Enhancement Of Nonlinear Optical Response Research Articles

Enhancement of nonlinear optical response of 26Adamanzane by doping with alkali metals exohedrally and alkaline earth metals endohedrally: a DFT study

Enhancement of nonlinear optical response of 26Adamanzane by doping with alkali metals exohedrally and alkaline earth metals endohedrally: a DFT study

Realizing the effect of s-block metals on a charge transfer crystal of indol-2-one for enhanced NLO responses with efficient energetic offsets.

Due to their unique photophysical properties, organic charge transfer crystals are becoming promising materials for next-generation optoelectronic devices. This research paper explores the impact of s-block metals on a charge transfer crystal of indol-2-one for enhanced nonlinear optical (NLO) responses with efficient energetic offsets. The study reveals that alkali metals can enhance NLO performance due to their free electrons. The Perdew-Burke-Ernzerhof functional of DFT with dispersion correction (D3) was used, and the λmax values ranged between 596 and 669nm, with the highest value for dichloromethane (DCM). Leveraging the unique properties of metals allowed for the development of nonlinear optical materials with improved performance and versatility. Softness (σ) values provide insight into electron density changes, with higher values indicating a greater tendency for changes and lower values indicating the opposite. The NLO results for the chromophores MMI1-MMI6 show varying linear polarizability (< α0 >) along with their first (β0) and second (γ0) hyperpolarizabilities. Chromophore MMI4 stands out with the highest NLO performance, having two potassium (K) atoms. Its < α0 > , β0, and γ0 values of 4.19, 7.09, and 17.43 (× 10-24 e.s.u), respectively, indicate a significant enhancement in NLO response compared to the other chromophores. The transitions involving (O20)LP → (C3-N5)π* and (O19)LP → (N12-C13)π* exhibit the highest level of stabilization, followed by (O23)π → (C10-C11)π*, while (C6-N12)π → (C6-C7)π* shows the lowest level of stabilization for chromophore MMI4. The present research work is facile in its nature, and it can be helpful for synthetic scientist to design the new materials for uniting crystal properties with metal doping for efficient NLO devices.

Enhancement in Nonlinear Optical Response of Oligothiophenes by Induction of Polarons

In this study, the electronic and nonlinear optical properties of neutral ((nTh) and polaronic states (nTh*) of oligothiophenes are studied. Electronic properties are evaluated through HOMO–LUMO gap, ionization potential (IP), and electronic affinity (EA). The results of global reactivity descriptors also indicate the stability of nTh*. The linear and nonlinear optical properties are evaluated through the polarizability and static and dynamic hyperpolarizabilities. The polaronic states of these polymers show high hyperpolarizability (βo) up to 2.7 × 104 au as compared to neutral counterparts. This remarkable increase is mainly due to low transition energies arising from the induction of polaron. The NLO response of polaron-based oligothiophenes are much better than their neutral counterparts. Furthermore, the frequency dependent calculations for polaronic state of oligothiophenes (nTh*) are also performed at commonly used laser frequencies of 532 and 1064 nm. The results of frequency dependent calculations reveal that the values of dynamic hyperpolarizability are more pronounced than static hyperpolarizability. Time-dependent calculations show enough transparency of polaronic state of nTh* in the UV region, which reveals that the materials show good NLO response and could be used in the field of optoelectronics.

Electronically tunable cyanoethynylethenes and Tetracyanobuta-1, 3-dienes based Push–pull organic chromophores for enhanced nonlinear optical Activity: A DFT perspective

Small organic molecules that have a few number of double and triple bonds will not show large optical excitation energies however, with a strategic design and substitution with donor and accepter group, enhance the second order nonlinear optical (NLO) properties. We have designed small organic molecules by modifying donor–acceptor (DA) substituent with compact π-conjugated systems. We have performed density functional theory calculations by using CAM-B3LYP/6–311+G (d,p) level of theory. The calculated results reviled that the proper donor group substitution leads to absorption within the visible region. The maximum absorption wavelength of the designed molecules shows a red shift trend. The observed trend in absorption and first hyperpolarizability indicate that the crucial transition energy become smaller and dipole moment is larger. Among the designed molecules, the largest first order hyperpolarizability of compound 9 is showing multifold large first hyperpolrizability than that of p-nitroaniline. Additional new peak arises in LUMO region that directly affect the band gap. Further, to see the structure property relationship towards enhancement of NLO response, we have calculated the frontier molecular orbital (FMO), transition density matrix (TDM) and molecular electrostatic potential (MESP) of the designed molecules.

DFT study of enhancement in nonlinear optical response of exohedrally and endohedrally alkaline earth metals (Be, Mg, Ca) doped adamanzane

AbstractIn this study, density functional theory has been used to investigate the geometric, electronic, linear and nonlinear optical properties of exohedrally and endohedrally doped adamanzane M1(26 adz)M2 where (M1 = M2 = Be, Mg and Ca). The multiple doping rendered excess electrons to the system which resulted in increased HOMO energies and resultantly reduced HOMO‐LUMO gap (from 8.85 eV to 4.87 eV). The significant changes in excitation energy and vertical ionization energy indicated the introduction of excess electrons to the system. The NBO analysis confirmed that both the dopants are electron donating moieties. The formation of new HOMOs were also evident from the density of state (DOS) analysis. The new complexes exhibited remarkable nonlinear optical response and maximum first hyperpolarizability (β = 8.19 × 103 au) and second hyperpolarizability (γ = 8.12 × 105 au) were observed for AM9. This nonlinear response enhanced significantly when materials were placed in the light of 1907 nm wavelength for determination of dynamic hyperpolarizabilities. The UV–Vis analysis confirmed the transparency of designed materials in deep UV region. The structural properties of new materials were also authenticated by IR‐spectra. The exceptionally high nonlinear response makes these materials desirable candidates for photonic, telecommunication and laser applications.

Graphene oxide induced the enhancement of nonlinear optical response of ITO films

Abstract The indium tin oxide-graphene oxide (ITO/GO) composite films with different thickness of GO for a mixed ITO thickness was synthesized by a facile solid-liquid thermal recombination. The structure and the optical properties of ITO/GO composites were analyzed by X-ray diffraction (XRD), Raman spectra, ellipsometer and the UV-VIS-NIR double beam spectrophotometer. The nonlinear optical properties of specimen were successfully investigated by a single Z-scan technique. The experimental results showed that the epsilon-near-zero (ENZ) wavelength of composites can be tuned from 1225 to 1940 nm by adjusting the thickness of GO. The nonlinear absorption coefficient ( β = − 4.0 × 10 8 cm/GW) for composites is about 1.8 times greater than that of the single-layer ITO films. Additionally, the results of Finite-Difference Time-Domain (FDTD) are in good agreement with those of the experiments.

Enhancement of nonlinear optical response of methylene blue and azure a during association with colloidal CdS quantum dots

The nonlinear optical response of thiazine dyes during association with colloidal CdS quantum dots (QDs) applying the z-scan technique at wavelength of 532 nm with use 10 ns pulses of Nd:YAG laser second harmonic were studied. Increasing in nonlinear absorption intensity in hybrid associates in comparison with the initial components were found. Moreover, UV–vis absorption spectrum shows the effective formation of dyes H-aggregates during association with colloidal QDs. Two-photon mechanism of observed nonlinear absorption in hybrid associates is proposed, based on a sharper dependence of the normalized transmittance on the incident intensity (distance between the sample and focal plane of focusing lens). And for pure solutions, the reverse saturated absorption is preferred nonlinear absorption mechanism. The nonlinear absorption coefficients for MB and AzA in the hybrid associates were found. They are β ≈ 8.4 × 10−9 cm W-1 и ≈ 1.34 × 10-8 cm W-1, respectively. It was shown that it is possible to control the parameters of nonlinear absorption of thiazine dyes via the hybrid association.

Solvent induced enhancement of nonlinear optical response of graphdiyne

Flat and crystalline materials with exceptional nonlinear optical (NLO) properties are highly desirable for their potential applications in integrated NLO photonic devices. Graphdiyne (GD), a new two-dimensional (2D) carbon allotrope, has recently evoked burgeoning research attention by virtue of its tunable bandgap along with a high carrier mobility and extended π-conjugation compared with most conventional optical materials. Here, we experimentally probe the third-order nonlinear optical response of GD dispersed in several common solvents (alcohols) using a femtosecond Z-scan technique. The measured nonlinear optical refractive index is in the order of ∼10−8 cm2/W, which is approximately one order of magnitude higher than that of most 2D materials. In particular, we find that different NLO responses can be observed from GD when dispersed in different solvents, with the strongest NLO response when dispersed in 1-propanol. It is proposed that some intrinsic properties of the solvents, such as the polarity and viscosity, could influence the NLO response of GD materials. Our experimental results confirm the assumptions on the NLO behavior in GD and demonstrate its great potential for future generations of Kerr-effect-based NLO materials and devices.

Enhancement of ultrafast nonlinear optical response of zinc selenide nanoparticle decorated reduced graphene oxide sheets

The synergistic effect of zinc selenide (ZnSe) nanoparticle functionalized into reduced graphene oxide (RGO) sheets on nonlinear optical (NLO) properties has been investigated by single beam z-scan technique. Comprehensive measurements on nonlinear absorption (NLA) as well as nonlinear refraction (NLR) have been performed on RGO, ZnSe, and RGO-ZnSe composites at 630 nm in the femtosecond regime. Both NLA and NLR of RGO-ZnSe show an enhancement in NLO properties compared to pure RGO and ZnSe in an intensity range of 37GW/cm2 to 130GW/cm2. The enhanced optical nonlinearity of RGO-ZnSe may have been caused due to strong interlayer coupling between RGO and ZnSe, as well as the availability of a large number of NLA states in the composite. The interlayer coupling between ZnSe nanoparticles and RGO sheets has been confirmed by transmission electron microscopy, UV-Visible, and photoluminescence spectroscopy. At low input pulse intensity (∼37GW/cm2), saturation absorption dominates, whereas NLA becomes prominent in the higher intensity regime (55GW/cm2–130GW/cm2) for RGO and ZnSe. NLA is the dominant phenomenon for RGO-ZnSe in the whole experimental intensity range. Moreover, it is observed that the dispersion of RGO, ZnSe, and RGO-ZnSe in dimethylformamide exhibits positive NLR. This study indicates an enhancement in nonlinear optical response of the RGO-semiconductor composite, which is very promising for graphene based photonic device applications.

Nonlinear optical response of collective modes in multiband superconductors assisted by nonmagnetic impurities

In multiband superconductors, multiple collective modes exist associated with the multiple order parameters. Oscillations of the amplitude and the relative phase of the order parameters are called Higgs and Leggett modes, respectively. Recently, it has been suggested that nonmagnetic impurity scattering would enhance nonlinear coupling between the Higgs mode and an electromagnetic wave with a frequency located in the superconducting gap region, while its effect on the Leggett mode is still unresolved. Here, we theoretically investigated the nonlinear optical response of multiband Bardeen-Cooper-Schrieffer-type superconductors in the presence of nonmagnetic impurities with a density matrix approach extending the Mattis-Bardeen model of linear response. We found that the drastic enhancement of nonlinear optical response due to the nonmagnetic impurity scattering occurs only for the Higgs modes and not for the Leggett mode. As a result, both the light-induced dynamics of the superconducting gaps and the resulting third-harmonic generation are dominated by the Higgs modes. We also examined the role of quasiparticle excitations to find that they give the subdominant contribution to the third-harmonic generation.

Anionic Effect of δ and χ Forms of Tris(alkoxo) Ligand Functionalized Anderson-Type Polyoxometalates on Nonlinear Optical Response of Porphyrin–POM Based Supramolecular Compounds

The electrostatic interaction of tris(alkoxo) ligand functionalized Anderson-type polyoxometalate (POM for short) anions [XMo6O18{(OCH2)3CNH2}2]3– (where X = Mn or Fe) having δ-type structures and [H2ZnMo6O18{(OCH2)3CNH2}2]2– having χ-type structure with porphyrin-based cation [H2TPP]2+ results in formation of three supramolecular compounds [H2TPP]1.5[MnMo6O18{(OCH2)3CNH2}2] (1), [H2TPP]1.5[FeMo6O18{(OCH2)3CNH2}2]·2C3H7NO (2), and [H2TPP][H2ZnMo6O18{(OCH2)3CNH2}2]·2(C2H5)2O (3). All the supramolecular compounds have significant nonlinear reverse saturated absorption (RSA) and self-defocusing behavior especially the compound 3 has noteworthy improvement of second hyperpolarizability γ value (1.35 × 10–27 esu) compared to parent porphyrin (7.7 × 10–28 esu). Fluorescence is quenched by ca. 74% in compound 3, 37% in compound 1 and 30% in compound 2 compared to that of parent porphyrin, respectively, indicating different quenching effect of the different POM anions. Parallelly, it was found that the three POM anions have different onset reduction potentials due to different central metal atom and overall cluster structure, corresponding to different HOMO–LUMO gaps (Eg) of the resulting supramolecular compounds with Eg (3) <Eg (1) <Eg (2) <Eg (parent porphyrin). Thus, we thought that the easier electronic charge transfer from porphyrin to POM anions by irradiation with laser light plays a key role in the enhancement of nonlinear optical response in supramolecular compounds.

Enhancement of nonlinear optical response and fluorescence spectra of cationic neutral red by anionic surfactant

Two-photon absorption (TPA) and fluorescence intensity have possibilities for application in photodynamic therapy and photonic devices. The nonlinear optical properties of the cationic neutral red dye (NR) encapsulated in nanodroplets were studied using the Z-scan technique. The nanodroplets were prepared with a mixture of water, oils, and anionic Bis (2-ethylhexyl) sulfosuccinate sodium salt (AOT). The TPA and nonlinear refractive (NLR) index were studied in three different systems; NR in nanodroplets, NR in AOT and water, and NR in a different solvent. The results indicated that the TPA and NLR index spectra of NR depend on the droplet size. The TPA of the NR dye in the nanodroplet is enhanced in comparison to the NR/solvent system. Moreover, the second-order hyperpolarizability and fluorescence activity of the NR are affected by the encapsulation in the nanodroplets.

Giant Enhancement of Nonlinear Optical Response in Nd:YAG Single Crystals by Embedded Silver Nanoparticles.

We report on the enhancement and modulation of nonlinear optical response in an Nd:Y3Al5O12 (Nd:YAG) laser crystal through embedded silver nanoparticles (NPs) fabricated by Ag+ ion implantation. The linear absorption spectrum of the sample clearly reveals a localized surface plasmon resonance (SPR) band from 350 to 700 nm correlated to the Ag NPs. By using the Z-scan technique with femtosecond pulses at a wavelength of 515 nm, which is considered as an optical excitation within the SPR band, the nonlinear refraction index reaches values as high as ∼10–12 cm2/W, enhanced by ∼4 orders of magnitude in comparison to that of unimplanted Nd:YAG (without Ag NPs). In addition, it has been shown that embedded Ag NPs in the Nd:YAG host reveal saturable absorption signifying the nonlinear responses. We have also observed that the nonlinear absorption coefficients depend significantly on the excitation energy and can be modulated by varying the fluence of Ag+ ions.

Vertically standing layered MoS2 nanosheets on TiO2 nanofibers for enhanced nonlinear optical property.

Vertical layered MoS2 nanosheets rooting into TiO2 nanofibers were successfully prepared by a facile two-step method: prefabrication of porous TiO2 nanofibers based on an electrospinning technique, and assembly of MoS2 ultrathin nanosheets through a simple hydrothermal reaction. Significant enhancement of nonlinear optical response of the MoS2/TiO2 nanocomposite was confirmed by an open-aperture z-scan measurement. The nanocomposite displayed strong optical limiting (OL) effects to ultrafast laser pulses with a low OL threshold of ~22.3 mJ/cm2, which is lower than that of pristine TiO2 nanofibers and MoS2 nanosheets. In addition to the contribution of the strong nonlinear absorption of MoS2 nanosheets and TiO2 nanofibers, such phenomenon is also attributed to the unique structure of vertically standing layered MoS2 nanosheets on TiO2 nanofibers with a large amount of exposed edge states, large surface areas and fast electron transfer between TiO2 and MoS2. This work broadens our vision to engineering novel hierarchical MoS2-based nanocomposite for efficiently enhanced nonlinear light-matter interaction.

Metal-induced efficient enhancement of nonlinear optical response in conjugated azo-based iminopyridine complexes

The nonlinear optical (NLO) properties of conjugated azo-based iminopyridine complexes with zinc and silver metal cations were studied. The processes of second and third harmonic generations in guest-host polymeric films were investigated and NLO parameters were extracted. Obtained second and third order NLO susceptibilities of zinc containing complex exceeds the latter of silver containing one. Using the Z-scan technique the NLO refractive index, NLO absorption coefficient, second order hyperpolarizability and NLO absorption cross section for the azo-based iminopyridine zinc (II) and silver (I) complexes were obtained and analyzed. Estimated nonlinearity/loss figure of merit of these complexes show promise for optical device applications.

Electronic structures and second hyperpolarizabilities of annulenes derivatives

Organic nonlinear optical materials have attracted considerable attention in recent years because of their potential applications in photonic devices and optical information processing. Recent studies have shown that annulene derivatives exhibit good second-order nonlinear optical properties, but their third-order nonlinear optical properties are studied little. In this paper, the values of molecular static linear polarizability α and second hyperpolarizability γ of substituted annulenes have been investigated with different levels of HF, B3LYP, BHandHLYP and CAM-B3LYP at different basis sets, respectively. Their ultraviolet spectra have also been calculated by using the TD-B3LYP method. It is found that the quality of the basis set is important for the hyperpolarizability calculations, and diffuse functions are important to obtain accurate results for the second hyperpolarizability. We also study the structure-optical property relationship for annulene. It is found that annulene molecular structure has a significant influence on third-order nonlinear optical response. Increasing the conjugation length and introducing push-pull electronic groups can enhance the second hyperpolarizability. But the introduction of push-pull electronic groups can enhance the hyperpolarizability more remarkably than increasing the conjugation length dose, which may be due to the fact that the introduction of push-pull electronic groups can provide a large number of polarizable electrons whereas increasing the conjugation length can only enhance the electron delocalization. Meanwhile the push-pull electronic group substituted annulenes can also exhibit high transparency in visible region. Thus, this work has a good reference for designing nonlinear optical material with high, nonlinear optical coefficient and good transparency. In addition, for the same push-pull electronic groups, the higher conjugation degree and the longer πup -conjugated bridge result in the decrease of HOMO-LUMO energy gap and transition energy which benefits the enhancement of nonlinear optical response. Our results demonstrate that annulene derivative shows both high transparency and large second hyperpolarizability, and thus becomes a promising candidate for third-order nonlinear optical material. In addition, the dynamic (hyper) polarizabilities of considered annulene molecules are calculated by using CAM-B3LYP method. It is found that in near-infrared region, with the increase of frequency of incident light, α (ω; ω), γ (-ω; ω, 0, 0) and γ (-2ω; ω, ω, 0) are all increased, and the near-resonance enhancement effect occurs. Under the condition of far resonance, α (ω; ω), γ (-ω; ω, 0, 0) and γ (-2ω; ω, ω, 0) change little. This dispersion effect may be helpful for the experimental study and applications as well.

Enhanced molecular first hyperpolarizability in s-triazine derivatives: Combined experimental and computational studies

Molecular first hyperpolarizabilities (nonlinear optical responses) of selected s-triazine based heteroaromatic molecules are determined using experimental methods. A large enhancement in nonlinear optical response, in spite of a relatively weak donor–acceptor system, is observed. We have carried out a detailed analysis using computational chemistry techniques to account for this behavior.

Ultrafast photoinduced enhancement of nonlinear optical response in 15-atom gold clusters on indium tin oxide conducting film

We show that the third order optical nonlinearity of 15-atom gold clusters is significantly enhanced when in contact with indium tin oxide (ITO) conducting film. Open and close aperture z-scan experiments together with non-degenerate pump-probe differential transmission experiments were done using 80 fs laser pulses centered at 395 nm and 790 nm on gold clusters encased inside cyclodextrin cavities. We show that two photon absorption coefficient is enhanced by an order of magnitude as compared to that when the clusters are on pristine glass plate. The enhancement for the nonlinear optical refraction coefficient is ~3 times. The photo-induced excited state absorption using pump-probe experiments at pump wavelength of 395 nm and probe at 790 nm also show an enhancement by an order of magnitude. These results attributed to the excited state energy transfer in the coupled gold cluster-ITO system are different from the enhancement seen so far in charge donor-acceptor complexes and nanoparticle-conjugate polymer composites.

Large Enhancement of Nonlinear Optical Response in a Hybrid Nanobiomaterial Consisting of Bacteriorhodopsin and Cadmium Telluride Quantum Dots

We report wavelength-dependent enormous enhancement of the nonlinear refractive index of wild-type bacteriorhodopsin in the presence of semiconductor quantum dots. The effect is strongest in the region just below the absorption edge of both constituents of this hybrid material and in samples that show strong Förster resonance energy transfer. We show that enhancements of up to 4000% can be achieved by controlled engineering of the hybrid structure involving variations of the molar ratio of the constituents. This new hybrid material with exceptional nonlinear properties will have numerous photonic and optoelectronic applications employing its photochromic, energy transfer, and conversion properties.

A new scheme for significant enhancement of the second order nonlinear optical response from molecules to ordered aggregates

How to achieve maximum nonlinear optical (NLO) properties from the molecular to the macro block is very crucial to the development of nonlinear optical materials, which is the impetus of the present work. Buckybowls present large first hyperpolarizability ascribed to noncentrosymmetric charge distribution due to the curved shape of the system. The role of their packing pattern in maximizing the NLO response of buckybowl aggregates is investigated. In (corannulene)(10) and (sumanene)(10) aggregates, the first order hyperpolarizabilities (β(0)) per molecule are enhanced 5.59 and 6.21 times with respect to a single entity respectively. For a larger buckybowl, C(36)H(12), the β(0) value per molecule of its pentamer reaches 191.4 × 10(-30) esu which is much higher than conventional dipolar or octupolar NLO chromophores ones. The cohesive coupling among electric dipoles in packing of buckybowls is responsible for significant enhancement of the nonlinear optical response of the aggregates, which could pave the way for designing large 2nd order NLO materials with a good balance of nonlinearity, transparency, and stability.