Nonlinear Optical Characteristics Research Articles

Synthesis, characterization, and nonlinear optical properties of copper (II) ligand Schiff base complexes derived from 3-Nitrobenzohydrazide and benzyl

A new series of Cu (II) complexes were prepared using Schiff base ligand of N–N′-(1,2-diphenyl ethane-1,2-diylidene)bis(3-Nitrobenzohydrazide). The prepared ligand and Cu (II) complex were characterized using various physicochemical investigations such as X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), and Energy dispersive X-ray analysis (EDX), Fourier Transform Infrared (FT-IR), {}^{13}C Nuclear Magnetic Resonance (NMR), {}^{1}H NMR, Diffuse Reflectance Spectroscopy (DRS), Vibrating Sample Magnetometer (VSM), and Z-Scan technique (Nonlinear optical (NLO) properties). In addition, the prepared samples have been examined for their NLO characteristics with the help of the Density Functional Theory calculations which proved that the Cu (II) Complex is more polarized than Ligand. According to XRD and FESEM results, the nanocrystalline nature of the samples is confirmed. The metal-oxide bond assigned in the functional studies by FTIR. Magnetic studies demonstrate weak ferromagnetic and paramagnetic nature for Cu (II) complex and diamagnetic nature for the ligand, respectively. DRS spectrum exhibited higher reflectance for Cu (II) than the ligand. The band gap energies of the synthesized samples were estimated by employing the Tauc relation and Kubelka–Munk theory on reflectance data and found to be 2.89 eV and 2.67 eV for Cu (II) complex and ligand, respectively. Extinction coefficient and refractive index values were calculated using the Kramers–Kronig method. The z-scan technique was applied to estimate the NLO properties by a 532 nm Nd:YAG laser.

Synthesis–dependent structural and optoelectronic properties of semicrystalline LiNbO3:SiO2 hybrid silicates

Polycrystalline ceramics of lithium niobate (LNO) were prepared via standard hydrothermal and solid–state chemistry reactions, and by the sol–gel method implementing acrylamide polymerization. Congruent LiNbO3 trigonal perovskite phases crystallized in the R3c (161) space group [3 m (C3v) polar point group] were obtained in all cases. Depending on the implemented synthetic route, the average grain and crystallite sizes were estimated to 127–895 nm and 35–40 nm, respectively. As prepared LNO powders were embedded in a–SiO2 mesoporous sonogel networks at different doping rates to conform LiNbO3:SiO2 semicrystalline hybrid silicates with differentiated structural and optoelectronic (OE) properties. Intensive morphological, structural, spectroscopic, and nonlinear optical (NLO) characterizations were performed to explore these novel composites’ structural and photophysical properties for lead–free ferroelectric and optical applications. Results show that the massive porosity of the sonogel glasses and related defective bonding environment promote generalized host–guest molecular interactions influencing the oxidation states and radiative transitions of the dopant compounds via surface–assisted mechanisms and chemical charge–transfers. Additionally, due to the ferroelectric nature of LNO and average macroscopic alignment attained along the polycondensation stage of the solid solutions, SHG activity was observed from the hybrid sonogel (HSG) phases. Bulk NLO susceptibilities and molecular hyperpolarizabilities were estimated within the 9.62 × 10−11 and 10−23 esu range, respectively. Finally, depending on the synthesis methodology and in–gap hybridized levels, energy gap (Eg) narrowing was also observed for all LNO/HSG glasses, showing Eg values as low as 3.05 eV.

Passively Q-switched Nd:GdVO4 lasers with core–shell ZIF-8@ZIF-67 saturable absorber at 1 and 1.34 µm

In the current paper, the polyhedral ZIF-8@ZIF-67 nanomaterials were successfully synthesized, and the nonlinear optical features were measured through the open-aperture (OA) Z-scan technique. By employing the ZIF-8@ZIF-67 as a saturable absorber (SA), the passively Q-switched (PQS) Nd:GdVO4 lasers were demonstrated at 1064 and 1340 nm for the first time. From the 1 µm Q-switching operation, we achieved the shortest stable pulse of 85 ns under the incident excitation of 7.15 W, while the pulse repetition rate was 975 kHz. In the PQS laser at 1340 nm, the pulse width was measured as short as 79 ns with a pump level of 9.98 W, and the pulse repetition rate was 767 kHz. These results imply that the ZIF-8@ZIF-67 SA has huge advantages in the PQS laser with stable short pulse generation under the high excitations in the near-infrared (NIR) region.

Nonlinear optical phase shift in blood plasmas for neoplasia diagnosis.

Detecting cancer at an early stage is crucial for timely treatment and better chances of survival. This research focuses on a scanning method for detecting cancer by examining the nonlinear optical characteristics of blood plasma samples. The study used both cancerous and noncancerous plasma samples and presented the results statistically by utilizing an incident laser power-dependent nonlinear optical phase shift variable called ζ in the Z-scan technique. The results showed a clear difference between the cancerous and non-cancerous samples with an accuracy of 92%. Furthermore, the study suggests the potential for measuring the cancer staging from the cancerous plasma. The study also confirmed a significant difference in ζ for plasma samples undergoing chemotherapy. A red laser with high power (above 18mW) was used to avoid the involvement of fluorophores or other chemical reagents in the plasma samples during the measurement.

Effect of different solvents, molecular level vibrational energies, electronic, electrostatic, donar-acceptor and pharmaceutical studies on 3-methoxy phenyl acetonitrile- anti depressant agent

The most economical method for analyzing molecular structure is density functional theory (DFT), which has several applications in the study of vibrational spectrum biological systems. In the context of biological in addition to NLO behavior, the density functional theory (DFT) technique has numerous purposes. It turned out to be the most financially sound approach for examining molecular geometry. 3-Methoxy phenyl acetonitrile (3MPAN) has been optimized and its skeletal parameters were computed using the basis function 6–311++ G(d,p). HOMO and LUMO analytics have been used to determine the transfer of charge within the molecule. By detecting internal charge transfer, hyperconjugation, and stabilization energy, the NBO research has been used to confirm the molecule's stability. Mulliken's charges and molecular electrostatic potential were thoroughly investigated utilizing DFT techniques. B3LYP basis functionals were used to look at the NLO properties of the drug molecule. Condensed Fukui functions and global descriptors have been extensively used to study the reactive sites and reactivity of the pharmacological molecule. 29.85 Kcal/mol equilibrium energy is the greatest one occurred between O1 of LP(2) to π*(C5-C8). In order to investigate solvation analysis, various solvents were used. Solvents drastically altered the molecule's global characteristics and structural reactivity. Compared to other sol-vents, methonal has the largest band gap value of 5.619 eV. The substance under study has extraordinary NLO (non-linear optical) characteristics. For both the gas phases and solvents, ELF, LOL and RDG were stimulated. Although and drug-likeness were used to support the bioactivities. The fact that this chemical adheres to five Lipinski's rule means therefore, ingesting effective dose of similar compounds should not pose an issue. The results of docking studies demonstrated the effectiveness of the ligand under research as an anti-depressant medication.

Hyperconjugation and Hydrogen Bonding Interactions Effect with the Nonlinear Optical Features of 4-Chlorophenoxy Acetonitrile: An Experimental and DFT Methodology

The compound 4-cholorophenoxy acetonitrile (CPAN) was examined using Nonlinear optical properties in the current study. With the aid of normal coordinate analysis and the SQMFF methodology, vibrational analysis of FT-IR and FT-Raman has been conducted. Natural bond orbital analysis is used to analyze the electronic stability of the compound created by hyper conjugative contacts and charge delocalization, and the Frontier molecular orbital energy gap confirms the molecule’s optical activity. ESP recognizes the nucleophilic and electrophilic areas of molecules, and the chemical implication of molecules was explained using ELF, LOL. Third-order nonlinear optical (NLO) investigations are carried out on a CPAN crystal using the Z-scan technique, and optical properties are established.

Linear and Nonlinear Optical Properties of Anthocyanin Dye from Red Cabbage in Different pH Solutions

This article studied some linear and nonlinear optical characteristics of different pH solutions from anthocyanin dye extract at 180 oC from red cabbage. First, the linear spectral characteristics, including absorption and transmittance in the range 400-800 nm for anthocyanin solution 5% v/v with different pHs, were achieved utilizing a UV/VIS spectrophotometer. The experimental results reveal a shift in the absorption toward the longer wavelength direction as pH values increment. Then, the nonlinear features were measured using the Z-scan technique with a CW 532 nm laser to measure the nonlinear absorption coefficient through an open aperture. A close aperture (diameter 2 mm) calculates the nonlinear refractive index. The open Z-scan shows that as the pH increases, the sample decreases transmittance, indicative a two-photon absorption process, and the samples act as a collecting lens for the laser beam. In contrast, the results with a closed Z-scan indicate that the nonlinear absorption coefficient displays a self-focusing nonlinearity. Also, the nonlinear susceptibility decreased by increasing the value of the pH solution. Due to obvious anthocyanin dye nonlinearity dependence value on dye pH, it is possible to use the natural anthocyanin dye as a photonic device

Tunable, efficient, ultrafast broadband nonlinear optical properties of TiO2–loaded complex phosphate glasses

On account of their excellent optical transparency from ultraviolet to far infrared spectral regions, phosphate glasses have become interesting nonlinear optical (NLO) materials for photonic nonlinear devices. However, small NLO coefficients tend to limit the usage of phosphate–based glasses in nonlinear photonic devices. Herein, we explored the NLO tunability in multicomponent phosphate glasses by increasing the coordination of orthophosphate (PO4)3– structural units with a great number of AlO4 groups through the addition of titanium dioxide (TiO2) in the composition. The NLO absorption and refraction characteristics were ascertained using open and closed–aperture Z–scan configurations respectively in a broadband spectral region ranging from 400 nm to 1200 nm under an ultrafast regime. The Z–scan results illustrate the increase of nonlinear susceptibility of glasses with titanium dioxide content in the composition due to the formation of non–π–conjugated orthophosphate groups which are in connection with AlO4 units. Typically, at 400 nm excitation, the NLO susceptibility improved by 119.91% upon addtion of 5 mol% of TiO2. The outcomes of the study acknowledge a new approach for conceiving highly NLO active phosphate glasses while maintaining deep–ultraviolet transparency through the polymerization of (PO4)3−groups. Consequently, the strategy explored in this work might pave the way for achieving the high NLO features of phosphate–based glasses to excel in their usage in data storage, signal transmission, optical limiting, and harmonic generation functionalities.

Second harmonic generation on crystalline organic nanoclusters under extreme nanoconfinement in functionalized silica–benzil composites

We demonstrate a series of organic–inorganic nanocomposite materials combining the mesoporous silica (PS) and benzil (BZL) nanocrystals embedded into its nanochannels (6.0–13.0 nm in diameter) by capillary crystallization. One aims to design novel, efficient nonlinear optical composite materials in which inactive amorphous host PS-matrix provides a tubular scaffold structure, whereas nonlinear optical functionality results from specific properties of the deposited guest BZL-nanocrystals. A considerable contraction of the BZL melt during its crystallization inside the silica nanochannels results in a formation of the texture consisting of (221)- and (003)-oriented BZL nanoclusters (22 nm in length), separated by voids. Specificity of the textural morphology similarly to the spatial confinement significantly influences the nonlinear optical features of composite PS:BZL materials being explored in the second harmonic generation (SHG) experiment. The light polarization anisotropy of the SHG response appears to be considerably reduced at channel diameters larger than 7 nm apparently due to the multiple scattering and depolarization of the light on randomly distributed and crystallographically oriented BZL-nanoclusters. The normalized SHG response decreases nonlinearly by more than one order of magnitude as the channel diameter decreases from 13.0 to 6.0 nm and vanishes when spatial cylindrical confinement approaches the sizes of a few molecular layers suggesting that the embedded BZL clusters indeed are not uniformly crystalline but are characterized by more complex morphology consisting of a disordered SHG-inactive amorphous shell, covering the channel wall, and SHG-active crystalline core. Understanding and controlling of the textural morphology in inorganic–organic nanocrystalline composites as well as its relationships with nonlinear optical properties can lead to the development of novel efficient nonlinear optical materials for the light energy conversion with prospective optoelectronic and photonic applications.

An experimental and DFT investigations of fused ring anthracenyl chalcones with effective modification in acceptor moiety: Nonlinear optical and optical limiting response

AbstractThe significance of the anthracene moiety on nonlinear optical (NLO) characteristics is thoroughly examined. The presence of strong electron donor and acceptor groups, large and prolonged conjugation transfer axis, amplifies the push–pull action and increases NLO responses. The values of χ3 obtained for AC derivatives are considerably larger (10−3 esu), indicating that they accurately reflect NLO reactions. According to the optical limiting (OL) investigation, AC has a strong limiting behavior with action beginning at 1.6 KW/cm2. The relationship between transmittance and intensity has demonstrated their potential use in OL applications. Nonlinear optical studies show that all conjugated anthracene chalcones are potential materials for OL devices.

Linear and nonlinear optical characterization of tellurium dioxide (α-TeO2) for generation of terahertz radiation using time-domain spectroscopy.

This paper reports the linear and nonlinear optical characterization of α-T e O 2 crystal in the optical and terahertz domains for efficient terahertz (THz) generation using a difference frequency mixing technique. We have ascertained the optical properties such as refractive index, absorption coefficients, real and imaginary dielectric constants, and coherence length l c=280m m at 1.77THz range using an indigenously developed THz spectrometer. The value of refractive index was ascertained from temporal and spectral THz profiles of the crystal and employed for calculating the Type I phase-matching angle, i.e.,θ=21.15∘ for the generation of tunable radiation between the 0.1 and 1.9THz range. The figure of merits in the optical and THz domains lie between the 0.02-0.015 range. The effective bandwidth of the crystal lies between the 0.1 and 3.0THz range.

Nonlinear optical characteristics of germanium and its application for generating bound state solitons within Er-doped fiber laser

Recently, germanium (Ge) was also considered as the two-dimensional (2D) material saturable absorber (SA) because of its excellent nonlinear saturable absorption properties. However, the research of Ge SA Er-doped fiber laser is still rare. In this work, bound state solitons were demonstrated in Ge SA Er-doped fiber laser. To be best of our knowledge, no previous work has ever achieved that. Three kinds of bound state solitons with 9.77 MHz fundamental frequency were investigated, indicating that Ge has excellent nonlinear optical characteristics to promote the development of bound state soliton.

Efficient synthesis of nicotinaldehyde-based crystalline organic derivatives: Comparative analysis between experimental and DFT study

The analogues of pyridine ring structures demonstrate various physiological as well as biological activities. The current research is based on experimental along with computational investigations of two new phenyl substituted nicotinaldehyde derivatives; 2-(2,4-difluorophenyl)pyridine-3-carbaldehyde (DFPPC) and 2-(2,5-dichlorophenyl)pyridine-3-carbaldehyde (DCPPC) . For structural optimization of DFPPC as well as DCPPC and to explore nonlinear optical properties, computational quantum chemical analysis was executed via density functional theory (DFT) calculations by employing M06 level with 6–311G(d,p) basis set. A consensus among theoretical (DFT) and experimental (SC-XRD) results was observed by the calculation of geometric parameters. Molecular electrostatic potential (MEP), natural bond orbital (NBO) analysis, natural population analysis (NPA), nonlinear optical (NLO), global reactivity parameters (GRPs), and frontier molecular orbital (FMO) exploration were carried out at M06/6–311G(d,p), to comprehend hyper-conjugative interactions, electron density, electronic communications and oscillation strength. The HOMO/LUMO energy gap of DCPPC (5.108 eV) was observed to be lower than DFPPC i.e., 5.170 eV, which resulted in its higher value of global softness (0.196 Eh) along with lower global hardness (2.554 Eh) value than DFPPC. The NLO attributes of DFPPC as well as DCPPC was calculated by evaluating the total dipole moment (μtot), average linear polarizability ⟨α⟩ and second hyperpolarizability (γtot) at aforementioned level. From the NLO results, it was observed that DCPPC exhibits a higher average linear polarizability value such as 3.0772 × 10−23esu than DFPPC i.e., 2.6116 × 10−23esu . Whereas, higher results of γtot were observed for DFPPC i.e., 3.2455 × 10−35 than DCPPC (3.0708 × 10−35esu). The distinguished NLO characteristics revealed that, both the chromophores (DFPPC and DCPPC) can be recognized as highly efficient NLO materials for future applications.

Dispersion of optical constants of Si:PbGeO crystal in the terahertz range

Objectives. Advances in laser physics over the last decade have led to the creation of sources of single-period electromagnetic pulses having a duration of about 1 ps, corresponding to the terahertz (THz) frequency range and a field amplitude of several tens of MV/cm. This allows the electrode-free application of an electric field to a ferroelectric for observing not only the excitation of coherent phonons, but also ultrafast (at the sub-picosecond timescale) dynamic polarization switching. To detect polarization switching, a pump-probe technique is used in which a THz pulse is used with an optical probe. Since its intensity is proportional to the square of the polarization, the signal of the optical second harmonic is used to measure polarization switching under the action of a THz pulse. To evaluate switching efficiency, both linear (refractive index and absorption coefficient) and non-linear optical characteristics (quadratic and cubic susceptibilities) are required. For any application of ferroelectric crystals in the THz range, knowledge of the relevant linear optical characteristics is also necessary.Methods. The technique of THz spectroscopy in the time domain was used; here, a picosecond THz pulse transmitted through the crystal is recorded by strobing the detector with a femtosecond optical pulse. The THz-induced dynamics of the order parameter in a ferroelectric was studied by detecting the intensity of a nonlinear optical signal at the frequency of the second optical harmonic.Results. The transmission of a THz wave and the intensity of second harmonic generation on a lead germanate crystal doped with silicon in the time and spectral domains were measured. On this basis, the absorption coefficient dispersion and cubic nonlinear susceptibility were calculated in the range of 0.5-2.0 THz. The presence of a region of fundamental absorption near the phonon modes was confirmed along with a resonant enhancement of the cubic nonlinear susceptibility for two phonon modes Ω1 = 1.3 THz and Ω2 = 2.0 THz.Conclusions. The proposed technique is effective for analyzing the dispersion of the optical characteristics of ferroelectric crystals. The significantly improved spectral resolution (0.1 THz) increases the accuracy of determining nonlinear susceptibility due to the detailed analysis of the linear and nonlinear contributions to the second harmonic intensity.

Influence of Zn2+ doping on the nonlinear optical limiting characteristics of Bi2WO6 nanostructures for optical device applications

The concentration-dependent non-linear absorption and optical limiting action of Zn-doped Bi2WO6 nanostructures synthesized by co-precipitation method is reported. The incorporation of Zn2+ ions in the host matrix was confirmed by X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) analysis. The optical properties and charge transfer mechanism were analyzed by UV-DRS and Photoluminescence studies. The surface morphology was studied by HRTEM and HRSEM techniques. The Nonlinear optical characteristics of the nanostructures were investigated by Q-switched nanosecond Nd: YAG laser pulses at 532 nm using Z-Scan technique. The open aperture Z-scan results exhibited reverse saturable absorption (RSA) for all the samples. The mechanism for RSA is attributed to Two-Photon Absorption (2 PA) via sequential process. The non-linear absorption coefficient (β) of Zn-doped Bi2WO6 nanostructure was found to increase while the optical limiting threshold decrease with increase in Zn doping concentration. The observed nonlinear absorption can be attributed to the impact of dopants on crystal structure, particle size, creation of oxygen vacancies, and defects on the host lattice.

Exploring the molecular spectroscopic and electronic characterization of nanocrystalline Metal-free phthalocyanine: a DFT investigation

The molecular structure optimization and harmonic vibrational frequencies of nanocrystalline metal-free phthalocyanine were investigated using the density functional theory (DFT) implemented in the Gaussian 09 program through B3LYP/6-311G basis set. Thermodynamic and non-linear optical (NLO) characteristics, total dipole moment, HOMO–LUMO energies, natural population analysis (NPA), and global chemical reactivity descriptors were examined. TD-DFT evaluations were used to interpret the electronic absorption. The experimental results and computed values match up adequately. An essential component of photovoltaic devices and the optimized HOMO–LUMO energy gap (2.16 eV) were estimated and compared with those obtained experimentally. The energy band model was used to check the probability of the transition type and estimate the values of energy gaps, which were found to be indirectly allowed. To provide a comprehensive picture for the characterization and determine the activation energy of the charge carriers, the DC electrical conductivity was also examined. It was revealed to have a value between 0.767 and 1.288 eV depending on the temperature range.

Layer‐By‐Layer Assembly of Asymmetric Linkers into Non‐Centrosymmetric Metal Organic Frameworks: A Thorough Theoretical Treatment

AbstractLayer‐by‐layer synthesis of surface‐coordinated metal–organic frameworks (SURMOF) enables the assembly of asymmetric, dipolar linkers into non‐centrosymmetric pillar‐layered structures. Using appropriate substrate terminations can yield oriented growth with the dipoles aligned perpendicular to the surface. The aligned pillar linkers give rise to a built‐in electrostatic field. In addition, the non‐centrosymmetric structure of the SURMOF gives rise to intriguing nonlinear optical features, such as second harmonic generation. Previous research with methyl‐functionalized bipyridine pillar linkers have demonstrated that this approach works in principle, but so far the total degree of alignment is only very small. Herein, a multiscale modelling approach is presented for in‐silico SURMOF assembly to identify and overcome limitations in the growth of pillar‐layered SURMOFs and to develop a strategy to maximize linker alignment. Using master equation models and kinetic Monte Carlo simulations, it is found that the formation of a highly ordered state corresponding to the thermodynamic equilibrium is often prevented by long‐lasting transient effects. Based on ab initio binding energies for a wide selection of hypothetical pillar linkers, a fast‐binding, slow‐relaxation scheme is able to be identified during the SURMOF growth for a range of different pillar linkers. These observations allow them to derive a rational strategy for the design of novel linkers to yield SURMOF‐based non‐centrosymmetric materials with substantially improved properties.

Spectroscopic characterization and quantum-chemical analysis of hydrazinyl thiazol-4(5H)-one functionalized materials to predict their key electronic and non-linear optical behavior

Organic chromophores are desirable as efficient nonlinear optical (NLO) substances because of their structural tunability, easy synthesis and promising NLO response. Herein, we synthesized series of organic compounds (EHT1-EHT5) containing hydrazinylthiazol-4(5H)-one (HT) as a base and explored their nonlinear optical (NLO) properties through quantum chemical investigations. Novel hydrazinylthiazol-4(5H)-ones were synthesized via two step synthetic approach. The synthesized structures were initially solved by different spectroscopic techniques. The authentication of the prepared structures was achieved with high resolution mass spectrometry (HRMS). Density functional theory (DFT) studies were executed at M06/6–311 G (d,p) functional. The optimized structures were used to perform further analysis including frontier molecular orbitals (FMOs), UV- Visible (UV–Vis), natural bond orbitals (NBOs), density of states (DOS), transition density matrix (TDM) along with nonlinear optical (NLO) characteristics. The quantum chemical insights led towards minimum Egap (4.797 eV) for EHT3 among all the compounds. Additionally, the outcomes of FMOs analysis were also supported by density of state (DOS) which further elucidated the proficient charge transference between HOMO and LUMO. The NBOs analysis revealed that all compounds had promising push-pull process through the existence of electron-accepting as well as donating groups. UV–Vis analysis indicated that all the investigated compounds (EHT1-EHT5) showed absorption wavelengths in the UV–Vis region, ranging from 290.1 to 303.7 nm. Among all these examined compounds (EHT1-EHT5), EHT3 displayed the highest value of λmax (303.717 nm) owing to its minimum band gap (4.028 eV). Furthermore, maximum values of first and second-order hyperpolarizabilities (βtot andγtot) were achieved for EHT3 as 7.756, 3.029 × 10−23 and 6.984 × 10−35esu, respectively. In summary, our investigation provides new insights for the potential use of HT-based organic compounds (EHT1-EHT5) in future NLO applications.

Gold Nanomaterial‐Based Optical Modulators for Wideband Pulse Laser Generation

Pulsed lasers have wide applications in several fields, such as basic research, telecommunications, and industrial materials processing. A saturable absorber (SA) is a key component for pulse laser generation. However, the current SAs exhibit certain limitations. Hence, developing new nonlinear optical materials as SAs for pulse lasers generation is significantly important in ultrafast photonics and related applications. Metallic nanomaterials have attracted considerable attention because of their higher nonlinearity coefficients and wideband nonlinear response, which are induced by the surface plasmon resonance (SPR) effect. The SPR effect depends on the size and morphology of materials. Thus, the nonlinear optical absorption effect of gold nanomaterials for pulse laser generation must be explored. In this review, the optical properties of gold nanomaterials are introduced, including SPR absorption, photoluminescence properties, and surface‐enhanced Raman scattering effect. Then, the synthesis and characterization of different gold nanomaterials are reviewed. Subsequently, the nonlinear optical characteristics and devices based on gold nanomaterials are also introduced. Furthermore, the generation of different types of lasers using gold nanomaterial‐based devices is also reviewed. A comparison between gold nanomaterials and other SA materials is presented. Finally, the conclusion and outlook on gold nanomaterial‐based nonlinear optical devices are presented.

Nonlinear Optical Properties and Phototunable Absorption of a Substituted Dihydroazulene-Vinylheptafulvene Pair of Photochromes.

Quantum calculations were used to study UV-vis absorption properties and nonlinear optical characteristics of a variety of substituted dihydroazulene (DHA)/vinylheptafulvene (VHF) photoswitches. The absorption properties are substantially based on the position and nature of the substituent. In general, electron-donating groups cause red shifts compared to the parent compound. Any electron-withdrawing group, on the other hand, would generate a blue shift. Furthermore, the steric effect at some positions is accountable for the loss of planarity and, as a response, a decrease in electronic conjugation within the molecule, which in most cases result in blue shifts in maximum absorption. The purpose of this research is to investigate the influence of substitution at the seven-membered ring of the DHA/VHF system on the absorption spectra and nonlinear optical characteristics of dihydroazulene photoswitches. UV-vis spectra and hyperpolarizability are determined since a prospective photoswitch should have a minimum overlap of absorption spectra from both isomers. Furthermore, the differential in hyperpolarizability between DHA and VHF is critical for practical applications.