Third-order Nonlinear Absorption Research Articles

Defect-controlled fabrication of reduced graphene oxide/ZnO/PMMA-based solid-state optical limiting filters with SA/RSA switching property

A solid-state optical limiting filter was fabricated by noncovalently functionalizing a graphene-based nanocomposite with a polymer. Graphene oxide was reduced by varying reducing agent concentration and functionalized with metal oxide nanoparticles to enhance electronic transitions and third-order nonlinear optical characteristics. The nanocomposite was dispersed over the PMMA polymer framework, and thin films with μm-scale thickness were fabricated using the dip coating method. XRD analysis confirmed the wurtzite crystal structure of ZnO nanoparticles and the amorphous nature of PMMA. The carbon structural integrity was analyzed using Raman spectra. Linear optical studies revealed a redshift in the π-π* transition peak in rGO, suggesting enhanced conjugation. Third-order nonlinear refraction and absorption properties were assessed using the Z-scan technique, revealing a switching behavior in nonlinear absorption at different input intensities. An increase in the relative concentration of sp2 domains enhanced the nonlinear absorption. Optical limiting potential, determined using open aperture Z-scan data, yielded a threshold value of 0.066 GW/cm2. This study aims to develop a solid-state optical filter with a high laser damage threshold by adjusting the reduction rate, tuning defect levels, and analyzing its effect on the optical limiting potential.

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.

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.

Introducing Optical Nonlinearity in PDMS Using Organic Solvent Swelling

The feasibility of introducing optical nonlinearity in poly-dimethyl siloxane (PDMS) using organic solvent swelling was investigated. The third-order nonlinear refraction and absorption properties of the individual materials, as well as the PDMS/solvent compounds after swelling were characterized. The well-established Z-scan technique served as characterization method for the nonlinear properties under picosecond pulsed laser excitation at a 532 nm wavelength. These experiments included investigations on the organic solvents nitrobenzene, 2,6-lutidine, and toluene, which showed inherent optical nonlinearity. We showed that nitrobenzene, one of the most well-known nonlinear optical materials, has proven suboptimal in this context due to its limited swelling effect in PDMS and comparatively high (non)linear absorption, resulting in undesirable thermal effects and potential photo-induced damage in the composite material. Toluene and 2,6-lutidine not only exhibited lower absorption compared to nitrobenzene but also show a more pronounced swelling effect in PDMS. The incorporation of toluene caused a weight change of up to 116% of PDMS, resulting in substantial nonlinear optical effects, reflected in the nonlinear refractive index of the PDMS/toluene composite n2=3.1×10−15 cm2/W.

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.

Defect-mediated saturable absorption and carrier dynamics in tin (II) monosulfide quantum dots.

Tin (II) monosulfide (SnS) has attracted considerable attention in emerging photonics and optoelectronics because of high carrier mobility, large absorption coefficient, anisotropic linear and nonlinear optical properties, and long-time stability. In this Letter, we report third-order nonlinear absorption and refraction of SnS quantum dots (QDs). Under excitation with 800-nm femtosecond pulses, QDs exhibit saturable absorption (saturation intensity ∼ 47.69 GW/cm2) and positive refractive nonlinearity (nonlinear refraction coefficient ∼ 1.24 × 10-15 cm2/W). Nonetheless, we investigate charge carrier dynamics using femtosecond transient absorption spectroscopy and propose the presence of midgap defect states which not only dictate carrier dynamics but also give rise to nonlinear optical properties in SnS QDs.

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.

Nonlinear optical properties of 3d transition metal oxides and applications in fiber lasers: Review and prospect

Transition metal oxides (TMOs) are distinguished by their thermal and chemical stability as well as excellent optical, electrical, and magnetic properties. Moreover, the 3[Formula: see text]-orbital electrons of the transition metal ions in TMOs have a strong [Formula: see text] Coulomb interaction, enabling them to exhibit a variety of unusual physical phenomena, dramatically different from conventional metals and semiconductors. Additionally, TMOs possess excellent nonlinear optical properties, such as third-order nonlinear response and saturation absorption, which make them broadly applicable for ultrafast photonics devices. Herein, a review is presented of the nonlinear optical properties of typical TMOs, as well as their employment as saturable absorbers in near-infrared pulsed fiber lasers in recent years. Finally, some challenges and promising prospects for nonlinear ultrafast photonic devices based on TMOs are discussed.

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.

The rich nonlinear optical responses in a squaraine derivative: Nonlinear absorption and transient nonlinear refraction dynamics

The abundant nonlinear optical responses of a squaraine derivative (2, 4-bis[4-(diethylamino)-2-hydroxyphenyl]squaraine, SQ-640) are explored at visible and near-infrared (NIR) regions. The sign and magnitude of the third-order (intensity depend) nonlinear absorption and refraction for SQ-640 are determined under different pluses with Z-scan method. The results of this work show reverse saturable absorption (RSA) of SQ-640 at visible and NIR region and its potential for optical limiting (OL) application. Moreover, SQ-640 shows self-focusing at visible wavelength while shows self-defocusing at NIR wavelengths. The transient refraction dynamics indicate that positive excited-state refraction causes self-focusing at visible region while negative nonlinear refraction at NIR region mainly originates from bound electron response (Kerr effect) and negative excited state refraction. Besides, the nonlinear refraction index of SQ-640 under 532 nm ranges from ∼ 10-19 m2/W at femtosecond pulses to ∼ 10-16 m2/W at nanosecond pulses and the second order hyperpolarizability is about 4 × 10-28 esu at nanosecond case. The Kerr refraction coefficient is about −6.54 × 10-19 m2/W at 700 nm under femtosecond laser pulses. The obtained OL thresholds at 532 nm are ∼ 26.8 mJ/cm2 for picosecond pulses and ∼ 85.6 mJ/cm2 for nanosecond pulses. The enriching information extracted from NLR in SQ-640 may offer an optional perspective to understand the structure–property relationships in these compounds. The results of optical nonlinearities in SQ-640 gained from this study may be of assistance to its better applications in laser protection and optical switching.

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.