Wide-Field Vibrational Phase Contrast Imaging Based on Coherent Anti-Stokes Raman Scattering Holography

We propose and implement a wide-field vibrational phase contrast detection to obtain imaging of imaginary components of third-order nonlinear susceptibility in a coherent anti-Stokes Raman scattering （CARS） microscope with full suppression of the non-resonant background. This technique is based on the unique ability of recovering the phase of the generated CARS signal based on holographic recording. By capturing the phase distributions of the generated CARS field from the sample and from the environment under resonant illumination, we demonstrate the retrieval of imaginary components in the CARS microscope and achieve background free coherent Raman imaging.

Fast fluorescence lifetime imaging techniques:A review on challenge and development

Fluorescence lifetime imaging microscopy(FLIM)is increasingly used in biomedicine,material science,chemistry,and other related research fields,because of its advantages of high specificity and sensitivity in monitoring cellular microenvironments,studying interaction between proteins,metabolic state,screening drugs and analyzing their efficacy,characterizing novel materials,and diagnosing early cancers.Understandably,there is a large interest in obtaining FLIM data within an acquisition time as short as possible.Consequently,there is currently a technology that advances towards faster and faster FLIM recording.However,the maximum speed of a recording technique is only part of the problerm.The acquisition time of a FLIM image is a complex function of many factors.These include the photon rate that can be obtained from the sample,the amount of information a technique extracts from the decay functions,the fficiency at which it determines fluorescence decay parameters from the recorded photons,the demands for the accuracy of these parameters,the number of pixels,and the lateral and axial resolutions that are obtained in biological materials.Starting from a discussion of the parameters which determine the acquisition time,this review will describe existing and emerging FLIM techniques and data analysis algo-rithms,and analyze their performance and recording speed in biological and biomedical applications.

Metalens-integrated compact imaging devices for wide-field microscopy

Metasurfaces have demonstrated unprecedented capabilities in manipulating light with ultrathin and flat architectures.Although great progress has been made in the metasurface designs and function demonstrations,most metalenses still only work as a substitution of conventional lenses in optical settings,whose integration advantage is rarely manifested.We propose a highly integrated imaging device with silicon metalenses directly mounted on a complementary metal oxide semiconductor image sensor,whose working distance is in hundreds of micrometers.The imaging performances including resolution,signal-to-noise ratio,and field of view(FOV)are investigated.Moreover,we develop a metalens array with polarization-multiplexed dual-phase design for a wide-field microscopic imaging.This approach remarkably expands the FOV without reducing the resolution,which promises a non-limited space-bandwidth product imaging for wide-field microscopy.As a result,we demonstrate a centimeter-scale prototype for microscopic imaging,showing uniqueness of meta-design for compact integration.

Chip-scale metalens microscope for wide-field and depth-of-field imaging

Microscopy is very important in research and industry,yet traditional optical microscopy suffers from the limited field-of-view(FOV)and depth-of-field(DOF)in high-resolution imaging.We demonstrate a simultaneous large FOV and DOF microscope imaging technology based on a chip-scale metalens device that is implemented by a SiNxmetalens array with a co-and cross-polarization multiplexed dual-phase design and dispersive spectrum zoom effect.A 4-mm×4-mm FOV is obtained with a resolution of 1.74μm and DOF of200μm within a wavelength range of 450 to 510 nm,which definitely exceeds the performance of traditional microscopes with the same resolution.Moreover,it is realized in a miniaturized compact prototype,showing an overall advantage for portable and convenient microscope technology.

Design of a wide-field target detection and tracking system using the segmented planar imaging detector for electro-optical reconnaissance

Detecting and tracking multiple targets simultaneously for space-based surveillance requires multiple cameras,which leads to a large system volume and weight. To address this problem, we propose a wide-field detection and tracking system using the segmented planar imaging detector for electro-optical reconnaissance. This study realizes two operating modes by changing the working paired lenslets and corresponding waveguide arrays： a detection mode and a tracking mode. A model system was simulated and evaluated using the peak signal-to-noise ratio method. The simulation results indicate that the detection and tracking system can realize wide-field detection and narrow-field, multi-target, high-resolution tracking without moving parts.

Simple and High-Efficiency Preparation Method of Biometric 3D Artificial Compound Eyes for Wide-Field Imaging

Three-dimensional(3D)artificial compound eyes(ACEs)are helpful for wide field-o-fview imaging and sensing system applications.However,existing batch preparation methods are technically challenging.A bio-inspired,simple,and high-efficiency batch preparation method is proposed,which involves bonding a sticky microlens array(MLA)polydimethylsiloxane(PDMS)film to an elastic PDMS hemisphere under pressure,followed by abrupt pressure removal.Characterizations from a scanning electron microscope and laser scanning confocal microscope show that 3D ACEs prepared using the proposed method have high numbers of uniformly distributed ommatidia with a high-quality finish.Furthermore,optical imaging investigations demonstrate that the proposed preparation method can achieve clear,distortionfree imaging with a wide field-of-view(up to 140.2°).

Pixel super-resolution using wavelength scanning

Undersampling and pixelation affect a number of imaging systems, limiting the resolution of the acquired images, whichbecomes particularly significant for wide-field microscopy applications. Various super-resolution techniques have been implemented to mitigate this resolution loss by utilizing sub-pixel displacements in the imaging system, achieved, for example, byshifting the illumination source, the sensor array and/or the sample, followed by digital synthesis of a smaller effective pixel bymerging these sub-pixel-shifted low-resolution images. Herein, we introduce a new pixel super-resolution method that is basedon wavelength scanning and demonstrate that as an alternative to physical shifting/displacements, wavelength diversity can beused to boost the resolution of a wide-field imaging system and significantly increase its space-bandwidth product. We confirmedthe effectiveness of this new technique by improving the resolution of lens-free as well as lens-based microscopy systems anddeveloped an iterative algorithm to generate high-resolution reconstructions of a specimen using undersampled diffraction patterns recorded at a few wavelengths covering a narrow spectrum (10–30 nm). When combined with a synthetic-aperture-baseddiffraction imaging technique, this wavelength-scanning super-resolution approach can achieve a half-pitch resolution of250 nm, corresponding to a numerical aperture of ~ 1.0, across a large field of view (420 mm^(2)). We also demonstrated theeffectiveness of this approach by imaging various biological samples, including blood and Papanicolaou smears. Compared withdisplacement-based super-resolution techniques, wavelength scanning brings uniform resolution improvement in all directionsacross a sensor array and requires significantly fewer measurements. This technique would broadly benefit wide-field imagingapplications that demand larger space-bandwidth products.

Spatio-temporal visualization of light transport in complex photonic structures

Spatio-temporal imaging of light propagation is very important in photonics because it provides the most direct tool available to study the interaction between light and its host environment.Sub-ps time resolution is needed to investigate the fine and complex structural features that characterize disordered and heterogeneous structures,which are responsible for a rich array of transport physics that have not yet been fully explored.A newly developed wide-field imaging system enables us to present a spatiotemporal study on light transport in various disordered media,revealing properties that could not be properly assessed using standard techniques.By extending our investigation to an almost transparent membrane,a configuration that has been difficult to characterize until now,we unveil the peculiar physics exhibited by such thin scattering systems with transport features that go beyond mainstream diffusion modeling,despite the occurrence of multiple scattering.