Third-order Optical Nonlinearity Research Articles

Kerr coefficient and third-order nonlinear optical absorption coefficient of isotropic diacrylate mesogens at 632.8 nm wavelength

ABSTRACT Third-order optical nonlinearities of diacrylate mesogens RM82 and RM257 in the isotropic phase for a low-power continuous wave laser irradiation at 632.8 nm wavelength have been studied. In their isotropic state, the diacrylate mesogens exhibit quite large nonlinear absorption. We observe a large two-photon absorption coefficients, on an order of 10−6 m/W, for the mesogens. The Kerr coefficients of the mesogens are characterised using single beam Z-scan technique, and found to reach an order of 10−7 m/W. Both diacrylate mesogens exhibit a good material figure of merit.

Directional growth of 2-ethylimidazolium d-tartrate crystal along (001) and investigation of optical properties for optical limiting applications

A single crystal of 2-Ethylimidazolium d-Tartrate (2EIMDT) was grown along the preferred direction of (001) by the Sankaranarayanan-Ramasamy method. The growth direction was confirmed by X-ray Diffraction analysis. The optical homogeneity and the defect analysis of the grown crystal were carried out using birefringence interferometry, Williamson-Hall plot, and chemical etching. They revealed that the grown crystal possesses good optical and crystalline quality. Using the optical transmission spectrum, the optical band gap and Urbach energy were estimated to be 5.1 eV and 140 meV, respectively. The temperature dependence of the refractive index and thermo-optic coefficient were measured using the prism coupling technique for different wavelengths. The thermo-optic coefficient was found to be negative with values ∼10−5/°C. The laser damage threshold was estimated to be 6.5 GW/cm2 for a 1064 nm laser. Vickers micro-hardness study revealed that the (001) plane of the crystal is characterized by Meyer's index of 1.93. From the Z-scan measurement, it was found that the grown crystal exhibits two-photon absorption characteristics and the obtained imaginary parts of the third-order nonlinear optical (TONLO) susceptibility is 1.95 × 10−14 esu. Additionally, the onset optical limiting threshold was estimated to be 3.89 × 1012 W/m2 which indicates the potential of 2EIMDT for optical limiting applications.

Effect of WO3 in the third-order optical nonlinearities of tungsten lead pyrophosphate glasses

The binary glassy system Pb2P2O7-WO3 demonstrates promising photonics applications owing to its high polarizability and chemical stability. The domain of glass's chemical state and linear and nonlinear optical properties have been investigated using X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, and the Z-scan technique, respectively. The optical absorption spectra revealed that the absorption edge was redshifted with increased WO3 content, suggesting a decrease in bandgap energy. Nonlinear refractive index increased with the WO3 content from an average value of 0.70 x 10−19 m2 W−1 to 0.98 x 10−19 m2 W−1. Such an increase is due to the rise of non-bridging oxygens and the polarizability of W6+ and W5+ species. XPS studies found that a high concentration of WO3 leads to the transformation of the oxidation state of W6+ and W5+ related to the presence of oxygen vacancies. Therefore, our high nonlinear refractive index and polarizability results indicate that the glass system studied here is a potential candidate for photonic devices.

Electro-Induced Phase Transformation of a Conductive Metal-Organic Framework Film for Nonlinear Optical Switching.

Achieving metal-organic frameworks (MOFs) with nonlinear optical (NLO) switching is profoundly important. Herein, the conductive MOFs Cu-TCNQ phase I (Ph-I) and phase II (Ph-II) films were prepared using the liquid-phase-epitaxial layer-by-layer spin-coating method and steam heating method, respectively. Electronic experiments showed that the Ph-II film could be changed into the Ph-I film under an applied electric field. The third-order NLO results revealed that the Ph-I film had a third-order nonlinear reverse saturation absorption (RSA) response and the Ph-II film displayed a third-order nonlinear saturation absorption (SA) response. With increases in the heating time and applied voltage, the third-order NLO response realized the reversible transition between SA and RSA. The theoretical calculations indicated that Ph-I possessed more interlayer charge transfer, resulting in a third-order nonlinear RSA response that was stronger than that of Ph-II. This work applies phase-transformed MOFs to third-order NLO switching and provides new insights into the nonlinear photoelectric applications of MOFs.

Designing the electron push-pull chromophores through the joining of triphenylamine and triphenylborane for efficient nonlinear optical and photovoltaic properties

The benzoxadiazole class of organic compounds demonstrates exceptional versatility, particularly in the realm of nonlinear optical (NLO) materials, where their unique properties find impactful applications. In the present study, we have focused on systematically designed six benzoxadiazole (BDZ) derivatives named as BDZ-1 to BDZ-6 by using 2,3,1-benzoxadiazole as a central core/π-spacer between the donor and acceptor. Triphenylamine and triphenylborane are used as donor and acceptor in all derivatives with addition of nitro and methoxy group as substitutions. B3LYP/6-311G* method of density functional theory (DFT) is employed for optimization of purposed systems while M06/6-311G* is used to check the NLO properties. The isotropic polarizability (αiso) and anisotropic polarizability (αaniso) of BDZ-6, were found to be 110.1 × 10−24 esu and 106.3 × 10−24 esu, respectively. Among our designed compounds, the BDZ-6 exhibits the highest third-order NLO polarizability, which was found to be 5954.8 × 10−36 esu corresponding to lowest transition energy of 2.00 eV. Additionally, frontier molecular orbitals (FMOs), molecular electrostatic potential maps (MEPs), electron difference density maps (EDD) and UV–Vis analysis were performed. BDZ-6 shows minimum energy gap of 2.24 eV, while it shows maximum absorption at 620 nm. The density of states (DOS) analysis reveals distinct electronic contributions of various fragments in the formation of HOMO and LUMO orbitals resulting in efficient intramolecular charge transfer (ICT). Photovoltaic findings revealed that BDZ-4 have maximum open circuit voltage of 1.70 eV with minimum dye regeneration value (0.30 eV). Our findings shed light on the design and development of novel NLO materials with BDZ derivatives.

Third-Order Nonlinear Optical Modulation Behavior of Photoresponsive Bimetallic MOFs.

Bimetallic metal-organic frameworks (MOFs) capable of sensing external stimuli will provide more possibilities for further regulating third-order nonlinear optical (NLO) properties. In this work, we synthesized bimetallic MOFs (ZnCu-MOF and ZnCd-MOF) through central metal exchange using a photoresponsive Zn-MOF as a precursor. Compared with Zn-MOF, both ZnCu-MOF and ZnCd-MOF exhibit significantly enhanced third-order NLO absorption properties. This is mainly attributed to the introduction of metal ions with different electron configurations that can adjust the bandgap of MOFs and enhance electron delocalization, thus promoting electron transfer. Interestingly, the bimetallic MOFs show a transition from reverse saturation absorption (RSA) to saturation absorption (SA) after exposure to ultraviolet irradiation, as they retain the properties of directional photogenerated electron transfer. Photoresponsive bimetallic MOFs not only have the effect of bimetallic modulation of electronic structures but also have the characteristics of photoinduced electron transfer, exhibiting diversified optical properties. These findings provide a novel method for the development of multifunctional NLO materials.

Third-order nonlinear optics and optical limiting of phenanthrenone derivatives

Organic nonlinear optical materials have attracted much attention due to their large nonlinear optical coefficients and ultrafast response speeds, as well as their potential applications in optical limiting (OL). Among them, nonlinear optical materials with phenanthrenone as the backbone are consistently understudied. We have successfully realized the transformation of organic small molecules in the nonlinear optical direction by replacing the carbonyl group on the structure of phenanthrenone with a malononitrile group. The nonlinear optical properties of CN-2 were investigated under different excitation conditions at 532 nm and the kinetic process of nonlinear optics was analyzed by transient absorption spectroscopy. In addition, we also investigated the OL properties of CN-2, and the OL experiments showed that CN-2 with a lower OL threshold has superior OL properties than C60.

Ultrafast Dynamics, Optical Nonlinearities, and Chemical Sensing Application of Free-Standing Porous Silicon-Based Optical Microcavities.

The present work demonstrates the ultrafast carrier dynamics and third-order nonlinear optical properties of electrochemically fabricated free-standing porous silicon (FS-PSi)-based optical microcavities via femtosecond transient absorption spectroscopy (TAS) and single-beam Z-scan techniques, respectively. The TAS (pump: 400 nm, probe: 430-780 nm, ∼70 fs, 1 kHz) decay dynamics are dominated by the photoinduced absorption (PIA, lifetime range: 4.7-156 ps) as well as photoinduced bleaching (PIB, 4.3-324 ps) for the cavity mode (λc) and the band edges. A fascinating switching behavior from the PIB (-ve) to the PIA (+ve) has been observed in the cavity mode, which shows the potential in ultrafast switching applications. The third-order optical nonlinearities revealed an enhanced two-photon absorption coefficient (β) in the order of 10-10 mW-1 along with the nonlinear refractive index (n2) in the range of 10-17 m2 W-1. Furthermore, a real-time sensing application of such FS-PSi microcavities has been demonstrated for detecting organic solvents by simultaneously monitoring the kinetics in reflection and transmission mode.

Nonlinear Optical Refraction and Absorption Features of Methyl Orange Dye in Polar Solvents.

Herein, we report the nonlinear optical (NLO) refraction and absorption features of azo dye namely, methyl orange (MO) dissolved in ethanol, methanol, acetone, 1-propanol, DMF and DMSO. The UV-Visible absorption study reveals that the maximum absorption spectrum of MO dye appeared towards longer wavelength by increasing the solvent polarizability is the result of red shift or bathochromic shift. The Z-scan method is utilized to measure the third-order NLO features of MO dye in different polar solvents. A continuous wave laser with 5-mW power and an excitation wavelength of 405nm is employed in the Z-scan technique. The NLO features including nonlinear index of refraction (n2), nonlinear coefficient of absorption (β) and third-order NLO susceptibility (χ3) are calculated to be the order of 10-7 cm2/W, 10-2cm/W and 10-7 esu, respectively. The NLO index of refraction shows peak-valley transmittance is the result of self-defocusing and NLO absorption coefficient exhibits both positive and negative nonlinearity owing to saturable absorption (SA) and reverse saturable absorption (RSA). The effect of solvent polarizability and dipole moment on third-order NLO susceptibility of MO dye is discussed. Based on the experimental results, an azo dye MO appears to be a promising option for NLO applications in the future.

Influence of Polar Solvents on Third-Order Nonlinear Optical Features of Methyl Red Dye.

This study emphasis the solvent effect on third-order nonlinear optical (NLO) features of methyl red (MR) dye dissolved in polar solvents including ethanol, methanol, acetone, 1-propanol, DMF and DMSO using low power diode laser. Z-scan technique operating at 405nm wavelength, is used to estimate the third-order NLO features of MR dye in various solvents. The dye discloses self-defocusing nonlinear index of refraction (n2), which is determined to be the order of 10-7 cm2/W. The nonlinear coefficient of absorption (β) of MR dye displays both negative and positive value owing to saturable absorption (SA) and reverse saturable absorption (RSA), respectively. The real and imaginary components of the third-order NLO susceptibility of MR dye in polar solvents are measured to be the order of 10-6 esu and 10-7 esu, respectively. The dye exhibits a large NLO susceptibility in DMSO, which is estimated to be 1.21 × 10-6 esu. The effect of solvent spectral features on MR dye is determined by applying a multi-parameter scale called Kamlet-Abboud-Taft. The experiment results indicate that MR dye is a promising NLO material that may find applications in photonics and optoelectronics.

Design and realization of plasmonic nanostructures with large third-order optical nonlinearity

We designed an optical structure comprising plasmonic and dielectric materials that exhibits large third-order optical susceptibility and low-power consumption. Finite-difference time-domain simulation results were used to select tightly-packed gold nanosphere (AuNS) film, indium tin oxide (ITO) films, and gold (Au) thin film to construct AuNS/ITO/Au sandwiched nanostructures. Local-field enhancement factors up to 425 and large third-order optical susceptibility (χ(3)) with an amplitude order of 4.4 × 10−2 esu were achieved under an excitation power of 0.1 mW. These χ(3) results are exceptionally high, thereby rendering AuNS/ITO/Au a promising material for future applications in optical switches and related nonlinear optical devices.

Third Harmonic Generation in Thin NbOI2 and TaOI2.

The niobium oxide dihalides have recently been identified as a new class of van der Waals materials exhibiting exceptionally large second-order nonlinear optical responses and robust in-plane ferroelectricity. In contrast to second-order nonlinear processes, third-order optical nonlinearities can arise irrespective of whether a crystal lattice is centrosymmetric. Here, we report third harmonic generation (THG) in two-dimensional (2D) transition metal oxide iodides, namely NbOI2 and TaOI2. We observe a comparable THG intensity from both materials. By benchmarking against THG from monolayer WS2, we deduce that the third-order susceptibility is approximately on the same order. THG resonances are revealed at different excitation wavelengths, likely due to enhancement by excitonic states and band edge resonances. The THG intensity increases for material thicknesses up to 30 nm, owing to weak interlayer coupling. After this threshold, it shows saturation or a decrease, due to optical interference effects. Our results establish niobium and tantalum oxide iodides as promising 2D materials for third-order nonlinear optics, with intrinsic in-plane ferroelectricity and thickness-tunable nonlinear efficiency.

Multifaceted Study of a Y-Shaped Pyrimidine Compound: Assessing Structural Properties, Docking Interactions, and Third-Order Nonlinear Optics.

In this study, we report the synthesis of a new compound, N4,N4-dimethyl-2-(methylsulfanyl)-N6-(4-phenoxyphenyl)pyrimidine-4,6-diamine (DMS), and its comprehensive analysis through structural and spectroscopic characterizations, reactivity parameters, and nonlinear optical properties, utilizing a combination of experimental and computational techniques. The experimental aspect of the investigation encompassed structural characterization using X-ray diffraction and spectroscopic assessments employing Fourier-transform infrared, Raman, and nuclear magnetic resonance techniques, along with thermal analysis. Our computational approach involved density functional theory (DFT) calculations and molecular dynamics (MD) simulations to examine the local reactivity properties of DMS. We employed fundamental reactivity descriptors to evaluate DMS's local reactivity and utilized MD simulations to identify DMS atoms engaging in significant interactions with water molecules. We conducted periodic DFT calculations on DMS's crystal structure to investigate the contributions of specific atoms and groups to the compound's overall stability as well as to analyze noncovalent interactions between DMS molecules. We assessed the nonlinear optical properties through dynamic second hyperpolarizability and third-order nonlinear susceptibility calculations. Additionally, we conducted a comparative analysis of the static and dynamic second hyperpolarizability for the DMS molecule within the sum-over-states framework. The obtained value for the third-order nonlinear susceptibility, (λ = 1907 nm), exceeds those of other organic materials reported in previous studies, indicating that the DMS crystal holds promise as a nonlinear optical material for potential application in photonic device fabrication. Furthermore, molecular docking studies were performed with the 3E5A, 4EUT, and 4EUU proteins, yielding binding affinities of -8.1, -8.2, and -8.3 kcal/mol, respectively, in association with the ligand.

Enhanced optical third-harmonic generation in phase-engineered nanostructured Zn1−x Cd x S thin films for optoelectronic device applications

A polycrystalline nanostructured thin film of zinc cadmium sulfide was meticulously fabricated on a glass substrate using the thermal evaporation method physical vapor deposition within a vacuum chamber. Different doping concentrations were introduced by varying the cadmium (Cd) content, resulting in Zn1-x Cd x S films with Cd concentrations ranging from x = 0.00–0.20 wt %. The impact of Cd doping on the third-order nonlinear optical (TONLO) properties of these films was thoroughly studied using the Z-scan method, employing a diode-pumped solid-state continuous-wave laser. To gain insight into the structural characteristics, the Zn1-x Cd x S thin films underwent analysis through x-ray diffraction. Optical studies confirmed the tunability of the optical band gap (Eg) in the Zn1-x Cd x S films, ranging from 3.88 eV for undoped ZnS to 2.80 eV for the film fabricated with 20 wt. % of Cd-content. This significant reduction in ‘Eg’ renders the films highly suitable for use as absorbing layers in applications such as solar cells and optoelectronics. Surface morphology analysis, performed via field emission scanning electron microscopy, revealed noticeable alterations with increased Cd doping. Significantly, the doped films exhibited a substantial redshift in the band edge and an increase in transmittance within the visible and near-infrared regions. The investigation of TONLO properties, including the nonlinear absorption coefficient (β), nonlinear refractive index (n 2) and susceptibility χ(3), yielded values ranging from 3.15 × 10−3 to 8.16 × 10−3 (cm W−1), 1.65 × 10−8 to 7.45 x 10–8 (cm2 W−1), and 3.12 × 10−5 to 7.86 × 10−5 (esu), respectively. These results indicate the presence of self-defocusing nonlinearity in the films. Overall, the outcomes underscore the potential of Cd-doped ZnS nanostructures in modifying surface morphology and enhancing NLO characteristics. Zn1-x Cd x S thin films exhibit promise for applications in nonlinear optical devices, as evidenced by these encouraging findings.

The band gap and nonlinear optical susceptibility of SrSn1-xVxO3 films

Perovskite-type oxide SrSn1-xVxO3 thin films with different concentrations x = 0.1–0.9 were fabricated by using pulsed-laser deposition, and the effects of V doping on the structure, optical band gap and the third-order optical nonlinearity were systematically investigated. With the increase of x value, the lattice parameters of SrSn1-xVxO3 decrease from 3.997 to 3.862 Å gradually, while the optical band gaps firstly increase and then decrease with boundary at x = 0.3. The third-order nonlinear optical responses were studied via the z-scan technique. The closed-aperture measurements show a negative nonlinear refractive index n2, and the open-aperture measurements demonstrate a saturable absorption β. Both the n2 and β responses vary with the increase of V doping level. The metal-oxygen chemical bond along with the localized V5+Sn2+V5+ complex contribute to the enhancement of optical nonlinearity, and the highest value of third-order susceptibility χ(3) is observed in SrSn0.5V0.5O3 film.

Investigation of structural, linear, and nonlinear optical properties of nanosized zinc oxide and cadmium oxide particles ingrained in graphitic carbon nitrides

The study aims to evaluate the third-order optical nonlinearity caused by laser irradiation in transition metal oxide incorporated into graphitic carbon nitrides. The work describes the synthesis of nano-sized hybrid g-C3N4/ZnO (14%) and g-C3N4/CdO (14%). Nano-sized transition metal oxides: ZnO and CdO, have been prepared by thermally decomposing the organic precursors; Zinc Acetate Dihydrate, Cadmium Acetate Dihydrate, and Urea at 873 K. Graphitic carbon nitrides are synthesized from urea, which also functions as a reducing agent. The synthesized sample’s structural and morphological characterization are investigated using x-ray diffraction (XRD), Fourier transforms infrared (FTIR), UV–vis. spectra, field emission scanning electron microscopy (FESEM), and energy dispersive x-ray spectroscopy (EDX). The grain size of the ZnO and CdO nanoparticles is observed to be ∼21 nm and ∼28 nm, respectively. The absorption in the samples is found to be 250–450 nm and transmit the light in the visible spectrum as observed in UV–vis. spectra. The bandgap values calculated from Tauc’s plot for the hybrid structure of g-C3N4/ZnO and g-C3N4/CdO are found to be 2.97 eV and 2.30 eV.The z-scan method is adopted to evaluate the nonlinear susceptibility (χ3), intensity-dependent absorption coefficient (β), and nonlinear index of refraction (n2) using a pulsed Nd:YAG laser (∼532 nm). The results of the composite of g-C3N4/ZnO and g-C3N4/CdO show good third-order susceptibility and hence are useful for use as an optical limiter.

Thickness-dependent nonlinear optical absorption of Sb2Se3 films grown by physical vapor deposition

Both experimental and theoretical works have demonstrated that two-dimensional materials exhibit strong thickness-dependent electronic and linear optical properties. However, the nonlinear optical (NLO) effect with respect to the thickness still needs to be further investigated, which is of great significance to design different photonic devices. Herein, we develop the physical vapor deposition technique to prepare a series of antimony selenide (Sb2Se[Formula: see text] films. The relationship between the thickness of Sb2Se3 film and the NLO absorption was investigated by a [Formula: see text]-scan system under 35[Formula: see text]fs, 800[Formula: see text]nm laser excitation. The result shows the thicker Sb2Se3 film ([Formula: see text]50[Formula: see text]nm) performs a larger third-order NLO susceptibility (Im[Formula: see text] approximately [Formula: see text] esu, which can be interpreted by the stronger photon absorption, lower saturable intensity, and larger absorption cross-section of ground-state. More importantly, the Im[Formula: see text] absolute value of thick Sb2Se3 film is also far larger than those of graphene, black phosphorus, transition metal dichalcogenide, MXenes, and heterostructure. This work demonstrates that Sb2Se3 film is an excellent saturable absorber and provides a promising application in nonlinear photonics.

Enhancement of nonlinear optical effects of pure and Mn-doped CsPbBr3 perovskite films by external voltage

CsPbBr3 and Mn:CsPbBr3 nanocrystal (NC) films were prepared on indium tin oxide (ITO) glass by a slow solvent evaporation method. The ITO layer was applied a voltage to enhance the nonlinear optical (NLO) properties of CsPbBr3 and Mn:CsPbBr3 nanocrystal (NC) films. When the voltage is zero, the Z-scan results show that the nonlinear absorption (NLA) coefficients β of CsPbBr3 and Mn:CsPbBr3 NC films are 1.60 × 103 cm/GW and 1.54 × 104 cm/GW, respectively. The nonlinear refraction (NLR) coefficients γ of CsPbBr3 and Mn:CsPbBr3 NC films are 2.07 × 10−5 cm2/W and 2.48 × 10−5 cm2/W, respectively. Subsequently, the voltages of 5.03–13.42 V were applied to the ITO layer. Finally, when the voltage is 13.42 V, the β values of CsPbBr3 (1.75 × 104 cm/GW) and Mn:CsPbBr3 (3.98 × 104 cm/GW) NC films are 10.9 and 2.6 times higher than those without the applied voltage, respectively. The γ values of CsPbBr3 and Mn:CsPbBr3 NC films are 3.73 × 10−5 cm2/W and 3.88 × 10−5 cm2/W, respectively. This research proposes an effective method to improve the third-order NLO performances of CsPbBr3 and Mn:CsPbBr3 NC films by applying voltage.

Designed metal-organic π-clusters combining the aromaticity of the metal cluster and ligands for a third-order nonlinear optical response.

The pivotal role of clusters and aromaticity in chemistry is undeniable, but there remains a gap in systematically understanding the aromaticity of metal-organic clusters. Herein, this article presents a novel metal-organic π-cluster, melding both metal-organic chemistry and aromaticity, to guide the construction of structurally stable Os-organic π-clusters. An in-depth analysis of these clusters reveals their bonding attributes, π-electronic composition, and origins of aromaticity, thereby confirming their unique metal-organic π-cluster properties. Furthermore, the Os5 cluster exhibits a promising third-order nonlinear optical (NLO) response, attributable to its narrow band gap and uniform electron/hole distribution, suggesting its potential as an optical switching material. This research introduces a fresh perspective on clusters, centered on delocalization, and broadens the domain of aromaticity studies. It also presents a novel method for designing efficient third-order NLO materials through consideration of the structure-activity relationship.

Third-order optical nonlinearities of Nb4C3 MXene and its application as an ultra-broadband mode-locker

The broadband nonlinear optical properties of Nb4C3 MXene were investigated using Z-scan techniques. Using Nb4C3 MXene, a single saturable absorber operating at both 1560 and 1930 nm was successfully fabricated for fiber laser mode-locking.