesses promising NLO properties, making it potentially suitable for the development of new photonic devices and applications, especially in areas where thermal nonlinearities are crucial, such as sensing and all-optical technologies.

Thickness-dependent optical properties and ultrafast carrier dynamics of 2D non-layered β-In2S3

Non-layered 2D materials, such as indium sulfide (In2S3), possess distinctive properties due to their unsaturated surface bonds and atomically thin structures, rendering them highly promising for state-of-the-art optoelectronic applications. Herein, we conduct a comprehensive investigation into the optical characteristics and ultrafast carrier dynamics of β-In2S3 nanoflakes. Through thickness-dependent Raman, photoluminescence (PL), and absorption spectra, we reveal the critical role of thickness in tuning the optical properties of β-In2S3. Notably, β-In2S3 exhibits broad PL emission and a robust nonlinear optical response in second-harmonic generation (SHG), largely attributed to inherent defect states. Thickness-dependent SHG surpasses conventional odd/even layer limitations, highlighting β-In2S3’s unique optical versatility. Ultrafast carrier dynamics further unveil two distinct defect-mediated recombination processes: a fast non-radiative pathway and a slower radiative pathway, both accelerating with increasing thickness, as revealed by thickness-dependent transient absorption spectroscopy. This finding underscores the significant modulation of recombination lifetime by varying the thickness of β-In2S3. These insights not only emphasize the versatility of β-In2S3 for optoelectronic applications but also pave the way for its integration into next-generation devices, offering a promising avenue for advancing the field of optoelectronics.

σ-Electrons rather than π-Electrons Inducing Sensitive Nonlinear Optical Responses in Planar and Quasi-Planar Boron Clusters.

Geometries and electronic structures of planar and quasi-planar boron clusters resemble those of aromatic hydrocarbons, providing opportunities for designing novel nonlinear optical materials. However, the nonlinear optical properties, optical-response mechanisms, and optimal optical-response geometries of boron clusters remain unclear. Accordingly, this study addresses these uncertainties. Boron clusters exhibit good nonlinear optical performance, significantly surpassing that of aromatic hydrocarbons of comparable size. An analysis method based on electron density decomposition is proposed to quantitatively determine the contributions of σ- and π-electrons to the optical responses. The findings reveal that σ-electrons dominate the nonlinear optical responses in planar boron clusters owing to their delocalized characteristics, in marked contrast to aromatic hydrocarbons. Using boron isomers as model systems, boron nanoribbons were confirmed to provide optimal nonlinear optical performances. This study offers valuable insights into the nonlinear optical behaviors of planar and quasi-planar boron clusters, substantially enhancing the rational design of novel nonlinear optical materials.

Transformation of Distinct Superatoms to Superalkalis by Successive Ligation of Thymine Nucleobases.

The ligation strategy has been widely used in the chemical synthesis of atomically precise clusters. A series of thymine (T)-ligated Al12M-Tn (M = Be, Al, C; n = 1-5) complexes have been studied to reveal the effect of DNA nucleobase ligands on the electronic structures of different superatoms in the present work. In addition to its protective role, the successive attachment of thymine ligands significantly lowers the adiabatic ionization energies (AIEs) of the studied Al12M superatoms with filled and unfilled electronic shells. The continuous decrease in the AIEs of Al12M-Tn is derived from the gradually raised highest occupied molecular orbital (HOMO) levels upon the addition of ligands. Interestingly, the lowering degree of AIEs for such nucleobase-protected superatoms is independent of the distinct shell fillings of Al12M superatoms but is significantly related to the types of nucleobases. Moreover, the obtained Al12M-T5 superalkalis not only exhibit excellent performance in activating the stable CO2 and O2 molecules but also have considerable nonlinear optical (NLO) responses. We, therefore, hope that this study could provide a viable strategy for synthesizing novel nucleobase-ligated superatom clusters with excellent reducing capability to enrich the family of multifunctional nanoclusters.

Nonlinear Optical Response of BiVO₄ and Its Application for Ultrafast Pulsed Fiber Lasers

Nonlinear Optical Response of BiVO₄ and Its Application for Ultrafast Pulsed Fiber Lasers

Ruthenium Oxide: A Near 0.8 µm Epsilon‐Near‐Zero Medium for Multipurpose Nonlinear Photonics

AbstractThe intriguing optical response associated with the vanishingly small dielectric primitivity in epsilon‐near‐zero (ENZ) materials has offered unprecedented opportunities for photonics. Due to the high‐limit of doping concentration, current homogeneous ENZ materials based on heavily doped conductive oxide including ITO usually exhibit a zero‐permittivity wavelength (λ0) longer than 1200 nm. Here, this is identified with combined theoretical and experimental investigations that stoichiometric rutile‐type RuO2 (r‐RuO2) exhibits the shortest λ0 of near 800 nm among conductive oxides, benefiting from the high free electron concentration with characteristic Drude‐type response. The ENZ effect is manifested by the strong field enhancement and the large nonlinear optical (NLO) response in colloidal processed r‐RuO2 nanoparticles (NPs) and thin films. By ultrafast transient spectroscopy, the strong NLO response in r‐RuO2 NPs is revealed to be the result of rapid thermalization/cooling of free electrons in the strong hybridized Ru‐4d/O‐2p orbitals. The ultrafast optical nonlinearity is exploited further for the development of multi‐purpose all‐optical switches that enable stable pulse laser generation in four mode‐locked and Q‐switched fiber lasers. Our results underscore the potential of stoichiometric metallic metal oxides as alternative ENZ materials for nonlinear photonics applications in the visible and NIR regions.

Defect state enhanced nonlinear absorption and optical limiting behaviour of erbium doped silver molybdate nanostructures

Transition metal based optical limiting materials have garnered significant attention due their crucial role in protecting sensitive optical system from high intense laser damage. Transition metal molybdates exhibits nonlinear optical (NLO) response, which attenuate highly intense light by transmitting light of desired intensity. Herein we report Silver molybdate (Ag2MoO4) nanostructures doped with erbium (Er) ions were successfully synthesized by simple co-precipitation technique. The proper incorporation of Er ions into the Ag2MoO4 lattice without altering the crystal structure was confirmed by XRD Analysis. The optical properties studied using UV–Vis absorption Spectroscopy exhibited maximum absorption in UV region and the absorption in the visible region is found to increase with the addition of Er ions into the host lattice. The XPS spectra confirmed the + 3 oxidation state of erbium and Ag0 state of silver. The NLO parameters such as, nonlinear absorption (NLA) and optical limiting (OL) was studied for the first time under 532 nm nanosecond laser excitation. Results suggest that erbium doped silver molybdate exhibited reverse saturable absorption originated from two photon absorption. The synthesized samples exhibited excellent nonlinear absorption and optical limiting performance. Also it is observed that with the addition of Er ions, the two photon absorption (2PA) is found to enhance from 0.85 × 10–10 m/W (pure Ag2MoO4) to 6.223 × 10–10 m/W for 0.5% Er doped sample. So, erbium doped silver molybdate nanostructures can be used for various tunable optoelectronic devices.

Ferroelectricity and Nonlinear Optical Responses in Two-Dimensional Distorted MX2Y (M = Cu, Ag, Au; X = Chalcogens; Y = Halogen) Monolayers.

Two-dimensional (2D) materials with spontaneous polarization can exhibit large second-order nonlinear optical (NLO) effects. Here, we present a series of stable distorted MX2Y monolayers by using first-principles calculations and lattice vibration analysis. The structural distortion leads to a lower polar symmetry, giving rise to intrinsic ferroelectricity with a Curie point up to room temperature. We show that the bulk photovoltaic effect (BPVE) in polar MX2Y monolayers has an enhanced shift current, an order of magnitude larger than that in the undistorted nonpolar counterparts. Meanwhile, the second harmonic generation (SHG) susceptibility reaches up to the order of 106 pm2/V, superior to that of 2D conventional materials such as MoS2, h-BN, and GeS. Our study advances the research in 2D ferroelectric materials and would stimulate more efforts in developing optoelectronic devices based on NLO effects.

Nonlinear frequency-asymmetric optical response in chiral systems

Nonlinear frequency-asymmetric optical response in chiral systems

A hydrazine-hydroxy-pyran-2-one derivatives as a potential anticancer and antibacterial agent: synthesis, spectroscopic, SC-XRD, DFT/TD-DFT, Hirshfeld surface analysis, in silico molecular docking and nonlinear optical responses studies

This study presents the synthesis and thorough characterisation of a hydrazine-hydroxy-pyran-2-one derivative referred to as compound (L1 : 3, 3′- [(1E.2E)-hydrazine-1, 2-diylidene-dieth-1-yl-1-ylidene] bis(4-hydroxy-6-methyl-2H-pyran-2-one). Structural elucidation using UV-vis, FT-IR and single crystal X-ray diffraction (SC-XRD) confirmed tautomeric forms of L1 . The SC-XRD analysis revealed a bi-zwitterionic form (BZL1 ), stabilised by the intramolecular proton transfer between two enol units and azine tautomerism. The planar molecular structure, supported by XRD, DFT and Hirshfeld surface analysis, showed charge-assisted hydrogen bonds [N+−H…O−] forming S(6) ring motifs. Crystals were stabilised by C-H…O hydrogen bonds and π-π stacking, analysed through Hirshfeld surfaces and 2D fingerprint plots. Compound L2 : 3-[(1E)-1-(9H-fluoren-9-ylidenehydrazinylidene)ethyl]-4-hydroxy-6-methyl-2H-pyran-2-one), is illustrated in this paper to compare two derivatives of dehydroacetic acid (DHA) and to enrich this study. Molecular docking revealed binding affinities of hybrid compounds with target proteins. DFT and TD-DFT analyses examined structural, electronic and optical properties, aligning well with experimental data. BZL1 exhibited higher electronic hardness (3.632 eV) than L2 (3.506 eV). Variations in α, Δα and ρ values were observed, with L1 showing stronger γ(0; 0, 0, 0) and γ(−ω; ω, 0, 0) while L2 excelled in γ(−2ω; ω, ω, 0). Consequently, these results highlight the potential of these compounds as promising candidates for use in third-order nonlinear optical applications.

Excitons in nonlinear optical responses: shift current in MoS2 and GeS monolayers

It is well-known that exciton effects are determinant to understanding the optical absorption spectrum of low-dimensional materials. However, the role of excitons in nonlinear optical responses has been much less investigated at the experimental level. Additionally, computational methods to calculate nonlinear conductivities in real materials are still not widespread, particularly taking into account excitonic interactions. We present a methodology to calculate the excitonic second-order optical responses in 2D materials relying on: (i) ab initio tight-binding Hamiltonians obtained by Wannier interpolation and (ii) solving the Bethe-Salpeter equation with effective electron-hole interactions. Here, in particular, we explore the role of excitons in the shift current of monolayer materials. Focusing on MoS2 and GeS monolayer systems, our results show that 2p-like excitons, which are dark in the linear response regime, yield a contribution to the photocurrent comparable to that of 1s-like excitons. Under radiation with intensity ~104W/cm2, the excitonic theory predicts in-gap photogalvanic currents of almost ~10 nA in sufficiently clean samples, which is typically one order of magnitude higher than the value predicted by independent-particle theory near the band edge.

Berry curvature and shift vector effects at high-order wave mixing in biased bilayer graphene

In this paper, we present a microscopic quantum theory that elucidates the nonlinear and nonperturbative optical response of biased bilayer graphene subjected to bichromatic strong laser fields. This response is analyzed using a four-band Hamiltonian derived from calculations. For the laser-stimulated dynamics, we employ structure gauge-invariant evolutionary equations to accurately describe the evolution of the single-particle density matrix across the entire Brillouin zone. The resonant generation of electron-hole pairs by the high-frequency component of the field, combined with the induction of high-order harmonic generation and high-order wave mixing by the strong low-frequency field component, leads to significant alterations in the resulting spectra. These changes are driven by the effects of Berry curvature and the shift vector, which modify the relative contributions of interband and intraband channels, thereby fundamentally reshaping the radiation spectra at high-order frequency multiplication. The numerical results are further supported by approximate analytical calculations, demonstrating that high-order wave mixing can be modeled using the classical trajectory analysis of electron-hole pairs, with Berry curvature and the shift vector significantly influencing the saddle-point equations. Published by the American Physical Society 2025

Toroidal dipole resonances enhanced second-harmonic generation with shallow etching of lithium niobate metasurface.

Lithium niobate (LiNbO3) has shown great potential for applications in nonlinear metasurfaces, thanks to its large second-order nonlinear coefficients and high integration capabilities. Optical resonances play a crucial role in further enhancing the nonlinear optical responses of LiNbO3 metasurfaces (LNMS). In this study, both numerically and experimentally, we designed and fabricated a metasurface structure that supports toroidal dipole (TD) resonance to enhance second-harmonic generation (SHG). This structure, which consists of an array of shallow-etched square columns on a continuous thin film, intensifies the SHG signal at 400 nm within the LiNbO3 film by means of strong local field confinement. Experimental results indicate that this signal is ten times stronger compared to that of lithium niobate on insulator (LNOI). These findings emphasize the potential of TD resonance in enhancing the performance of LiNbO3 in integrated nonlinear nanophotonic applications.

Superfluorescence and nonlinear optical response of CH3NH3PbBr3-based mesostructures: applications to amplified spontaneous emission and ultrafast lasers.

Metal halide perovskites have unique luminescent properties that make them an attractive alternative for high quality light-emitting devices. However, the poor stability of perovskites with many defects and the long cycle time for the preparation of perovskite nanocomposites have hindered their production and application. Here, we prepared the perovskite mesostructures by embedding MAPbBr3 nanocrystals in the mesopores on the surface of silica nanospheres and mixing the nanospheres with silver nanowires and poly(methyl methacrylate) (PMMA), and further explored their optical properties. The perovskite mesostructures exhibited superfluorescence (SF) under 785 nm laser excitation and the decay time was as short as 0.59 ps using a double exponential decay fit. The optical nonlinearity of these perovskite mesostructures under two-photon excitation was investigated by the Z-scanning technique. The samples exhibited both two-photon absorption (TPA) and saturation absorption (SA) with nonlinear absorption coefficients β ranging approximately 0.15 to 0.89 cm/GW corresponding to the TPA, and a saturation intensity of about 0.026 GW/cm2 was determined. In addition, the quality of the perovskite mesostructures was shown to be significantly improved, including an increase in radiative efficiency and an extension of the optical gain lifetime. The samples were excited by a two-photon femtosecond laser pump at room temperature and atmospheric pressure, and the laser peak appeared at 540.1 nm with a low amplified spontaneous emission (ASE) threshold of 0.52 mJ/cm2. Moreover, the perovskite mesostructures have been added to the fiber laser system as a saturable absorber, and the Q-switched pulse is generated at the wavelength of 1.5 µm. Our work effectively demonstrates that perovskite mesostructured materials can be functionalized for photonic devices, paving the way for further exploration of complex, functional and practical perovskite.

2D Chiral Ag(I) Complexes with A-π-A- and D-π-A-Type Dicarboxylic Acid Ligands: Presenting Significant Differences in Nonlinear Optical Responses.

Three two-dimensional (2D) chiral Ag(I) complexes with formulas [Ag4(LR)4(5-nipa)2]n (1), [Ag4(LS)4(5-nipa)2]n (2), and {[Ag4(LS)4(5-hipa)2]·2H2O}n (3) were prepared through the reactions of Ag2O with enantiopure bis-monodentate N-donors (LR/LS) and different dicarboxylic acids bearing A (acceptor)-π-A- and D (donor)-π-A-type structural features, where LR/LS = (-)/(+)-2-(4'-pyridyl)-4,5-pinene-pyridine, 5-H2nipa = 5-nitroisophthalic acid, and 5-H2hipa = 5-hydroxyisophthalic acid. A study of their nonlinear optical responses reveals that chiral 1 and 2 enantiomeric pairs with the A-π-A-type dicarboxylic acid ligand simultaneously display second- and third-harmonic generation (SHG and THG) responses, while chiral 3 containing the D-π-A-type dicarboxylic acid ligand only exhibits a very strong THG response. The THG intensity of 3 is 451 × α-SiO2, being about 27 and 24 times larger than those of 1 and 2, respectively.

Co-assemblies of Silver Nanoclusters and Fullerenols With Enhanced Third-Order Nonlinear Optical Response.

Exploring potential third-order nonlinear optical (NLO) materials attracts ever-increasing attention. Given that the atomically precise and rich adjustable structural features of silver nanoclusters (Ag NCs), as well as the unique π-electron conjugated system of carbon-based nanomaterials, a supramolecular co-assembly amplification strategy to enhance the luminescent intensity and NLO performance of the hybrids of the two components, are constructed and the relationship between structures and optical properties are investigated. By combining water soluble Ag NCs [(NH4)6[Ag6(mna)6] (H2mna = 2-mercaptonicotinic acid, abbreviated to Ag6─NCs hereafter) containing uncoordinated carboxyl groups with water-soluble fullerene derivatives modified with multiple hydroxyl groups (fullerenols, C60─OH), the π-electron delocalization is expanded owing to non-covalent hydrogen bonding effect between Ag6─NCs and C60─OH, which provides a feasible basis for realizing the NLO response. Then, the co-assemblies are doped into a PMMA matrix to prepare composite film and its NLO properties are evaluated by Z-scan technique. Remarkably, the effective nonlinear absorption coefficients β is of two orders magnitude higher than those of the Ag6─NCs assemblies at the absence of C60─OH. This work showcases a new approach for amplifying NLO responses which greatly facilitates the development of integrated photonic devices.

Chiral exceptional point enhanced active tuning and nonreciprocity in micro-resonators

Exceptional points (EPs) have been extensively explored in mechanical, acoustic, plasmonic, and photonic systems. However, little is known about the role of EPs in tailoring the dynamic tunability of optical devices. A specific type of EPs known as chiral EPs has recently attracted much attention for controlling the flow of light and for building sensors with better responsivity. A recently demonstrated route to chiral EPs via lithographically defined symmetric Mie scatterers on the rim of resonators has not only provided the much-needed mechanical stability for studying chiral EPs, but also helped reduce losses originating from nanofabrication imperfections, facilitating the in-situ study of chiral EPs and their contribution to the dynamics and tunability of resonators. Here, we use asymmetric Mie scatterers to break the rotational symmetry of a microresonator, to demonstrate deterministic thermal tuning across a chiral EP, and to demonstrate EP-mediated chiral optical nonlinear response and efficient electro-optic tuning. Our results indicate asymmetric electro-optic modulation with up to 17 dB contrast at GHz and CMOS-compatible voltage levels. Such wafer-scale nano-manufacturing of chiral electro-optic modulators and the chiral EP-tailored tunning may facilitate new micro-resonator functionalities in quantum information processing, electromagnetic wave control, and optical interconnects.