High Nonlinear Optical Susceptibility Research Articles

One- and Two-Photon Photophysical Properties, Ultrafast Dynamics, and DFT Study of Three Modified Zinc Phthalocyanines.

As two-photon absorption (TPA) materials, phthalocyanine molecules have promising application prospects due to their large TPA absorption cross-section, high third-order nonlinear optical susceptibility, and ultrafast response characteristics. In this work, optical properties and the ultrafast response of three modified zinc phthalocyanine molecules (P-HPcZn, Pc-P-Pc, and (DR1)4PcZn) were analyzed. No obvious side-shoulder absorption peaks in the Q-band can be observed from the steady-state absorption spectra of the three molecules, confirming the lack of aggregation products in the solutions of our measurement. Open-aperture Z-scan results show relatively large TPA cross-section values of 136.4 and 55.3 GM for Pc-P-Pc and (DR1)4PcZn, respectively. The nonlinear optical results show that the absorption process observed under the excitation of femtosecond pulses is a reverse saturable absorption (RSA) mechanism. Up-conversion fluorescence spectra of (DR1)4PcZn in THF solution indicate that the fluorescence emission mechanism is TPA. In the study of ultrafast dynamics, the transient absorption spectra were investigated and the decay lifetime of the dynamic traces corresponding to some representative probe wavelengths was obtained through data fitting with a multi-exponential function. Finally, the charge transfer and excited state properties of the modified zinc phthalocyanine molecules were discussed in depth by the DFT method. The energy gaps of P-HPcZn, Pc-P-Pc, and (DR1)4PcZn are 2.16, 1.39, and 2.13 eV, respectively. The results indicate that the Pc-P-Pc of donor-acceptor-donor (D-A-D) structure has the smallest energy gap as well as the best charge transfer properties.

Structural Study of alumino(boro)silicate glasses containing tin-doped indium oxide (ITO) nanocrystals with nonlinear optical and enhanced UV/ NIR-shielding properties

Transparent alumino(boro)silicate glasses containing tin-doped indium oxide nanocrystals were fabricated using conventional melt-casting and heat treatment. Structural characterization was carried out by Raman spectroscopy to study glass-forming species, coordination, type and number of oxygens, and possible connectivity of silicate, aluminate, and borate species. A changing role of indium, acting as a modifier in the glass structure, but leaving a less modified glass after clustering and crystallization was also revealed. X-ray photoelectron spectroscopy confirmed that indium was in the trivalent state only. HR-TEM provided insights into the distribution and morphology of the nanocrystals in the glass ceramic sample, yielding a mean size of 4.75 nm. The nonlinear optical behavior of aluminoborosilicate glass samples was evaluated using the Z-scan technique, demonstrating high third-order nonlinear optical susceptibility for both glass and glass ceramic samples, accompanied by a change in the signs of nonlinear refractive indices before and after crystallization from negative to positive.

Z-scan and degenerate four wave mixing studies on newly synthesized copper complexes of curcumin

Designing novel metal complexes with high nonlinear optical (NLO) susceptibilities is a special interest for coordination compounds. They include a wider selection of metals with a variety of ligands and oxidation states, which can result in tuneable electronic capabilities. Paramagnetic Copper (II) complexes of curcumin were synthesized using different metal precursors and keeping curcumin as the base ligand. All the complexes were characterized by elemental analysis, magnetic susceptibility, and spectroscopic methods (UV–vis, FT-IR, ESR, and mass spectrometry). Nonlinear optical transmission measurements were carried out using nanosecond laser pulses with 532 nm wavelength, via a Z-scan and Degenerate four-wave mixing (DFWM) techniques. CuAcCur, CuClCur, and CuThCur complexes provided with 1.34 × 1024, 3.61 × 1024, and 4.05 × 1024 m3/W2, proved that these complexes possess excellent NLO properties and CuThCur being best among them. The NT dropped from 100 % to 78 %, 65 %, and 75 % in CuAcCur, CuClCur, and CuThCur respectively, showing that all the complexes have great potential for optical limiting (OL) application. The Conceptual-Density-Functional-Theory (CDFT) were employed to perform the theoretical analyses of complexes. Calculations on the various CDFT-based parameters such as electronegativity, HOMO-LUMO energy gap, molecular hardness, softness, dipole moment, and electrophilicity index of both species are performed. This work introduces three copper complexes with curcumin that show an excellent NLO and OL behavior.

Towards high nonlinear optical susceptibility of Acid Fuchsin dye deposited on FTO substrate for optoelectronic applications

Towards high nonlinear optical susceptibility of Acid Fuchsin dye deposited on FTO substrate for optoelectronic applications

The ferroelectric nematic phase: an optimum liquid crystal candidate for nonlinear optics

ABSTRACT Materials that exhibit high nonlinear optical (NLO) susceptibilities are considered as promising candidates for a wide range of photonic and electronic applications. Here, we argue that the ferroelectric nematic (NF) materials have sufficient potentialities to become materials for the next-generation of NLO devices. We have carried out a study of the efficiency of optical second-harmonic generation in a prototype NF material, finding a nonlinear susceptibility of 5.6 pm.V−1 in the transparent regime, one of the highest ever reported in ferroelectric liquid crystals. Given the fact that the studied molecule was not specifically designed for NLO applications, we conclude there is still margin to obtain NF materials with enhanced properties that should allow their practical use.

Bloch Surface Wave‐Assisted Ultrafast All‐Optical Switching in Graphene

AbstractGraphene has ultrafast charge carrier dynamic and shows strong light–matter interaction allowing the use in photovoltaic devices, fast photodetectors, saturable absorbers, and electro‐optical modulators. However, despite the high nonlinear optical susceptibilities, the small amount of material significantly limits the use of graphene for nonlinear optical applications. In this work, Bloch surface waves (BSWs) are employed, enhancing the graphene–light interaction, for all‐optical switching realization. By placing a graphene monolayer on top of a 1D photonic crystal, it is shown that for the wavelength corresponding to the BSW resonance, the reflection coefficient is modulated on the sub‐picosecond time scale by an order of magnitude larger than that for bare graphene. The magnitude of the reflection change reaches 0.3% at the fluence of 40 µJ cm−2. The reported results are proof of priciple possibility of BSW‐assisted enhancing the reflection modulation of any 2D materials and transparent thin films while maintaining their inherent ultrafast dynamics, which is useful for the further development of all‐optical switches.

Mode-locked fiber laser based on [formula omitted]-Fe2O3 nanosheets as saturable absorbers

With broadband saturable absorption properties and a high third-order nonlinear optical susceptibility, α-Fe2O3 exhibits potential applications in nonlinear optics. In this study, α-Fe2O3 nanosheets are embedded into polyvinyl alcohol (PVA) films to fabricate thin-film saturable absorbers (SAs) that feature an uninterrupted broad absorption band spanning over 2000 nm and a modulation depth of 16.13%. In α-Fe2O3-PVA SA-based erbium-doped fiber lasers, two stable mode-locked operations are achieved: dark-bright pulse pairs and bright solitons. The results indicate that α-Fe2O3 nanosheets are excellent candidates for two-dimensional saturable absorption materials.

High refractive index and third-order nonlinear optical susceptibility of nanostructured ZnSe/FTO thin films: Towards smart multifunctional optoelectronic materials

The present work aims to prepare the nanostructured ZnSe films with high quality onto a fluorine-doped tin oxide glass substrate (FTO/glass) by using the thermal evaporation technique. The X-rays diffraction was used to investigate the structural properties of ZnSe thin films onto FTO glass. The XRD main peaks are corresponding to FTO glass expect the [111], and [311] peaks are related to the ZnSe film. The atomic force microscope supports the nanostructured of the studied films. The linear and nonlinear optical parameters were evaluated and analyzed based on spectroscopic measurements. The dielectric constant and dielectric loss were calculated for ZnSe/FTO thin film. It is clear from the optical analysis and their related refractive index that the nanostructured ZnSe/FTO film has a high refractive index and high third-order nonlinear optical susceptibility. ZnSe/FTO optical system is recommended for the new generation of electronic and optoelectronic devices, especially for telecommunications and nonlinear media.

Four-wave mixing of Weyl semimetals in a strong magnetic field

We theoretically investigate the four-wave mixing process in Weyl semimetals in a strong magnetic field using quantum theory. Weyl semimetals in a strong magnetic field have an extremely high third-order nonlinear optical susceptibility (several orders larger than that of the usual three dimensional materials) originating from the linear energy dispersion near the Weyl points. The third-order response of Weyl semimetal is nearly independent on the Fermi level, which is quite different from the sensitive dependence (on the Fermi level) of the linear response. The unusual polarization dependent selection rules lead to rich nonlinear optical properties, which can be tuned by the polarization of the incident light fields and the magnetic fields.

Crystal structure features of nitro derivatives of methylcytizine and their relationship with second-order nonlinear optical susceptibility

The crystal packings of mono- (1) and dinitro derivatives (3) of methylcytizine are analyzed in terms of combined geometric and energy approaches and based on the evaluation of the degree of molecular deformation (a decrease in the molecular volume) in going from the free molecule to the crystal. An increase in the crystal density in going from the mono- to dinitro derivative (1.440 g cm−3 for 1 and 1.528 g cm−3 for 3 at 120 K) is associated with an increase in the density of the isolated molecule rather than with an increase in the packing density, which is almost equal in the crystals of compounds 1 and 3. The second-order nonlinear optical susceptibility of crystals was estimated in terms of a charge model, the prediction error of which is within 10%, being comparable with experimental accuracy. The similarity of the packing densities of compounds 1 and 3 enabled a detailed comparative analysis of the eff ect of the crystal fi eld on the nonlinear optical properties. Both compounds are characterized by relatively high nonlinear optical susceptibility, which is higher than that of urea, a commonly accepted standard, by a factor of 10 and 6.5 for compounds 1 and 3, respectively.

Ultrafast dynamics and third-order nonlinear optical response of meso-(2-thienyl)porphyrin derivatives

Meso-(2-thienyl) porphyrin derivatives were synthesized. Excited state reverse saturable absorption was observed at 532 nm while two-photon absorption was observed at 800 nm. The nonlinear optical properties are increased by introducing the donator of thienyl group. Meso-(2-thienyl) porphyrin derivatives showed good nonlinear response at low energy. High third-order nonlinear optical susceptibility values (10−10 esu) of metal-free porphyrin derivatives were obtained. The mechanisms of third-order nonlinearity were proposed by the pump-probe experiment. With the observed fast electronic nonlinearities the studied molecules are potential candidates for use as optical limiters or optical switches.

Investigation on structural, optical, dielectric, mechanical and thermal properties of 4-methoxyaniline hydroquinone cocrystal: A promising optical power limiting material

A new non proton transfer compound, Bis(4-methoxyanline) hydroquinone (4MAHQ) has been produced and crystal obtained by the room temperature solvent evaporation technique. The corresponding crystal structure and influence of intra-molecular hydrogen bonding interactions have been reported. SCXRD study exposes that 4MAHQ crystallizes in triclinic system. The crystals were subjected to thermal, mechanical, dielectric and optical and NLO studies. The thermal stability was studied by TG/DTA and the crystal is found to have been stable up to 185 °C. The mechanical properties were obtained from Vickers’s hardness studies. The dielectric responses of the crystal were studied for different frequencies versus variable temperature between 303 and 373 K. The transparency of the crystal in the range 330–1100 nm was confirmed by Ultraviolet–visible spectral studies. The Z-scan study confirmed the existence of high third order nonlinear optical susceptibility in 4MAHQ.

Synthesis, supramolecular architecture, thermal and optical behavior of 4-methoxyanilinium perchlorate: A promising third-order NLO material for optical limiting device applications

A novel hydrogen bonded supramolecular single crystals of 4-methoxyanilinium perchlorate (4MAPC) has been synthesized by solvent slow evaporation method. Structural and crystallographic data of 4MAPC has been studied by single crystal XRD technique. Three dimensional networks formed by the classical hydrogen bond between nitrogen and oxygen and also the nonclassical intermolecular interaction between carbon and oxygen keeping the crystal structure more stable. Protonation is observed at nitrogen site of 4-methoxyaniline from the perchloric acid. The results of thermal gravimetric and differential themal analysis showed that the grown crystal is stable upto 167 °C. The wide transparency from 340 to 1100 nm was observed by optical studies. The high nonlinear optical susceptibility and nonlinear refraction was obtained from Z-Scan studies.

Optical harmonic generation in monolayer group-VI transition metal dichalcogenides

Monolayer transition metal dichalcogenides (TMDs) exhibit high nonlinear optical (NLO) susceptibilities. Experiments on MoS$_2$ have indeed revealed very large second-order ($\chi^{(2)}$) and third-order ($\chi^{(3)}$) optical susceptibilities. However, third harmonic generation results of other layered TMDs has not been reported. Furthermore, the reported $\chi^{(2)}$ and $\chi^{(3)}$ of MoS$_2$ vary by several orders of magnitude, and a reliable quantitative comparison of optical nonlinearities across different TMDs has remained elusive. Here, we investigate second- and third-harmonic generation, and three-photon photoluminescence in TMDs. Specifically, we present an experimental study of $\chi^{(2)}$, and $\chi^{(3)}$ of four common TMD materials (\ce{MoS2}, \ce{MoSe2}, \ce{WS2} and \ce{WSe2}) by placing different TMD flakes in close proximity to each other on a common substrate, allowing their NLO properties to be accurately obtained from a single measurement. $\chi^{(2)}$ and $\chi^{(3)}$ of the four monolayer TMDs have been compared, indicating that they exhibit distinct NLO responses. We further present theoretical simulations of these susceptibilities in qualitative agreement with the measurements. Our comparative studies of the NLO responses of different two-dimensional layered materials allow us to select the best candidates for atomic-scale nonlinear photonic applications, such as frequency conversion and all-optical signal processing.

Particle size reduction of thallium indium disulphide nanostructured thin films due to post annealing

Chalcogenide semiconductors are widely used, due to their versatile structural, optical and electrical properties. They are used in image sensors, energy conversion, non-volatile memory, and waveguides applications. Due to these versatilities in the properties, nanostructured thin films of TlInS2 are successfully prepared by thermal evaporation. The average particle size changes due to thermal treatment are examined by X-ray diffraction (XRD), and transmission electron microscope (TEM). A sharp reduction in the average particle size of the pristine nanostructured films is reported upon annealing processes at 423 K and 523 K. Besides, thermal treatment temperatures induce changes in the dispersion parameters viz oscillator energy, dispersion energy, high-frequency dielectric constant and dielectric constant. Of these, only the oscillator energy decreases with the annealing temperatures while all the other parameters increase. Moreover, the non-linear optical calculations have revealed that the nanostructured TlInS2 films exhibit high third-order nonlinear optical susceptibility of order 10−11 esu and strong nonlinear refractive index of order 10−10 esu.

Comparative Interrelationship of the Structural, Nonlinear-Optical and Other Acentric Properties for Oxide, Borate and Carbonate Crystals

The structure and the maximal nonlinear optical (NLO) susceptibility χ(2) are tabulated for more 700 acentric binary oxides, 220 crystals of simple, binary and complex borates and for the same set of 110 carbonates, tartrates, formates, oxalates, acetates and fluoride-carbonates used in ultraviolet and deep ultraviolet optoelectronics. According to the chemical formula, the structural symbols of these crystals have been plotted on the plane of two minimal oxide bond lengths (OBL). It is shown that acentric crystals are positioned on such plane inside the vertical, horizontal and slope intersected ellipses of “acentricity”. The oxide and borate crystals with moderate NLO susceptibility are found in the central parts of these ellipses intersection and, with low susceptibility, on top, at the bottom and border of the ellipses rosette. The nonpolar fluoride-carbonate crystals with high NLO susceptibility are found in the curve-side rhombic parts of the slope ellipse of “acentricity”. The unmonotonous fuzzy dependence “χ(2)” on the OBL of these crystals is observed, and their clear-cut taxonomy on compounds with π– or σ–oxide bonds is also established. It is shown that the correlations of χ(2) with other acentric properties are nonlinear for the whole set of the oxide crystals having their clear maximum at a certain value of the piezoelectric or electro-optic coefficient. The correlation “hardness–thermoconductivity-fusibility” is plotted for oxide crystals, part of which is used at the creation of self-frequency-doubling solid state lasers.

Subtle local structural variations in oxygen deficient niobium germanate thin film glasses as revealed by x-ray absorption spectroscopy

The local electronic and crystal structure of niobium-lead-germanate, Nb2O5-PbO- GeO2 (NPG), glass thin films on silicon substrates were probed by XANES and EXAFS. NPG glasses are promising candidates for applications in nonlinear optical devices because they exhibit interesting optical characteristics such as high nonlinear third order optical susceptibility. In this work NPG glasses were prepared with pulsed laser deposition method with varying oxygen partial pressure to induce thin films with different oxygen stoichiometry. Previously, it was shown that oxygen stoichiometry has a very important effect to produce unusual high optical susceptibility. Detailed EXAFS and XANES analyses in a series of NPG thin films revealed the subtle variations in the local environment around Nb atoms and the Nb oxidation states caused by oxygen deficiencies.

Efficient phase-matched third harmonic generation in a metal-clad plasmonic double-slot waveguide

We propose a metal-clad plasmonic double-slot waveguide with DDMEBT integrated into the slot region as the interactive material for third harmonic generation (THG) from the mid-IR (3600 nm) to the near-IR (1200 nm) region. Typically, an efficient THG process in a waveguide platform relies on three key aspects: high third-order nonlinear susceptibility of the interactive material, fulfillment of the phase-matching condition (PMC), and large pump-harmonic modal overlap. Although it has been theoretically predicted to be possible, designing waveguides to achieve the three key aspects simultaneously is still a major challenge. In the metal-clad plasmonic double-slot waveguide, the PMC between the zeroth mode at the fundamental wave (FW) and the second mode at the third harmonic (TH) is achieved. Taking advantage of the channel plasmon polariton (CPP), the electric fields at both FW and TH are tightly confined in the slot region. The specific slot waveguide structure is exploited to significantly enhance the pump-harmonic modal overlap by greatly reducing the counteractive electric field portion of the second mode at TH. According to our simulation, THG conversion efficiency reaches 1.4732 × 10−5 with 3 W pump power at a waveguide length of 12.3 μm. This THG efficiency is greatly enhanced because of the high third-order nonlinear optical susceptibility of the DDMEBT, the specific plasmonic slot waveguide structure, and the CPP nature of the guided modes—it is more than two times that obtained by simply considering a single slot under the same slot-width condition.

Organized Chromophoric Assemblies for Nonlinear Optical Materials: Towards (Sub)wavelength Scale Architectures

Photonic circuits are expected to greatly contribute to the next generation of integrated chips, as electronic integrated circuits become confronted with bottlenecks such as heat generation and bandwidth limitations. One of the main challenges for the state-of-the-art photonic circuits lies in the development of optical materials with high nonlinear optical (NLO) susceptibilities, in particular in the wavelength and subwavelength dimensions which are compatible with on-chip technologies. In this review, the varied approaches to micro-/nanosized NLO materials based on building blocks of bio- and biomimetic molecules, as well as synthetic D-π-A chromophores, have been categorized as supramolecular self-assemblies, molecular scaffolds, and external force directed assemblies. Such molecular and supramolecular NLO materials have intrinsic advantages, such as structural diversities, high NLO susceptibilities, and clear structure-property relationships. These "bottom-up" fabrication approaches are proposed to be combined with the "top-down" techniques such as lithography, etc., to generate multifunctionality by coupling light and matter on the (sub)wavelength scale.

Dispersion of Linear, Nonlinear Optical Susceptibilities and Hyperpolarizability of C11H8N2O (o-Methoxydicyanovinylbenzene) Crystals

Linear and nonlinear optical susceptibility dispersion and hyperpolarizability of C(11)H(8)N(2)O, o-methoxydicyanovinylbenzene, crystals were performed by means of density functional theory (DFT). The exchange and correlation potential was described within a framework of the local density approximation (CA-LDA) and gradient approximation (GGA) based on exchange-correlation energy optimization to calculate the total energy. Engel-Vosko generalized gradient approximation (EV-GGA) and the modified Becke-Johnson potential (mBJ) were used for the electronic crystal structure and optical susceptibility dispersion calculations. We have established systematically increasing energy gap from 2.25 eV (LDA), 2.34 eV (GGA), 2.50 eV (EVGGA), and 2.96 eV (mBJ). The crystal possesses a direct band gap which is an important key factor to make the crystal optically active with high linear and nonlinear optical susceptibilities and hyperpolarizability. Additionally, the studied crystal has a considerable anisotropy of birefringence which is necessary for phase matching conditions during the optical second harmonicexperiments. We have found that the theoretically evaluated second harmonic generation achieves about 5.8 × 10(-8) esu in good agreement with the experimental value (4.9 × 10(-8) esu). Additionally, we have found that our calculated value of β(222) is about 2.3 × 10(-30) esu at zero energy and 6.6 × 10(-30) esu at λ = 1.064 μm. We should emphasize that our calculated value of β(222) (6.60 × 10(-30) esu at λ = 1.064 μm) shows better agreement with the experimental data (5.04 × 10(-30) esu at λ = 1.064 μm) than other calculations.