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In this work, SSPM effects of VP Ns and their reaction dynamics were studied for the first time (left). Using the superior coherence electronic nonlinearity of VP Ns, all-optical switches based on the SSPM effect (right) were prepared.

Spatiotemporal (ST) wave packet carrying pure transverse orbital angular moment (OAM) with subwavelength spatial size has attracted increasing attentions in recent years, which can be obtained by tightly focusing a linear superposition of ST vortices with different topological charges. In this work, numerical models are proposed to explore the impact of the pulse width of the ST vortex on the characteristics of its focal field. We demonstrate that the rigorous model for calculating the focused ST wave packet is essential for ultrashort optical pulse, while the simplified model has the advantage of high efficiency but can only provide credible results when the pulse width of the illumination is long enough. Specifically, when the pulse width decreases from 100 fs to 5 fs, the accuracy of the simplified model would decrease significantly from 99% to 65.5%. In addition, it is found that the pulse duration would still lead to the collapse of transverse OAM structure near the focus of a high numerical aperture lens, even though the ST astigmatism has already been corrected. To analyze the physical mechanism behind this distortion, Levenberg-Marquardt algorithm is adopted to retrieve the OAM distribution of the focal field. It is shown that the contributions from undesired OAM modes would become nontrivial for short pulse width, leading to the formation of the focal field with hybrid OAM structures. These findings provide insight for the focusing and propagation studies of ultrashort ST wave packets, which could have wide potential applications in microscopy, optical trapping, laser machining, nonlinear light-matter interactions, etc.

Second-harmonic generation and third-harmonic generation have been widely investigated in nonlinear topological photonics. However, due to the weak nonlinear effect and the strict phase matching condition, it is a challenge to observe the high-order harmonic generation in general bulky or periodic structures. In this work, through the design of a binary one-dimensional photonic crystal, we obtain the topological edge states (TESs) with equal frequency spacing based on the electro-optic modulation effect. The designed structure has generated the high-order harmonic waves with the nonlinear effect excited by intense femtosecond laser pulses. The uniformly distributed TESs satisfy the request of phase matching. The nonlinear sum-frequency effect combined with the unique TESs leads to high-order harmonic waves. The presented work provides a feasible scheme to generate the high-order harmonic waves from the simple 1D structure.

Due to the high performance and low cost, spintronic terahertz emitters (STEs) have been a hot topic in the field of terahertz sources. However, most of the research focuses on the THz generation process and little attention has been paid to the control and modulation of the THz wave generated by the STE. In this Letter, a unidirectional spintronic terahertz emitter (USTE) integrating a common STE with a metal grating is proposed to manipulate the THz emission process. The dyadic Green’s function method and finite element method are adopted to survey the characteristics of the USTE. Simulations show that the metal grating not only has a transmission larger than 97% in the optical band, but also has a higher reflectivity larger than 99% in the THz band. As a result, the USTE has a unidirectional THz emission along the direction of the pump beam with a larger than 4-fold enhancement in intensity. Moreover, the USTE has the capability of tuning the central frequency and THz wave steering by adjusting the distance and angle between the STE and the metal grating. We believe that this USTE can be used in THz wireless communications and holographic imaging, especially in the field of THz bio-sensing, which needs some resonance frequencies to sense.

Since chirality is a fundamental building block of nature, the identification of the chiral specimen’s structure is of great interest, especially in applications involving the modification and utilization of proteins. In this work, by exploiting photoinduced force exerted on an achiral tip placed in the vicinity of a reciprocal chiral sample, a novel technique is proposed to detect the sample’s chirality in nanoscale spatial resolution. Under separate excitation of focal field carrying chiral dipole moment with opposite handedness, there is a differential optical force ΔF exerted on the tip apex, which is connected to the enantiomer type and quasi-linearly depends on specific component of the sample’s chirality parameter. With the help of time-reversal approach, we prove that the required excitation can be derived by radiation fields from the superposition of parallel electric and magnetic dipoles. Through adjusting the orientation of the chiral dipole moment, all the diagonal components of the sample’s chirality can be exclusively retrieved. In addition, the sensitivity of the proposed technique is demonstrated to enantiospecify nanoscale chiral samples with chirality parameter on the order of 0.001. The proposed technique may open new avenue for wide applications in biomedicine, material science and pharmaceutics.

Hybrid cylindrical vector vortex beam (HCVVB) has attracted increasing attentions in recent years due to its unique highly focusing properties. In this work, by decomposing the HCVVB into the linear combination of radial and azimuthal polarization and project the focal field onto the circular polarization basis, we studied the Gouy phase and wave-front spacing of tightly focused HCVVB. It is found that the state of polarization directly affects the Gouy phase behaviors and wave-front spacing distribution in the focal region. By adjusting the polarization weight of the incident HCVVB, not only the distribution and symmetry of the Gouy phase near the focus would be changed, but also the wave-front spacing can be tuned from less than λ to nearly 2 λ Besides, the focusing condition and the topological charge of the light are found to influence the trend and symmetry of the Gouy phase and the effective wavelength. Our findings provide a way to understand the variation of phase structure in the focal region and may have applications in interferometry and metrology.

The generation, propagation, and applications of different types of integer vector beams have been extensively investigated. However, little attention focuses on the photophysical and photomechanical properties of the fractional vector beam (FVB). Herein, we theoretically and experimentally investigate the spin angular momentum (SAM) separation and propagation characteristics of weakly focused FVBs. It is demonstrated that such a beam carrying no SAM leads to both the transverse separation of SAM and the special intensity patterns in the focal region. Furthermore, we study the intensity, SAM, and orbital angular momentum (OAM) distributions of the tightly focused FVBs. It is shown that both three-dimensional SAM and OAM are spatially separated in the focal region of tightly focused FVBs. We investigate the optical forces, spin torques, and orbital torques on a dielectric Rayleigh particle produced by the focused FVBs. The results reveal that asymmetrical spinning and orbiting motions of optically trapped particles can be realized by manipulating FVBs.

Optical tweezers are the craft of manipulating objects with light. Since its invention in 1970, this technique has become a powerful tool in scientific areas such as biology, physical chemistry and soft matter physics. Nonetheless, optical trapping of objects at the nanoscale range is still challenging. During the past decade, with the increasing interest in structured light with spatially inhomogeneous state of polarizations and optical singularities, numerous optical beams have been proposed to manipulate, sort, and separate various nanoparticles in stable and flexible ways. In this review, starting from basic theories and computational approaches, we highlight the latest techniques of optically manipulating nanoparticles using structured light, which might lead to future advancements in the field.

Ag@ZnO core–shell nanostructures, ZnO nanoparticles (NPs), and Ag NPs were synthesized by laser ablation in water using 8 ns, 1064 nm, and 50 mJ/pulse. The structural, morphological, componential, and optical properties of as-synthesized NPs were examined by X-ray diffraction, transmission electron microscopy, electron diffraction spectrum, and ultraviolet–visible absorption, respectively. The third-order nonlinear optical properties of aqueous dispersions of three NPs were characterized by performing Z-scan experiments with femtosecond laser pulses at 800 nm. It is shown that three NPs exhibit the positive refractive nonlinearity in the absence of nonlinear absorption and the third-order nonlinear refraction index increases in the order of NPs ZnO

In this paper, according to the inverse Faraday effect (IFE), the amplitude, phase, polarization and field distribution of the first higher order mode of an optical fiber are tailored carefully, and a magnetic field with arbitrary orientation is generated in the focal region. Compared with traditional strategies to generate a magnetic field with arbitrary orientation, where the configurations are complicated and the components employed for the system are costly, the first higher order mode of a fiber, which has two lobes with opposite instantaneous electric fields, draws more attention for generating a magnetic field with arbitrary orientation. We believe that such an arbitrary orientation state of magnetic field can be applied in the field of confocal and magnetic resonance microscopy and spin dynamics, especially for the use of optical magnetic recording, where laser pulses are used to trigger the magnetization switching.

Supplemental Document

Spin angular momentum (SAM) is widely used in spin-dependent unidirectional optical interfaces, optical manipulation, integrated optical signal processing, laser structuring and other fields, but its physical mechanism has not been fully understood so far. In this work, we investigate the three-dimensional (3D) SAM in tightly focused x-polarized first-order vortex beams from the perspectives of light field itself, phase distribution, and focusing propagation. It is shown that the distribution of three orthogonal components of SAM at the focal plane has pseudo two-fold rotational symmetry, because the cycloidal rotation of the electric field of the tightly focused vortex beam is opposite. The 3D SAM distribution in the focal region is visualized by mapping the 3D distribution of state of polarization (SoP). In addition, a principle experimental method for identifying the transverse SAM by using the direction of particle’s rotation axis in optical tweezers is proposed.

Integer-order vector beams maintain their physical polarization properties under the paraxial diffraction condition. Fractional-order vector beam with irregular phase change that leading to changeable focusing properties has aroused huge interest research. Herein, we proposed and experimentally generated a double-mode concentric annular fractional vector beam. Based on the modal superposition, the intensity and spin angular momentum (SAM) density are characterized by periodic changes from rotational symmetry to axial symmetry as the topological coefficient increases. These results reveal that the fractional topological coefficients have a great potential degree of freedom. The experimental results are exploited in this manuscript to emphasize the important connection between fractional coefficient and SAM density.

The propagation properties of a variety of laser beams in uniaxial crystals are extensively investigated by numerical simulations. However, the related experimental demonstrations are sporadic up to now. Herein, we report an experimental investigation of the polarization characteristics of arbitrary cylindrical vector beams (i.e., radially polarized beam, azimuthally polarized beam, high-order vector beam, and fractional vector beam) passing through a rutile crystal whose optical axis is orthogonal to the beam axis. It is shown that the polarization modulation of the uniaxial crystal results in the polarization evolution of cylindrical vector beams from the localized linear polarization to hybrid polarization with 2m-fold rotational symmetry (where m is the topological charge), which agrees well the theoretical result. The polarization modulation using the uniaxial crystal has the applications in the generation of complex vector beams and the material characterization.

The fluorescence and effective three-photon absorption (3PA) properties of Zn(II)-[meso-tetrakis(4-octyloxyphenyl)porphyrin] (labeled Zn(II)-porphyrin) dissolved in three different polar solvents were systematically investigated. The electrochemical and photophysical properties of Zn(II)-porphyrin were investigated by 1H NMR spectra, IR spectra, mass spectroscopy, and electronic absorption spectra. The fluorescence emission of Zn(II)-porphyrin in three different solvents excited at the wavelengths of 420 nm (Soret band) and 550 nm (Q-band) were analyzed. By performing Z-scan experiments with femtosecond laser pulses at a wavelength of 800 nm, the effective 3PA process of Zn(II)-porphyrin in three different solvents was observed and the underlying mechanism was discussed in detail. It is found that the fluorescence spectra slightly depend on the polarity of the solvent. Interestingly, the effective 3PA properties of Zn(II)-porphyrin strongly depend on the solvent polarity. The lower the solvent polarity is, the larger effective 3PA cross-section is. Low polar solvents are beneficial to applications of Zn(II)-porphyrin in optical limiting, photodynamic therapy, etc.

In femtosecond-pulsed optical tweezers, the high peak intensity of each laser pulse results in the instantaneous trapping of a particle, while the high-repetition-rate ensures the repetitive trapping of a particle by pulse trains. Therefore, the high peak intensity and high-repetition-rate inevitably lead to the third-order optical nonlinearity and the thermal–optical nonlinearity, respectively. Herein, we investigate the optical forces on the Rayleigh particle using a high-repetition-rate femtosecond-pulsed Gaussian beam when the Kerr nonlinearity and thermal–optical nonlinearity are considered simultaneously. With the help of thermally induced nonlinearity of the surrounding medium to change the relative refractive index of particles, the three-dimensional stable trapping of slightly low-refractive-index particles is realized by the use of high-repetition-rate femtosecond-pulsed Gaussian beams. Besides, we study the influence of thermal–optical nonlinearity on optical trapping of high-refractive-index particles. It is shown that the trapping stiffness increases nonlinearly with the increase of power due to the thermal–optical​ nonlinearity. This work opens up the possibility of trapping the low-refractive-index beyond the linear optics regime, successfully explains the reported experimental observations, and provides the theoretical support for tapping nonlinear optical particles in femtosecond optical tweezers.

Tailoring the magnetic field induced by the inverse Faraday effect has received much attention due to their potential applications in data storage. However, much issues remains, hindering the application of all-optical magnetic storage technology, e. g, the challenges in the speed and precision of recording and deleting different bits of information in different positions of the magnetic recording film. To achieve on-the-fly magnetic recording and deleting of information with a high degree of accuracy, pure longitudinal magnetization spots with opposite directions are theoretically produced in this paper. Firstly, twin pure longitudinal magnetization spots with opposite directions are induced by tailoring the amplitude and phase of a tightly focused azimuthally polarized beam (APB). These pure longitudinal magnetization spots with opposite directions opens a route for writing and deleting recording bits with high writing speed as well as high degree of accuracy. Then we proved that this strategy can also be used to generate multiple longitudinal magnetization spots with opposite directions, which will facilitate the high-density 3D optomagnetic recording. Compared with traditional methods, which require complex optical systems to generate longitudinal magnetization spots with opposite directions, we only need to tailor the amplitude and phase of the APB. More importantly, the directions of the induced magnetization spots can be tuned easily, and the magnetization spots have the same intensity distribution.

Many ferromagnets exhibit the inverse Faraday effect (IFE), and based on the IFE, magnetic fields with different distributions can be induced conveniently in these ferromagnets by tailoring the laser fields. Besides, the magnetic field induced by IFE has been conceived as a far-field and non-invasive method to manipulate the magnetization. Up to now longitudinal magnetic fields, transverse magnetic fields and even a vector magnetic field, where its polarization is along the azimuthal direction, have been generated. However, another vector magnetic field, where its polarization along the radial direction has not been reported yet. In this paper, by focusing two counter-propagating cylindrical vector beams (CVBs) in a 4Pi tightly focusing system, we theoretically tailor the polarization and distribution of the highly confined focused electric field, and a radially polarized magnetic field (RPMF) is generated in the focal plane through the IFE. This RPMF can facilitate the development of the technology of magneto-optical recording. The distribution of induced magnetization in the defocus plane of the 4pi tightly focusing system is also surveyed in this paper.

Optical trapping and manipulation have emerged as a powerful tool in the biological and physical sciences. In this work, we present a miniature optical tweezers device based on multifocal optical vortex metalens (MOVM). The MOVM is capable of generating multiple focal fields with specific orbital angular momentum at arbitrary position. The optical force of the vortex field exerted on both high-refractive-index particle and low-refractive-index particle are analyzed. The simulation results show that the two kinds of dielectric particles can be trapped simultaneously. Besides, it is also feasible to manipulate plasmonic nanoparticles even under the resonant condition, which is realized by constructing a 4Pi focusing system with metalenses. Moreover, the metalens can be made into an array format that is suitable for trapping and manipulating various nanoparticles with diverse motion behaviors. The work illustrates the potential of such optical tweezers for further development in lab-on-a-chip devices, and may open up new avenues for optical manipulation and their applications in extensive scientific fields.

Light with an optical orbital angular momentum (OAM) has attracted an increasing amount of interest and has found its way into many disciplines ranging from optical trapping, edge-enhanced microscopy, high-speed optical communication, and secure quantum teleportation to spin-orbital coupling. In a variety of OAM-involved applications, it is crucial to discern different OAM states with high fidelity. In the current paper, we review the latest research progress on OAM detection with micro- and nano-optical structures that are based on plasmonics, photonic integrated circuits (PICs), and liquid crystal devices. These innovative OAM sorters are promising to ultimately achieve the miniaturization and integration of high-fidelity OAM detectors and inspire numerous applications that harness the intriguing properties of the twisted light.

We report the third-order nonlinear optical properties of the homoleptic bis(phthalocyaninato) rare earth double-decker complex Pr(OOPc)2 (1), the oxidized species [Pr(OOPc)2]+ (2), and the reduced species [Pr(OOPc)2]- (3), by performing the femtosecond-pulsed Z-scan experiments at the wavelength of 800 nm. It is found that the second-order hyperpolarizability in complex molecules decreases in the order of 1>2>3. More interestingly, the observed nonlinear absorption process changes from two-photon absorption in the oxidized 2 to saturable absorption in the reduced 3. The results demonstrate that the nonlinear optical properties of sandwich-type phthalocyanine rare earth complexes could be altered by the redox reaction. Furthermore, the figures of merit of three complexes were evaluated for nonlinear photonic applications in optical limiter, saturable absorber, or all-optical switch.

Metasurfaces with tunable/switchable circular dichroism (CD) response have great potential to serve as important elements for plenty of advanced applications. In this work, we proposed a novel metasurface absorber integrated with periodic G e 2 S b 2 T e 5 (GST) resonators and numerically demonstrated its capability in reconfiguration of the CD effect. Due to the strong chiral plasmonic resonance, a strong CD of about 0.75 can be achieved in a prescribed spectrum. Additionally, the phase transition of GST resonators enables the quasi-linearly modification of CD strength in a broad range (from 0.03 to 0.75). Furthermore, reversible chirality of the metasurface absorber can be realized by controlling the states of the left- and right-hand GST resonators separately, enabling the CD signal to be readily switched between on-, off-, and reverse-state.

The spectroscopic methods of circular dichroism (CD) is commonly used in analysing the chirality of molecules, which plays an important role in pharmaceutical compounds. However, the current methods require high sample density due to the weak CD effect of natural material, making it challenging to detect the signal of individual chiral molecule. In this work, we propose a technique to enhance CD signal of individual chiral molecule with the use of superchiral optical field, which is acquired by focusing a twisted radially polarized vortex onto a one-dimensional photonic band gap structure. Through adjusting the topological charge and the focusing angle of the illumination, a deep subwavelength optical field with full width at half maxima (FWHM) of 0.02λ and 22.4-fold superchirality factor enhancement can be generated. In addition, we demonstrate that up to 20-fold CD enhancement can be obtained by introducing 2 nm on-resonant chiral molecule into the superchiral optical field. This finding will have widely potential applications in CD spectroscopy and superresolution imaging for sparse subdiffraction chiral objects.

Vortex beams carrying optical angular momentum (AM) could drive the orbital motion of a small particle around the optical axis. In general, the orbital rotation speed of trapped particles increases linearly with the increasing laser power. Beyond the linear optics regime, in this work, we investigate both the optical force and torque on a two-photon absorbing Rayleigh particle produced by the tightly focused femtosecond-pulsed circularly polarized vortex beam. Different from the trapping dynamics of particles without two-photon absorption (TPA), it is shown that the orbital motion of trapped particles with TPA accelerates nonlinearly as the laser power increases. Moreover, the orbital motion acceleration of trapped particles is proportional to the TPA coefficient. The corresponding underlying mechanism is discussed in detail. Our results may find interesting applications in the characterization of the optical nonlinearity of a single nanoparticle, and AM manipulation and particle transportation in the nonlinear optics regime.

Since the fundamental building blocks of life are built of chiral amino acids and chiral sugar, enantiomer separation is of great interest in plenty of chemical syntheses. Light-chiral material interaction leads to a unique chiral optical force, which possesses opposite directions for specimens with different handedness. However, usually the enantioselective sorting is challenging in optical tweezers due to the dominating achiral force. In this work, we propose an optical technique to sort chiral specimens by use of a transverse optical needle field with a transverse spin (TONFTS), which is constructed through reversing the radiation patterns from an array of paired orthogonal electric dipoles located in the focal plane of a 4Pi microscopy and experimentally generated with a home-built vectorial optical field generator. It is demonstrated that the transverse component of the photonic spin gives rise to the chiral optical force perpendicular to the direction of the light’s propagation, while the transverse achiral gradient force would be dramatically diminished by the uniform intensity profile of the optical needle field. Consequently, chiral nanoparticles with different handedness would be laterally sorted by the TONFTS and trapped at different locations along the optical needle field, providing a feasible route toward all-optical enantiopure chemical syntheses and enantiomer separations in pharmaceuticals.

In the last decade, the plasmonic vortex field has been studied extensively due to intriguing properties such as high field enhancement, optical singularity, and orbital angular momentum. In this work, we propose metananoslots that consist of paired orthogonal nanoslots arranged in an Archimedes spiral distribution. The metananoslots work as a plasmonic vortex lens that enables the synthesis of a highly tunable plasmonic vortex via the strong interaction between the illumination and the slots etched on the gold film. By adjusting the orientation of the orthogonal nanoslots pair, the metananoslots exhibit strong and controllable spin-dependent effects. The topological charge of the plasmonic vortex is found to be determined by both the incident spin and the geometrical topological charge of the metananoslots, making it suitable for applications such as optical manipulation, optical trapping, and optical data storage.

With features of fast and energy-efficient data writing, all-optical helicity-dependent switching (AO-HDS) has emerged as a competitive technology to satisfy the demand for the next-generation volume data storage. Unfortunately, to switch the magnetizations in different positions of the magnetic-optic film, the laser beam, the objective lens, or the magnetic recording film should be moved, limiting the advantage of AO-HDS in fast data writing. To achieve on-the-fly magnetization switching, the induced magnetization should be fully controllable. In this Letter, by focusing an azimuthally polarized vortex beam (APVB) and introducing an additional phase, a feasible strategy constructing subwavelength light-induced pure longitudinal multi-magnetization spots is proposed. In addition, the position of the multi-magnetization spots can be dynamically controlled. The distributions of the focused APVBs with different orbital angular momentum, and the induced magnetizations are surveyed. We believe that this is a practical and flexible three-dimensional magnetic recording technique with dynamic control of the recording position.

Near-field optical trapping can be realized with focused evanescent waves that are excited at the water-glass interface due to the total internal reflection, or with focused plasmonic waves excited on the water-gold interface. Herein, the performance of these two kinds of near-field optical trapping techniques is compared using the same optical microscope configuration. Experimental results show that only a single-micron polystyrene bead can be trapped by the focused evanescent waves, whereas many beads are simultaneously attracted to the center of the excited region by focused plasmonic waves. This difference in trapping behavior is analyzed from the electric field intensity distributions of these two kinds of focused surface waves and the difference in trapping behavior is attributed to photothermal effects due to the light absorption by the gold film.

We investigate anisotropic two-photon absorption (TPA) effects in a cubic-symmetry crystal excited by scalar and vectorial optical fields. First, we present the anisotropic TPA coefficient, which depends on the anisotropy coefficient, the dichroism coefficient, the crystal orientation angle, and the ellipticity of the polarized ellipse. Second, we develop the elliptically polarized light Z-scan technique for characterizing anisotropic two-photon absorbers, which is demonstrated experimentally. Last, we present the laser beam shaping of vectorial optical fields with Gaussian intensity distribution into a flat-top profile through anisotropic TPA effects. It is shown that the anisotropic TPA offers a new avenue to manipulate the intensity distribution of the polarization-structured light field, which may find interesting applications in beam shaping, optical limiting, and photodetection.

We investigate femtosecond laser trapping dynamics of two-photon absorbing hollow-core nanoparticles with different volume fractions and two-photon absorption (TPA) coefficients. Numerical simulations show that the hollow-core particles with low and high-volume fractions can easily be trapped and bounced by the tightly focused Gaussian laser pulses, respectively. Further studies show that the hollow-core particles with and without TPA can be identified, because the TPA effect enhances the radiation force, and subsequently the longitudinal force destabilizes the trap by pushing the particle away from the focal point. The results may find direct applications in particle sorting and characterizing the TPA coefficient of single nanoparticles.

All-optical magnetization switching with features of low-power consumption and high writing speed is a promising road map to satisfy the demand for volume data storage. To promote denser and faster magnetic recording technologies, herein, all-optical helicity-dependent switching (AO-HDS) in multi-layer magnetic recording is proposed based on the chromatic aberration of an optical lens (Thorlabs’s N-BK7 plano-convex uncoated lens). The power of the incident beams and the thickness of the multi-layer magnetic recording film are designed carefully. Besides, the uniformity of this multi-layer magnetic recording is optimized. At last, a prototype system of information multiplexing based on this multi-layer magnetic recording technology is constructed as well. Flexible and controllable magnetization reversals in different layers are also demonstrated by tuning the wavelength and helicity of working beams. We believe that such a prototype system can pave the way for increasing the storage density in an effective and low-cost mode.

In this paper, we demonstrate a time-reversal methodology to create diffraction-limited optical focal spot with arbitrarily oriented magnetic dipolar field component using a 4pi microscopic configuration. Through combining the magnetic dipole radiation pattern and the Richards–Wolf vectorial diffraction method, the required illuminations at the pupil plane of a 4pi focusing configuration for the reconstruction of magnetic dipole focal field are found analytically. In general, the calculated pupil field is a complex optical field with amplitude, phase and polarization variations within the cross section. Such required pupil fields can be experimentally generated with the recently develop Vectorial Optical Field Generator. Furthermore, the orientation of the magnetic field component within the doughnut shape focal field can be rotated arbitrarily by modulating the pupil field distribution carefully while maintaining the diffraction-limited focal spot size. These unique focal field distributions are expected to exhibit novel phenomena when interact with various type of structured-materials. These interactions may find important applications in super-resolution microscopy, particle trapping and manipulation, materials characterization, as well as three-dimensional high-density optical storage.

Generation of vectorial optical fields with arbitrary polarization distribution is of great interest in plenty of applications. In this work, we propose and experimentally demonstrate the generation of a second-order full Poincare (FP) beam and its application in two-dimensional (2D) flattop beam shaping with spatially variant polarization under a high numerical aperture focusing condition. In addition, the force mechanism of the focal field with 2D flattop beam profile is numerically studied, demonstrating the feasibility to trap a dielectric Rayleigh particle in three-dimensional space. The results show that the additional degree of freedom provided by the FP beam allows one to control the spatial structure of polarization, to engineer the focusing field, and to tailor the optical force exerted on a dielectric Rayleigh particle. The findings reported in the work may find useful applications in laser micromachining, optical trapping, and optical assembly.

Optical trapping and manipulation using focused laser beams has emerged as a powerful tool in the biological and physical sciences. However, scaling this technique to nanoparticles remains challenging. In this work, we propose a novel strategy to optically trap nanoparticles even under the most challenging situation using engineered optical field. The distribution of the optical forces can be tailored through optimizing the spatial distribution of a vectorial optical illumination to favor the stable trapping of a variety of nanoparticles. It is shown that the proposed optical tweezers has the ability of supporting stable three-dimensional trapping for nanoparticles while avoiding trap destabilization due to optical overheating. Besides, the interaction between the angular momentum of the light and the nanoparticle is also explored to control the movement behavior of the nanoparticle. The technique presented in this work offers a versatile solution for trapping nanoparticles and may open up new avenues for optical manipulation.

Optical trapping and manipulation have emerged as a powerful tool in the biological and physical sciences. In this work, we present a miniature optical tweezers device based on multifocal optical vortex metalens (MOVM). The MOVM is capable of generating multiple focal fields with specific orbital angular momentum at arbitrary position. The optical force of the vortex field exerted on both high-refractive-index particle and low-refractive-index particle are analyzed. The simulation results show that the two kinds of dielectric particles can be trapped simultaneously. Besides, it is also feasible to manipulate plasmonic nanoparticles even under the resonant condition, which is realized by constructing a 4Pi focusing system with metalenses. Moreover, the metalens can be made into an array format that is suitable for trapping and manipulating various nanoparticles with diverse motion behaviors. The work illustrates the potential of such optical tweezers for further development in lab-on-a-chip devices, and may open up new avenues for optical manipulation and their applications in extensive scientific fields.

Dynamical propagation characteristics of optical vortices embedded in Full Poincare (FP) beams with rotationally polarization symmetry are studied in this paper to illustrate that polarization map alone does not provide a unique description of electromagnetic field. It is shown that different combinations of optical vortices embedded in FP beams lead to different propagation dynamics, even though the polarization maps of electromagnetic fields are identical. We investigate the interaction between optical vortices and the background field by numerical methods. The rotation, reversion of rotation and annihilation behaviors of the optical vortices with the same and opposite topological charges embedded in the FP beams are investigated in details. Numerical results show that FP beams with stable optical vortices in the center maintain the polarization distribution better. Moreover, we find that whether or not equality between the map area of right hand and left hand polarization in the source plane can affect the distribution of polarization map. The results of this study may help to develop more intuitive understanding of optical vortices motion embedded in vector beams and offer a new perspective for analyzing polarization rotation in the process of propagation.

Recently there is an increasing interest in complex optical fields with spatially inhomogeneous state of polarizations and optical singularities. Novel effects and phenomena have been predicted and observed for light beams with these unconventional states. Nanostructured metallic thin film offers unique opportunities to generate, manipulate and detect these novel fields. Strong interactions between nano-metallic surfaces and complex optical fields enable the development of highly compact and versatile functional devices and systems. In this review, we first briefly summarize the recent developments in complex optical fields. Various nano-metallic surface designs that can produce and manipulate complex optical fields with tailored characteristics in the optical far field will be presented. Nano-metallic surfaces are also proven to be very effective for receiving and detection of complex optical fields in the near field. Advances made in this nascent field may enable the design of novel photonic devices and systems for a variety of applications such as quantum optical information processing and integrated photonic circuits.

Optical trapping and manipulation using focused laser beams has emerged as a powerful tool in the biological and physical sciences. However, scaling this technique to metallic nanoparticles remains challenging due to the strong scattering force and optical heating effect. In this work, we propose a novel strategy to optically trap metallic nanoparticles even under the resonant condition using engineered optical field. The distribution of the optical forces can be tailored through optimizing the spatial distribution of a vectorial optical illumination to favour the stable trapping of a variety of metallic nanoparticles under various conditions. It is shown that this optical tweezers has the ability of generating negative scattering force and supporting stable three-dimensional trapping for gold nanoparticles at resonance while avoiding trap destabilization due to optical overheating. The technique presented in this work offers a versatile solution for trapping metallic nanoparticles and may open up new avenues for optical manipulation.