Generation Of Optical Fields Research Articles

Meta-optics empowered by all-silicon quarter-wave plates for generating focused vortex beams

The Poynting vector associated with the focused vortex beam (FVB) that carries orbital angular momentum (OAM) is oriented in a twisted manner relative to the principal axis of propagation. This characteristic has significant applications in advanced fields, including high-dimensional information processing, high-resolution imaging, and particle manipulation. Currently, complex optical systems that operate on alignment principles for generating FVBs have been miniaturized by metasurfaces, resulting in the achievement of polarization-dependent vectorized behavior. Nevertheless, generating and manipulating FVBs that carry OAM in the terahertz (THz) range remains a significant challenge. This difficulty arises particularly when utilizing quarter-wave plates (QWPs) that serve both polarization conversion and polarization filtering functions. Here, we experimentally demonstrate a planar all-dielectric array capable of generating FVBs with high power density within a single-handed circularly polarized channel. Engineered QWP meta-atoms are utilized as candidates for the efficient generation of the desired FVB through the application of dynamic phase gradients. A series of samples were fabricated to assess the effectiveness of this design strategy in converting an incident linearly polarized THz beam into arbitrary single-handed circularly polarized FVBs. Leveraging the high degree of freedom inherent in polarization multiplexing coding, the proposed QWP metasurface can generate FVBs exhibiting topological charge evolution along the longitudinal direction. This capability further underscores its robust polarization modulation proficiency. This work presents a generalized framework for the polarization-dependent generation of ultracompact structural optical fields, which may have potential applications in highly integrated THz communication systems.

(Invited) Near Field Photocatalysis for Site-Selective Reactions By Using ZnO Nanoplates

Nanofabrication is a technology for control of the morphology, orientation, and configuration of nanomaterials. When ordinary, propagating light is employed as a processing tool, subwavelength fabrication is difficult due to the diffraction limit. However, if optical near field, which is localized in a subwavelength region is used, nanofabrication beyond the diffraction limit is possible.We have demonstrated that subwavelength nanofabrication is possible by taking advantage of the optical near field. Since hot electron-hole pairs are generated at around the plasmonic resonance sites, the energetic carriers can be used to drive oxidative dissolution of Ag,1,2 oxidative deposition of PbO2,3,4 and reductive deposition of Ag,5 in a site-selective manner. These techniques have been applied to subwavelength photochromic data storage,1,2 fabrication of chiral nanoparticles,4-7 and site-selective modification of a plasmonic photocatalyst with a co-catalyst.8 Generation of optical near field is possible even at non-plasmonic, semiconducting or dielectric nanostructures. Here we employed In-doped ZnO (In:ZnO) as a semiconductor photocatalyst. Hexagonal In:ZnO nanoplates were synthesized and adsorbed onto a glass substrate, and irradiated with linearly polarized UV light in the presence of Ag ions for reductive deposition of Ag. The optical near field generated under polarized UV light gave rise to site-selective Ag deposition. Also, the sample exhibited linear dichroism (LD) signals, indicating that the nanoparticles have optical anisotropy. On the other hand, unpolarized UV light gave no optical anisotropy. Electromagnetic simulations successfully reproduced the LD spectra. We have also performed site-selective oxidation reactions by using the hexagonal In:ZnO nanoplates. Tanabe, I.; Tatsuma, T. Nano Lett. 2012, 12, 5418–5421. Saito, K.; Tanabe, I.; Tatsuma, T. J. Phys. Chem. Lett. 2016, 7, 4363–4368.Nishi, H.; Sakamoto, M.; Tatsuma, T. Chem. Commun. 2018, 54, 11741–11744.Saito, K.; Tatsuma, T. Nano Lett. 2018, 18, 3209–3212.Ishida, T.; Isawa, A.; Kuroki, S.; Kameoka, Y.; Tatsuma, T. Appl. Phys. Lett. 2023, 123, 061111.Morisawa, K.; Ishida, T.; Tatsuma, T. ACS Nano 2020, 14, 3603–3609.Shimomura, K.; Nakane, Y.; Ishida, T.; Tatsuma, T. Appl. Phys. Lett. 2023, 122, 151109.Kim, K.; Nishi, H.; Tatsuma, T. J. Chem. Phys. 2022, 157, 111101.

Field‐Driven Inverse Design of High‐Performance Polarization‐Multiplexed Meta‐devices

AbstractDuring the past few years, metasurface polarization optics has experienced remarkable advances, resulting in revolutionary applications in imaging, sensing, computing, etc. The realization of complex optical operations requires the consideration of both the individual meta‐atoms as well as their intricate couplings. However, conventional design methods face challenges as design degrees of freedom and functionality complexity. Additionally, previous studies are restricted to the local design of single meta‐atoms based on explicit mapping relationships while ignoring interactions, resulting in an inability to meet the on‐demand requirements of complex light‐field operations. Here, a global design strategy based on field‐driven polygon evolution to achieve the inverse design of large‐scale coupled meta‐atoms is proposed. Through two global simulations, it can effectively reshape any given target optical field into an optimal structural distribution of devices without knowing mapping relationship. Near‐perfect spin‐decoupled beam‐splitting and high‐performance focusing, as well as the generation of arbitrary vector optical fields on the Poincaré sphere with a maximal diffraction efficiency closely approaching 100%, are experimentally demonstrated. This strategy opens up a new avenue for a rapid inverse design of large‐scale, high‐performance multifunctional meta‐devices, which can hold significant implications for both classical and quantum information processing domains.

Physical conversion and superposition of optical skyrmion topologies

Optical skyrmions are quasiparticles with nontrivial topological textures that have significant potential in optical information processing, transmission, and storage. Here, we theoretically and experimentally achieve the conversion of optical skyrmions among Néel, Bloch, intermediate skyrmions, and bimerons by polarization devices, where the fusion and annihilation of optical skyrmions are demonstrated accordingly. By analyzing the polarization pattern in Poincaré beams, we reveal the skyrmion topology dependence on the device, which provides a pathway for the study of skyrmion interactions. A vectorial optical field generator is implemented to realize the conversion and superposition experimentally, and the results are in good agreement with the theoretical predictions. These results enhance our comprehension of optical topological quasiparticles, which could have a significant impact on the transfer, storage, and communication of optical information.

Reconfigurable generation of chiral optical fields with multiple selective degrees of freedom.

Chiral optical fields caused by vortex beams possessing orbital angular momentum (OAM) can be used to fabricate helically structured materials and identify chiral molecules, in which the materials or molecules are associated with the character of the irradiated light. However, previously reported chiral optical fields can control only some of the parameters including the number of fringes, size, ellipticity, orientation, and local intensity distribution, which may hamper their applications. Thus, in this work, we propose both theoretically and experimentally an approach to fabricate chiral optical fields with five separately controllable degrees of freedom by overlapping two anisotropic vortices whose wavefronts have a nonlinear phase variation with the azimuthal angle. The local intensity distribution, number of fringes, size, orientation, and ellipticity of the chiral optical field can be dynamically controlled by adjusting the nonlinear coefficient, topological charges, axicon parameter, rotation angle, and stretching factor of the anisotropic vortices. Furthermore, the OAM density was investigated and proven to be continuously enhanced with the variation of the field's local intensity distribution, which gives the proposed approach the ability to continuously manipulate the OAM density of chiral optical fields. This work, supporting chiral optical fields by five separately controllable parameters, may make the applications of chiral optical fields in the fields of nanostructure fabrication and optical tweezers more flexible.

Simultaneous three-wave and six-wave mixing of microwave and optical fields in an atomic medium.

We experimentally investigate near-infrared optical field generation through simultaneous three-wave mixing (TWM) and six-wave mixing (SWM) processes in room-temperature 85Rb atoms. The nonlinear processes are induced using three hyperfine levels in the D1 manifold, which cyclically interact with pump optical fields and an idler microwave field. The simultaneous appearance of TWM and SWM signals in discrete frequency channels is made possible by breaking the three-photon resonance condition. This gives rise to coherent population oscillations (CPO), which are observed experimentally. We explain through our theoretical model the role of CPO in the generation of the SWM signal and its enhancement due to parametric coupling with the input seed field in contrast to the TWM signal. Our experiment proves that a single tone microwave can be converted to multiple optical frequency channels. The simultaneous existence of TWM and SWM processes can potentially enable various types of amplification to be achieved with a single neutral atom transducer platform.

A tool-free neuronavigation method based on single-view hand tracking

ABSTRACT This work presents a novel tool-free neuronavigation method that can be used with a single RGB commodity camera. Compared with freehand craniotomy placement methods, the proposed system is more intuitive and less error prone. The proposed method also has several advantages over standard neuronavigation platforms. First, it has a much lower cost, since it does not require the use of an optical tracking camera or electromagnetic field generator, which are typically the most expensive parts of a neuronavigation system, making it much more accessible. Second, it requires minimal setup, meaning that it can be performed at the bedside and in circumstances where using a standard neuronavigation system is impractical. Our system relies on machine-learning-based hand pose estimation that acts as a proxy for optical tool tracking, enabling a 3D-3D pre-operative to intra-operative registration. Qualitative assessment from clinical users showed that the concept is clinically relevant. Quantitative assessment showed that on average a target registration error (TRE) of 1.3 cm can be achieved. Furthermore, the system is framework-agnostic, meaning that future improvements to hand-tracking frameworks would directly translate to a higher accuracy.

Recent Development of Ultrafast Optical Characterizations for Quantum Materials.

The advent of intense ultrashort optical pulses spanning a frequency range from terahertz to the visible has opened a new era in the experimental investigation and manipulation of quantum materials. The generation of strong optical field in an ultrashort time scale enables the steering of quantum materials nonadiabatically, inducing novel phenomenon or creating new phases which may not have an equilibrium counterpart. Ultrafast time-resolved optical techniques have provided rich information and played an important role in characterization of the nonequilibrium and nonlinear properties of solid systems. Here, some of the recent progress of ultrafast optical techniques and their applications to the detection and manipulation of physical properties in selected quantum materials are reviewed. Specifically, the new development in the detection of the Higgs mode and photoinduced nonequilibrium response in the study of superconductors by time-resolved terahertz spectroscopy are discussed.

Nonlinear magnetoelectric effect in atomic vapor and its application to precision radio-frequency magnetometry

We demonstrate the nonlinear magnetoelectric (ME) effect in atomic vapor achieved through the parametric interaction of optical electric and radio-frequency (rf) magnetic fields leading to the generation of new optical electric fields. Density matrix calculations are performed to validate the experimental results. Moreover, the predicted dependence of the generated optical electric field amplitudes on the rf magnetic field strength is experimentally verified to confirm the ME effect. The system provides a technique for precision rf magnetometry based on this phenomenon. We could experimentally achieve an rf magnetic field sensitivity of 70 $\mathrm{fT}/\sqrt{\text{Hz}}$ at 1 kHz to 7.5 $\mathrm{pT}/\sqrt{\text{Hz}}$ at 3 MHz for zero bias field in an unshielded environment. The appealing features of the proposed rf magnetometer using our system include a high dynamic range up to ${10}^{12}$, 6 dB bandwidth of 450 kHz, and arbitrary frequency resolution, which are intrinsic to the nonlinear ME effect in the medium.

Compact vectorial optical field generator using a single phase-only spatial light modulator.

In this study, we demonstrate a compact vectorial optical field generator for any coherent light, including femtosecond laser beams. The apparatus utilizes a single Köster prism for both beam splitting and recombining. A phase-only spatial light modulator is used as a diffractive optical element to encode the two complex fields that recombine after being converted to orthogonal polarizations, generating an arbitrary vectorial optical field. We apply this setup to shape focused femtosecond pulses in producing patterned structures.

Compact vectorial optical field generator based on a 10-megapixel resolution liquid crystal spatial light modulator

Vectorial optical fields have attracted great attention with potential applications such as optical micromachining, optical nano-fabrication, surface plasmon excitation, optical micro-manipulation, optical imaging and so on. In this study, a compact vectorial optical field generator that can generate arbitrary complex beam with greatly reduced space and optical elements is designed, constructed and tested. Based on a reflective liquid crystal spatial light modulator with 10-megapixel resolution, the generator can control the four degrees of freedom in the spatial distributions of an optical field including phase, amplitude, polarization ratio and retardation on pixel by pixel level. Several typical complex vectorial optical fields are experimentally generated and quantitatively characterized by the Stokes parameter measurement to demonstrate the feasibility and versatility of the compact generator.

Optical framed knots as information carriers

Modern beam shaping techniques have enabled the generation of optical fields displaying a wealth of structural features, which include three-dimensional topologies such as Möbius, ribbon strips and knots. However, unlike simpler types of structured light, the topological properties of these optical fields have hitherto remained more of a fundamental curiosity as opposed to a feature that can be applied in modern technologies. Due to their robustness against external perturbations, topological invariants in physical systems are increasingly being considered as a means to encode information. Hence, structured light with topological properties could potentially be used for such purposes. Here, we introduce the experimental realization of structures known as framed knots within optical polarization fields. We further develop a protocol in which the topological properties of framed knots are used in conjunction with prime factorization to encode information.

Enantioselective optical trapping of chiral nanoparticles using a transverse optical needle field with a transverse spin

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.

Simultaneous polarization filtering and wavefront shaping enabled by localized polarization-selective interference

The ability of simultaneous polarization filter and wavefront shaping is very important for many applications, especially for polarization imaging. However, traditional methods rely on complex combinations of bulky optical components, which not only hinder the miniaturization and integration but also reduce the efficiency and imaging quality. Metasurfaces have shown extraordinary electromagnetic properties to manipulate the amplitude, polarization, and wavefront. Unfortunately, multi-layer metasurfaces with complex fabrication are often required to realize complex functions. Here, a platform of monolayer all-dielectric metasurfaces is proposed to simultaneously achieve polarization filtering and wavefront shaping, based on the principle of local polarization-selective constructive or destructive interference. The transmission efficiency surpassing 0.75 and polarization extinction ratio exceeding 11.6 dB are achieved by the proposed metasurface at the wavelength of 10.6 μm. These results are comparable to those of multi-layer metasurfaces. Considering these good performances, this work may prove new ideas for the generation of complex optical field and find wide applications in polarization imaging.

Controllable propagation and transformation of chiral intensity field at focus.

As an intrinsic feature of the optical field, chirality could induce many novel phenomena due to the interaction between chiral light and matter. Thus, the generation of optical fields possessing 2D or 3D chiral intensity patterns, called chiral intensity fields, has been widely studied. However, the control of chiral intensity field along the optical axis is still a challenge. Here, we propose a method to manipulate the axial propagation property of a focused chiral intensity field. Two modulation effects are realized: extended chiral intensity field with a focal depth >2λ at 90% mode correlation and tunable transformation of chirality during the axial propagation. This method is simple, stable, and easy to perform and therefore offers broad applications especially in optical tweezers and metamaterial fabrication.

Dynamical generation of multiple focal spot pairs with controllable position and polarization

We report a flexible method to dynamically generate multiple sub-wavelength focal spot pairs with adjustable polarization, position and number at the focal plane of a high numerical aperture (NA) objective lens. The desired incident field on the pupil plane can be analytically derived by employing the time-reversed method combined with the dipole antenna radiation theory. The numerical simulations of the corresponding tightly focused field are conducted using the Richards-Wolf vectorial diffraction theory. The validity of the presented method is demonstrated through experimental generation of several designed pupil fields with a versatile vectorial optical field generator and characterization of the produced focused fields with Stokes parameter measurements.

Generation of controllable chiral optical fields by vector beams.

Chirality is common in nature, describing not only the geometrical property of a three-dimensional object, but also an intrinsic feature of an optical field. Chiral optical fields are attracting increasing attention due to their potential applications in chiral light-matter interaction. Here we demonstrate a strategy to realize a controllable chiral optical field by tightly focusing two tailored vector beams in a 4π optical microscopic system. By modulating the wavefronts of the incident vector beams with appropriately designed phase masks, a chiral optical field with multiple spots carrying switchable handedness or controllable chirality can be generated. The location, the number and the handedness of such chiral spots can be arbitrarily adjusted depending on the actual application requirements. In addition to trapping and manipulating multiple particles, this controllable chiral optical field may find applications in enantioselective separation, chiral detection and chiral sensing at the nanoscale.

Generation of Tunable Fractional Vector Curvilinear Beams With Controllable Phase Distribution

An approach to generate the tunable fractional vector curvilinear beams (VCBs) was proposed. The scheme is based on the vector optical field generator (VOFG) system, where the two orthogonal polarized scalar curvilinear beams (SCBs) are generated to be the base vector components, and coaxially superposed by a Ronchi grating. We design a new phase distribution with several loops of 0 to π in order to generate more dark gaps. The phase distribution becomes nonuniform by varying the phase variation rate and the positions of the dark gaps are changed. Using the different parameters of the curves, the fractional VCBs with different shapes are achieved. The two orthogonal polarized SCBs with the opposite topological charges are modulated to perform the beam conversion by a phase-only computer-generated hologram (CGH). Our experimental results comply with the theory and the radial opening of the dark gaps may have some applications for guiding and transporting particles.

Dynamic shaping of vectorial optical fields based on two-dimensional blazed holographic grating**Project supported by the National Natural Science Foundation of China (Grant Nos. 91750202 and 11534006) and the National Key R&D Program of China (Grant Nos. 2018YFA0306200 and 2017YFA0303700).

We propose a vectorial optical field generation system based on two-dimensional blazed grating to high-efficiently generate structured optical fields with prescribed amplitude, phase, and polarization. In this system, an optimized blazed grating hologram is written on a spatial light modulator (SLM) and can diffract the majority of the incident light into the first-order diffractions of the x and y directions, which then serve as base vectors for synthesizing desired vector beams. Compared with the conventional cosine grating used in the previous work, the proposed two-dimensional, blazed grating has a much higher efficiency. Both computer simulation and optical experiment validate that a conversion efficiency up to 5 times that of the former work is achieved. Our method can facilitate applications of the optical field manipulation.

Generation of complex optical fields by double phase modulation in a SLM

We employ a setup, based on a phase spatial light modulator (SLM), for generation of arbitrary optical fields. The process is based on two sequential phase modulations of a laser beam at two different zones of the SLM. The input beam is transformed in the first contact with the SLM by a phase modulation that includes a diffractive phase element (DPE), which encodes the desired complex field, and a Fourier transforming lens. The Fourier transform of the DPE is projected, using a mirror, to the second SLM modulation area, whose transmittance includes a second Fourier transforming lens and a phase spatial filter, used to eliminate non-desired parts of the DPE Fourier spectrum.