Field Of Nonlinear Optics Research Articles

Self‐Referencing 3D Characterization of Ultrafast Optical‐Vortex Beams Using Tilted Interference TERMITES Technique

AbstractFemtosecond light pulses carrying optical angular momentums (OAMs), possessing intriguing properties of helical phase fronts and ultrafast temporal profiles, enable many applications in nonlinear optics, strong‐field physics, and laser micromachining. While generation of OAM‐carrying ultrafast pulses and their interactions with matters are intensively studied in experiments, 3D characterization of ultrafast OAM‐carrying light beams in spatiotemporal domain has, however, proved difficult to achieve. Conventional measurement schemes rely on the use of a reference pulsed light beam, which needs to be well characterized in its phase front and to have sufficient overlap and coherence with the beam under test, largely limiting practical applications of these schemes. Here a self‐referencing set‐up is demonstrated based on a tilted interferometer that can be used to measure complete spatiotemporal information of OAM‐carrying femtosecond pulses with different topological charges. Through scanning one interferometer arm, the spectral phase over the pulse spatial profile can be obtained using the tilted interference signal, and the temporal envelope of the light field at one particular position around its phase singularity can be retrieved simultaneously, enabling 3D beam reconstruction. This self‐referencing technique, capable of measuring spatiotemporal ultrafast optical‐vortex beams, may find many applications in fields of nonlinear optics and light–matter interactions.

Nickel curcumin complexes: Physico chemical studies and nonlinear optical activity

Current work presents a unique material for nonlinear optical applications. Two Ni-complexes: Nickel-Chloride-Curcumin NiCl2(Cur).2H2O (NiClCur) and Nickel-Acetate-Curcumin Ni(C2H2O3)2·2H2O (NiAcCur) were synthesized using curcumin (Cur) as a base ligand. Various spectroscopic techniques like UV–Vis, FT-IR, 1H NMR, 13C NMR, Mass spectrometry, and Elemental analysis have been used to determine both complexes’ structural characteristics. 1H NMR study discloses the complexation between metal and ligand. Theoretical analysis of NiClCur and NiAcCur is accomplished by using Conceptual-Density-Functional-Theory (CDFT) methodology. CDFT-based descriptors such as HOMO-LUMO energy gap, dipole moment, molecular hardness, softness, electronegativity, and electrophilicity index of both species are calculated. HOMO-LUMO energy gap of NiClCur and NiAcCur are found as 2.699 eV and 2.400 eV respectively. The Ni-complexes were studied for nonlinear optics (NLO) and transmission measurements were performed using a Z-scan method with nanosecond laser pulses at 532 nm. Along with transmission measurements, the optical limiting (OL) behavior of Ni-complexes was calculated. Quantitative analysis of the two-photon absorption coefficients for NiClCur and NiAcCur was determined to be 5 × 10−11 m/W and 9 × 10−12 m/W, respectively. The normalized transmittance (NT) dropped from 100% to 60% in both NiClCur and NiAcCur. This work opens up a new insight into the field of NLO, where Cur-based metal novel complexes are implemented.

Linear and Nonlinear Optical Field Manipulations with Multifunctional Chiral Coding Metasurfaces

AbstractOptical chirality, which describes the property of asymmetric light–matter interactions for different handedness of polarization, plays an important role in physical photonics, biochemical processes, and molecular recognition. Recently, asymmetric optical responses of chiral nanostructures provide a wide platform for arbitrary and artificial manipulation of optical chirality. Here, a design strategy is theoretically and experimentally introduced to realize a spin‐selective coding metasurface in both linear and third harmonic regimes with giant chirality. Significant chiral transmission and wavefront control are realized by a chiral coding metasurface composed of amorphous silicon (a‐Si) resonators with C2 symmetry. The resonators and the enantiomers are encoded with different transmission amplitude and phase. The information channels are expanded to six‐fold with simultaneous multi‐foci focusing and multi‐vortex generation operating in different polarization and linear/nonlinear channels. The nonlinear chiral high‐contrast imaging is also achieved for spin‐selective pattern information transmission. The study significantly expands the information capacity of coding metasurfaces, and can be readily applied in optical systems for information transmission in both linear and nonlinear regimes.

Efficient two-process cascaded frequency conversion based on Stark-chirped rapid adiabatic passage

A comprehensive study of two simultaneous three wave mixing processes and second harmonic generation, followed by difference frequency generation, based on Stark-chirped rapid adiabatic passage (SCRAP), is presented. The complete conversion from the input pump laser to the signal laser and the idler laser pair is achieved without exciting intermediate laser, and the frequencies of the signal laser and the idler laser are close to the input pump laser. This process is similar to the Stark-chirped rapid adiabatic passage for atomic population transfers, and we bring the analogy from atomic systems to our field of nonlinear optics. A two-process cascaded frequency conversion model based on Stark-chirped rapid adiabatic passage is established, and we analytically obtain the adiabaticity condition required for complete conversion. The research results show that this theoretical model results in a large tuned wavelength of about 380 nm with almost complete conversion of the input pump laser to the signal laser and idler laser.

Research progress of nonlinear optical properties of integrated two-dimensional materials

Photonic platforms with excellent nonlinear optical characteristics are very important to improve the devices' performance parameters such as integration, modulation speeds and working bandwidths for all-optical signal processing. The traditional processing technology of photonic platforms based on silicon, silicon nitride and silicon oxide is mature, but the nonlinear function of these optical platforms is limited due to the characteristics of materials; Although two-dimensional (2D) materials possess excellent nonlinear optical properties, their nonlinear potentials cannot be fully utilized because of their atomic layer thickness. Integrating 2D materials with mature photonic platforms can significantly improve the interaction between light and matter, give full play to the potentials of 2D materials in the field of nonlinear optics, and improve the nonlinear optical performances of the integrated platforms on the basis of fully utilizing the mature processing technology of the photonic platforms. Based on the above ideas, starting from the basic principle of nonlinear optics (Section 2), this review combs the research progress of various nonlinear photonic platforms (resonators, metasurfaces, optical fibers, on-chip waveguides, etc.) heterogeneously integrated with 2D materials, realized by traditional transfer methods (Section 3) and emerging direct-growth methods (Section 4) in recent years, and the introduction is divided into second-order and third-order nonlinearity. Comparing with the transfer methods, the advantages of using direct-growth methods to realize the heterogeneous integration of 2D materials and photonic platforms for the study of nonlinear optics are expounded, and the technical difficulties to be overcome in preparing the actual devices are also pointed. In the future, we can try to grow 2D materials directly onto the surfaces of various cavities to study the enhancement of second-order nonlinearity; we can also try to grow 2D materials directly onto the on-chip waveguides or microrings to study the enhancement of third-order nonlinearity. Generally speaking, the research on integrated nonlinearity by directly growing 2D materials onto various photonic structures has aroused great interest of researchers in this field. As time goes on, breakthrough progress will be made in this field, and technical problems such as continuous growth of high-quality 2D materials onto photonic structures and wafer-level large-scale preparation will be broken through, further improving the performance parameters of chips and laying a good foundation for optical communication, signal processing, optical sensing, all-optical computing, quantum technology and so on.

Strong non-linear optical response of Sb2Se3 nanorods in a liquid suspension based on spatial self-phase modulation and their all-optical photonic device applications.

The field of nonlinear optics is constantly expanding and gaining new impetus through the discovery of fresh nonlinear materials. Herein, for the first time, we have performed spatial self-phase modulation (SSPM) experiments with an emerging anisotropic Sb2Se3 layered material in a liquid suspension for an all-optical diode and all-optical switching application. The third-order broadband nonlinear optical susceptibility (χ(3)single layer ∼ 10-9 esu) and nonlinear refractive index (n2 ∼ 10-6 cm2 W-1) of Sb2Se3 have been determined using a 671 nm laser beam. This result could be unambiguously explained by the anisotropic hole mobility of Sb2Se3. The linear relationship of χ(3) and carrier mobility emphasizes the establishment of nonlocal hole coherence, the origin of the diffraction pattern. Consequently, the time evolution of diffraction rings follows the 'Wind-Chime' model. A novel photonic diode based on Sb2Se3/SnS2 has been demonstrated using the nonreciprocal propagation of light. The self-phase modulation (SPM) technique uses laser lights of different wavelengths and intensities to demonstrate the all-optical logic gates, particularly OR logic gates. The exploration of nonlinear optical phenomena in Sb2Se3 opens up a new realm for optical information processing and communication. We strongly believe that this result will help to underpin the area of optical nonlinearities among its various applications.

Study of nonlinear optical diffraction patterns using machine learning models based on ResNet 152 architecture

As the advancements in the field of artificial intelligence and nonlinear optics continues, new methods can be used to better describe and determine nonlinear optical phenomena. In this research, we aimed to analyze the diffraction patterns of an organic material and determine the nonlinear optical phase change and nonlinear refraction index of the material in question by utilizing the ResNet 152 convolutional neural network architecture in the regions of laser intensity that the diffraction rings are not clearly distinguishable. This approach can open new sights for optical material characterization in situations where the conventional methods do not apply.

Multi-Pulse Bound Soliton Fiber Laser Based on MoTe2 Saturable Absorber.

Bound solitons have become a hot topic in the field of nonlinear optics due to their potential applications in optical communication, information processing and radar systems. However, the trapping of the cascaded bound soliton is still a major challenge up to now. Here, we propose and experimentally demonstrate a multi-pulse bound soliton fiber laser based on MoTe2 saturable absorber. In the experiment, MoTe2 nanosheets were synthesized by chemical vapor deposition and transferred to the fiber taper by optical deposition. Then, by inserting the MoTe2 saturable absorber into a ring cavity laser, the two-pulse, three-pulse and four-pulse bound solitons can be stably generated by properly adjusting the pump strength and polarization state. These cascaded bound solitons are expected to be applied to all-optical communication and bring new ideas to the study of soliton lasers.

Large-area opposing double nanocrescents-nanoparticle arrays for polarization dependent SERS effects

An efficient fabrication route is developed to produce a large-area and highly-ordered Ag opposing double nanocrescents-nanoparticle (AODCP) array by combining the ultra-thin alumina membrane (UTAM) mask, annealing and angle deposition techniques. This strategy exhibits a controllable fabrication process of crescent-shaped plasmonic nanostructures wherein the number and orientation of the nanocrescents can be independently tuned. The localized electrical fields are extremely enhanced in the nanogaps and at the tips of the nanocrescents due to the coupling between the nanocrescents and nanoparticles, and their distributions depend on the polarization of the incident light, which are confirmed by numerical simulations. Polarization-dependent surface enhanced Raman scattering (SERS) is experimentally demonstrated on this AODCP substrate with remarkable sensitivity and reproducibility. The results suggest the proposed AODCP arrays are promising for the applications in the fields of nonlinear optics, optical sensors and surface enhanced spectroscopy.

Optical nonlinearity of a dual-frequency nematic liquid crystal via temperature-mediated mapping of dielectric anisotropy.

Liquid crystals are of great interest in the field of nonlinear optics due to their efficient response to low intensity light fields. Here we present a new, to the best of our knowledge, mechanism of a nonlinear optical response which is observed for a dye-doped dual-frequency nematic liquid crystal. The local increase in temperature caused by the absorption of light beam in the liquid crystal medium leads to spatial variation and inversion of the sign of the dielectric anisotropy. When an alternating current electric field with a frequency close to the cross-over frequency is applied to the liquid crystal cell, the planar orientation sustains at the beam periphery, but elastic deformation occurs in the irradiation region. In the case of a dye dopant with negative absorption dichroism, a first-order orientational transition with large bistability region is obtained.

Interface engineering of modified ZnO@MoS2 heterostructure to efficiently enhance charge transfers and carrier regulation

The metal oxide combined with transition metal dichalcogenides (TMDs) was used to regulate the absorption band range and nonlinear transmittance for TMDs base materials. The interfacial charge transfers and carrier regulation of ZnO and TMDs are very important for the novel two-dimensional semiconductor optoelectronic device technology in the future. Herein, the synthesis, properties and applications of ZnO and MoS2 composites are reviewed. The syntheses of modified ZnO@MoS2 heterostructure by the two-step hydrothermal were reported for the first time. The growth and electron transfer mechanisms of heterostructure were systematically studied. The surface of the ZnO@MoS2 heterostructure can be confirmed by scanning electron microscopy, which is self-assembled into nanoflowers from MoS2 nanosheets. The X-ray diffractometer (XRD) and Raman spectra of ZnO@MoS2 heterostructure were measured, and it was confirmed that ZnO can promote the accumulation of MoS2 nanosheets. The flower-like MoS2 nanosheets were “planted” on the surface of ZnO nanorods, attributing to the two growth orientations of MoS2 in C-axis C// and C⊥. Based on the linear optical behavior of the samples in the UV–Vis bands, the position and effective state density of defect state can be estimated qualitatively. The above behavior is beneficial to understand the band gap narrowing of MoS2 and the effect of ZnO nanorods on the photoelectric properties of MoS2 was studied in detail. In addition, type-I band alignment was established at the interface between ZnO nanorods and MoS2 nanosheets, which increase electron-hole pairs separation of modified ZnO@MoS2 heterostructure. The modified ZnO@MoS2 heterostructure with controllable photoelectric structure display excellent photoelectric characteristics, which are desirable for field of nonlinear optics, photoelectric functional devices, energy environment and other fields.

New solitary wave and computational solitons for Kundu–Eckhaus equation

The goal of this research is to find novel optical solutions to the Kundu–Eckhaus equation, which possess crucial roles in the field of nonlinear optics. A collective variable (CV) strategy is adopted to solve governing equation including the Raman effect and quintic nonlinearity. This method is a suitable to deal with both conservative and non-conservative systems by exposing a set of equations of motion regardless of nonlinearities or dissipative components. The parameters employed in this approach are chirp, temporal position, phase, amplitude, frequency and width, namely, collective variables. The fourth order Runge–Kutta technique is a well-known numerical scheme that aims towards the solution of the resulting system of ordinary differential equations representing the variables involved in the pulse ansatz. This technique presents the evolution of pulse parameters with regard to propagation variables. The graphical profiles at suitable values of pulse parameters are also provided. The unified technique is also applied to find soliton solutions. The obtained solution is a periodic solitary wave, showed graphically. The results developed in this article are found to be new in the literature and the approach utilized, can be applied to solve a variety of nonlinear problems in the mathematical sciences.

Derivation of optical solitons and other solutions for nonlinear Schrödinger equation using modified extended direct algebraic method

Optical solitons is one of the fastest growing areas of research in the field of nonlinear fiber optics. In the current work, the modified extended direct algebraic method is implemented to obtain optical solitons for the nonlinear Schrödinger’s equation with group velocity dispersion and second order spatiotemporal dispersion that describe the propagation of optical solitons in nonlinear media. Bright soliton solutions, dark soliton solutions and singular soliton solutions are obtained. Also, periodic solutions, exponential solutions, Jacobi elliptic solutions and Weierstrass elliptic solutions are extracted. Under specific parameter values, 2D, 3D and contour graphs are introduced to visualize the model and demonstrate their accurate physical behaviors.

Cascaded amplification via three-beam double stimulated Raman scattering in benzene

As stimulated Raman scattering (SRS) microscopy has emerged as a powerful tool for label-free imaging of biomolecules in biological systems, SRS has also received much attention in the field of nonlinear optics. Here, we enhanced the cascade SRS of benzene through an energy competition mechanism in the three-beam double SRS processes. A three-beam (pump, Stokes, and anti-Stokes beam) SRS scheme was formulated and demonstrated to simultaneously induce the parallel and cascaded SRS processes, which were related to the Raman active modes in the same molecule. Both two SRS processes generated high-order Stokes SRS through resonance enhancement of the double sample cell configuration, which effectively suppressed the CARS (Coherent anti-Stokes Raman Scattering) signal. It was shown in the experimental results that the cascaded SRS up to six orders from 562 to 780 nm were generated, and the SRS threshold of the multi-order Stokes components was lowered. The present work can potentially contribute to the development of super-resolution SRS microscopy.

Studies of self-design taper algorithms for free-electron lasers with planar and helical undulators

The article presents a numerical study of self-design taper algorithms for free-electron lasers (FELs) with planar and helical undulators. Tapering is a technique that changes the undulator parameters in order to increase the efficiency and the radiation power in FELs. Undulator tapering is one of the methods for designing multi-terawatt X-ray FELs (XFELs), which are necessary for research in the field of non-linear optics and 3D bioimaging. In this article, we study methods to optimize the taper profile K(z) that can enhance the efficiency of extracting energy from the electron beam in FELs with planar and helical undulators. Using the numerical code we apply the Kroll–Morton–Rosenbluth (KMR) model and its modification to a case of the FEL at the MAX IV Laboratory, as well as a case of the European XFEL, compare our results with previous ones and discuss the new results. The program was validated on the PAL-XFEL experiment. The application of the modified KMR method for FELs with helical undulators is also studied.

Theoretical simulation structural, elastic, electronic, optical, vibrational and thermal properties of AgGaxIn1-xS2 (x = 0, 0.25, 0.5, 0.75, 1)

The elasticity, vibration and thermodynamic properties of single crystal materials are very important in the field of laser and nonlinear optics. Therefore, it is very important to understand the physical mechanism of thermal properties in such systems. In this work, the structural, elastic, vibrational and thermodynamic properties of the AgGaxIn1-xS2 (x = 0, 0.25, 0.5, 0.75, 1) have been performed systematic within generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE). The results show that the AgGaxIn1-xS2 series have similar physical properties. When Ga concentration increases gradually, the lattice constants (a and c) decrease drastically with the increase of Ga content x. The polycrystalline elastic moduli including bulk modulus B, Young's modulus E, shear modulus G and Poisson's ratio v have also been successfully calculated. The brittle and ductile properties were judged by using B/G and Poisson's ratio. The anisotropy was characterized by calculating several different anisotropic indexes and the 3D figures of directional dependences of reciprocals of bulk modulus. Use the hybrid functional HSE06 to study the electronic properties of AgGaxIn1-xS2, and suggest that the HSE06 hybrid functional can obtain a more reasonable band. In addition, the optical spectrum are derived and main spectral features are interpreted in terms of the electronic structure. The calculated results of vibrational characters indicate that AgGaxIn1-xS2 (x = 0, 0.25, 0.5, 0.75, 1) are dynamic stability as increasing of Ga concentration from 0.0 to 1. Finally, the thermodynamic properties related to phonons have been realized and explored.

Evaluation of the surface topography quality of large-area diamonds by image processing and mathematical modeling

Diamond with ultra-smooth and flat surface plays a crucial role in the various fields of nonlinear optics, NV center, waveguide, and so on, due to its remarkable physical properties. Consequently, the fast and efficient polishing and evaluating of diamond surfaces are indispensable to obtain high-quality smooth and flat diamond surfaces. As one of the most widespread techniques, atomic force microscope (AFM) and optical profilometry (OP) are enslaved to their small measurement regions and high time consuming, especially in the case of high-resolution measurement of large area diamond surfaces. Therefore, a novel approach to evaluate the polished diamond surface with high-efficiency and accuracy is desperately required. In this works, we propose a novel approach, surface topography quality (STQ) mathematical model, to achieve fast and large area evaluation to the polished diamond surface. Specifically, by combining currently popular image processing with mathematical statistics, STQ mathematical model generates a concept called surface topography quality rate (STQR) to quantitatively evaluate the surface quality of diamond. The results from large-area scanning electron microscope images before and after ion beam polishing demonstrates its reliability and preponderant advantage in dealing with large area surface compared to that of the conventional use of atomic force microscope. The mathematical model provides a unique and reliable approach to comprehensively and objectively evaluate diamond surface, which may promote the advancement of high-performance diamond-based devices.

Ferroelectric chiral nematic liquid crystals: new photonic materials with multiple bandgaps controllable by low electric fields

ABSTRACT We have carried out a spectroscopic study on a prototype ferroelectric nematic material (RM734) doped with a non-polar chiral compound. The mixture presents two chiral nematic phases, one conventional (N*) and the other polar (NF*), whose behaviours under electric fields E are totally different. On the one hand, the N* phase shows a single reflection band if E is not very high, while fields perpendicular to the helix of a few V/mm are already sufficient to produce multiple bands in the NF* phase. On the other hand, the pitch of the NF* phase grows notably on increasing fields, however remaining practically constant in the N* phase. Both effects have been explained in terms of the different type of interaction with E in each phase (ferroelectric in NF* and dielectric in N*). We argue that the NF* phase behaves as a photonic material with multiple gaps tunable by small fields, which presents important potentials for applications. A study of the bandgaps has been carried out through the analysis of the dispersion relation of the optical eigenmodes in the NF* phase under field. Finally, an example of the potentials of the NF* phase within the field of nonlinear optics is briefly presented.

Optical Properties of New Third-Order Nonlinear Materials Modified by Click Chemistry.

A high-yielding click reaction was used to synthesize a series of highly conjugated, symmetrical, as well as asymmetrical compounds with a benzene core. Cyclic voltammetry and ultraviolet/visible absorption spectroscopy were carried out, and proved that the side groups of the benzene derivatives played an important role in the energy gaps, and affected the third-order non-linear optical response. The maximum absorption wavelength of the series of benzene derivatives showed an obvious red-shift. Moreover, the addition of resilient electron-withdrawing groups significantly narrowed the energy levels as compared with precursors. The third-order nonlinear properties of this benzene derivative were tested by the Z-scan technique. The expected properties of this series of molecules were obtained, and it was found that the series of molecules undergoes a transition from reverse saturable absorption to saturable absorption, which has certain reference significance for a nonlinear optical field.

The ultrafast tunable saturable absorption of three azo-Schiff base ligands and related metal complexes

Three azo-Schiff base ligands with large conjugated systems and five related transition metal complexes were synthesized and investigated by femetosecond open-aperture Z-scan and pump-probe system. The ultrafast tunable saturable absorption of the ligands and their metal complexes were observed at 400 nm wavelength. The obtained third-order nonlinear optical (NLO) absorption coefficients of eight compounds are evaluated to be −8.49 ∼ −80.63 cm/GW. Meanwhile, the ultrafast carrier relaxation time (187–592 fs) of all compounds was observed in the pump-probe experiment. The modulated impacts of metal coordination on NLO responses are analyzed by a five-level energy system. We deem that the performance of metal complexes is determined by the number of shell electrons of central metal. All the results indicate that those compounds have potential applications for tunable saturable absorber in NLO field.