Nonlinear Refraction Properties Research Articles

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.

Nonlinear refraction and absorption properties of optical materials for high-peak-power long-wave-infrared lasers

Optical materials transparent in the CO2 laser wavelength range have been evaluated regarding their suitability for components in ultrashort-pulse (≤ a few ps), high-peak-power (≥ a few TW) long-wave infrared (LWIR) lasers. We provide values for the nonlinear refractive index (n2) for seventeen materials, and onsets for nonlinear absorption for eleven materials. Characterizations were performed using a 2 ps laser pulse at λ=9.2μm. This paper methodically presents the newly acquired data in conjunction with existing literature on linear optical properties, establishing it as a comprehensive reference for designing high-peak-power LWIR laser systems.

Study of the Nonlinear Optical Properties of Ag/CdTe Composites

CdTe films, Ag nanoparticles, and Ag/CdTe composites are successfully fabricated on substrates by means of the physical vapor deposition process. The morphological structure, crystal growth and bandgap of the samples are specifically characterized by scanning electron microscopy, X‐ray diffractometer, and UV–vis spectrophotometer. Picosecond (ps) Z‐scan technology is used to investigate the nonlinear optical (NLO) properties of the composites under 532 nm. The results indicate that all samples exhibit saturated absorption nonlinear absorption properties and self‐dispersion nonlinear refraction properties. In addition, Ag nanoparticles can improve the NLO properties of Ag/CdTe composites, and this improvement is more obvious with the increase of Ag power. The results show that the excellent properties of the Ag/CdTe composites are expected to make them an ideal material for use in the photoelectric field.

Nonlinear optics properties of Ni-Sb2Se3 nanofilms in the near-infrared region.

S b 2 S e 3 is an emerging material in recent years, and past studies have shown that it has good optoelectronic properties when doped with metals. In this paper, pure S b 2 S e 3 films and N i-S b 2 S e 3 films with different doping contents (1, 2, 3W) were prepared by magnetron sputtering technology. The nonlinear optics properties of the sample films were investigated using femtosecond (fs) Z-scan technology under 800nm. The results showed that both pure S b 2 S e 3 and doped films exhibited reverse saturated absorption (RSA), and the occurrence of the reverse saturated absorption behavior of the doped films was mainly due to two-photon absorption (TPA), free carrier absorption (FCA), and the presence of defective energy levels. Compared with pure S b 2 S e 3 films, N i-S b 2 S e 3 films exhibit significantly enhanced nonlinear absorption properties and nonlinear refractive properties. By increasing Ni sputtering power and incident laser energy, the nonlinear optic properties of N i-S b 2 S e 3 films are enhanced. By testing the sample films using SEM, XRD, and UV-Vis techniques, we found that Ni metal doping greatly improved and optimized the crystallinity of the films and adjusted the optical band gap.

Nonlinear absorption and refraction of Cs3Cu2Br5 perovskite

Halide perovskite (Cs3Cu2Br5) is synthesized by a thermal injection method. The X-ray diffraction (XRD) proves that the Cs3Cu2Br5 crystal phase is an intersection phase. The Cs3Cu2Br5 organic glasses are fabricated by dispersing Cs3Cu2Br5 materials in methyl methacrylate (MMA). The nonlinear absorption (NLA) and the nonlinear refraction (NLR) performances of Cs3Cu2Br5/PMMA organic glasses are measured via the open-aperture (OA) and the closed-aperture (CA) Z-scan technique, respectively. The samples show typical reverse saturable absorption (RSA) and self-focusing effect with the change of input energy (40–72 μJ). Meanwhile, the room-temperature photo-luminescence (PL) measurement reveals light emission for Cs3Cu2Br5. The effects on nonlinear optical (NLO) properties are investigated by controlling the input energy and the amount of the sample. The Cs3Cu2Br5/PMMA organic glasses exhibit excellent NLA and NLR properties. The NLA coefficient of (Cs3Cu2Br5)18/PMMA organic glass is much higher than those of lead-containing perovskite such as CsPbCl3 and CsPbBr3 nanosheets. This results in Cs3Cu2Br5/PMMA organic glasses show superior optical limiting (OL) performance. The Cs3Cu2Br5 perovskite materials show great potential in devices such as light-emitting diodes and optical switches.

Nonlinear Optical Studies of [Pt17(CO)12(PPh3)8]n+ Metal Nanoclusters and Their Enhancement via All-Plastic Photonic Crystal Cavity

Metal nanoclusters of atomic precision have recently emerged as potential candidates for nonlinear optical applications owing to their strong quantum confinement effects. Herein, we report the nonlinear absorptive and refractive properties of platinum-17 (Pt17) metal nanoclusters stabilized by carbon monoxide and triphenyl phosphine ligands. The open aperture z-scan studies in the nanosecond regime reveal a transmittance dip at the focus characteristic of molecule-like behavior and discrete energy levels. The clusters also exhibited a significantly lower optical limiting threshold value and self-defocusing behavior which can be deployed to resist intense optical radiation. We also demonstrate a photonic crystal cavity-assisted enhancement in the absorptive nonlinearity of the synthesized clusters as a result of intense field localization in the defect layer. Our study throws light on the application of these ultrasmall structures in nanophotonic devices.

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.

Nonlinear absorption and nonlinear refraction in single-phased Ti1−xInxO2 (x = 0∼0.1) thin films

In this study, single-phased rutile T i 1 - x I n x O 2 ( x = 0 ∼ 0.1 ) thin films were deposited on fused quartz substrates using a pulsed laser deposition technique. The transmission spectra reveal that the films show good transparency in the wavelength range of 330–900 nm. The absorption edge of the T i 1 - x I n x O 2 thin films is blueshifted compared with that of undoped T i O 2 films. A single-beam z -scan method using a pulse laser operating at 532 nm with a duration of 55 ps was employed to evaluate the films’ nonlinear optical characteristics. The results show that the prepared T i 1 - x I n x O 2 films exhibit nonlinear saturable absorption and negative nonlinear refraction properties. The doping of In ions into T i O 2 does not change the nonlinear optical absorption significantly. However, the nonlinear refractive index of T i 1 - x I n x O 2 film obviously increases with the increasing doping of In ions. The local electron-pinned defect-dipoles and widening bandgaps in the T i 1 - x I n x O 2 thin films could be used to explain the observed results.

Nonlinear optical properties of tin telluride topological crystalline insulator at a telecommunication wavelength

Topological crystalline insulators (TCIs) have a new topological state where topological nature comes from crystal symmetries without necessitating spin-orbit coupling. Their superb electronic, magnetic, and superconducting properties have intensively been studied. Despite great potential, however, their nonlinear optical properties are rarely examined. For the first time, this study investigates the nonlinear refraction and absorption properties of SnTe TCIs using the Z-scan techniques. A high nonlinear refractive index of -0.111 ± 0.004 cm2/GW and a nonlinear absorption coefficient of -(2.02 ± 0.135)× 103 cm/GW are obtained from SnTe TCIs at the commercially important telecommunication wavelength, being superior and/or comparable to two dimensional (2D) materials and/or renowned photonic crystals. Ab-initio simulations show that SnTe TCIs are suitable for ultrabroad-band application and mechanically stable at high thermal conditions. Lastly, we demonstrate that 1550 nm mode-locked femtosecond lasers can readily be achieved by exploiting the conspicuous nonlinear optical absorption of SnTe TCIs without using any nano-engineered ones like quantum dots. This study strongly indicates a promising potential of SnTe TCIs in a wide range of nonlinear optics, opening an avenue toward advanced TCIs-based photonic technologies.

Single crystal structure of cobalt and nickel complexes constructed by imidazole ligand and their polycrystalline thin films for nonlinear optical refraction properties

The single crystals of new cobalt and nickel complexes constructed by the imidazole ligand: hexakis(imidazole)-cobalt(II) dichloride tetrahydrate ((C18H24N12Co)Cl2•4(H2O), HICDCTH) and hexakis(imidazole)-nickel(II) acetate dihydrate ((C18H24N12Ni)(CH3COO)2•2(H2O), HINADH) have been obtained and their single crystal structure were determined by X-ray single crystal diffraction. Their polycrystalline thin films on quartz substrates were prepared using in-situ crystallization methods. The surface morphology of the polycrystalline thin films were studied by atomic force microscopy. The nonlinear optical refraction properties of the polycrystalline thin films were investigated by using closed aperture Z-scan technique with 20 picosecond pulses at wavelength 532 nm. Time-dependent density-functional theory with the basis set LanL2DZ were used in theoretically computing their maximum absorption wavelengths, frontier molecular orbitals and molecule′s second hyperpolarizability γ values.

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.

Nonlinear absorption, refraction and optical limiting properties of cobalt molybdate microcrystals

Cobalt molybdate (CoMoO4) microcrystal was synthesized by a hydrothermal method. The CoMoO4 microcrystal was dispersed in methyl methacrylate (MMA) that was polymerized to polymethyl methacrylate (PMMA) to prepare CoMoO4/PMMA organic glass. The successful synthesis of CoMoO4 was verified by Raman spectroscopy. The CoMoO4 microcrystal was characterized by scanning electron microscopy (SEM). The results indicate that the CoMoO4 microcrystal is microrod. The diameter and length of the sample are about 0.5–3 μm and 2–20 μm. The band gap of CoMoO4/PMMA is about 3.5 eV. The nonlinear absorption (NLA) and refraction properties of CoMoO4/PMMA organic glasses were investigated for the first time by a Z-scan technique. The laser pulse energy is 7–20 μJ. The results indicate that CoMoO4/PMMA organic glasses exhibit good reverse saturable absorption (RSA) and self-defocusing effects. NLA and refraction coefficients are β = 68 cm GW−1 and γ = −1.4 × 10−4 cm2 GW−1 at the laser pulse energy of 20 μJ, respectively. The enhanced RSA and self-defocusing effects make the CoMoO4/PMMA organic glasses exhibit excellent optical limiting (OL) performance. The nonlinear absorption, refraction and OL properties of CoMoO4/PMMA organic glasses can be controlled by adjusting the laser pulse energy and the amount of CoMoO4 in PMMA.

Nonlinear optical behavior of Au@Ag core- shell nanostructures

Core-shell structure has been getting tremendous research interest due to their tunable multifunctional properties, induced as a result of the co-occurrence of more than one nanostructured phases. Here we report detailed nonlinear optical studies of Au@Ag core-shell nanostructures under ns pulse excitation. The size and shell thickness of the core-shells were obtained from TEM images. A significant blue shift from 519 nm to 411 nm in surface plasmon maxima is observed on forming Ag (shell) layer on Au (core) nanosphere and a slight red shift (411 nm to 425 nm) was observed as the shell thickness increases from 7.5 to 22.5 nm. All the samples exhibited reverse saturable absorption behavior and the extent of optical limiting activity enhanced on increasing the shell thickness. Nonlinear refraction properties of the samples were also analyzed and all the samples were found to be exhibiting negative nonlinearity. Improved optical limiting activity on increasing shell thickness of the studied system could be attributed to enhanced local field effect and nonlinear scattering effect, which is confirmed from the finite difference time domain simulation analysis. The good nonlinear optical properties of Au@Ag core-shell structures ensure its potential for future nonlinear optical applications.

Regulation and enhancement of the nonlinear optical properties of reduced graphene oxide through Au nanospheres and Au@CdS core-shells.

Regulating nonlinear optical (NLO) absorption and refraction properties of graphene is significant in nonlinear photonics. In this work, the functionalizing strategy of quantum dots (QDs) was used for the regulation of the NLO properties of reduced graphene oxide (rGO) with Au nanospheres and Au@CdS core-shells. The third-order NLO properties of rGO-Au and rGO-Au@CdS nanocomposites were investigated by Z-scan technique with 38 ps laser pulses at 532 nm wavelength. The saturation absorption (SA) of rGO was weakened when it was combined with Au nanospheres and switched to reverse saturation absorption (RSA) when combined with Au@CdS core-shells as irradiance intensity increased. The strength of RSA was tunable with the size of Au@CdS core-shells. Meanwhile, the nonlinear susceptibility of rGO was weakened with the complex Au but was tunable with the complex Au@CdS and realized two times enhancement. The effect of charge transfer mechanism was proposed to explain the regulated effect.

Intense nonlinear optical properties of ZnS quantum dot doped nematic liquid crystal compounds

The present work is devoted to the study of third order optical nonlinearity of pure and zinc sulfide (ZnS) quantum dot doped nematic liquid crystal (NLC). The nonlinear absorption and nonlinear refraction properties of pristine and quantum dot doped nematic liquid crystals are discussed. ZnS quantum dots of average size 4 nm are synthesized by chemical co-precipitation method using PVA as a capping agent. The nanostructure of prepared ZnS QDs was confirmed through XRD, TEM, and UV–Visible absorption characterizations. A sensitive, single beam z-scan technique is implemented to determine the nonlinear absorption coefficient and nonlinear refraction coefficient of the samples. The pump radiation is at 532 nm, the second harmonic generation of Q switched Nd: YAG laser having a pulse width of 7 ns and a repetition rate of 10 Hz. The maximum value obtained for third order susceptibility for the 5PCH-ZnS system is 7.07 × 10−10 esu and that for the 5CB-ZnS system is 5.145 × 10−10 esu. The possible mechanisms for the observed nonlinear absorption and refraction are discussed. We observed a notable increase in the optical nonlinearity for the doped system and found to be decreasing at the highest doping concentration under consideration. An optical limiting threshold of 1.99 J/cm2 obtained for the 5PCH-ZnS system indicates that the sample under study can be a potential candidate for optical limiting application.

Experimental and Theoretical Study of the Nonlinear Refraction Properties of Cobalt and Nickel Complexes Polycrystal Thin Films Constructed by Imidazole Ligand

Experimental and Theoretical Study of the Nonlinear Refraction Properties of Cobalt and Nickel Complexes Polycrystal Thin Films Constructed by Imidazole Ligand

Tunable Non-linear Refraction Properties and Ultrafast Excited State Dynamics of Dicyanomethylene Dihydrofuran Derivative.

The third order non-linear optical response of a dicyanomethylene dihydrofuran compound (DCDHF-2V) was investigated using a Z-scan technique in picosecond and nanosecond time regimes. The results show that DCDHF-2V has excellent excited state non-linear refraction properties on both time regimes, and the non-linear refraction index is also solvent-dependent in the nanosecond regime. The excited state relaxation dynamics of DCDHF-2V were demystified via femtosecond transient absorption spectroscopy. The TA spectra reveal that the solvent viscosities have a substantial impact on the excited state relaxation of DCDHF-2V. The exotic photophysical phenomena in DCDHF-2V reported herein can shed new light on future development of small organic non-linear optical materials with large non-linear coefficients and fast response.

Cobalt and zinc tetraphenylporphyrins thin films for all optical switching application

Abstract Cobalt and zinc tetraphenylporphyrins have been obtained and characterized by X-ray single crystal diffraction. Their crystal thin films were prepared using direct growth on quartz substrates. The surface morphology of the thin films were studied by atomic force microscopy. The nonlinear optical refraction properties of the thin films were investigated by using closed aperture Z-scan technique with 20 ps (ps) pulses at wavelength 1064 nm. Time-dependent unrestricted Hartree-Fock (TDUHF) with the basis set LanL2DZ were used in computing the linear and non-linear optical properties.

Nonlinear optical modulation of MoS2/black phosphorus/MoS2 at 1550 nm

A sandwich structure of black phosphorus nanosheets coupled with MoS2 nanosheets was prepared via liquid exfoliation and hydrothermal methods. An enhancement of saturated absorption was observed at the long wavelength of 1550 nm via the femtosecond Z-scan technique, which is much stronger than its nonlinear response at 400 and 800 nm. According to the ultrafast pump-probe results, this strong saturated absorption can be attributed to the dominant role of a slow relaxation process, corresponding to the enhanced interface and defects effects. Moreover, the nonlinear refractive properties were found to transform from self-focusing to self-defocusing with the increasing of excitation wavelength from visible to near-infrared region, which can be qualitatively explained by an effective medium approach, similar to noble metal nanomaterials. These results suggest that the synthesized MoS2/BP/MoS2 may have potential applications for nonlinear optical devices.

Cubic Nonlinearity of Molybdenum Disulfide Nanoflakes.

The cubic optical nonlinearity of molybdenum disulfide (MoS₂) nanoflakes was characterized by Z-scan and I-scan with resonant excitation. The excitation source was a ~6 ns laser at 532 nm with a 10 Hz repetition rate. The open and closed Z-scan analyzed the nonlinear absorption and nonlinear refraction properties of MoS₂ nanoflakes. The I-scan technique characterized the nonlinear transmittance properties of MoS₂ nanoflakes at the peak and valley of closed Z-scan trace as a function of excitation intensity.