High Nonlinear Optical Response Research Articles

Theoretical study of the spectroscopic and nonlinear optical properties of trans- and cis-4-hydroxyazobenzene.

We investigate the molecular structure, vibrational and electronic absorption spectra, and electronic hyperpolarizabilities of trans and cis isomers of 4-hydroxyazobenzene (HOAB) via density functional theory. Results show that the azo dye exhibits a high third-order nonlinear optical response and good optical transparency. Both the basis set and the functional are important influences on the results obtained when calculating the absorption spectrum and NLO response. We also study the effect of the solvent on the electronic absorption spectrum to assess the ability of the functional to reproduce the experimental spectrum in combination with a suitable solvent model. Our calculations show that the SMD model of Truhlar et al. handles the electrostatic and the non-electrostatic effects of hydrogen-bonding solvents on the absorption spectrum better than the traditional polarizable continuum model does. In addition, our results indicate that the dye trans-HOAB exhibits a high second hyperpolarizability and excellent optical transparency. Also, although the second hyperpolarizability of cis-HOAB is much lower than that of trans-HOAB, it is non-negligible when calculating the optical nonlinearity of HOAB under an optical pump. We also examine the effect of frequency dispersion on second harmonic generation. This study provides the basis for further research on the spectroscopic and nonlinear optical properties of novel azo dyes and other π-conjugated compounds.

Passively Q-switched erbium-doped fibre laser using cobalt oxide nanocubes as a saturable absorber

We demonstrate a Q-switched Erbium-doped fibre laser (EDFL) utilizing cobalt oxide (Co3O4) nanocubes film based saturable absorber (SA) as a passive Q-switcher. Co3O4 nanocubes are embedded into a polyethylene oxide film to produce a high nonlinear optical response, which is useful for SA application. It has saturation intensity and modulation depth of 3 MW/cm2 and 0.35%, respectively. The proposed laser cavity successfully generates a stable pulse train where the pulse repetition rate is tunable from 29.8 to 70.92 kHz and the pulse-width reduces from 10.9 to 5.02 μs as the 980 nm pump power increases. This result indicates that the Co3O4 is excellent for constructing an SA that can be used in producing a passively Q-switched fibre laser operating at a low pump intensity. To the best of our knowledge, this is the first demonstration of Co3O4 film based fibre laser.

Transition metal dichalcogenides based saturable absorbers for pulsed laser technology

Ultrashort pulsed laser is an indispensable tool for the evolution of photonic technology in the present and future. This laser has been progressing tremendously with new pulse regimes and incorporating novel devices inside its cavity. Recently, a nanomaterial based saturable absorber (SA) was used in ultrafast laser that has improved the lasing performance and caused a reduction in the physical dimension when compared to conventional SAs. To date, the nanomaterials that are exploited for the development of SA devices are carbon nanotubes, graphene, topological insulators, transition metal dichalcogenides (TMDs) and black phosphorous. These materials have unique advantages such as high nonlinear optical response, fiber compatibility and ease of fabrication. In these, TMDs are prominent and an emerging two-dimensional nanomaterial for photonics and optoelectronics applications. Therefore, we review the reports of Q-switched and mode-locked pulsed lasers using TMDs (specifically MoS2, MoSe2, WS2 and WSe2) based SAs.

High Second-Order NLO Response Exhibited by the First Example of Polymeric Film Incorporating a Diimine–Dithiolate Square-Planar Complex: The [Ni(o-phen)(bdt)

A novel square-planar diimine–dithiolate nonlinear optical (NLO) chromophore, the complex [Ni(o-phen)(bdt)] (1), is reported in this paper (o-phen = dianion of 1,2-phenylendiamina; bdt =1,2-benzenedithiolate). This compound has been fully characterized by single-crystal X-ray diffraction, UV–vis–NIR spectroscopy, cyclic voltammetry, DFT, and TD-DFT calculations. 1 crystallizes in the P21 space group and shows an almost planar molecule. The cyclic voltammetry measurements present an irreversible anodic peak at 0.87 V and reversible and quasi-reversible reduction waves at −0.35 and −1.13 V, respectively. A medium-intense (e = 1.91 × 104 mol–1 dm3 cm–1) absorption with a maximum at 728 nm appears in the UV–vis–NIR spectrum. The molecular second-order NLO properties of 1 have been measured by the electric field induced second-harmonic generation technique in DMF solution, giving values of −1000 × 10–48 esu for μβ1.907 and −356 × 10–48 esu for μβ0. Furthermore, remarkable solid-state responses have been measur...

Zinc oxide (ZnO) nanoparticles as saturable absorber in passively Q-switched fiber laser

We demonstrate a passively Q-switched erbium-doped fiber laser using zinc oxide (ZnO) nanoparticles thin film as saturable absorber (SA). ZnO exhibits high nonlinear optical response and fast recovery time, fulfilling the requirements of an ideal SA. The nonlinear optical absorption is characterised by modulation depth of 3.5% with saturation intensity of 0.016MWcm−2. We insert the SA into the laser cavity and obtain stable Q-switched pulse whereby the repetition rate increases from 41.7kHz to 77.2kHz while the pulse width decreases from 9.6μs to 3.0μs as the pump power is increased from 60mW to 360mW. This result suggests that ZnO could be a promising SA for photonic applications.

Spectroscopic and nonlinear optical properties of new chalcone fluorescent probes for bioimaging applications: a theoretical and experimental study.

In this study, the newly synthesized non-centrosymmetric, 4-dimethylamino-3'-isothiocyanatochalcone (PKA) compound was presented. This compound belongs to the chalcone group, and its main purpose is to be used in biomedical imaging as a fluorescence dye. For this reason, the linear and nonlinear properties in solvents of different polarity were thoroughly studied. In accordance with the requirements for a fluorochrome, the PKA compound is characterized by strong absorption, large Stokes' shifts, relatively high fluorescence quantum yields and high nonlinear optical response. Moreover, the isothiocyanate reactive probe was conjugated with Concanavalin A. Conventional fluorescence microscopy imaging of Candida albicans cells incubated with the PKA-Concanavalin A, is presented. The results of this study show that the novel conjugate PKA-Concanavalin A could be a promising new probe for cellular labelling in biological and biomedical research. Graphical abstract Spectroscopic behavior of the PKA dye.

Linear and nonlinear optical waveguiding in bio-inspired peptide nanotubes

Unique linear and nonlinear optical properties of bioinspired peptide nanostructures such as wideband transparency and high second-order nonlinear optical response, combined with elongated tubular shape of variable size and rapid self-assembly fabrication process, make them promising for diverse bio-nano-photonic applications. This new generation of nanomaterials of biological origin possess physical properties similar to those of biological structures. Here, we focus on new specific functionality of ultrashort peptide nanotubes to guide light at fundamental and second-harmonic generation (SHG) frequency in horizontal and vertical peptide nanotubes configurations. Conducted simulations and experimental data show that these self-assembled linear and nonlinear optical bio-waveguides provide strong optical power confinement factor, demonstrate pronounced directionality of SHG and high conversion efficiency of SHG ∼10−5. Our study gives new insight on physics of light propagation in nanostructures of biological origin and opens the avenue towards new and unexpected applications of these waveguiding effects in bio-nanomaterials both for biomedical nonlinear microscopy imaging recognition and development of novel integrated nanophotonic devices.

Synthesis, spectroscopic characterization, and computed optical analysis of green fluorescent cyclohexenone derivatives

Cyclohexenone containing chalcones core is one important class of materials, which exhibit high nonlinear optical (NLO) responses and good crystallizability. The present study reports the successful development of six new fluorescent cyclohexenone derivatives (CDs) via conventional Robinson annulation method. The molecular structures of these newly synthesized CDs were confirmed by using various analytical techniques such as 1H NMR, 13C NMR, FTIR, EIMS, UV–Vis spectroscopy and single crystal X-ray diffraction. The crystallographic data revealed that the spatial structure of the representative CD (4BE) belongs to monoclinic, P21/c space group. The results from luminescence studies show that the CDs molecules apparently emit intense green light at room temperature in aqueous media. The relative polarity and molecular chemical stability of the CDs molecules were predicted by measuring the molecular electrostatic potential and frontier molecular orbital energy. In addition, the UV–Vis spectra, transition character and electronic structures of these CDs were computed by using quantum chemical methodology. It was interesting to note that the values of computed and experimental electronic transitions (λmax) were in good agreement and these CDs display high hyperpolarizability (β) values. The present work will be helpful for systematical understanding of the structures and the optical properties of CDs for studying the structure–activity relationship that will suggest their potential application in photonic devices. Copyright © 2015 John Wiley & Sons, Ltd.

A Family of IrIII Complexes with High Nonlinear Optical Response and Their Potential Use in Light‐Emitting Devices

AbstractWe synthesized a new family of IrIII complexes [Ir(R1‐ppy)2(R2‐ppl)](PF6), where R1‐ppy = 2‐phenylpyridine (ppy) or 2,4‐difluorophenylpyridine (F2‐ppy) and R2‐ppl = pyrazino[2,3‐f][1,10]phenanthroline (ppl) or 2,3‐diethoxycarbonylpyrazino [2,3‐f][1,10]phenanthroline (deeppl). The complexes were experimentally and theoretically characterized, noting the importance of the R1 substituent on the modulation of HOMO level and its impact on the electronic properties. These compounds exhibit high second‐order nonlinear optics (NLO) activity, especially, those with F2‐ppy ligands; this substituent modulates the charge transfer, optimizing the NLO response. The compounds also show blueshifted emissions, both in solution and as a solid film, which is desirable for use in light‐emitting devices. This is the first use of the synthesized complexes for application in the two tasks.

Enhancement of nonlinear optical (NLO) properties of indigo through modification of auxiliary donor, donor and acceptor

In this study, indigo based dyes with high non-linear optical response have been investigated. Density functional theory (DFT) was used to study non-linear optical properties of indigo and newly designed dyes (IM-Dye-0, IM-Dye-1, IM-Dye-2 and IM-Dye-3). The time dependant density functional theory (TDDFT) was used to calculate the excitation energies. The HOMO–LUMO energy gaps of newly designed dyes were smaller as compare with indigo dye. Absorption maxima of newly designed dyes strongly red shifted as compare with indigo dye. High non-linear optical (NLO) response of newly designed dyes revealed that these materials would be excellent for NLO applications. This theoretical approach of designing will pave the way for experimentalists to synthesize high response NLO compound.

Nonlinear optical and magnetic properties of BiFeO3 harmonic nanoparticles

Second Harmonic Generation (SHG) from BiFeO3 nanocrystals is investigated for the first time to determine their potential as biomarkers for multiphoton imaging. Nanocrystals are produced by an auto-combustion method with 2-amino-2-hydroxymethyl-propane-1,3-diol as a fuel. Stable colloidal suspensions with mean particle diameters in the range 100–120 nm are then obtained after wet-milling and sonication steps. SHG properties are determined using two complementary experimental techniques, Hyper Rayleigh Scattering and nonlinear polarization microscopy. BiFeO3 shows a very high second harmonic efficiency with an averaged 〈d〉 coefficient of 79 ± 12 pm/V. From the nonlinear polarization response of individual nanocrystals, relative values of the independent dij coefficients are also determined and compared with recent theoretical and experimental studies. Additionally, the particles show a moderate magnetic response, which is attributed to γ-Fe2O3 impurities. A combination of high nonlinear optical efficiency and magnetic response within the same particle is of great interest for future bio-imaging and diagnostic applications.

Plasmon assisted enhanced nonlinear refraction of monodispersed silver nanoparticles and their tunability.

Nonlinear optical characterizations were performed on monodispersed silver (Ag) nanoparticles (NPs) of various sizes using a picosecond Z-scan technique with excitation wavelengths of 532 nm and 1064 nm. The Ag NPs were fabricated using a heterogeneous condensation technique in a gas medium. The nonlinear refraction values were higher for the monodispersed Ag NPs whose surface plasmon resonance (SPR) peak is closer to the excitation wavelength. The higher nonlinear optical response is explained in terms of an electric field enhancement near the SPR. Moreover, the fabrication method allows the tailoring of the nonlinear refraction index of the Ag NPs by tuning the SPR peak of the sample. A comparison of the nonlinear refraction index of the monodispersed and polydispersed Ag NPs showed that the nonlinear refractive index of the monodispersed Ag NPs is higher.

ChemInform Abstract: Push—Pull Systems Bearing a Quinoid/Aromatic Thieno[3,2‐b]thiophene Moiety: Synthesis, Ground State Polarization and Second‐Order Nonlinear Properties.

Chromophores bearing a 2-dicyanomethylenethieno[3,2-b]thiophene moiety in their quinoidal form have been synthesized, exploring for the first time the reactivity of this system towards aldehydes. Their ground state polarization and linear and second-order nonlinear optical (NLO) properties have been determined by a combined experimental and theoretical study, and compared to those of analogous compounds featuring an aromatic thienothiophene unit. Due to the gaining of aromaticity, quinoid systems have been found to display more polarized electronic ground states and higher NLO responses with respect to their aromatic counterparts.

Molecular orbital closed loops analysis of the third-order NLO response of polyanion [M8O26]4− (M = Cr, Mo, W): a TDDFT study

Molecular orbital closed loops theory was used to explain the mechanism of the third-order nonlinear optical (NLO) response of polyanion cage structure of polyoxometalate by TDDFT study. The third-order NLO properties of three octa-polyoxometalate anion clusters of VIB group metals, β-[Cr8O26]4−, β-[Mo8O26]4−, and β-[W8O26]4−, were studied by DFT/TDDFT method systematically. The geometric structures of β-[Cr8O26]4− and β-[W8O26]4− were separately simulated by DFT method, based on the crystallographically determined geometry of the β-[Mo8O26]4− ion, and the thermo stability, and the second static hyperpolarizabilities, γ iiii , γ iijj , and γmean were calculated by finite-field method as an extension of the usual DFT energy run, and the results suggest that with no ligands coordinated, all of the three clusters possess moderately large hyperpolarizabilities, and the molybdate ion possess much larger NLO response than the chromate and the tungstate ions. In order to find out the reason of the big difference in the hyperpolarizabilities of the three polyoxometalates of the same group metals, the electronic properties were also studied by DFT method for the discussion of the origination of the NLO response, specially, the mechanism of the electronic structure change affecting the NLO response is analyzed and exhibited by the molecular orbital “closed loops” theory which has usually been used to estimate the thermo stability and redox ability of the polyoxometalate anion cages. Without the coordination by any ligands, polyanion [M8O26]4− (M = Cr, Mo, W) in high symmetry structures present moderately high third-order NLO response by TDDFT study, even higher than the one-dimensional metal–metal bond compounds Cr(II)4, Mo(II)4, and some C60 derivatives. A new thought of molecular “orbital loops” for the theoretical exploration of the mechanism of NLO response were introduced, and applied to the polyanions and proved to be an effective analyzing method .

Optimization of malaria detection based on third harmonic generation imaging of hemozoin

The pigment hemozoin is a natural by-product of the metabolism of hemoglobin by the parasites which cause malaria. Previously, hemozoin was demonstrated to have a very high nonlinear optical response enabling third harmonic generation (THG) imaging. In this study, we present a complete characterization of the nonlinear THG response of natural hemozoin in malaria-infected red blood cells, as well as in pure isostructural synthesized hematin anhydride, in order to determine optimal imaging parameters for detection. Our study demonstrates the wavelength range for optimal pulsed femtosecond laser excitation of THG from hemozoin crystals. In addition, we show the hemozoin crystal detection as a function of crystal size, incident laser power, and the emission response of the hemozoin crystals to different incident laser polarization states. Our systematic measurements of the nonlinear optical response from hemozoin establish detection limits, which are essential for the optimal design of malaria detection technologies that exploit the THG response of hemozoin.

NLO chromophores containing dihydrobenzothiazolylidene and dihydroquinolinylidene donors with an azo linker: Synthesis and optical properties

We report the synthesis of a series of nonlinear optical chromophores containing either a dihydrobenzothiazolylidene or dihydroquinolinylidene donor with an azo linker. The results demonstrate the versatility of coupling a diazonium salt to a donor–methylidene nucleus in order to access novel materials with good thermal stabilities and high nonlinear optical responses. From hyper-Raleigh scattering studies it was found that the use of the well-known TCF acceptor yields the best performing chromophores, one of which has a dynamic first hyperpolarizability of 1900 × 10 −30 esu at 800 nm. The results from this study suggest the use of pro-aromatic donors such as dihydrobenzothiazolylidene or dihydroquinolinylidene results in compounds with higher nonlinear optical responses than those containing donors based on either indoline or aniline . ► A series of chromophores with aromatizable donors and azo linkers are reported. ► The methodology allows for the synthesis of the target molecules in high yield. ► The compounds have first hyperpolarizabilities of up to 1900 × 10 −30 esu. ► The compounds have decomposition temperatures between approx 215–250 °C.

Push–pull systems bearing a quinoid/aromatic thieno[3,2-b]thiophene moiety: synthesis, ground state polarization and second-order nonlinear properties

Chromophores bearing a 2-dicyanomethylenethieno[3,2-b]thiophene moiety in their quinoidal form have been synthesized, exploring for the first time the reactivity of this system towards aldehydes. Their ground state polarization and linear and second-order nonlinear optical (NLO) properties have been determined by a combined experimental and theoretical study, and compared to those of analogous compounds featuring an aromatic thienothiophene unit. Due to the gaining of aromaticity, quinoid systems have been found to display more polarized electronic ground states and higher NLO responses with respect to their aromatic counterparts.

Water dispersible functionalized graphene fluoride with significant nonlinear optical response

Graphene fluoride (G.F.) is the youngest in the family of graphene derivatives. Being optically transparent in the visible spectrum, G.F. is unique among other low dimensional carbon materials. In this work, colloidal dispersions are prepared by aqueous-phase exfoliation of graphite fluoride through non-covalent functionalization with perfluorooctanoate units. Light scattering and electrophoresis reveal the exceptional stability of the dispersion, while the formation of ultrathin G.F. sheets is verified by electron and atomic force microscopy. In addition, for the first time it is reported that G.F. colloids exhibit high third-order nonlinear optical response, suggesting their potential application in photonic and opto-electronic devices.

Thermally stable ferrocenyl “push–pull” chromophores with tailorable and switchable second-order non-linear optical response: synthesis and structure–property relationship

A combined UV-visible, cyclic voltammetric theoretical and hyper-Rayleigh scattering study has been carried out on a new series of ferrocenyl chromophores (2a–2d and 7–11) to develop a structure–property relationship, by varying the acceptor strength and the conjugation path length between the donor and the acceptor and by disubstitution of the ferrocene moiety. This allowed systematic establishment of the contribution of the conjugation bridge, acceptor strength and substitution on both rings of ferrocene towards non-linear optical response as well as its redox switchability with one of the chromophores (8) having an on/off ratio of 25, the highest for ferrocenyl chromophores, and also thermal stability up to 300 °C. To deduce the participation of the available polarizable electrons towards the overall non-linear optical properties (with electron contribution from both the rings as observed from average bond length calculation from crystal data of 2c and 7 and the absorption studies), respective intrinsic hyperpolarizability (β0int) of the dipolar chromophores was calculated. Interestingly, the shorter chromophore 2c showed exceptionally high non-linear optical response and intrinsic hyperpolarizability compared to its longer counterparts.

Static NLO responses of fluorinated polyacetylene chains evaluated with long-range corrected density functionals

As an alternative to oligomeric systems with different skeleton atoms it is shown that asymmetry introduced by substitution on a symmetric π-conjugated chain can lead to molecular systems with high non-linear optical responses. First hyperpolarizability and related properties such as the bond-length alternation parameter, dipole moment and polarizability of polyfluoroacetylene (PFA) oligomers are investigated by the Hartree-Fock, DFT and MP2 approaches. Particular attention is paid to long-range corrected DFT methods (LR-DFT). Systematic behavior of the MP2/LR-DFT ratio enables to estimate Δ β L for the eicosamer to 76 × 10 3 a.u. what makes PFA oligomers attractive candidates for NLO applications.