Robust and high-speed rotation control in optical tweezers by using polarization synthesis based on heterodyne interference

The rotation control of particles in optical tweezers is often subject to the spin or orbit angular momentum induced optical torque,which is susceptible to the mechanical and morphological properties of individual particle.Here we report on a robust and high-speed rotation control in optical tweezers by using a novel linear polarization synthesis based on optical heterodyne interference between two circularly polarized lights with opposite handedness.The synthesized linear polarization can be rotated in a hopping-free scheme at arbitrary speed determined electronically by the heterodyne frequency between two laser fields.The experimental demonstration of a trapped vaterite particle in water shows that the precisely controlled rotation frequency of 300 Hz can be achieved.The proposed method will find promising applications in optically driven micro-gears,fluidic pumps and rotational micro-rheology.

Reflective ultrathin light-sheet microscopy with isotropic 3D resolutions

Light-sheet fluorescence microscopy(LSFM)has played an important role in bio-imaging due to its advantages of high photon efficiency,fast speed,and long-term imaging capabilities.The perpendicular layout between LSFM excitation and detection often limits the 3D resolutions as well as their isotropy.Here,we report on a reflective type light-sheet microscope with a mini-prism used as an optical path reflector.The conventional high NA objectives can be used both in excitation and detection with this design.Isotropic resolutions in 3D down to300 nm could be achieved without deconvolution.The proposed method also enables easy transform of a conventional fluorescence microscope to high performance light-sheet microscopy.

Temporal compressive super-resolution microscopy at frame rate of 1200 frames per second and spatial resolution of 100 nm

Various super-resolution microscopy techniques have been presented to explore fine structures of biological specimens.However,the super-resolution capability is often achieved at the expense of reducing imaging speed by either point scanning or multiframe computation.The contradiction between spatial resolution and imaging speed seriously hampers the observation of high-speed dynamics of fine structures.To overcome this contradiction,here we propose and demonstrate a temporal compressive super-resolution microscopy(TCSRM)technique.This technique is to merge an enhanced temporal compressive microscopy and a deep-learning-based super-resolution image reconstruction,where the enhanced temporal compressive microscopy is utilized to improve the imaging speed,and the deep-learning-based super-resolution image reconstruction is used to realize the resolution enhancement.The high-speed super-resolution imaging ability of TCSRM with a frame rate of 1200 frames per second(fps)and spatial resolution of 100 nm is experimentally demonstrated by capturing the flowing fluorescent beads in microfluidic chip.Given the outstanding imaging performance with high-speed super-resolution,TCSRM provides a desired tool for the studies of high-speed dynamical behaviors in fine structures,especially in the biomedical field.

Super-resolution fluorescence-assisted diffraction computational tomography reveals the threedimensional landscape of the cellular organelle interactome

The emergence of super-resolution(SR)fluorescence microscopy has rejuvenated the search for new cellular substructures.However,SR fluorescence microscopy achieves high contrast at the expense of a holistic view of the interacting partners and surrounding environment.Thus,we developed SR fluorescence-assisted diffraction computational tomography(SR-FACT),which combines label-free three-dimensional optical diffraction tomography(ODT)with two-dimensional fluorescence Hessian structured illumination microscopy.The ODT module is capable of resolving the mitochondria,lipid droplets,the nuclear membrane,chromosomes,the tubular endoplasmic reticulum,and lysosomes.Using dual-mode correlated live-cell imaging for a prolonged period of time,we observed novel subcellular structures named dark-vacuole bodies,the majority of which originate from densely populated perinuclear regions,and intensively interact with organelles such as the mitochondria and the nuclear membrane before ultimately collapsing into the plasma membrane.This work demonstrates the unique capabilities of SR-FACT,which suggests its wide applicability in cell biology in general.

Direct observation of ultrafast plasmonic hot electron transfer in the strong coupling regime

Achieving strong coupling between plasmonic oscillators can significantly modulate their intrinsic optical properties.Here,we report the direct observation of ultrafast plasmonic hot electron transfer from an Au grating array to an MoS_(2) monolayer in the strong coupling regime between localized surface plasmons(LSPs)and surface plasmon polaritons(SPPs).By means of femtosecond pump-probe spectroscopy,the measured hot electron transfer time is approximately 40 fs with a maximum external quantum yield of 1.65%.Our results suggest that strong coupling between LSPs and SPPs has synergetic effects on the generation of plasmonic hot carriers,where SPPs with a unique nonradiative feature can act as an‘energy recycle bin’to reuse the radiative energy of LSPs and contribute to hot carrier generation.Coherent energy exchange between plasmonic modes in the strong coupling regime can further enhance the vertical electric field and promote the transfer of hot electrons between the Au grating and the MoS_(2) monolayer.Our proposed plasmonic strong coupling configuration overcomes the challenge associated with utilizing hot carriers and is instructive in terms of improving the performance of plasmonic opto-electronic devices.

An actively ultrafast tunable giant slow-light effect in ultrathin nonlinear metasurfaces

A slow-light effect based on metamaterial-induced transparency(MIT)possesses great practical applications for integrated photonic devices.However,to date,only very weak slow-light effects have been obtained in metamaterials because of the intrinsic loss of metal.Moreover,no active control of slow-light has been achieved in metamaterials.Here,we report the realization of a giant slow-light effect on an ultrathin metasurface that consists of periodic arrays of gold nanoprism dimers with a thickness of 40 nm sandwiched between a multilayer-graphene micro-sheet/zinc oxide nanoparticle layer and a monolayer graphene/polycrystalline indium tin oxide layer.The strong field confinement of the plasmonic modes associated with the MIT ensures a tremendous reduction in the group velocity around the transparency window.A group index of more than 4×10^(3) is achieved,which is one order of magnitude greater than that of previous reports.A large tunable wavelength range of 120 nm is achieved around the center of the transparency window when the pump light intensity is only 1.5 kW cm^(-2).The response time is as fast as 42.3 ps.These results demonstrate the potential for the realization of various functional integrated photonic devices based on metasurfaces,such as all-optical buffers and all-optical switches.

Solving the missing cone problem by deep learning

In order to extract the quantitative three-dimensional(3-D)distribution of refractive index(RI)in live cells noninvasively,optical diffraction tomography(ODT)uses the non-ionizing light sources instead of x-rays to perform a computational holographic tomography.

Frequency-domain diagonal extension imaging

The pixel size of a charge-coupled device(CCD)camera plays a major role in the image resolution,and the square pixels are attributed to the physical anisotropy of the sampling frequency.We synthesize the high sampling frequency directions from multiple frames acquired with different angles to enhance the resolution by 1.4×over conventional CCD orthogonal sampling.To directly demonstrate the improvement of frequency-domain diagonal extension(FDDE)microscopy,lens-free microscopy is used,as its resolution is dominantly determined by the pixel size.We demonstrate the resolution enhancement with a mouse skin histological specimen and a clinical blood smear sample.Further,FDDE is extended to lens-based photography with an ISO 12233 resolution target.This method paves a new way for enhancing the image resolution for a variety of imaging techniques in which the resolution is primarily limited by the sampling pixel size,for example,microscopy,photography,and spectroscopy.

New soliton dynamics revealed in the normal dispersion region

Birefringence-involved phase matching is demonstrated to be a novel mechanism to generate transform limited solitary pulses in an ultrafast mode-locking fiber laser cavity with normal dispersion.

Detour-phased perovskite ultrathin planar lens using direct femtosecond laser writing

Perovskite-enabled optical devices have drawn intensive interest and have been considered promising candidates for integrated optoelectronic systems.As one of the important photonic functions,optical phase modulation previously was demonstrated with perovskite substrate and complex refractive index engineering with laser scribing.Here we report on the new scheme of achieving efficient phase modulation by combining detour phase design with 40 nm ultrathin perovskite films composed of nanosized crystalline particles.Phase modulation was realized by binary amplitude patterning,which significantly simplifies the fabrication process.Perovskite nanocrystal films exhibit significantly weak ion migration effects under femtosecond laser writing,resulting in smooth edges along the laser ablated area and high diffractive optical quality.Fabrication of a detour-phased perovskite ultrathin planar lens with a diameter of 150μm using femtosecond laser scribing was experimentally demonstrated.A high-performance 3D focus was observed,and the fabrication showed a high tolerance with different laser writing powers.Furthermore,the high-quality imaging capability of perovskite ultrathin planar lenses with a suppressed background was also demonstrated.