Nonlinear Optically Research Articles

Integration of Open Metal Sites in an Amino-Functionalized Sm(III)-Organic Framework toward Enhanced Third-Order Nonlinear Optical Property.

A variety of new inorganic and organic materials have emerged to advance laser technologies and optical engineering. A rational design approach can contribute significantly to fabricating nonlinear optically active metal-organic frameworks (MOFs) by considering the underlying structure-property linkage. Here, it has been embarked on a study of novel samarium(III) MOF, ([Sm2(ata)3(DMF)4]·DMF (ata2-: 2-aminoterephthalate), abbreviated as NH2-Sm-MUM-4) with enhanced nonlinear optical (NLO) properties. The crystal structure of this MOF represents a 6-connected framework with a pcu topology and distinctive characteristics, including open metal sites, free amine groups, and great stability, making it suitable for third-order NLO activity. The nonlinear index of refraction (n2) revealed the self-focusing impacts of NH2-Sm-MUM-4 at different incident intensities. The highest value of n2 and β related to 10 mw power of incident intensity are 5.15 cm2/W and 2.65 cm/W, respectively. As far as the authors know, this is the first study examining the potential systematic structural-property associations in Sm-MOFs considering improved third-order NLO properties.

Enhancement in Two-Photon Absorption and Photoluminescence in Single Crystals of Cd(II) Metal Organic Frameworks.

The emergence of metal organic frameworks (MOFs) as advanced photonic materials has placed them at the forefront of exploration. Nonlinear optical (NLO) phenomena such as simultaneous two-photon absorption and consequent upconversion emission have been in demand for promising applications. A rational design approach based on the fundamental structure-property relationship is key for the fabrication of nonlinear optically active MOF materials. Here, we investigate two-photon-absorption (2PA)-induced photoluminescence of four new Cd(II) MOFs based on an acceptor-π-donor-π-acceptor trans, trans-9, 10-bis(4-pyridylethenyl)anthracene chromophore linker. The use of auxiliary carboxylate linkers resulted in the variation of crystal structures, leading to the modulation of NLO properties. On comparison with a standard Zn(II)-MOF, two MOFs showed enhancement in 2PA, while the other two showed a mild decrease. We tried to establish a structural correlation to explain the trend in NLO activity. The interplay of various factors such as chromophore density, degree of interpenetration, chromophore orientation, and π···π interactions between the individual networks affects the NLO activities. These results show the modulation of the optical properties of MOFs based on a combined strategy for the development of tunable single crystal NLO devices.

Designing a Propellane-based Nonlinear Optically Active System Absorbing in Three Different Wavelength Regions.

The aim of this work is to demonstrate the possibility of using propellane in designing a molecule that can absorb in three different wavelength regions and their nonlinear optical (NLO) activity can be fine-tuned by varying the three wings. We considered 22 tailor-made propellane derivatives consisting of phenyl, naphthyl, and biphenyl wings for this purpose. Using the state-of-the-art linear and quadratic response methods within TD-DFT and RI-CC2 theories and a suitable generalized few-state model that quantifies the effect of orientation of different transition moments on NLO properties, we discussed how and why the linear and nonlinear optical activity of propellane vary when the three wings are assembled successively to construct a full-propellane.

Synthesis, conformational study and DFT analysis of novel nonlinear optically active 2r,6c-diaryl-3t-methylpiperidin-4-one N-(2′-furoyl)hydrazones

A series of nonlinear optical (NLO) active 2-furoic acid hydrazide derivatives, 2r,6c-diaryl-3t-methylpiperidin-4-one N-(2′-furoyl)hydrazones (6–10), were synthesized. The structures of these hydrazones were confirmed unambiguously by Fourier transform infrared spectroscopy, mass spectrometry, elemental analysis, 1H, 13C, HOMO-COSY, HSQC, and HMBC nuclear magnetic resonance spectroscopy. The piperidine core of all the targeted hydrazones (6–10) adopted the chair conformation with the equatorial orientations of all the substituents and the ‘E’ configuration about the C=N bond observed. Density functional theory using the B3LYP/6–31G(d,p) level of theory indicated that all hydrazones favor the ‘E’ isomer state. The Mulliken population, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) surfaces, and reactivity parameters were also evaluated and showed a good correlation with the experimental data. The efficiency of hydrazones (6–10) in terms of the nonlinear optical (NLO) activity was proven, and the hydrazones (6–10) showed higher NLO activity compared to that of the reference molecule, as determined by the molecular hyperpolarizability measurements. The structural, spectral, and electrochemical properties were also determined, and DFT analysis was consistent with the experimental outcomes. The FMO, MEP, and reactivity parameter analyses revealed intramolecular charge transfer and high reactive features, leading to superior NLO property of hydrazones (6–10).

Nonlinear optical absorption and optically detected electrophonon resonance in GaAs based n − i − p − i superlattices

The quantisation of electronic energy into subbands in low-dimensional structures originates many interesting physical effects, one of which is the electrophonon resonance effect. In this work, we investigate the electrophonon resonance by theoretically calculating the optical absorption power in n − i − p − i superlattices (SLs) subjected to a high frequency electromagnetic wave. The absorption power is calculated up to the first-order nonlinear term using the projection operator technique taking account of the effect of electron – optical phonon interaction. Numerical results are obtained and discussed for the GaAs:Si/GaAs:Be SL. The linear and nonlinear optically detected electrophonon resonance (ODEPR) peaks are observed in the absorbance. The full width at half maximum (FWHM) of ODEPR peaks increases with increasing the doping concentration as well as temperature. In particular, the results show that the two-photon absorption is of great importance and should be considered in nonlinear optics. This investigation provides a theoretical basis for potential applications of n − i − p − i SLs in optoelectronic devices.

PNO: a promising deep-UV nonlinear optical material with the largest second harmonic generation effect.

In this work, the polar tetrahedron [PN2O2] was revealed as a new deep-ultraviolet (deep-UV) nonlinear optically active unit. Accordingly, a thermodynamically stable compound (PNO) consisting of the polar [PN2O2] units was predicted and suggested as a promising candidate for deep-UV nonlinear optical (NLO) materials. Compared with other deep-UV materials known to date, PNO possesses the strongest second harmonic generation (SHG) coefficient (about 6 times that of KH2PO4 (KDP)). Moreover, its three-dimensional connectivity endows it with good mechanical and thermal properties. Therefore, PNO should be a new option for non-π-conjugated deep-UV NLO materials.

Strong nonlinear optical effects in micro-confined atmospheric air

Historically, nonlinear optical phenomena such as spectral broadening by harmonic generation have been associated with crystals owing to their strong nonlinear refractive indices, which are in the range of ∼10−14 cm2/W. This association was also the result of the limited optical power available from early lasers and the limited interaction length that the laser–crystal interaction architecture could offer. Consequently, these limitations disqualified a large number of materials whose nonlinear coefficient is lower than n2∼10−16 cm2/W as suitable materials for nonlinear optics applications. For example, it is a common practice in most of optical laboratories to consider ambient or atmospheric air as a “nonlinear optically” inert medium due to its very low nonlinear coefficient (∼10.10−19 cm2/W) and low density. Today, the wide spread of high-power ultra-short pulse lasers on one hand, and low transmission loss and high-power handling of Kagome hollow-core photonic crystal fiber on the other hand, provide the necessary ingredients to excite strong nonlinear optical effects in practically any gas media, regardless of how low its optical nonlinear response is. By using a single table-top 1 mJ ultra-short pulse laser and an air exposed inhibited-coupling guiding hollow-core photonic crystal fiber, we observed generation of supercontinuum and third harmonic generation when the laser pulse duration was set at 600 fs and Raman comb generation when the duration was 300 ps. The supercontinuum spectrum spans over ∼1000 THz and exhibits a typical spectral-density energy of 150 nJ/nm. The dispersion profile of inhibited-coupling hollow-core fiber imprints a distinctive sequence in the supercontinuum generation, which is triggered by the generation of a cascade of four-wave mixing lines and concluded by solitonic dynamics. The Raman comb spans over 300 THz and exhibits multiple sidebands originating from N2 vibrational and ro-vibrational Raman transitions. With the growing use of hollow-core photonic crystal fiber in different fields, the results can be applied to mitigate air nonlinear response when it is not desired or to use ambient air as a convenient nonlinear medium.

Cocrystals of 2-Aminopyrimidine with Boric Acid—Crystal Engineering of a Novel Nonlinear Optically (NLO) Active Crystal

Crystal engineering of novel materials for nonlinear optics (NLO) based on 2-aminopyrimidine yielded two molecular cocrystals with boric acid—trigonal (P3221 space group) 2-aminopyrimidine—boric acid (3/2) and monoclinic (C2/c space group) 2-aminopyrimidine—boric acid (1/2). In addition to crystal structure determination by single crystal X-ray diffraction, the cocrystals were characterized by powder X-ray diffraction and vibrational spectroscopy (FTIR and FT Raman). Large single crystals of the non-centrosymmetric cocrystal 2-aminopyrimidine—boric acid (3/2) were grown to study the optical properties and determine the second harmonic generation (SHG) efficiency (using 800 nm fundamental laser line) of powder samples.

A Nonlinear Optically Active Bismuth–Camphorate Coordination Polymer

The novel 2D bismuth–camphorate IEF‐1, formulated as [Bi(L)(HL)] (where H2L = camphoric acid), has been successfully isolated as large single crystals and easily scaled up by hydrothermal synthesis. The crystalline structure of IEF‐1 was unveiled by single‐crystal X‐ray diffraction, in the monoclinic space group P21, and fully characterized by using several standard solid‐state techniques. IEF‐1 material is thermally stable up to ca. 240 °C without any visible structural change. In addition, the study of the nonlinear optical (NLO) properties of IEF‐1 by second harmonic generation (SHG) microscopy evidenced that IEF‐1 is noncentrosymmetric and has a more intensive blue component that may be explained by the ligand to metal charge transfer behavior.

Emergence of Nonlinear Optical Activity by Incorporation of a Linker Carrying the p-Nitroaniline Motif in MIL-53 Frameworks.

p-Nitroaniline presents the typical motif of a second-order nonlinear optically (NLO) active molecule. However, because of its crystallization in an antiparallel and hence centrosymmetric structure, the NLO activity is lost. In this contribution, the p-nitroaniline motif was built successfully into the MIL-53 metal–organic framework. More precisely, MIL-53 was synthesized with 2-amino-5-nitroterephthalate as organic linker, with Al3+, Ga3+, or In3+ as inorganic cation. The Al and Ga structures are polar, as confirmed by second-harmonic generation microscopy, yielding stable NLO materials. Indeed, they contain a 22–36% surplus of the dipolar 2-amino-5-nitro-terephthalate oriented in a parallel fashion. The indium compound was shown to be less crystalline and centrosymmetric. Ab initio modeling of the second-order NLO response shows that the Al and Ga materials show a response comparable to typical inorganic commercial NLO materials such as KDP. As a hybrid material, capable of low-temperature synthesis and processing and the ultrafast NLO responses associated with organic materials, this material can potentially provide an interesting venue for applications with respect to traditional inorganic NLO materials.

Poling Induced Mass Transport in Thin Polymer Films

In this study we report investigation of the polymer film morphology modifications during their corona poling for fabrication of nonlinear optically (NLO) active materials. We demonstrate that at certain poling conditions surface and spatial inhomogeneities in the poled area of the sample appear. Densities of the inhomogeinities depend on the strength of the poling field, the sample temperature during the poling, and the prepoling conditions. Optimization of the poling conditions directed toward avoiding surface modifications enables us to increase the overall observable effective nonlinearity of the sample up to 10 times. To investigate, understand, and eventually explain the formation of the spatial and surface structure inhomogeinites in the poled material we have used optical, second harmonic, and scanning electron microscope measurements, as well as the conductivity measurements of the thin films. We present results of poled polymer host-guest films where (dimethylamino)benzylidene-1,3-indandione and low dipole moment 2,2',2″-(4,4',4″-nitrilotribenzylidene)triindan-1,3-dione were used as guests in poly(methyl methacrylate), polystyrol, and polysulfone matrixes doped at 10 wt %.

Urea-based constructs readily amplify and attenuate nonlinear optical activity in response to H-bonding and anion recognition

Urea-based molecular constructs are shown for the first time to be nonlinear optically (NLO) active in solution. We demonstrate self-assembly triggered large amplification and specific anion recognition driven attenuation of the NLO activity. This orthogonal modulation along with an excellent nonlinearity-transparency trade-off makes them attractive NLO probes for studies related to weak self-assembly and anion transportation by second harmonic microscopy.

Synthesis and overall nonlinear optical characterization of poly(hexa-2,4-diynylen-1,6-dioxydibenzoate) containing 2,2′-(4-((4-nitrophenyl)ethynyl)phenylazanediyl)diethanol

A new polymer, poly(p-propargyloxybenzoate) containing a polar tolan as nonlinear optically active chromophore was synthesized and characterized. This polymer shows a Tg-value of ∼98°C and is soluble in typical organic solvents. These properties allowed us to fabricate mechanically stable and high quality semi-transparent thin films by spin coating of N-methylpirrolidone based solutions; obtained samples were adequate for linear and nonlinear photophysical characterizations. In order to explore the quadratic nonlinear optical (NLO) properties, molecular chromophore ordering was electrically induced within the polymeric films via the corona poling method. According to the Maker fringes technique, oriented films with an order parameter of ∼0.25 were able to display large and stable off-resonant second-order NLO-effects such as second harmonic generation (SHG, @ 532nm); the estimated χzzz(2) and χzxx(2) macroscopic NLO-coefficients were in the order of 186.8 and 71.2pmV−1, respectively. On the other hand, the cubic NLO-properties of these films were also studied via the Z-Scan technique, where the deposited films displayed an outstanding NLO refractive (n2) and absorptive (β) performance. Indeed, due to the high conjugation degree and intra-molecular charge transfer (ICT) properties, poled and unpoled polymer films displayed huge n2-values in the order of 10−8m2W−1 with negative sign and NLO saturable absorption β-coefficients in the order of 10−1mW−1. The large quadratic and cubic NLO-coefficients obtained for this novel polymer evidence its potentiality in the development of organic-based opto-electronic and photonic prototypes.

Insight in NLO Polymer Material Behavior from Langevin Dynamic Modeling of Chromophore Poling

Calculation of chromophore polar order, i.e. the polarization of nonlinear optically (NLO) active polymers poled by external field, is challenging. One possible solution is to reproduce the orientation polarization of chromophores under external field using Langevin dynamics (LD) molecular modeling. The present work investigates the influence of chromophore dipole moment, density and field extent on NLO efficiency and polarization/relaxation dynamics. Results of simulations convince us, that the method is applicable for modeling real NLO polymers. In the spotlight of this investigation we would like to describe a NLO polymer as a “ferrofluid” where chromophores are active particles or electrets.

A New Nonlinear Optically Active Donor–Acceptor-Type Conjugated Polymer: Synthesis and Electrochemical and Optical Characterization

A new donor–acceptor-type poly[3-{5-[3,4-didodecyloxy-5-(1,3,4-oxadiazol- 2-yl)thiophen-2-yl]-1,3,4-oxadiazol-2-yl}-9-dodecyl-9H-carbazole] (P) has been synthesized through multistep reactions. The new polymer P exhibited good thermal stability and film-forming behavior. The electrochemical band gap is estimated to be 2.15 eV. The polymer emits intense green fluorescence in the solid state. Third-order nonlinear optical (NLO) studies showed that the strong absorptive nonlinearity observed for the polymer is of the optical limiting type, which is due to an “effective” three-photon absorption (3PA) process. This 3PA process can have potential applications in photonic devices. The studies revealed that the new polymer P is a promising material for development of efficient optoelectronic devices.

Studies on the feasibility of recycled polystyrene doped with NLO active meta -Nitroaniline for optoelectronics applications

A Guest–Host system based on meta-Nitroaniline (m-NA) and recycled polystyrene (RPS) susceptible to generate nonlinear optically (NLO) active property such as second harmonic generation (SHG) has been prepared. Pure, sublimed, optical grade, crystalline m-NA is used as a guest and RPS from the disposable packaging waste as available utilized as the host polymer. In this paper we report the effect of NLO active m-NA on the bulk and optical properties of RPS. The purified m-NA was incorporated from 1–10 wt% in the RPS polymer matrix by conventional solution casting method. Thin, transparent, freestanding films obtained were characterized with optical microscope, scanning electron microscope (SEM), viscosity measurement, and UV–Visible (UV–Vis) spectroscopy for bulk properties evaluation and Nd:YAG laser studies for optoelectronics application such as SHG through frequency doubling. Copyright © 2010 John Wiley & Sons, Ltd.

SECOND HARMONIC GENERATION IN Λ-SHAPED ORGANIC MOLECULES

In epoxy based polymeric nonlinear optical (NLO) materials, the nonlinear optically active moiety forms crosslink between polymer chains. Some of the important moieties include 4, 4'diamino diphenyl sulfone (DADS). We have examined second harmonic generation (SHG) in DADS and have compared it with 4, 4'diamino diphenyl methane (DADM). The geometry optimization suggests that both molecules have Λ-shaped structure. The theoretical calculations as well as experimental observations of SHG in both the molecules suggest the suitability of DADS over DADM for making polymeric NLO materials.

Atom Transfer Radical Polymerization and Third‐Order Nonlinear Optical Properties of New Azobenzene‐Containing Side‐Chain Polymers

AbstractThe atom transfer radical polymerization (ATRP) technique has been successfully applied to synthesize a series of nonlinear optically (NLO) active homopolymers, 4‐(4‐nitrophenyl‐diazenyl) phenyl acrylate (P‐NPAPA) and 4‐(4‐methoxyphenyl‐diazenyl) phenyl acrylate (P‐MPAPA), containing azobenzene groups on the side chain. The third‐order NLO properties of the polymer films were measured by the degenerated four‐wave mixing (DFWM) technique. A dependence of the χ(3) values and response times of polymers on their number‐average molecular weight and the electronic effect of the substituent (nitro‐ or methoxy‐) on the azobenzene group have been evidenced. The increasing χ(3) value of the polymer films at the magnitude of about 10−10 was displayed with increasing molecular weight and the presence of the push‐pull electronic system contributes much in enhancing the third‐order NLO susceptibility of polymers.magnified image

Optically Active Organic Microrings

Rings of p-hexaphenyl molecules are generated on mica surfaces, possessing narrow size distributions with mean diameters of a few micrometers, wall widths of 100 to 200 nm, and wall heights of several hundred nanometers. Polarized linear and nonlinear optics reveals that the rings are made up of radially oriented and nonlinear optically active molecules. They lay parallel to the substrate surface and coexist with a wetting layer of upright oriented molecules.

THERMALLY STABLE NLO MATERIALS BASED ON ORGANOSOLUBLE POLYIMIDES AND AN ALKOXYSILANE DYE VIA SOL-GEL PROCESS

A series of organic-inorganic materials based on organosoluble polyimides and an alkoxysilane dye for second-order nonlinear optics have been developed. A sol-gel reaction of a nonlinear optically active alkoxysilane dye (ASD) is utilized to grow a network in polymer matrices or create an interpolymer network among polyimide chains. SEM results indicate that the inorganic networks are distributed uniformly throughout the polymer matrices on the molecular scale. The silica particle sizes are well under 1 μm. Second harmonic coefficients, d33 of 8.4 to 47.6 pm/V have been obtained for the poled/ cured polyimide/ASD samples. Excellent temporal stability was obtained for these NLO materials at 100°C. The composition effect on the second order nonlinearity is also reported.