Third-order Optical Nonlinearity Research Articles

Electrically controlled liquid crystal nonlinear optical devices prepared by multi-layer composite structures

In this study, a multi-layer composite structure is used to prepare nonlinear optical devices from multi-walled carbon nanotubes (MWCNTs)/liquid crystal (LC) composite systems. Their third-order optical nonlinearity is investigated. The MWCNTs were coated and modified to improve their dispersion in the solvent. The coated and modified MWCNTs were characterized by IR absorption spectroscopy and transmission electron microscopy (TEM). The nonlinear optical (NLO) properties of the devices prepared by the multi-layer composite structures with varying design parameters were studied. The conventional devices were also prepared by mixed doping method for comparison with the proposed devices. Both devices underwent Z-scan testing. The third-order nonlinear polarizability of the conventional hybrid-doped devices was calculated with a value of 5.39 × 10-10 esu. The third-order nonlinear polarizability of the proposed devices prepared by the multi-layer composite structures has a value of 2.97 × 10-9 esu, which is about five times the corresponding value for the hybrid-doped devices. So, the devices prepared by the multi-layer composite structures have better NLO properties. Moreover, the third-order nonlinear polarizability of the proposed devices was further increased up to 3.88 × 10-9 esu, which is an increase of almost 31% after applying voltage to these devices prepared by the multi-layer composite structures. The limiting threshold of S-CTAB/MWCNTs@BHR33400 is 0.245 J/cm2 after voltage application. Applying voltage plays a role in promoting the NLO properties of the devices. Using the multi-layer composite structure to prepare the liquid crystal nonlinear optical devices can significantly improve the NLO properties of the devices. Such prepared devices can be electrically tuned, providing new avenues for preparing nonlinear optical devices.

π-Extended Octupolar Cyclized Indole Tetramer and Trimer Derivatives with Second- and Third-Order Nonlinear Optical Properties.

Several aromatic-fused octupolar tetraindole (TTI) and triindole (TI) derivatives have been synthesized via POCl3-promoted cyclopolymerization of the aromatic-fused oxindoles. As a result, the terminal phenyls of TTI and TI are fused with the phenyl group, indenyl group, and benzothienyl group separately in the π-extended target compounds TTIp and TIp, TTIid and TIid, and TTIbt and TIbt (including pairs of syn- and anti-isomers). Single-crystal X-ray diffraction disclosed that the tetramer syn-TTIbt keeps an S4-symmetric architecture and crystallizes in the P42/n space group. With the extension of the π-conjugation, the absorption and emission bands of the above tetramers and trimers are remarkably red-shifted. The second-order nonlinear optical (NLO) coefficients (β value) of syn-TTIbt and anti-TTIbt have been calculated to be 1.5 and 2.1 times that of their parent compound TTI, respectively. In the domain of the third-order NLO, the two-photon absorption sections (δ value) of syn-TIbt and anti-TIbt have been measured to be 37 and 102 times that of TI, respectively. These results indicate that the π-extension strategy here is successful, and the anti-isomers have better NLO properties and better π-conjugation than their corresponding syn-isomers.

Design, crystal growth and characterizations of novel bis morpholinium zinc bromide single crystals for optoelectronic applications

A novel metal-organic third-order nonlinear optical (NLO) material with promising excellent properties in the crucial solar blind UV region. For the first time, high NLO active metal-organic complex of bis-morpholinium zinc bromide (BMZB) single crystal has been rationally designed and single crystals have been grown by slow evaporation solution technique (SEST). Remarkably, the grown crystal exhibits competitive and even superior physical properties including high thermal stability and wider transparency than the standard NLO single crystal. The title compound crystallizes in the monoclinic crystal system with the space group of P21/cc and four molecules are accumulated in the unit cell (unit cell parameters are a = 6.7860 (6) Å, b = 16.6239 (2) Å, c = 14.8875 (2) Å, β = 94.937 (3)° and Z = 4). Further, the phase purity and the crystallinity of the grown sample were analyzed through powder X-ray diffraction (PXRD) analysis. The Fourier transform infrared (FTIR) spectroscopy analysis has been used to determine the presence of multifarious functional groups in the grown crystal. The recorded optical transmittance spectrum reveals that the BMZB crystal possesses good optical transparency in the range between deep ultraviolet (UV) and near-infrared (NIR) regions. Intriguingly, the short cut-off edge of the grown crystal is found to be about 227 nm which is more favorable for developing modern photonic and optoelectronic devices in the solar blind UV region. The thermal and mechanical stabilities of the grown crystals have been studied using Vickers microhardness and thermogravimetry (TG) and differential thermal analysis (DTA) respectively. Moreover, key requirements for designing practical NLO devices such as large laser damage threshold (LDT) and excellent third-order NLO response have been observed in the grown single crystal. Therefore, our findings open up a new avenue to the rational design of thermally stable and large NLO active metal-organic complexes for practical NLO applications.

Coordination-Induced Symmetry Breaking on Metal-Porphyrinic Framework Thin Films for Enhanced Nonlinear Optical Limiting

Structural asymmetry affecting the nonlinear optics (NLO) of metal-organic frameworks (MOFs) is very important in fundamentals and applications but is still a challenge. Herein we develop a series of indium-porphyrinic framework (InTCPP) thin films and provide the first study on the coordination-induced symmetry breaking on their third-order NLO. The continuous and oriented InTCPP(H2) thin films were grown on quartz substrates and then postcoordinated with different cations (Fe2+ or Fe3+Cl-) in InTCPP(H2) (named InTCPP(Fe2+) and InTCPP(Fe3+Cl-)). The third-order NLO results reveal the Fe2+ and Fe3+Cl- coordinated InTCPP thin films have substantially enhanced NLO performance. Moreover, InTCPP(Fe3+Cl-) thin films cause symmetry breaking of microstructures, resulting in a 3-fold increase in the nonlinear absorption coefficient (up to 6.35 × 10-6 m/W) compared to InTCPP(Fe2+). This work not only develops a series of nonlinear optical MOF thin films but also provides new insight into symmetry breaking on MOFs for nonlinear optoelectronic applications.

Synthesis, physico-chemical characterization and quantum chemical studies of 2, 3-dimethyl quinoxalinium-5-sulphosalicylate crystal

2,3-dimethylquinoxalinum-5-sulphosalicylate (MQSA) was synthesized and grown into single crystals by slowly evaporating the solvent in methanol at room temperature. According to the lattice parameters found by the SCXRD analysis method (a = 8.8031 (17) Å, b = 17.768(3) Å, c = 10.7979(16) and α = γ = 90°, β = 90.611 (7) °), the crystal belongs to monoclinic crystal system with the P21/n space group. Moreover, powder X-ray diffraction investigation supported the crystalline nature. The compound's UV–Vis spectra exhibited a CT-band with a wavelength maximum of 372 nm, as well as its NIR spectra revealed good optical transmittance in the visible region with a low cut-off wavelength of 376 nm and an optical band gap of 5.12 eV. Dual emission bands at 418 and 484 nm are observed in the PL emission spectra. The synthesized crystal was examined using FT-IR, FT-Raman, and NMR spectral methods. The crystal is thermally stable up to 274 °C, furthermore, TG-DTA and DSC methods were employed to study the degradation process. The second and third-order NLO efficiencies of the crystal was analyzed by Kurtz-Perry powder and Z-scan methods, respectively. The single crystal of MQSA is further studied through Hirshfeld surface analysis, fingerprint plots, and crystal voids analysis to understand the intermoleculiar interactions and individual atomic arrangements inside the crystal. The H…H and O…H/H…O interactions are greatly aided by crystal structure. Additionally, the quantum computational methods were used to assess several molecular level electronic properties, including molecular orbitals, molecular electrostatic potentials maps, linear polarizability and static third-order nonlinear optical (NLO) polarizability, which is a molecular-level NLO response property. The isotropic linear polarizability and NLO polarizability of MQSA are 29.99 × 10−24 esu and 28.45 × 10−36 esu, respectively, in the M06–2X/6–311G* method, which demonstrates the decent potential of the synthesized crystal for its use as NLO materials. Furthermore, the frontier molecular orbitals, molecular electrostatic potentials, and UV–Visible spectrum were calculated and discussed.

Imaging Low-Temperature Phases of Ice with Polarization-Resolved Hyperspectral Stimulated Raman Scattering Microscopy.

Water freezes into various phases of ice under different cryogenic temperatures and pressure conditions, such as ice Ih and ice XI at normal pressure. Vibrational imaging with high spectral, spatial, and polarization resolutions could provide detailed information on ice, including the phases and crystal orientations at the microscopic level. Here, we report in situ stimulated Raman scattering (SRS) imaging of ice to analyze the vibrational spectral changes of the OH stretching modes associated with the phase transition between ice Ih and ice XI. In addition, polarization-resolved measurements were performed to reveal the microcrystal orientations of the two phases of ice, with the spatial-dependent anisotropy pattern indicating the inhomogeneous distribution of their orientations. Furthermore, the angular patterns were theoretically explained by third-order nonlinear optics with the known crystal symmetries of the ice phases. Our work may provide new opportunities to investigate many intriguing physical chemistry properties of ice under low-temperature conditions.

Nonlinear optical properties of symmetrical and asymmetrical benzene derivatives with click chemistry modification

PurposeThis paper aims to prepare third-order nonlinear optical (NLO) organic materials with large nonlinear optimization value, high damage threshold and ultrafast response time.Design/methodology/approachA series of novel symmetric and asymmetric compounds possessing third-order NLO properties were synthesized using 1,3,5-tribromobenzene as the basis. The photophysical and electrochemical properties, as well as the click reactions, were characterized by means of UV–VIS–NIR absorption spectroscopy and cyclic voltammetry.FindingsThe donor–acceptor chromophores were inserted into compound, making the molecule to have a broader absorption in the near-infrared regions and a narrower optical and electrochemical band gap. It also formed an electron-delocalized organic system, which has larger effects on achieving a third-order NLO response. The third-order NLO phenomenon of benzene ring complexes was experimentally studied at 532 nm using Z-scan technology, and some compounds showed the expected NLO properties.Originality/valueThe click products exhibit more NLO phenomena by performing different click combinations to the side groups, opening new perspectives on using the system in a variety of photoelectric applications.

Enhancing Third-Order Nonlinear Optical Property by Regulating Interaction between Zr4(embonate)6 Cage and N, N-Chelated Transition-Metal Cation

Herein, the combination of anionic Zr4L6 (L = embonate) cages and N, N-chelated transition-metal cations leads to a series of new cage-based architectures, including ion pair structures (PTC-355 and PTC-356), dimer (PTC-357), and 3D frameworks (PTC-358 and PTC-359). Structural analyses show that PTC-358 exhibits a 2-fold interpenetrating framework with a 3,4-connected topology, and PTC-359 shows a 2-fold interpenetrating framework with a 4-connected dia network. Both PTC-358 and PTC-359 can be stable in air and other common solvents at room temperature. The investigations of third-order nonlinear optical (NLO) properties indicate that these materials show different degrees of optical limiting effects. It is surprising that increasing coordination interactions between anion and cation moieties can effectively enhance their third-order NLO properties, which can be attributed to the formation of coordination bonds that facilitate charge transfer. In addition, the phase purity, UV-vis spectra, and photocurrent properties of these materials were also studied. This work provides new ideas for the construction of third-order NLO materials.

Ultrafast Third-Order Optical Nonlinearity of Indigo Carmine Excited by Pico-second Pulsed Laser at 405 nm

Ultrafast Third-Order Optical Nonlinearity of Indigo Carmine Excited by Pico-second Pulsed Laser at 405 nm

Third-order optical nonlinearity and passively Q-switching operation with BiOCl nanosheets at 1.3 µm.

In this contribution, we measured the third-order nonlinear optical response of bismuth oxychloride (BiOCl) nanosheets with the open-aperture (OA) and the closed-aperture (CA) Z-scan techniques with a variable excitation intensity at 1.34 µm. The effective nonlinear absorption coefficient βeff and the nonlinear refractive index n2 of the prepared BiOCl nanosheets with abundant oxygen vacancies were obtained under the excitation intensity. The third-order nonlinear optical susceptibility |χ(3)| was 1.64 × 10-9 esu. The nonlinear optical features of BiOCl enabled it as a superb saturable absorber for pulse laser generation. As a consequence, we demonstrated the first passively Q-switched Nd:GdVO4 laser with the BiOCl saturable absorber, producing a shortest pulse duration of 543 ns and a highest repetition rate of 227 kHz, leading to a maximum pulse energy of 74 nJ. Our findings show that BiOCl nanosheets with oxygen vacancies have large nonlinear optical sensitivities and can be exploited to generate optical pulses.

Donor–Acceptor Covalent Organic Frameworks Films with Ultralow Band Gaps to Enhanced Third-Order Nonlinear Optical Properties

Covalent organic frameworks (COFs) have attracted much attention in porous materials because of their structural tunability and stability. However, the problems of low transmittance and large light scattering due to the difficulty of powder phase processing have severely limited their practical applications in third-order nonlinear optics (NLO). Herein, we report the first successful synthesis of a series of donor–acceptor (D–A) COFs films (thickness of ∼100 nm) with uniform transparency and narrow optical band gap by the solvothermal and solid–liquid interface methods for third-order NLO applications. Most importantly, the designed PT–PA film exhibits excellent NLO performance, including a normalized transmission value of ∼2.55 at the beam focus, a modulation depth (As) of 139%, and a high nonlinear absorption coefficient (β) of 1.83 × 106 cm GW–1 at the pulse energy of 1 μJ, which is superior to most recently reported third-order NLO materials. The excellent third-order NLO properties are mainly attributed to the homogeneous transparency of the COFs films and the extended-ordered conjugated structure and narrow optical band gap of the COFs films, which enhance the charge transfer in their structures and thus yield excellent third-order NLO behavior. This work provides an option for the development of high-performance NLO optical devices and opens a new path for the future development of COFs films in the optical fields.

Third-Order Optical Nonlinearities of 2D Materials at Telecommunications Wavelengths

All-optical signal processing based on nonlinear optical devices is promising for ultrafast information processing in optical communication systems. Recent advances in two-dimensional (2D) layered materials with unique structures and distinctive properties have opened up new avenues for nonlinear optics and the fabrication of related devices with high performance. This paper reviews the recent advances in research on third-order optical nonlinearities of 2D materials, focusing on all-optical processing applications in the optical telecommunications band near 1550 nm. First, we provide an overview of the material properties of different 2D materials. Next, we review different methods for characterizing the third-order optical nonlinearities of 2D materials, including the Z-scan technique, third-harmonic generation (THG) measurement, and hybrid device characterization, together with a summary of the measured n2 values in the telecommunications band. Finally, the current challenges and future perspectives are discussed.

Coherent terahertz radiation from indium tin oxide film via third-order optical nonlinearity

Coherent terahertz (THz) wave emission from indium tin oxide (ITO) in epsilon-near-zero region had been reported recently as a second-order nonlinear process. However, THz radiation from ITO through third-order nonlinear process has not been reported yet. Here, we demonstrate coherent THz radiation from an ITO film via four-wave mixing, a third-order nonlinear process, under the excitation of two-color pulsed laser fields. Experimentally, an in-line phase compensator is utilized to synthesize the asymmetric optical fields to induce photocurrent in an ITO film and consequently emit THz waves. Our experimental results show that THz radiation from ITO films can be coherently controlled by the relative phase between the two-color laser fields. Such a THz wave generation process can be attributed to the fast intra-band nonlinearity in the conduction band. Our demonstration reveals that the fast nonlinearity in ITO can be used to generate THz waves and promotes the investigation of ITO in ultrafast photonics.

A comparison of the crystal structure and optical properties of reduced graphene oxide and aminated graphene nanosheets for optoelectronic device applications

Optical properties of graphene transform in presence of amine or amide groups. So, the comparison of the linear and nonlinear optical (NLO) properties of reduced graphene oxide (RGO) nanosheets and aminated graphene (AMG) nanosheets will significantly accelerate the development of a flexible optoelectronic device based on this material in the future. In this paper, the structural and optical properties of RGO and AMG are investigated by TEM, XRD, Raman, and UV-Vis analysis. TEM images show the formation of the very thin layer of RGO and AMG nanosheets. The peak of XRD spectra (26.6◦) for both indicate the good quality of crystallization of RGO and AMG. Raman spectra result in ID/IG of about 0.9 and 1.1 for RGO and AMG, respectively. Also, different functional groups for RGO and AMG nanosheets are shown in FTIR spectra. Then, Kramers-Kronig (KK) method was employed to determine the dielectric function, ε̃(λ), extinction coefficient, k(λ) and refractive index, n(λ). Third-order optical nonlinearities of nanosheets dispersed in DMF are investigated with the Z-scan method. The nanosheets achieve an appropriate figure of merit (FOM) due to their high nonlinear refractive (NLR) index, n2 (10−8cm2/W) and low nonlinear absorption (NLA) coefficient, β (10−4cm/W).

Improvement of third-order NLO properties of vacuum deposited Cd1-xPbxS nanostructured thin films for optoelectronic device applications

A polycrystalline nanostructured cadmium lead sulfide thin film was deposited using the thermal evaporation (PVD) technique (Cd1-xPbxS with x = 0.00, 0.01, 0.05 and 0.1 wt.% of Pb). Structural parameters of as-prepared Cd1-xPbxS thin films have been studied through X-ray diffraction. The optical investigation demonstrates that Cd1-xPbxS film's optical band gap (Eg) may be adjusted from the visible to the near-infrared region. (2.64 - 2.42 eV). The film is substantially more appropriate for absorbing layers in solar cells and optoelectronic applications due to the large decrease in ‘Eg.’ The enhanced Pb doping was found to have altered the surface morphology, verified by Field Emission Scanning Electron Microscopy (FESEM) images. The doped films also showed a significant red shift in the band edge and increased transmittance in the visible and NIR regions. The third-order nonlinear optical (TONLO) parameters of the samples were determined from the Q-switched Nd: YAG laser with 65-ps pulse duration at 1064 nm. The investigated TONLO components such as nonlinear absorption coefficient (β), nonlinear refractive index (n2) and the susceptibility χ(3)were found to be in the range from 1.16 × 10−3 to 4.12 × 10−3 (cmW−1), 1.06 × 10−8 to 3.32 × 10−8 (cm2 W−1) and 1.23 × 10−4 to 5.62 × 10−4 (esu) respectively. The results indicate that Pb-doping on CdS nanostructures on surface morphology can be used to modify NLO characteristics.Cd1-xPbxS thin film is a potential and able material for optoelectronic device applications, as seen by these encouraging NLO results.

Synthesis, growth, crystal structure analysis, optical characterization, thermal and dielectric studies on 2-amino-5-chloropyridinium phenoxyacetate (2A5CPA): An efficient new organic single crystal for nonlinear optical applications

The new organic 2-amino-5-chloropyridinium phenoxyacetate (2A5CPA) nonlinear optical (NLO) crystal was synthesized and grown from methanol solvent by slow evaporation method successfully. The complete 2A5CPA crystal structure was solved by single crystal XRD analysis and it indicates that the 2A5CPA crystal belongs to the tetragonal crystal system with the space group P41212. From the structure, the possible hydrogen bonding interactions have been analyzed. The presence of distinctive functional peaks in the 2A5CPA crystal was affirmed by FTIR analysis. The optical investigation reveals that the crystal was completely transparent in the UV–Vis–NIR region. The TG-DTA investigation assured that the 2A5CPA compound is thermally stable up to 134°C without any decomposition. The sharp endo thermic peak at 205°C in the DTA trace indicates the melting point of the crystal. The broad emissive band at 382[Formula: see text]nm implies the violet emission characteristics of the 2A5CPA crystal. The dielectric study of the 2A5CPA crystal portrays the normal behavior to that of optical materials. The high work-hardening coefficient of 2.94 indicates the soft material nature of the crystal. The LDT value of the 2A5CPA crystal is estimated as 0.6135[Formula: see text]GW/cm2. The third-order NLO properties of the 2A5CPA crystal were analyzed through Z-Scan experiment.

A self-defocusing third-order nonlinear optical material l-Alanine Barium Chloride single crystal used in optoelectronic device applications

Slow evaporation method was used to produce a single crystal of l-Alanine Barium Chloride (LABC), a semi-organic nonlinear optical material. The grown crystal non-centrosymmetric nature can be seen in the results of a single-crystal XRD analysis. Using Fourier transform infrared spectral analysis, the unique functional groups and chemical makeup of LABC compounds were found. The lower cut-off wavelength is observed down to 253 nm and direct optical band gap was calculated as 4.54 eV. A photoluminescence experiment found the LABC crystal emission spectrum. EDAX spectrum analysis revealed the crystal metal ion (Ba) existence. The Z-scan method with an Nd: YAG laser at 532 nm was used to analyse the third-order optical nonlinearity characteristics of LABC in detail. A Vicker's microhardness tester was used to measure the microhardness of the LABC crystal under the same load.

Effect of geometry, anisotropy and composition on the third-order optical nonlinearities of multilayer hyperbolic metamaterials -INVITED

Quantum technologies require advanced optical metamaterials whose properties can be tailored and controlled as desired. Hyperbolic metamaterials have great potential for applications in nonlinear nanophoton-ics, such as all-optical switching, optical limiting, mode-locking and optical sensing. In this work, we show how to obtain strong third-order optical nonlinearities in hyperbolic multilayers exploiting the effect of bulk plas-mon polaritons. We demonstrate the tunability of these properties with angle and polarization, and we propose a model to predict them. We evidence the enhancement of the nonlinear response in low-loss metamaterials.

Modulation of epsilon-near-zero wavelength and enhancement of third-order optical nonlinearity in ITO/Au multilayer films

We report the modulation of epsilon-near-zero (ENZ) wavelength and enhanced third-order nonlinearity in indium tin oxide (ITO)/Au multilayer films. The samples consisting of five-layer 40 nm ITO films spaced by four-layer ultrathin Au films of different thickness, i.e., ITO(40 nm)/[Au(x)/ITO(40 nm)]4, were prepared by magnetron sputtering at room temperature. The ENZ wavelength in the multilayer films is theoretically calculated and experimentally confirmed. The nonlinear refractive index and nonlinear absorption coefficient of the samples of x=0, 2, 3, 4 nm were determined using the Z-scan method at a wavelength of 1.064 µm. The large nonlinear refractive index n2=1.12×10-13 m2/W and nonlinear absorption coefficient β=-1.78×10-7 m/W in the sample of x = 4 nm are both four times larger than those in the single-layer ITO film. The large optical nonlinearity due to the ENZ enhancement and carrier concentration is discussed. The results indicate that the ITO/Au multilayer films are promising for advanced all-optical devices.

Third-order Optical Nonlinearities of 2D Materials at Telecommunications Wavelengths in the 1550nm Band

Third-order Optical Nonlinearities of 2D Materials at Telecommunications Wavelengths in the 1550nm Band