Positive Nonlinear Refraction Research Articles

Correlation of quantum well periods on the 3rd order nonlinear optical responses of InGaN/GaN heterostructures

Semiconductor multi quantum well (MQW) design allows for the compression of electron-interaction dimensions, offering advantages for various applications, particularly in nonlinear optics. Despite the potential improvements in nonlinear optical responses, the influence of quantum well periods remains unexplored. In this study, we report the correlation of quantum well periods on the 3rd order nonlinear optical properties in In0.15 Ga0.85 N/GaN MQW using z-scan technique under femtosecond and continous wave laser regime. In0.15 Ga0.85 N well/GaN barrier with x1, x5, x10, x15 periods were grown by MOCVD technique. Good structural quality of grown MQWs were confirmed via HRTEM imaging, EDS, AFM and XRD. Absorption coefficient from UV-Vis coupled with PL emission spectrum shows systematic response of optical linear properties which provide an insight on the overall band gap structure. Positive nonlinear refraction, n2 and nonlinear absoprtion, β trends is observed under femtosecond an CW laser albeit differences of one order magnitude in χ3 value. The increase in χ3 value is shown to be monotonous with the increasing number of quantum well suggesting that compounding effect took place. This findings indicate the possibility of manipulating and tuning nonlinear reponses of MQW structures leading to improvement in semiconductor design in various areas such as optoelectronics, photonics, solar cell research, as well as quantum information processing.

Nonlinear optical properties in Pr3+-Er3+-codoped tellurite glasses

In this investigation, we systematically probe the structural, optical, and, notably, the nonlinear optical properties of Pr3+-Er3+-codoped tellurite glasses to understand the potential new functionalities of the glass and, thus, their applicability. The glass samples were synthesized employing the melt-quenching technique and subsequently characterized using X-ray photoelectron spectroscopy (XPS) and femtosecond (fs) pulse Z-scan measurements at 720 and 750 nm wavelengths. XPS analyses unveiled increased non-bridging oxygens (NBO) with ascending Pr2O3 content. It was observed that the increasing concentrations of Pr3+ ions show a linear dependence with the increase of NBO in the glass network (r2 > 0.95). This trend further supported the formation of Te3+ ions via the oxidation of Te4+ for charge compensation and was affirmed by a decrement in average TeO bond as Pr2O3 concentrations increased. The tellurite glasses showcased positive nonlinear refraction on the nonlinear optical (NLO) front. The rise in n2 values was directly linked to the Pr2O3 content, a phenomenon attributed to the increased presence of non-bridging oxygens and the inherent polarizability of Pr3+ ions. Collectively, our findings offer pivotal insights into the modulation of NLO attributes in Er3+-doped tellurite glasses via Pr3+ ion doping, underscoring their potential in advanced NLO device applications.

Structurally influenced optical nonlinearities and ultrafast dynamics in β-acroleyl- and β-dicyanobutadienyl-appended cobalt corroles.

The strong two-photon induced nonlinear absorption and self-focusing type positive nonlinear refraction are pronounced by the structural engineering in β-functionalized cobalt corroles.

Cubic Nonlinearity of Graphene-Oxide Monolayer.

The cubic nonlinearity of a graphene-oxide monolayer was characterized through open and closed z-scan experiments, using a nano-second laser operating at a 10 Hz repetition rate and featuring a Gaussian spatial beam profile. The open z-scan revealed a reverse saturable absorption, indicating a positive nonlinear absorption coefficient, while the closed z-scan displayed valley-peak traces, indicative of positive nonlinear refraction. This observation suggests that, under the given excitation wavelength, a two-photon or two-step excitation process occurs due to the increased absorption in both the lower visible and upper UV wavelength regions. This finding implies that graphene oxide exhibits a higher excited-state absorption cross-section compared to its ground state. The resulting nonlinear absorption and nonlinear refraction coefficients were estimated to be approximately ~2.62 × 10-8 m/W and 3.9 × 10-15 m2/W, respectively. Additionally, this study sheds light on the interplay between nonlinear absorption and nonlinear refraction traces, providing valuable insights into the material's optical properties.

The Comparative Third‐Order Nonlinearities of Titanium Carbide and Tungsten Carbide in the Visible Regain

AbstractThis study investigates the structure and properties of Titanium carbide (TiC) and Tungsten carbide (WC) nanoparticles. The X‐ray diffraction patterns confirm the presence of a hexagonal structure in WC nanoparticles and cubic structure in TiC nanoparticles. Transmission electron microscopy analysis reveals the particle sizes to be within the range of 30–50 nm. The bandgap of TiC and WC nanoparticles are 3.5 and 3.6 eV, respectively based on diffuse reflectance spectroscopy (DRS) along with Kubelka–Munk. Furthermore, the optical phonons and dielectric function of WC and TiC nanoparticles are investigated using the reflectance spectra along with the Kramers–Kronig (KK) method. Furthermore, the Z‐scan technique, employing a Nd:YAG laser operating at a wavelength of 532 nm, is utilized to assess the nonlinear optical (NLO) characteristics of WC and TiC nanoparticles. The open aperture Z‐scan measurements of WC nanoparticles indicate reverse saturable absorption (RSA) behavior and a positive nonlinear refraction (NLR) coefficient. On the other hand, TiC nanoparticles show RSA behavior with a negative NLR effect. The order of NLR, nonlinear absorption coefficient, and the susceptibility of TiC and WC are 10−8 cm2 W−1, 10−4 cm W−1, and 10−6 esu, respectively.

Ultrafast Dynamics and Strong Two-Photon Absorption Properties of Nonplanar β-Functionalized “Push–Pull” Copper Corroles with a Mixed Substituent Pattern

A new series of nonplanar and unsymmetrically β-functionalized "push-pull" copper corroles, CuTPC(CHO)R7 [R = H, Br, Ph, Me, or 2-thienyl (Th)], were synthesized and characterized to elucidate the effect of β-functionalization and nonplanarity on the photophysical, redox, and nonlinear optical (NLO) properties on the corrole ring. The synthetic route to unsymmetrically β-octasubstituted copper corroles includes bromination of CuTPC(CHO) to get CuTPC(CHO)Br7 in 80% yield, which was further subjected to the Pd-catalyzed Suzuki reaction. CuTPC(CHO)Br7 exhibited a large red shift in the Soret band (Δλmax = 35-40 nm) and both the Q bands (Δλmax = 10-50 nm), as compared to CuTPC and CuTPC(CHO). CuTPC(CHO)Br7 was 510 and 290 mV anodically shifted in the first oxidation and the first reduction compared to CuTPC owing to the strong -I effect of CHO and Br groups. Density functional theory studies revealed that all the β-octasubstituted copper corroles exhibited highly nonplanar saddle-shape conformation of the corrole ring. Very high torsional saddling was observed for CuTPC(CHO)Th7 (79-83°) than that for CuTPC (49-53°), even larger than that for CuTPCBr8 (67-70°). Femtosecond laser-induced third-order NLO studies from these copper corroles showed strong two-photon absorption cross-sections (0.48-6.98 × 104 GM) and self-focusing-type positive nonlinear refraction behavior. The observed structure-dependent two-photon absorption coefficients (β) are in the range of ∼2.7-20.9 × 10-12 m/W, and the n2 values are in the range of ∼0.64-6.45 × 10-18 m2/W. The present results may facilitate a new window for these copper corroles in nonlinear optical devices, femtosecond optical limiters, and many other ultrafast photonic applications.

Mass ratio-dependently tunable enhancement of the optical nonlinearities of SnO2/RGO composites

The composite of graphene and semiconductor nanoparticles has attracted increasing interest in the search for novel nonlinear optical materials. Herein, composites of reduced graphene oxide (RGO) and SnO2 nanoparticles with different mass ratios were synthesized via a facile hydrothermal method. The structural morphology and basic physical properties of the SnO2/RGO composites were characterized using TEM, SEM, XRD, Raman, XPS and UV–Vis spectra, indicating that SnO2 nanoparticles were uniformly anchored on the surface of graphene nanosheets through covalent and partial-ionic bonds. The third-order optical nonlinearities of the composites were studied for the first time by the Z-scan technique using a picosecond laser at 532 nm. It was found that the composites demonstrated saturable absorption and positive nonlinear refraction properties, and both were significantly enhanced compared with pure SnO2 nanoparticles and RGO nanosheets, and the enhancement was tunable with the variation of SnO2:GO mass ratio. The maximum saturable absorption coefficient and the third-order susceptibility of the as-prepared SnO2/RGO composites were obtained to be −2.93×10–11 m W−1 and 2.25 × 10–11 esu, respectively. The maximum saturable absorption modulation depth obtained was 10% with the corresponding saturation light intensity of 0.3 GW cm−2. Moreover, the optimised third-order susceptibility of SnO2/RGO was found much greater than many other materials ever studied. Several involved factors contributing to the nonlinearities were discussed. The results propose that the third-order optical nonlinearities of SnO2/RGO and other similarly structured composites can be potentially tuned to meet certain application requirements of nonlinear optical devices by controlling the mass ratio of semiconductor to graphene.

Annealing duration dependent optical, nonlinear optical, and optical limiting properties of rare-earth doped glasses embedded with gold nanoparticles

In this work, the Eu2O3 doped B2O3 glass specimen embedded with gold nanoparticles (NPs) was designed by the process of melt-quenching and subjected for thermal treatment to understanding the efficacy of thermal dependency on the optical and nonlinear optical (NLO) characteristics. Linear optical studies have revealed a decrease trend in the energy band gap as the function of annealing duration, indicating the increase of non-bridging oxygen concentration in the glass host. The NLO properties were assessed in near-infrared region utilizing 150 fs laser pulses delivered at the rate of 80 MHz. The aperture free Z-scan measurements exhibited an increased nonlinear absorption coefficient with annealing duration. Further, the closed aperture Z-scan data depicted an increase trend in the positive nonlinear refraction with annealing duration and eventually reduced at the greater duration of annealing. The optical limiting studies demonstrated similar behaviour to the nonlinear absorption characteristics of studied glass samples. These results are related to the local field stimulated by surface plasmons of gold NPs near the Eu3+ ions during the exposure of glass to high fluence laser beam. Our results indicate that B2O3 glasses embedded with Au NPs heat-treated for 30 h at 450 °C are good candidates for nonlinear photonic, optoelectronic, and optical power limiting applications in photonics.

Femtosecond excited-state dynamics and ultrafast nonlinear optical investigations of ethynylthiophene functionalized porphyrin

Ethynylthiophene functionalized D-π-A porphyrin (LG5) belongs to a class of porphyrin molecules with proven application in organic solar cell devices. In this report, we present a comprehensive optical and non-linear optical characterization of ethynylthiophene functionalized porphyrin molecule, denoted as LG5. Femtosecond transient absorption (TA) spectroscopy was used to study the ultrafast excited-state properties with 400 nm, 70 fs photoexcitation. Global and target fitting analysis of the obtained TA spectra established a reliable photophysical model of excited state population relaxation and extracted the various rate constants. Considering the good performance of LG5 as a photosensitizer in dye-sensitized solar cells (DSSCs), electron injection studies on LG5 sensitized mesoporous TiO2 were also performed. Both integrated and transient photoluminescence (PL) data for LG5 sensitized TiO2 samples confirms efficient electron injection. The target analysis on TA data of LG5–TiO2 films revealed a multi-step electron injection from different excited energy levels with both ultrafast (≈370 fs) and slow injections times. Additionally, the non-linear optical (NLO) properties of LG5 are studied using the single-beam Z-scan technique upon photoexcitation of 800 nm, 70 fs laser pulses. The open aperture data demonstrated two-photon absorption (2PA), and closed aperture data indicated the presence of positive nonlinear refraction. The calculated values of 2PA cross-section and 3rd order NLO susceptibility were 1723 GM and 1.89 × 10−13 esu (2.64×10−21m2V−2), respectively.

Nonlinear Optical Limiting and Radiation Shielding Characteristics of Sm2O3 Doped Cadmium Sodium Lithium Borate Glasses.

Strong nonlinear absorption (NLA), reduced optical limiting (OL) thresholds, and high radiation shielding parameters are required for the effective use of glasses in the laser radiation and nuclear radiation protecting materials. In view of this, the efficacy of Sm2O3 on the nonlinear optical (NLO) and OL properties were ascertained (at 532 nm) along with radiation shielding characteristics. The open and closed aperture Z-scan profiles revealed the presence of positive NLA and nonlinear refraction (NLR) phenomena respectively. OL measurements showed the existence of limiting behavior in the studied glasses. The NLA and NLR coefficients were improved while the OL thresholds were decreased as the doping of Sm2O3 elevated to a higher doping level. These improvements in NLA, NLR coefficients and OL efficiencies were attributed to the non-bridging oxygens and high polarizable Sm3+ ions. The NLA and OL results clearly suggest the high (5 mol %) Sm2O3 doped glass (Sm5CNLB) glass is beneficial to protect the delicate devices and human eye by suppressing the high energy laser light. The theoretical linear attenuation coefficients (LAC) values of the presented SmxCNLB glasses were obtained with the help of Phy-X software between 0.284 and 1.333 MeV. At 0.284 MeV, the maximum values occur and take values between 0.302 (for Sm0CNLB) and 0.409 cm−1 (for Sm5CNLB). We found that the LAC for the presented SmxCNLB glasses is a function of Sm2O3 content, where the LAC tends to increase, corresponding to the high probabilities of interaction, as the content of Sm2O3 changes from 0 to 5 mol %. The effective atomic number (Zeff) for the presented SmxCNLB glasses was examined between 0.284 and 1.333 MeV. As the amount of Sm2O3 is added, the Zeff increases, and this was observed at any energy.

Highly improved nonlinear optical responses of reduced graphene oxide via the decoration of Ni doped ZnS nanoparticles

The application of graphene and graphene-like materials in photonics has attracted extensive attention in recent years. However, their nonlinear optical (NLO) properties need to be improved urgently. Herein, we demonstrate a method to improve the NLO properties of reduced graphene oxide (RGO) via the decoration of Ni transition element doped ZnS nanoparticles on RGO sheet. The samples of Ni doped ZnS decorated RGO (Ni-ZnS/RGO) composites with different Ni doping concentrations and ZnS particles sizes were synthesized via a facile solvothermal method. The NLO responses of Ni-ZnS/RGO composites were investigated via the Z-scan technique under a picosecond laser at 1064 nm. The results indicated that Ni-ZnS/RGO composites exhibited saturation absorption and positive nonlinear refraction properties, and they could be adjusted by controlling the doping concentration of Ni and the size of ZnS nanoparticles. The maximum saturation absorption coefficient, nonlinear susceptibility and nonlinear refractive index of Ni-ZnS/RGO among all the samples were obtained to be − 2.5 × 10−10 mW−1, 3.2 × 10−13cm2/W and 14.1 × 10−14cm2/W, which were 25, 18 and 23 times of those of RGO, and 3.6, 11.7 and 4.2 times of those of ZnS doped with 2.5%Ni, respectively. They were also much greater than those of the direct sum of the two independent units, RGO and Ni-doped ZnS. These highly improved NLO responses of Ni-ZnS/RGO composites were ascribed to the inhibition of the direct electron-hole recombination due to the introduction of Ni doped impurity energy levels within the band gap of ZnS, as well as the charge transfer and synergism between ZnS and RGO. The results of this investigation may promote the development and applications of Ni-ZnS/RGO materials in photonic devices.

Third-order optical nonlinearities of exfoliated Bi2Te3 nanoparticle films in UV, visible and near-infrared ranges measured by tunable femtosecond pulses.

We characterize the nonlinear optical properties of synthesized Bi2Te3 nanoparticle-contained thin films using the tunable femtosecond laser in the spectral range of 400-1000 nm. These nanoparticles possess a strong saturable absorption and positive nonlinear refraction (-6.8×10-5 cm W-1 in the case of 500 nm, 150 fs probe pulses, and 3×10-10 cm2 W-1 in the case of 400 nm, 150 fs probe pulses, respectively). The spectral, intensity, and temporal variation of saturable absorption and nonlinear refraction of the thin films containing exfoliated Bi2Te3 nanoparticles are discussed.

Synthesis and Third-Order Nonlinear Synergistic Effect of ZrO2/RGO Composites.

Tuning the third-order nonlinear properties of graphene by hybrid method is of great significance in nonlinear optics research. ZrO2/reduced graphene oxide (RGO) composites with different ZrO2 concentrations were prepared by a simple hydrothermal method. The morphology and structure show that ZrO2 nanoparticles were uniformly dispersed on the surface of graphene nanosheets. The nonlinear optical (NLO) characteristics of composites with different ZrO2 concentrations were studied by the Z-scan technique of 532 nm picosecond pulsed laser. The results showed that ZrO2/RGO composites had saturated absorption and positive nonlinear refraction characteristics. Meanwhile, the third-order nonlinear susceptibility of the ZrO2/RGO composite with a 4:1 mass ratio of ZrO2 to graphene oxide could reach 23.23 × 10−12 esu, which increased tenfold compared to RGO, and the nonlinear modulation depth reached 11.22%. Therefore, the NLO characteristics could be effectively adjusted by controlling the concentration of ZrO2, which lays a foundation for further research on the application of ZrO2/RGO composites in NLO devices.

Transformation from Self-Focusing to Self-Defocusing of Silver Nanoparticles.

The nonlinear refraction of silver nanoparticles (AgNPs) in n-hexane was studied by using the closed-aperture Z-scan technique with a 532 nm nanosecond laser. It was found that, the nonlinear refraction of AgNPs shows the coexistence and transformation from self-focusing to self-defocusing. Specifically, self-focusing occurs at low excitation intensity, self-defocusing occurs at high excitation intensity, and coexistence of self-focusing and self-defocusing occurs at relatively moderate excitation intensity. The experimental results were analysed and discussed in terms of third-order and fifth-order nonlinear refractive effect. Specifically, the self-focusing is caused by the positive third-order nonlinear refraction, the self-defocusing is induced by the negative fifth-order nonlinear refraction, and the transformation from the self-focusing to self-defocusing at medium excitation intensity is caused by the competition of third-order and fifth-order nonlinear refraction. Finally, the third-order refractive index and fifth-order refractive index were obtained.

Enhanced nonlinear optical properties of the Cu2Se/RGO composites

Tuning the third-order nonlinear optical (NLO) properties of graphene (G) is of great significance in nonlinear optics. In this work, Cu2Se/reduced graphene oxide (RGO) composites with different Cu2Se contents were prepared via a solvothermal method. The structure and morphology indicated that the Cu2Se nanoparticles were uniformly dispersed on the surface of the graphene nanosheets. The NLO properties of the composites with different Cu2Se contents were investigated via the Z-scan technique with a picosecond-pulse laser at 532 nm. The results showed that the Cu2Se/RGO composites had the properties of reverse saturated absorption (RSA) and positive nonlinear refraction, and their NLO properties could be effectively regulated by controlling the Cu2Se contents. The third-order nonlinear susceptibility of the Cu2Se/RGO composite with a 1.5:1 mass ratio of Cu2Se to graphene oxide could reach 6.52 × 10−11 esu, which increased five-fold compared to G. The introduction of Cu2Se improved the NLO response of G, which might be attributed to the content effect of Cu2Se in the composites and the synergistic effects stemming from charge transfer between the Cu2Se and RGO This paper lays a foundation for the further study on the applications of the Cu2Se/RGO composite materials in NLO devices.

Effect of Co-doping level on physical properties of ZnO thin films

Abstract In this work pure and Co doped ZnO thin films have been deposited onto glass substrate at different levels of Co-doping. XRD, SEM, EDX, XPS and optical spectroscopy (linear and nonlinear) techniques have been used to investigate all films. The grain size was found to increase upon Co doping from 26.2 nm to 50.3 nm. The elemental percentage obtained by EDX and XPS confirm the existence of Co in doped films which increases as increasing the percentage of cobalt salt in the starting solution. The optical band gap was estimated and found to decrease in the low Co concentrations and increases again in higher Co concentration. The dispersion was found to change from anomalous to normal upon Co-doping. In Co-doped ZnO films the dispersion changes to be normal again were modelled using the single oscillator model. The plasma frequency, the refractive index at high wavelength, the optical moments of the films were determined. The nonlinear optical properties of all films were studied using nanosecond 532 nm laser, the doped materials exhibit reverse saturable absorption and negative nonlinear refraction in contrary to pure ZnO which has positive nonlinear refraction.

Efficacy of Eu3+ on improving the near–infrared optical nonlinearities and optical limiting properties of antimony sodium borate glasses

Efficacy of Eu3+ ions nonlinear optical and optical limiting performances of antimony sodium borate gasses was investigated and discussed in detail. Nonlinear optical absorption and refraction features were evaluated in open and closed aperture Z–scan modes, respectively. The open aperture Z–scan profiles of the glasses demonstrated a reverse saturable absorption behaviour attributed to two photon absorption. The closed aperture Z–scan profiles exhibited positive type nonlinear refraction due to self–focusing effect. The two photon absorption coefficients demonstrated an increasing trend while the optical limiting threshold values demonstrated a decreasing trend as the function of Eu3+ concentration in the composition. This improved two photon absorption and decreased OL threshold coefficients with respect to Eu2O3 concentration in the compositions endorse the glasses as contending materials for the fabrication of optical limiters, which are promising use for protection of eyes and other sensitive instruments from laser induced damages.

Preparation of antimonene by laser irradiation in different solvents for optical limiting

Abstract Antimonene and antimonene oxides were prepared by laser irradiation in different solvents, including deionized water, ethanol and isopropanol. The results showed that isopropanol was proven to be more suitable for preparing high-quality antimonene with good dispersion and slight surface oxidation, which was probably attributed to its chain length and no reaction with antimony under laser irradiation. In addition, open aperture and closed aperture Z-scan experiments were carried out to study the optical limiting properties of antimonene. It was observed that antimonene prepared in isopropanol exhibited stronger optical limiting ability with a NLO absorption coefficient βeff of ~2.00 cm/GW and a positive nonlinear refraction index n2 of ~1.10 × 10−13 cm2/W, making it a good candidate for applications in optical limiting devices and laser protection.

Effect of Eu3+ in tuning the ultrafast third-order optical nonlinearity in heavy metal borate glasses

Abstract Photonic vitreous materials with high optical nonlinearities and fast response times are beneficial for designing next generation nonlinear photonic devices. Herein, large concentration of heavy metal oxide (PbO and Bi2O3) containing borate glasses activated with different Eu3+ concentrations have been designed through the melt quench technique. The non-linear optical (NLO) attributes such as nonlinear optical absorption and refractions were ascertained by utilizing the open aperture (OA) and closed aperture (CA) Z-scan techniques respectively in the spectral regions of 750–1000 nm using femtosecond laser pulses. The OA and CA Z-scan profiles demonstrated a reverse saturable absorption (RSA) nonlinearity (ascribed to two-photon absorption) and a positive nonlinear refraction nonlinearity (attributed to self-focusing effect) respectively. The NLO coefficients such as α2, n2 and χ(3) values were improved with respect to Eu3+ content in the glasses composition due to non-bridging oxygen and hyperpolarizability of Eu3+ ions. The NLO studies suggested that the examined glasses could be constructive materials for NLO device utilizations in the near infrared spectral regime.

Nonlinear optical switching and all-figures of merit in Bi2S3-xSex/PMMA nanocomposite films investigated by Z scan under visible CW laser

Bi2S3-xSex/poly(methyl methacrylate) (PMMA) nanocomposite films were prepared using microwave assisted synthesis with different compositions of x. Crystal structure, surface morphology, and optical properties were investigated to characterize the prepared nanocomposite films. The crystallinity and optical band gap of the prepared Bi2S3-xSex/PMMA were affected by x. The prepared samples showed a blue shift in the absorption edge. The laser power dependent nonlinear refraction and absorption of Bi2S3-xSex/PMMA nanocomposite films were investigated by using the Z-scan technique. The optical nonlinearity of the nanocomposite films exhibited switchover from negative nonlinear refraction to positive nonlinear refraction to negative nonlinear refraction effects, and from saturable absorption to reverse saturable absorption to saturable absorption with an increase and decrease in the composition. An interesting all-optical figure of merit was reported to assess the nanocomposite films for a practical device. It was calculated that the device all-figures of merit were based on the nonlinear response, which is important for the all-optical switching device. The results demonstrate that the optimized all-optical figures of merit can be achieved by adjusting the composition and input laser power, which can be used for the design of different all-photonic devices, and the results of nonlinear switching behavior can open new possibilities for using the nanocomposite films in laser Q-switching and mode-locking.