Third-order Nonlinear Response Research Articles

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.

Two solvent-dependent Al16 nanorings: design, synthesis and nonlinear optical limiting behavior

Presented herein is a study focusing on the effect of organic shell ligands on the configuration of the ring structure with the same nuclearity, and their photo-related applications, such as fluorescence and third-order nonlinear response.

Highly efficient octave-spanning long-wavelength infrared generation with a 74% quantum efficiency in a χ(2) waveguide

The realization of compact and efficient broadband mid-infrared (MIR) lasers has enormous impacts in promoting MIR spectroscopy for various important applications. A number of well-designed waveguide platforms have been demonstrated for MIR supercontinuum and frequency comb generations based on cubic nonlinearities, but unfortunately third-order nonlinear response is inherently weak. Here, we propose and demonstrate for the first time a χ(2) micrometer waveguide platform based on birefringence phase matching for long-wavelength infrared (LWIR) laser generation with a high quantum efficiency. In a ZnGeP2-based waveguide platform, an octave-spanning spectrum covering 5–11 μm is generated through optical parametric generation (OPG). A quantum conversion efficiency of 74% as a new record in LWIR single-pass parametric processes is achieved. The threshold energy is measured as ~616 pJ, reduced by more than 1-order of magnitude as compared to those of MIR OPGs in bulk media. Our prototype micro-waveguide platform could be extended to other χ(2) birefringence crystals and trigger new frontiers of MIR integrated nonlinear photonics.

Enhanced Mechanical, Thermal, Surface, Self-Defocusing, Electro-Optic and Photoelastic Characteristics of Doped Potassium Dihydrogen Phosphate Solitary Crystals for Optoelectronic Applications

Potassium dihydrogen phosphate (KDP) is an effective NLO substance. Much research has been concentrated on KDP crystals to increase the effectiveness of KDP's nonlinear optical property. The effectiveness of laser radiation conversion can be increased by altering its expansion. The excellent molecular chirality of organic acids is employed to improve the properties of KDP. Our main objective in this study was to describe the studies on the mechanical, thermal, surface, antibacterial, self-defocusing, and electro-optic properties of doped potassium dihydrogen phosphate solitary crystals for optical, electronic, and biological applications. The effect of itaconic acid (ITA) at concentrations ranging from 1, 3, and 5 mol% on the thermal, SEM, microhardness behaviors, NLO, antibacterial properties, and half-wave voltage of KDP (potassium dihydrogen phosphate) single crystals grown by the slow cooling technique. The existence of dopants was proved with energy-dispersive spectrometry. The mechanical properties of various temperatures for undoped and doped-KDP crystals with rising dopant combinations have been prepared, and the hardness was expanded due to doping. In contrast to several potentially dangerous microorganisms like Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, the produced crystals were exposed to antibiotic activity. The superiority of the fully-fledged crystal is determined by the etching studies. Using the Z-scan method, the good third-order nonlinear response for different planes (2 0 0), (2 1 1), and (1 1 2) of the ITA-doped KDP crystal sample was determined. Half-wave voltage may be discovered in the crystal produced via electro-optic examination. The Z-scan analysis of pure and ITA-doped KDP crystals for different planes reveals good self-defocussing and NLO responses. The electro-optic experiment generated a significant and consistent half-wave voltage. The photoelastic behavior of KDP crystals with ITA as a variable birefringent compensator has been investigated.

Influence of Au on the nucleation of Ag nanoparticles in GeO2-PbO glasses and characterization of their ultrafast third-order nonlinear responses within the plasmon resonance region

Germanate (GeO2-PbO) glasses doped with AgNO3 and co-doped with AgNO3 and Au2O3 were synthesized via melting-quenching technique. Silver nanoparticles were nucleated within the sample doped only with AgNO3 and its plasmon resonance was characterized. The influence of the addition of Au2O3 on the silver nanoparticles nucleation and on the spectroscopic properties of the produced composite materials were investigated using TEM, STEM and UV–Vis spectroscopy. Using the nonlinear ellipse rotation technique, the pure electronic contribution to the samples nonlinear refraction and absorption were characterized within the visible range, including the localized surface plasmon (LSP) resonance wavelength of the metallic nanoparticles. The real and imaginary parts of the third-order nonlinear susceptibility of the glass, composite samples and of the individual nanoparticles were also obtained. In addition, all-optical switching figures of merit of the samples were also calculated. From these results, the dispersion curves of the electronic contribution to the third-order susceptibility of the metallic nanoparticles were obtained and two figures of merit for all-optical switching of the composite materials were calculated. The studied samples are potential candidates for all-optical switching applications with exception to the one with the highest volume filling factor, whose linear and nonlinear absorption coefficients associated to the local field factor deplete the material performance around the LSP resonance wavelength. As far as we know nonlinear ellipse rotation technique was not used before to evaluate the influence of metallic nanoparticles on the nonlinear optical properties of glasses.

Measuring the Ultrafast Correlation Dynamics of a Multilevel System Using the Center Line Slope Analysis in Two-Dimensional Electronic Spectroscopy.

In a two-dimensional (2D) optical spectrum of a multilevel system, there are diagonal peaks and off-diagonal cross-peaks that correlate the different levels. The time-dependent properties of these diagonal peaks and cross-peaks contain much information about the dynamics of the multilevel system. The time-dependent diagonal peakshape that depends on the spectral diffusion dynamics of the associated transition and characterized by the frequency-fluctuation correlation function (FFCF) is well studied. However, the time-dependent peakshape of a cross-peak that provides the correlation dynamics between different transitions is much less studied or understood. We derived the third-order nonlinear response functions that describe the cross-peaks in a 2D electronic spectrum of a multilevel system that arise from processes sharing a common ground state and/or from internal conversion and population transfer. We can use the center line slope (CLS) analysis to characterize the cross-peaks in conjunction with the diagonal peaks. This allows us to recover the frequency-fluctuation cross-correlation functions (FXCFs) between two transitions. The FXCF and its subsidiary quantities such as the initial correlation and the initial covariance between different transitions are important for studying the correlation effects between states in complex systems, such as energy-transfer processes. Furthermore, knowledge of how various molecular processes over different timescales affect simultaneously different transitions can also be obtained from the measured FXCF. We validated and tested our derived equations and analysis process by studying, as an example, the 2D electronic spectra of metal-free phthalocyanine in solution. We measured and analyzed the diagonal peaks of the Qx and Qy transitions and the cross-peaks between these two transitions of this multilevel electronic system and obtained the associated FFCFs and FXCFs. In this model system, we measured negative components of FXCF over the tens of picosecond timescale. This suggests that in phthalocyanine, the Qx and Qy transitions coupling with the solvent molecule motion are anticorrelated to each other.

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.

Third-order nonlinear response of a novel organic acetohydrazide derivative: Experimental and theoretical approach

A novel nonlinear optical (NLO) organic material of N'-[(E)-(5-bromofuran-2-yl)methylidene]-2-(6-chloropyridin-3-yl)acetohydrazide (BCA) was synthesized by reflux method. The synthesized material was characterized using various analytical techniques, including spectroscopic methods (NMR, FTIR, PXRD). The UV–Vis absorption spectrum of BCA was recorded in different solvents. A strong absorption peak was observed in the 280–350 nm range, indicating its potential for UV-based optoelectronic applications. BCA shows good NLO responses (αCT, βCT, γCTvalues) with different solvents. The dielectric measurements were performed using impedance spectroscopy with varying temperatures as a function of frequency. Thermal stability of the material was evaluated using thermogravimetric analysis, indicating high thermal stability up to 153.28°C. The FMO, MEP, and NBO analyses were implemented using density functional theory (DFT) calculations to investigate the BCA molecule's electronic structure and charge distribution. The topology studies were carried out using the QTAIM and NCI to understand the structure's chemical bonding and intermolecular interactions and the structure's chemical bonding and intermolecular interactions. NLO properties of the BCA material were investigated using the Z-scan technique with a continuous wave (CW) laser, revealing a strong third-order nonlinear susceptibility (χ(3)) value of 2.44 × 10−6 e.s.u. and potential optical limiting behavior (OL threshold = 3.437 × 103 Wcm−2). The TD-HF method performed the calculated molecular static and dynamic of NLO parameters with frequency. The computed γ value of 6.2 × 10−36 e.s.u. was found to be consistent with the experimental value. The results of this study recommend that the synthesized hydrazide derivative material has potential NLO applications.

Nonlinear optical properties and transient absorption in Hibiscus Sabdariffa dye solution probed with femtosecond pulses

Highly conjugated organic molecules are attractive chromophores for nonlinear optics due to their significant third-order nonlinear response near the absorption bands located in the broad spectral range from 200 to 900 nm. In this work, we report on the wavelength-dependence of one- and two-photon absorption processes in Hibiscus sabdariffa organic dye excited by femtosecond (fs) laser pulses centered at 1030 nm and 515 nm. Z-scan and transient absorption (TA) techniques have been employed to investigate the absorption and relaxation processes in the target dye. The dye is found to have a significant negative nonlinear absorption coefficient (β) of value ∼ −2.7 × 10−11 cm/W at 515 nm probing laser pulses, while it has a positive value equal to +2.1 × 10−13 cm/W when 1030 nm laser pulses were employed. The TA decay measurements using 40 fs laser pulses, centered at 515 nm wavelength, reveal that the dye exhibits a short relaxation time of ∼3 ps attributed to the involvement of the excited state proton transfer (ESPT) process in the Hibiscus dye solution. Moreover, our time-integrated fluorescence measurements revealed that no fluorescence emission could be detected. The application of ultrashort pulses of ∼40 fs duration enabled the tracking of ESPT in the Hibiscus dye, which was not detected in previous studies that employed laser pulses of picoseconds and nanoseconds duration.

Mapping LiNbO_{3} Phonon-Polariton Nonlinearities with 2D THz-THz-Raman Spectroscopy.

Two-dimensional terahertz-terahertz-Raman spectroscopy can provide insight into the anharmonicities of low-energy phonon modes-knowledge of which can help develop strategies for coherent control of material properties. Measurements on LiNbO_{3} reveal THz and Raman nonlinear transitions between the E(TO_{1}) and E(TO_{3}) phonon polaritons. Distinct coherence pathways are observed with different THz polarizations. The observed pathways suggest that the origin of the third-order nonlinear responses is due to mechanical anharmonicities, as opposed to electronic anharmonicities. Further, we confirm that the E(TO_{1}) and E(TO_{3}) phonon polaritons are excited through resonant one-photon THz excitation.

A giant self-Kerr nonlinearity using phase-sensitive excitation in a closed three-level atomic system

A third-order nonlinear response is investigated theoretically using a closed lambda system. In this scheme, a pair of optical fields and a microwave field connect three hyperfine levels in a cyclic fashion, rendering the atomic response sensitive to the relative phase of all three fields. Changing the relative phase, we can suppress the linear response of the probe field and enhance its third order self-Kerr nonlinear response using the underlying electromagnetically induced transparency (EIT) effect. The resultant giant self-Kerr nonlinear response is comparable to or exceeding that found in atomic systems at room temperature. Most importantly, we show that the self-Kerr nonlinear response at an optical frequency can be controlled using the phase and amplitude of a frequency-separated microwave field.

Non-instantaneous third-order optical response of gases in low-frequency fields.

It is commonly assumed that for low-intensity short optical pulses far from resonance, the third-order optical nonlinear response is instantaneous. We solve the three-dimensional time-dependent Schrödinger equation for the hydrogen atom and show that this is not the case: the polarization is not simply proportional to the cube of the electric field even at low intensities. We analyze the fundamental-frequency and third-harmonic nonlinear susceptibilities of hydrogen, investigate their dependence on intensity, and find that the delays in the Kerr response rapidly approach the femtosecond time-scale at higher intensities, while the delays in the third harmonic generation remain much lower. We also propose an experimental scheme to detect and characterize the above effects.

Third-order nonlinear responses of symmetrical meso-substitutes porphyrin derivatives

A series of porphyrin derivatives with an electron-accepting group (EAG), electron-donating group (EDG) attached in phenyl at a meso-position have been prepared and studied using the Z-scan technique. Due to EAG and EDG effects, the nonlinear refractive index, n2 and nonlinear absorption coefficient, β were measured with the order of 10−5(cm2/W)and 100(cm/W), respectively. Herein, Hydroxy and methoxy groups as electron donor indicate better result in comparison with electron accepting groups like methoxycarbonyl substituted in phenyl group or pyridine attached at a meso-position of porphyrin. Although the cobalt as substituted in porphyrin can increase nonlinearity responses, EDG has more effective in enhancement of nonlinearity than metal substituted. Nonlinear optical properties of the products were discussed to the effect of cobalt ion substitution at the core of porphyrin structure. The main results indicated some symmetric porphyrins can have higher nonlinearity responses than some asymmetric porphyrins. Considering results, symmetric porphyrins can more improve nonlinearity responses than metal substituted in porphyrins. The good results of these type of porphyrins causes to be a good candidate in nonlinear optical devices.

Structure-dependent optical nonlinearity of indium tin oxide

We use post-deposition vacuum annealing of epsilon-near-zero (ENZ) indium tin oxide (ITO) nanolayers in order to modify their structural properties and enhance the third-order optical nonlinear response around the ENZ wavelength. We find that room temperature magnetron sputtering deposition results in polycrystalline thin films with an intrinsic tensile strain and a ⟨110⟩ fiber axis preferentially oriented normal to the substrate. Moreover, we demonstrate that post-deposition vacuum annealing treatments produce a secondary anisotropic phase characterized by compressive strain that increases with the annealing temperature. Finally, we use the Z-scan optical technique to accurately measure the complex nonlinear susceptibility χ(3) and the intensity-dependent refractive index change Δn for samples with different structural properties despite featuring similar ENZ wavelengths. Our intensity-dependent analysis demonstrates that an enhancement of the optical nonlinearity can be achieved by tuning the structure of ENZ nanolayers with values as large as χR(3)=(5.2 ± 0.3)×10−17m2/V2. This study unveils the importance of structural control and secondary phase formation in ITO nanolayers with ENZ optical dispersion properties for the engineering of integrated highly nonlinear devices and metamaterials that are compatible with the scalable silicon photonics platform.

Rocking Curves of X-Ray Asymmetrical Laue Diffraction in a Crystal with the Third-Order Nonlinear Response

Rocking Curves of X-Ray Asymmetrical Laue Diffraction in a Crystal with the Third-Order Nonlinear Response

Growth and characterization of barium bis para-nitrophenolate para-nitrophenol tetrahydrate single crystal for NLO applications

Single crystals of barium bis para-nitrophenolate para-nitrophenol tetrahydrate (BBPNT) was grown using slow evaporation technique with the crystal dimensions of 15 × 10 × 6 mm3. The structure of the BBPNT crystal was examined by X-ray diffraction and the functional groups present in the compound were identified using FTIR spectrum. The optical and electrical properties were characterized by UV–Vis spectrum and dielectric studies respectively. Thermal properties of the grown crystal were investigated by using thermo-gravimetric (TG) and differential thermal analyses (DTA). The mechanical behavior of the grown crystal was studied using Vickers microhardness test. Using the Kurtz-Perry powder method, the second-harmonic generation efficiency was found to be 15.75 times greater than to that of KDP. Third-order nonlinear response was studied using Z-scan technique with a He-Ne laser (632.8 nm) and NLO parameters such as intensity dependent refractive index, nonlinear absorption coefficient and third-order susceptibility were also estimated. In the PL spectra, a broad band observed at 525 nm suggests its applications for fabricating green laser and new tunable laser system. The laser damage threshold value of BBPNT was found to be 5.09 GW/cm2 using an Nd: YAG laser.

Effect of intravalley and intervalley electron-hole exchange on the nonlinear optical response of monolayer MoSe2

The coherent third-order nonlinear response of monolayer transition-metal dichalcogenide semiconductors, such as ${\mathrm{MoSe}}_{2}$, is dominated by the nonlinear exciton response, as well as biexciton and trion resonances. The fact that these resonances may be spectrally close together makes identification of the signatures, for example in differential transmission (DT), challenging. Instead of focusing on explaining a given set of experimental data, a systematic study aimed at elucidating the roles of intravalley and intervalley long-range electron-hole $(e\ensuremath{-}\mathrm{h})$ exchange on the DT spectra is presented. Previous works have shown that the $e\ensuremath{-}\mathrm{h}$ long-range exchange introduces a linear leading-order term in the exciton dispersion. Based on a generalized Lippmann-Schwinger equation, we show that the presence of this linear dispersion term can reduce the biexciton binding energy to zero, contrary to the conventional situation of quadratic dispersion where an arbitrarily weak (well-behaved) attractive interaction always supports bound state(s). The effects of spin scattering and the spin-orbit interaction caused by $e\ensuremath{-}\mathrm{h}$ exchange are also clarified, and the DT line shape at the exciton and trion resonance is studied as a function of $e\ensuremath{-}\mathrm{h}$ exchange strength. In particular, as the exciton line shape is determined by the interplay of linear exciton susceptibility and the bound-state two-exciton resonance in the $T$ matrix, the line shape at the trion is similarly determined by the interplay of the linear trion susceptibility and the bound-state exciton-trion resonance in the $T$ matrix.

The effect of nanorod on the nonlinear optical properties of quantum dot in a hybrid structure: under a quasistatic approximation

In a hybrid structure consisting of a nanorod and a core/shell quantum dot, the interparticle interactions of elements and the effect of the optical response of nanorod on the third-order nonlinear optical response of quantum dot are investigated. The effective parameters in these interactions such as the enhancement factors, type of structural configuration, dimensional ratio, type of background medium, quantum dot size and interparticle distance are studied in the structure for engineering the system to an optimum response. The enhancement factors of field due to the presence of nanorod are obtained in the site of quantum dot, followed by the third-order optical nonlinear response quantum dot is calculated by using the local field theory. It is seen for the situation where quantum dot is perpendicular to the axis of nanorod, the interparticle interactions and enhancement factors have maximum amount at a given aspect ratio of nanorod (about 2.5), depending on the type of surrounding environment. Therefore, the nanorod can produce great nonlinearities atthe quantum dot compared to the spherical nanoparticle into the hybrid structure . As well, it is found that the larger sizes of quantum dot and less interparticle distances cause to the stronger coupling and thereby larger optical nonlinearity in the quantum dot.

The Study of Platinum Coated Carbon Nanotubes as Third-Order Nonlinear Optical Materials

Platinum-multiwall carbon nanotubes (Pt-MWCNTs) was prepared through a chemical reduction and was characterized by using UV–Vis Spectrophotometer, Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microscopy with Energy Dispersive X-Ray (FESEM/EDX) and Raman Spectroscopy. Through this chemical reduction, Pt ions were reduced by the addition of sodium dodecyl sulfate (SDS) and Pt was in-situ deposited on the exterior walls of MWCNTs. TEM and FESEM/EDX analyses have confirmed the presence of Pt on the surface of MWCNTs. From Raman Spectroscopy, the ID/IG of MWCNT is 0.66 while ID/IG of Pt-MWCNT is 0.71, showing that not much defects were resulted by the functionalization of Pt on the surface of MWCNT, while from UV-Vis spectra, Pt-MWCNT is found to absorb at about 265 nm due to the presence of Pt nanoparticles that caused a weak surface plasmon resonance (SPR) absorption in the UV region which will contribute to the NLR measurement. The resulted Pt-MWCNTs was then investigated its third-order nonlinearity response as suspension in water using continuous wave laser and z-scan measurement at 532 nm. Pt-MWCNT displays good transmittance profile and self-defocusing effect with excitation intensity is in order of 10-9 cm2/W. The presence of Pt on the surface of MWCNT has contributed to intrinsic properties and resulted in nonlinear refractive (NLR) effect. Thus, Pt-MWCNT is considered to possess significant third-order nonlinear responses considering its low Pt content and has potential in the development of photonics devices.

Giant Third-Order Nonlinear Response of Liquids at Terahertz Frequencies

The nonlinear response of liquids in the terahertz regime has recently attracted significant interest, even though very few measurements have been reported. Here, we report on our measurements based on a $z$-scan technique of the nonlinear refractive-index coefficient ${n}_{2}$ at terahertz frequencies for several liquids with noncentrosymmetric molecules, specifically, water, ethanol, and $\ensuremath{\alpha}$-pinene. We describe how the value of ${n}_{2}$ depends on the physical parameters of these molecules. The measured values of ${n}_{2}$ of the liquids in the terahertz region are as much as 6 orders of magnitude larger than their corresponding values in the visible or near-IR. Through a simple theoretical model, we confirm that the predominant source of this large third-order nonlinearity is the second-order perturbative component of the vibrational response of these molecules, which have resonances in the mid-IR.