Third-order Nonlinear Absorption Coefficients Research Articles

Giant excited-state absorption in resonant absorption band and intensity-depend ultrafast sign switching of nonlinear absorption in azonaphthalene compound

The ultrafast optical nonlinearity of an azonaphthalene derivative, hydroxy naphthol blue (HNB) disodium salt, is investigated using transient absorption spectra (TAS) and Z-scan technique. Reverse saturable absorption (RSA) is observed within the resonant absorption band, which is usually dominated by ground-state bleaching (GSB) and stimulated emission (SE) in most organic compounds. This observation indicates a remarkably strong excited-state absorption (ESA) in HNB. Global analysis of TAS suggests an ultrafast conversion from saturable absorption (SA) to RSA, which is assigned to the internal conversion from locally excited (LE) state to the first singlet (S1) state. Further Z-scan study verifies the above results and reveals another intensity-depend SA-RSA transition, indicating increased S1 population under strong laser irradiation. The calculated value of third-order nonlinear absorption coefficient at 650 nm, 190 fs is determined as 1.23 × 10−12 m/W. These studies demonstrate significant potential of azonaphthalene in ultrafast laser protection if further modulation of excited-state absorption can be achieved.

Improved near-resonant two photon absorption of α-MnO2 nanowires surface functionalized reduced graphene oxide sheets

The versatile study of graphene derivatives has resurgence of interest on understanding its nonlinear optical response at different nanoscales. Nanostructured manganese dioxide: reduced graphene oxide (MnO2: rGO) hybrids were synthesized by reduction method by varying the content of rGO (5, 10, 15 & 20 wt%). X-ray Photoelectron Spectroscopy studies confirmed the surface functionalization of MnO2 on rGO. Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Tunnelling Electron Microscopy (HRTEM) witness that with respect to the content of rGO, the morphology of MnO2 varies radically from clusters to nanorods to nanowires over the surface of rGO sheets. Ground state absorption spectra of the hybrids have absorption edge at 268 nm corresponding to combined metal oxide charge transfer between rGO (π-π* transition of CC and n-π transition of C-O bonds) and MnO2 (d-d transition). Moreover, hierarchical MnO2 nanowire network resided on 2D rGO sheets involves broad absorption at the visible spectral domain due to polaron transition as well the localization of π- π* transited electrons that facilitates the probability of occurrence of excited state absorption. Intensity dependent open aperture Z-scan technique of the prepared hybrids using Q-switched Nd: YAG 532 nm nanopulsed laser reveals unusual transitions and enhanced nonlinear absorption. MnO2:(5 wt%) rGO shows saturable absorption (SA) at low intensity and changeover dynamically to reverse saturable absorption (RSA) at higher intensity. MnO2:(10 & 15 wt%) rGO exposes coupled nonlinear absorption (SA + RSA) owing to the combined effect of graphene (π-states) and MnO2 (σ-states). MnO2:(20 wt%) rGO exhibits a stronger RSA ascribed to sequential two photon absorption. The third-order nonlinear absorption coefficient and limiting threshold of MnO2: rGO (20 wt%) are 4.04 ×10-10 m/W and 0.84 ×1012 W/m2, which shows five-fold increase compared to bare rGO and MnO2. The obtained results propose that the optical nonlinearity of MnO2 nanowires surface functionalized rGO sheets can significantly be tuned to meet the requirements for fabricating laser safety devices.

Novel polymorph of 2-amino-6-methyl pyridinium-4-methyl benzoate (2A6MP4MB) single crystals: Synthesis, crystal structure, optical, spectroscopic and self-defocusing capabilities for nonlinear optical applications

By using the slow evaporation solution growth technique, the 2-amino 6-methyl pyridinium 4-methyl benzoate (2A6MP4MB) is crystallized in a single, high-quality crystal. Single crystal X-ray diffraction (SXRD) was used to determine the crystal structure. The different functional groups of the substances were identified using Fourier Transform Infrared Spectroscopy (FTIR) analysis. The 2A6MP4MB crystal exhibits a significant optical transmittance throughout the complete visible spectrum and a lowered UV cutoff wavelength, according to studies conducted using UV-Vis spectrometers. The optical band gap energy (Eg) of a single crystal of 2A6MP4MB is 4.768[Formula: see text]eV. The compound’s photoluminescence (PL) spectrum in the title illustrates the green emission technique. We analyze the produced single crystal’s dielectric tensorial behavior at various frequencies. The produced 2A6MP4MB crystal’s third-order susceptibility, nonlinear refraction, and nonlinear absorption coefficient were evaluated using the [Formula: see text]-scan technique. A Vickers hardness tester was used to assess the created crystal’s mechanical stability.

Investigation of linear and nonlinear optical properties in quantum dots: Influence of magnetic and AB flux fields

In the present work, analytical expressions for the energy eigenvalues and eigen functions are obtained by solving the radial Schrödinger equation for inverse quadratic Hellmann plus Yukawa (IQHY) potential using Nikiforov-Uvarov functional analysis method. As an application part of this work, expressions for the linear and third-order nonlinear absorption coefficients and refractive index changes are computed to study the optical properties of the spherical GaAs quantum dots. We extend the investigation of the IQHY potential by incorporating the effects of magnetic and Aharonov–Bohm (AB) flux fields. Our results reveal that the optical properties of the GaAs quantum dots are strongly influenced by variations in the dot radius, potential height and intensity of incident photons. Specifically, we observe that the introduction of magnetic and AB flux fields significantly alters the energy eigenvalues and eigenfunctions, leading to distinct optical characteristics. The results of present study are found in consistent with other theoretical studies available in the literature.

Polarization Z-Scan Studies Revealing Plasmon Coupling Enhancement Due to Dimer Formation of Gold Nanoparticles in Nematic Liquid Crystals.

We investigate the plasmon coupling of gold nanoparticle (AuNP) dimers dispersed in a nematic liquid crystal matrix using the polarization z-scan technique. Our experimental setup includes the precise control of incident light polarization through polarization angles of 0°, 45°, and 90°. Two distinct cell orientations are examined: parallel and twisted nematic cells. In parallel-oriented cells, where liquid crystal molecules and AuNPs align with the rubbing direction, we observe a remarkable 2-3-fold increase in the nonlinear absorption coefficient when the polarization of the incident light is parallel to the rubbing direction. Additionally, a linear decrease in the third-order nonlinear absorption coefficient is noted as the polarization angle varies from 0° to 90°. In the case of twisted nematic cells, the NPs do not have any preferred orientation, and the enhancement remains consistent across all polarization angles. These findings conclusively establish that the observed enhancement in the nonlinear absorption coefficient is a direct consequence of plasmon coupling, shedding light on the intricate interplay between plasmonic nanostructures and liquid crystal matrices.

Impact of intense laser Bessel beam on excitonic complexes in ellipsoidal quantum dot

This theoretical study investigates the response of a strongly oblate GaAs ellipsoidal quantum dot to an intense laser field with a Bessel intensity profile at non-resonant extreme violet and simultaneously resonant mid-infrared laser irradiation. Mainly, the linear and nonlinear optical properties of biexcitons in quantum dot are observed. Due to the complexity of the considered particle, all calculations are performed in the framework of the variational method. Biexciton variational function is constructed on the one-particle wave functions, which are correlated with each other by exponents with variational parameters. The biexciton energies for different values of applied intense laser field magnitude on the small geometrical parameter of ellipsoidal quantum dot are calculated. The nonlinear optical properties, including the oscillator strength, third-order nonlinear susceptibility, absorption coefficient, and refractive index change, are evaluated. Numerical results reveal the dependence of the exciton and biexciton energies on the intensity of the laser field and the geometrical parameters of the quantum dot. Additionally, the dependencies of the third-order susceptibility, absorption coefficient, and induced refractive index change on photon energy near the one-photon resonance and two-photon resonance are analyzed. The two-photon absorption coefficient of the biexciton in GaAs ellipsoidal quantum dot is computed, and the spectra of refractive index changes induced by biexciton transitions between ground states are analyzed for different magnitudes of the intense laser field. Biexciton recombination radiative lifetime on the small semiaxis of the ellipsoidal quantum dot for the different values of the laser field influence is estimated. Finally, the visualization of the localization region of biexciton in the ellipsoidal quantum dot is performed.

Thickness-Dependent nonlinear optical absorption of InSe/Graphene van der Waals heterostructures

InSe/Graphene van der Waals heterostructures emerge as promising candidates for optoelectronic applications. In this work, we systematically examine the saturable absorption properties of InSe/Graphene heterostructures with varying thickness of InSe. We establish a positive correlation between the third-order nonlinear absorption coefficient and heterostructure thickness. Furthermore, we uncover the interplay of carrier dynamics within the heterostructures, revealing prolonged interlayer transfer times and slowed carrier relaxation as InSe thickness increases. These insights shed light on the potential of InSe/Graphene heterostructures for advanced optoelectronic devices, fostering further advancements in this field.

Ultrafast nonlinear optical properties of Ag/WTe2 composite films

WTe2 thin films and Ag/WTe2 composite films were successfully prepared by magnetron sputtering technology. The nonlinear absorption (NLA) characterization of the Ag/WTe2 composite system at 532 nm was also investigated by the ps Z-scan technique. The results show that both WTe2 films and Ag/WTe2 composite films exhibit saturable absorption (SA) effect and self-dispersion phenomenon. In addition, the nonlinear absorption performance of the composite films are significantly enhanced compared to that of a single WTe2. With the increase of Ag sputtering power, their third-order nonlinear absorption coefficients β increase by one order of magnitude, indicating that Ag enhances the nonlinear absorption performance of Ag/WTe2 composite films. This study provides a new idea for the application of Ag/WTe2 composite films in optoelectronic devices.

Chitosan, a Cationic Polymer-Loaded CuS:Ni Nanoparticles Well Suited for Pseudocapacitors, Optical Switching and Spintronic Devices

Chitosan, a cationic polymer, is loaded on Ni-doped copper monosulfide (CuS) NPs with optimal Ni doping concentration, and electrochemical, third-order nonlinear, magnetic and antibacterial characteristics of chitosan unloaded and loaded CuS:Ni nanoparticles are compared. The crystallite size of pure CuS increased with Ni doping and the 10[Formula: see text]wt.% Ni-doped CuS NPs exhibit a maximum crystallite size of 41[Formula: see text]nm. The presence of Ni in the doped samples was acknowledged by the existence of Ni 2p[Formula: see text] and Ni 2p[Formula: see text] peaks at binding energies 851[Formula: see text]eV and 873.1[Formula: see text]eV, respectively from the XPS spectrum. Optical reflectance decreased with Ni doping and the optical band gap varied from 2.56[Formula: see text]eV to 2.4[Formula: see text]eV. Specific capacitance increased with Ni doping. Diamagnetic nature of CuS changed to ferromagnetic with Ni doping. The 10[Formula: see text]wt.% Ni-doped CuS exhibits a high third-order nonlinear absorption coefficient and susceptibility value. Bacterial growth inhibition nature of CuS improved with Ni doping. Among the doped samples, the 10[Formula: see text]wt.% Ni-doped sample exhibits improved electrochemical, third-order nonlinear, magnetic and antibacterial properties. Keeping this as the optimized Ni concentration, chitosan was loaded. Chitosan-loaded samples exhibited a reduction in crystallite size and an increase in band gap. A high specific capacitance of 96[Formula: see text]F/g was realized for the chitosan-loaded sample. Saturation magnetization of 10[Formula: see text]wt.% CuS:Ni decreased with chitosan loading.

Excellent Nonlinear Optical Limiting Behavior of Tetra (C60) Lanthanum Phthalocyanine in Solid Poly(methyl methacrylate) Films

This work reports on the exceptional optical limiting performance of a novel D–A-type compound, namely, LaPc-4(C60), wherein the lanthanide phthalocyanine is used as a donor and four C60 are used as acceptors. In addition, phenyl ether bonds were introduced into the molecule, making it semirigid and increasing its solubility. At the same time, the phenyl ether bond could act as a π-electron bridge, which increases the electron transfer pathway, expands the π-conjugated system, and reduces the spatial site resistance of the molecule. Furthermore, the uniform poly(methyl methacrylate) (PMMA) composite film (LaPc-4(C60)/PMMA) was prepared by a simple solution casting method. In comparison with individual C60 or LaPc(CHO)4, both LaPc-4(C60) in solution and in the solid PMMA composite film exhibited larger third-order nonlinear absorption coefficients and lower limiting thresholds at 532 nm. In particular, LaPc-4(C60)/PMMA exhibits huger nonlinear absorption coefficient (2900 cm/GW) and larger third-order susceptibility (4.91 × 10–9 esu), which can be attributed to the synergistic effect of the different non-linear absorption mechanisms and efficient photoinduced electron transfer process between C60 and LaPc.

Third-order optical nonlinearity and multiferroicity of nanoparticles thin films of isovalent rare earth Y3+ ion substituted BiFeO3

Present work reveals the multiferroic and nonlinear optical properties of pristine and Yttrium (Y3+) substituted BiFeO3 nanoparticles synthesized by sol-gel technique, and fabricated thin films of the nanoparticles. The nanoparticles thin films were deposited on glass substrates with an average thickness of 85 nm by the thermal evaporation method in a high vacuum of 10−6 Torr. The structural and morphological studies were done by using XRD, Fullprof, XPS, AFM, FESEM and TEM with SAED. Further BET method was used to find out the surface area, pore size and pore volume of the nanoparticles. The multiferroic properties of Bi1-xYxFeO3 (x = 0.0, 0.5, 0.10, 0.15) have been investigated using VSM (magnetic) and P-E loop tracer (electrical). The doping of magnetic Y3+ions in host BiFeO3 nanoparticles modified and improved the optical, structural, multiferroic properties enormously. Linear optical properties were characterized by UV–Visible, Raman, and Photoluminescence. Third-order nonlinear absorption coefficient (β) and the imaginary part of third-order susceptibility (χi3) of Bi1-xYxFeO3 (x = 0.0, 0.5, 0.10, 0.15) have been investigated using a single beam Z-scan technique with a continuous wave (CW) diode laser of 520 nm wavelength. The films exhibit saturation absorption (SA) behavior and it increases on increasing the Yttrium (Y3+) substitution in BiFeO3. Thus, the NLO behavior of the films makes it an auspicious material for application in optoelectronic devices.

Effect of Gaussian and Bessel laser beams on linear and nonlinear optical properties of vertically coupled cylindrical quantum dots

Vertically coupled quantum dots are one of the most interesting and promising structures, which find application in a wide range of fields. Particularly, they are noteworthy candidates as a source of single photon and entangled photon pair sources, as qubits and quantum gates in quantum computation, etc. Various external perturbations can act as an instrument for the manipulation of the properties of these structures and an intense laser field is a great example of this. In this work, vertically coupled cylindrical quantum dots made of InAs in a GaAs matrix with a modified Pöschl–Teller potential have been considered under intense laser fields with two laser beam profiles: Gaussian and Bessel. The energy levels and wave functions have been obtained for this structure. Linear and third-order nonlinear absorption coefficients, refractive index changes and second and third harmonic generation susceptibilities have been investigated at different temperatures and for different values of the laser parameters.

Theoretical investigation of laser field effect on nonlinear optical properties of quantum dots

In this work, we have theoretically investigated the effects of a high-frequency intense laser field on the nonlinear optical properties of a two-dimensional Gaussian quantum dot system. A non-resonant monochromatic intense laser field with circular polarization applied to the system is considered in the framework of a non-perturbative approach. The nonlinear optical properties of the system have been investigated by using the compact-density matrix approach and iterative procedure. The laser field effect on the linear and the third-order nonlinear absorption coefficients and refractive index changes have been examined. Results reveal that the optical characteristics of the two-dimensional Gaussian quantum dot system are considerably influenced by the strength of the intense laser field in addition to structure parameters.

Large-area vapor-deposited Cs3Cu2I5 perovskite thin films for highly effective third-order nonlinear optics

Zero-dimensional (0D) lead-free perovskites hold promise for efficient optoelectronic and photonic devices, but there are still critical challenges in fabricating large-area, high-quality thin films for practical applications. Herein, we report a simple vapor route to prepare 0D lead-free Cs3Cu2I5 perovskite thin films of high optical quality over large areas. Importantly, the deposition approach can be applied to diverse substrates, including mica, fused silica, MgO, and indium tin-oxide (ITO) coated glass. The deposited Cs3Cu2I5 thin films are phase pure and highly uniform. These Cs3Cu2I5 thin films exhibit strong blue emission upon UV light illumination, a broad band centered at 445 nm assigned to the self-trapped exciton emission. Furthermore, third-order nonlinear optical properties of the as-prepared thin films were determined by means of the Z-scan method. These thin films showed the third-order nonlinear absorption coefficient β as ∼ 1.07 × 10−7 m/W, which is five orders of magnitude larger than three-dimensional counterpart, CsPbI3. Thus, we demonstrate that large-area, high-quality Cs3Cu2I5 thin films can be vapor-deposited and have great potentials in optical switching and optical limiting applications.

The Matrix Effect on Nonlinear Optical Responses of Disperse Orange 25: Optical Bistability and Z-Scan.

The nonlinear behaviours of an azo dye, Disperse Orange 25 (DO25), doped on two polymers (PVP and PMMA), with different weight percentages are investigated under irradiation of 300mW continuous Nd-YAG Laser (λ = 532nm). The optical bistability (OB) of samples was examined using the Mach-Zehnder interferometer. The obtained results show that the PVP matrix doped with DO25 has better nonlinear responses due to their efficiency and stability depend on the properties of the matrix such as the glass transition temperature which is higher for PVP and the structural properties. Also, the third-order refractive index and nonlinear absorption coefficient are measured by (CA) and (OA) Z-scan techniques, respectively.

Tunable optical nonlinearity of indium tin oxide for optical switching in epsilon-near-zero region

Abstract The propagation of light in the epsilon-near-zero (ENZ) region of materials exhibits intriguing linear and nonlinear optical phenomenon that have been extensively exploited for a plethora of applications. Here, we show that the optical properties as well as the ENZ wavelength of magnetron-sputtered indium tin oxide (ITO) thin films could be judiciously engineered. The measurement of nonlinear optical properties reveals that the control of deposition conditions allows for the tuning of absorptive optical nonlinearity between saturable absorption and reverse saturable absorption. The ENZ wavelength for the ITO film is deduced as around 1553 nm. We obtain the highest third-order nonlinear absorption coefficient and imaginary part of third-order nonlinear susceptibility for the ITO thin film through Z-scan method as −50.56 cm/GW and ∼38 × 10−14 e.s.u. at 1050 nm, and −64.50 cm/GW and ∼45 × 10−14 e.s.u. at 1550 nm, respectively. We demonstrate further that the strong saturable absorption of the ITO thin film enables Q-switched pulse laser generation in ∼1050 and ∼1550 nm regions with tunable repetition rates and pulse energies. The present results suggest the great application potential of the ITO thin film in the field of nonlinear optical devices.

Linear and nonlinear optical properties in spherical quantum dots: Modified Möbius squared potential

The optical properties of quantum dots (QDs) in modified Möbius squared (MMS) potential are studied. To obtain the energy expressions and the wave functions, we solved the Schrödinger equation by using Nikiforov-Uvarov (NU) method. We investigated the linear, third-order nonlinear and total absorption coefficients (AC) and refractive index changes (RIC) using the density matrix. The numerical results show that the structure parameters and optical intensity have a strong influence on AC and RIC.

Plasmon-enhanced third-order optical nonlinearity of monolayer MoS2

Transition metal dichalcogenides (TMDs) have attracted broad interest in photonics owing to their unique electric band structures, which triggers various applications for functional devices. However, the optical absorbance of TMDs is relatively low because of the atomic-scale thickness, limiting further development of TMDs-based nonlinear optical devices. Here, we propose an effective method to enhance the nonlinear optical properties of TMDs using plasmons, which are from embedded silver (Ag) nanoparticles (NPs) inside the fused silica substrate. In such a configuration, the third-order nonlinear absorption coefficient of MoS2 with non-contact Ag NPs is one order of magnitude higher than that of pure monolayer MoS2 under excitation of 515 nm light, and at 1030 nm, the reverse saturable absorption switches to the saturable absorption due to the plasmonic implication. In addition, the mechanism of plasmon-enhanced nonlinear optical properties is confirmed by results of both transient absorption spectroscopy and near-field electromagnetic field simulation. This study on plasmon-enhanced third-order nonlinearity of MoS2 expands the boundaries of TMDs-based optical nonlinearity engineering.

Linear and nonlinear optical properties of vertically coupled cylindrical double quantum dots with modified Pöschl-Teller potential

Linear and third-order nonlinear absorption coefficients have been theoretically investigated in a system of vertically coupled cylindrical double quantum dots with the modified Pöschl-Teller potential in the axial direction and parabolic potential in the radial direction. Also, changes in the refractive index in these conditions were obtained. For intraband optical transitions of charge carriers in such system the selection rules have been obtained. The behaviour of the linear, nonlinear and total absorption spectra and changes in the refractive index have been theoretically observed for different lattice temperatures and illustrated by the corresponding graphs for two temperatures.

Linear, third-order nonlinear and total absorption coefficients of a coupled InAs/GaAs lens-shaped core/shell quantum dots in terahertz region

Linear, third-order nonlinear and total absorption coefficients of a coupled InAs/GaAs lens-shaped core/shell quantum dots in terahertz region