Large Depth Of Field Research Articles

Bio-imaging with the helium-ion microscope: A review.

Scanning helium-ion microscopy (HIM) is an imaging technique with sub-nanometre resolution and is a powerful tool to resolve some of the tiniest structures in biology. In many aspects, the HIM resembles a field-emission scanning electron microscope (FE-SEM), but the use of helium ions rather than electrons provides several advantages, including higher surface sensitivity, larger depth of field, and a straightforward charge-compensating electron flood gun, which enables imaging of non-conductive samples, rendering HIM a promising high-resolution imaging technique for biological samples. Starting with studies focused on medical research, the last decade has seen some particularly spectacular high-resolution images in studies focused on plants, microbiology, virology, and geomicrobiology. However, HIM is not just an imaging technique. The ability to use the instrument for milling biological objects as small as viruses offers unique opportunities which are not possible with more conventional focused ion beams, such as gallium. Several pioneering technical developments, such as methods to couple secondary ion mass spectrometry (SIMS) or ionoluminescence with the HIM, also offer the possibility for new and exciting research on biological materials. In this review, we present a comprehensive overview of almost all currently published literature which has demonstrated the application of HIM for imaging of biological specimens. We also discuss some technical features of this unique type of instrument and highlight some of the new advances which will likely become more widely used in the years to come.

Design of imaging optical system for space target with large depth of field

Design of imaging optical system for space target with large depth of field

超表面透镜的宽带消色差成像（特邀）

Metalens, the specific type of lens designed with the surfaces mading of two dimensional array at the subwavelength scale, has shown great flexibilities to control the light field, including the arbitrary modulation abilities of amplitude, phase and polarization at the subwavelength scale. Moreover, the metalens possesses the unique advantages of low loss, integratable and conformable design and ultrathin, therefore attracts immense attentions in recent years. However, in most cases, the metalens designed for a specific wavelength may penetrate through the large chromatic aberration, which limits their usefulness in multi-wavelength or broadband applications. On the other hand, the metalens has renewed new degrees of freedom due to its two-dimensional planar structure, which has the potential in the elimination of chromatic aberration. Some different typical achromatic metalens designs and their achromatic modulation mechanism were reviewed, the existing achromatic metalens were classified from the types of modulated light bands, such as the achromatic matelens for discrete and continuous wavelength respectively, and the latter can be classified as transmissive and reflective from the working mode. Finally, the application of metalenses array in imaging and their prospect of broadband achromatic devices of large depth of field were introduced.

Effect of water-guided laser machining technology on micro-morphology of 316L stainless steel

Water-jet guided laser (WJGL) machining is a novel processing technology using water beam fibers to guide the laser to machine the work-piece surface. This processing technology has the advantage of almost no mi-cro-cracks, small heat-affected zone, pollution-free, less recast layer, high processing accuracy, parallel cuffing, etc. This work aims to investigate the effect of different WGLM parameters on the micro-morphology of materials and the mechanism between lasers and materials. The experiments for slotting and grooving 316L stainless steel thin samples were used by the WGLM system developed by our research group in this work. The 2D micro-topography after experiments were tested by the Zeiss Vert.A1 metalloscope, and the 3D micro-topography of samples after experiments were tested by the Leica DVM6 optical microscope with the large depth of field & Bruke Contour Elite I white-light interferometer. Experimental results show that a certain width deposition layer can be occurred in the machining region, and the width of deposition layers does not change with the parameter of the machining time and the number of machining times. From the 2D micro-topography of samples, it can be found that the ‘dr’ of slotting samples and the ‘wl’ of grooving samples also do not change with the machining parameters. From the 3D micro-topography of grooving samples, it can be found that the cross-section shape is inverted trapezoid.

Effect of copper or carbon fiber addition to the 3D printing of polylactid samples

Abstract This paper presents the effect of additives on the quality of a product created by 3D print. The product is created by the most widely used 3D printing method - Fused Deposition Modeling (FDM). Polylactic acid (PLA) filaments are tested without and with the addition of carbon fibers or copper. The specimens are characterized by different methods, such as mechanical testing, measuring roughness by digital microscope with a large depth of field and thermal analysis. In fact, FDM is a problematic process with numerous criterions that affect printing quality. Printing parameters such as print temperature, pad temperature, print speed for 3D printing, printing orientation etc. have an important impact on the performance and quality of FDM components. Due to the correct parameters, the product of the required quality with a longer service life is obtained. The results of testing show that the quantity and choice of the right ingredient has a major impact on the mechanical properties and overall quality of the investigated product.

Optimized all-fiber laser Doppler velocimeter with large depth of field

• The structure of the existing laser Doppler velocimeter has been improved to measure a greater depth of field: 0–25 m. • For the first time, the changes of the echo signal strength of the laser Doppler velocimeter at different distances were tested and given graphically, and the signal-to-noise ratio is higher than 15 dB within the whole detection range. • An apparatus for calibrating the speed accuracy of all fiber laser Doppler velocimeter was designed and made. The experimental results showed that the speed accuracy was better than ±0.1 m/s at different distances. Due to the low spatial coupling efficiency of optical fiber and large energy loss, the depth of field in the all-fiber laser Doppler velocimeter is short, and the focus needs to be adjusted before measurement, so it is impossible to continuously measure the velocity of object moving along the optical axis. To solve this problem, an all-fiber Doppler velocimeter based on the Mach-Zehnder interferometer structure is designed, also, in the optical antenna section, C-lens is used to change the divergence angle of the light coming out of the optical fiber. The optimized design achieves the detection with large depth of field. The experiment is designed to verify the intensity of the echo signal, signal-to-noise ratio (SNR) and the speed accuracy of the velocimeter taken in different depths of field. The test results show that the depth of field in this system is superior to 25 m. The SNR is stable around 16 dB with small fluctuation in the range of depth of field, and the speed accuracy is better than ±0.1 m/s.

Impact of the microstructure of polycarboxylate superplasticizers on the dispersion of graphene

Graphene can not only toughen cement-based materials, but also give them sensing ability. However, the uniform dispersion of graphene in a cement matrix is the major problem in the fabrication process. Four polycarboxylate superplasticizers (PCEs) with different charge densities and side-chain lengths were synthesized and the effects of their microstructures on the dispersibility of graphene in deionized water and in solution in cement pores were examined by UV-Vis spectroscopy, dynamic light scattering and optical microscopy with a large depth of field. A mechanism for the dispersion of graphene in the two media was also proposed. In deionized water, PCEs with a higher charge density showed more electrostatic repulsion, which improved the graphene dispersion efficiency. Conversely,PCEs with a lower charge density and longer side-chains gave a lower graphene dispersion. In solution in the cement pores, however, a PCE with a high charge-density produced a low graphene dispersibility, due to a cross-linking Ca2+-bridging effect. This effect was insignificant in cement pores for a solution containing low charge-density PCEs. Moreover, it was found that PCEs with the longer side-chains produced the worst graphene dispersion efficiency in both media. Overall, PCEs with a low charge density and relatively short side chains are more suitable for the preparation of graphene-composited cement pastes.

Depth-of-Field-Extended Plenoptic Camera Based on Tunable Multi-Focus Liquid-Crystal Microlens Array.

Plenoptic cameras have received a wide range of research interest because it can record the 4D plenoptic function or radiance including the radiation power and ray direction. One of its important applications is digital refocusing, which can obtain 2D images focused at different depths. To achieve digital refocusing in a wide range, a large depth of field (DOF) is needed, but there are fundamental optical limitations to this. In this paper, we proposed a plenoptic camera with an extended DOF by integrating a main lens, a tunable multi-focus liquid-crystal microlens array (TMF-LCMLA), and a complementary metal oxide semiconductor (CMOS) sensor together. The TMF-LCMLA was fabricated by traditional photolithography and standard microelectronic techniques, and its optical characteristics including interference patterns, focal lengths, and point spread functions (PSFs) were experimentally analyzed. Experiments demonstrated that the proposed plenoptic camera has a wider range of digital refocusing compared to the plenoptic camera based on a conventional liquid-crystal microlens array (LCMLA) with only one corresponding focal length at a certain voltage, which is equivalent to the extension of DOF. In addition, it also has a 2D/3D switchable function, which is not available with conventional plenoptic cameras.

Effect of copper or carbon fiber addition to the 3D printing of polylactid samples

Abstract This paper presents the effect of additives on the quality of a product created by 3D print. The product is created by the most widely used 3D printing method - Fused Deposition Modeling (FDM). Polylactic acid (PLA) filaments are tested without and with the addition of carbon fibers or copper. The specimens are characterized by different methods, such as mechanical testing, measuring roughness by digital microscope with a large depth of field and thermal analysis. In fact, FDM is a problematic process with numerous criterions that affect printing quality. Printing parameters such as print temperature, pad temperature, print speed for 3D printing, printing orientation etc. have an important impact on the performance and quality of FDM components. Due to the correct parameters, the product of the required quality with a longer service life is obtained. The results of testing show that the quantity and choice of the right ingredient has a major impact on the mechanical properties and overall quality of the investigated product.

Conical ring array detector for large depth of field photoacoustic macroscopy.

Photoacoustic microscopy and macroscopy (PAM) using focused detector scanning are emerging imaging methods for biological tissue, providing high resolution and high sensitivity for structures with optical absorption contrast. However, achieving a constant lateral resolution over a large depth of field for deeply penetrating photoacoustic macroscopy is still a challenge. In this work, a detector design for scanning photoacoustic macroscopy is presented. Based on simulation results, a sensor array geometry is developed and fabricated that consists of concentric ring elements made of polyvinylidene fluoride (PVDF) film in a geometry that combines a centered planar ring with several inclined outer ring elements. The reconstruction algorithm, which uses dynamic focusing and coherence weighting, is explained and its capability to reduce artefacts occurring for single element conical sensors is demonstrated. Several phantoms are manufactured to evaluate the performance of the array in experimental measurements. The sensor array provides a constant axial and lateral resolution of 95 µm and 285 µm, respectively, over a depth of field of 20 mm. The depth of field corresponds approximately to the maximum imaging depth in biological tissue, estimated from the sensitivity of the array. With its ability to achieve the maximum resolution even with a very small scanning range, the array is believed to have applications in the imaging of limited regions of interest buried in biological tissue.

Snapshot multifocal light field microscopy.

Light field microscopy (LFM) is an emerging technology for high-speed wide-field 3D imaging by capturing 4D light field of 3D volumes. However, its 3D imaging capability comes at a cost of lateral resolution. In addition, the lateral resolution is not uniform across depth in the light field dconvolution reconstructions. To address these problems, here, we propose a snapshot multifocal light field microscopy (MFLFM) imaging method. The underlying concept of the MFLFM is to collect multiple focal shifted light fields simultaneously. We show that by focal stacking those focal shifted light fields, the depth-of-field (DOF) of the LFM can be further improved but without sacrificing the lateral resolution. Also, if all differently focused light fields are utilized together in the deconvolution, the MFLFM could achieve a high and uniform lateral resolution within a larger DOF. We present a house-built MFLFM system by placing a diffractive optical element at the Fourier plane of a conventional LFM. The optical performance of the MFLFM are analyzed and given. Both simulations and proof-of-principle experimental results are provided to demonstrate the effectiveness and benefits of the MFLFM. We believe that the proposed snapshot MFLFM has potential to enable high-speed and high resolution 3D imaging applications.

A Novel 3-D High-Temperature Industrial Endoscope With Large Field Depth and Wide Field

Obtaining a high-precision 3-D burden surface (BS) shape of a blast furnace (BF) is of significance for improving energy efficiency in the ironmaking process, and for stabilizing the operation of the BF. However, existing methods used for detecting the BS cannot provide precise data to guide the burden distribution operation of the BF effectively, because they cannot overcome the harsh environment inside the BF. Therefore, to obtain a reliable BS shape under a high-temperature, high-pressure, high-dust, and low-light environment, a 3-D high-temperature industrial endoscope with a large depth of field and wide field of view is proposed in this article. First, image-forming optical system indices are obtained by analyzing the environmental factors and geometry of the BF. Based on these indices, an optical system with a large depth of field, wide field of view, and low-light imaging capacity is designed. Next, a 3-D depth calculation method based on a virtual and real twin binocular optical system is used to obtain 3-D depth of feature points on the burden distribution ring. Furthermore, a functional relationship model between the image defocusing degree and depth of the BS is established, based on the 3-D depth. Finally, a monocular vision 3-D reconstruction method based on the depth from defocus parameter is used to realize the 3-D reconstruction of the BS. Experimental industrial applications of the proposed device demonstrate that it can provide data support for the BF burden distribution operation and has a significant industrial application value.

Computer-generated photorealistic hologram using ray-wavefront conversion based on the additive compressive light field approach

The conventional computer-generated hologram reconstructing photorealistic three-dimensional (3D) images based on ray-wavefront conversion has the disadvantage of spatio-angular resolution trade-off. In this Letter, we propose for the first time, to the best of our knowledge, a computer-generated photorealistic hologram without spatio-angular resolution trade-off based on the additive compressive light field (CLF) approach. The original light field is compressed into multiple layer images through numerical optimization based on the additive light field principle. Then, by independently calculating the wave propagation from each layer image to the hologram plane and adding them together, a CLF hologram is generated. Since the CLF information is presented through a holographic method, the advantage of high resolution in CLF is preserved while the limitation of the number of physically stacked layers (such as liquid crystal displays) is removed, leading to higher quality, larger depth of field, and higher brightness compared with a conventional CLF display. The proposed method is verified with a photorealistic optical experiment.

Three-dimensional tracking of multiple particles in large depth of field using dual-objective bifocal plane imaging

Tracking moving particles in cells by single particle tracking is an important optical approach widely used in biological research. In order to track multiple particles within a whole cell simultaneously, a parallel tracking approach with large depth of field was put forward. It was based on distorted grating and dual-objective bifocal imaging, making use of the distorted grating to expand the depth of field, dual-objective to gather as many photons as possible, and bifocal plane imaging to realize three-dimensional localization. Simulation of parallel tracking of two particles moving along the z axis demonstrated that even when the two are axially separated by 10 μm, they can both be localized simultaneously with transversal precision better than 5 nm and axial precision better than 20 nm.

Scheimpflug Camera-Based Stereo-Digital Image Correlation for Full-Field 3D Deformation Measurement

To further extend the scope of stereo-digital image correlation (stereo-DIC) to more challenging environments, a novel Scheimpflug camera-based stereo-DIC is developed for full-field 3D deformation measurement, wherein the Scheimpflug condition, consisting of tilting the sensor plane with respect to the lens plane for the sake of larger depth of field (DOF) of the camera, is employed. The geometric imaging model of the Scheimpflug camera is described, on the basis of which a robust and effective stepwise calibration strategy is performed to calculate the intrinsic and extrinsic parameters of the stereo Scheimpflug rig. With the aid of a specially tailored stereo triangulation method and well-developed subset-based DIC algorithms, the three-dimensional shape and displacement of the specimen can be retrieved. Finally, practical experiments, including rigid motion tests and three-point bending tests, demonstrate the effectiveness and accuracy of the proposed approach.

Generating and 2-D Steering Large Depth-of-Field Beam by Leaky-Wave Antenna Array With a Modified Parabolic Reflector

A millimeter-wave substrate-integrated waveguide (SIW) antenna with the ability of generating 2-D steerable large depth-of-field beam is presented in this article. First, a transverse antenna topology feeding with the series- and the parallel-network is employed to generate the limited-diffractive beam with large depth of field to overcome the problem that the conventional radial generator cannot steer its beam electronically. The proposed antenna is achieved by combining a modulated leaky-wave slot array antenna with a modified multibeam SIW parabolic reflector. The modulated leaky-wave slot array with stepped-width is designed to able to steer the limited-diffractive beam in the horizontal dimension with the frequency, which validates the frequency scanning feasibility of the limited-diffractive beam. Then a modified SIW parabolic reflector with matching loads is used to feed the modulated leaky-wave SIW slot array antenna to generate multiple limited-diffractive beams in the vertical dimension. A large depth of field of about 43λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is achieved of the central limited-diffractive beam. The measurements are in good agreement with the simulated results.

Surface profiling of object using varifocal lens with image contrast

The measurement of automated and fast focusing on the improvement of speed and accuracy is an important issue in industrial inspection and biomedical microscopy. In this study, we developed a novel optical imaging system in which varifocal lenses are used to characterize the 3D surface topography of samples. The performance of the proposed system was evaluated using twelve focusing algorithms. Experimental results demonstrate the feasibility and effectiveness of the proposed system in the near real-time construction of multi-focus fusion images with large depth of field from which to derive 3D surface profiles.

Design of a Single-Lens Freeform-Prism-Based Distortion-Free Stereovision System

Stereo vision can be achieved with a single camera aided by a flat-face prism. However, large optical distortions may be caused by irregular refraction. To mitigate this deficiency and minimize distortion, a new freeform prism design is proposed to replace the flat-face prism. All refracting surfaces of the prism are designed for freeform features, which can process object points at a large depth of field. Differential equations are derived to express the freeform surface, and the Runge–Kutta method is used to numerically solve the differential equations.

Post-failure fracture surface analysis of notched steel specimens after bending-torsion fatigue

This paper contains analysis of fatigue fracture surfaces parameters of circumferential v-notched 10HNAP (S355J2G1W) steel specimens. Fatigue tests were performed under bending, torsion and combinations of bending MB and torsional MT moments. Stationary and ergodic random loadings had normal probability distribution and wide-band frequency spectra from 0 to 60 Hz.Thirty years after fatigue tests, the fracture surfaces of the specimens were subjected to observations with the use of a focus variation microscope (FVM), which allows data sets with a large depth of field to be obtained. Surface topography analysis was performed on the entire fracture using height parameters and functional parameters (volume) in accordance with ISO 25178, as was the fractal dimension.Tendencies of changes in height, functional and fractal fracture surface texture parameters for three types of loadings were analysed. The examined fracture surfaces showed the dependence of the loading history on their topography. Parameters that were responsive to surface irregularities were selected, because they can be used, for example, to investigate the causes of material damage. Regression analysis of the relationship between values of areal parameters was also carried out.

Depth detection capability and ultra-large depth of field in imaging through a thin scattering layer

A wavelength-depth-matching method based on speckle correlation is proposed to achieve an ultra-large depth of field (DOF) of 90.5 mm experimentally on one side in imaging through a thin scattering layer. By making rational use of chromatic aberrations to compensate for the effects of depth differences, we determine the depth information of a target object using a incoherent wavelength-tunable light source. A random matrix that satisfies the distribution with a root mean square of 1 μm and a correlation length of 100 μm is generated to simulate the varying heights of the scattering surfaces which is used to demonstrate that larger DOF can be attained theoretically. This method, with its improved depth detection capability and ultra-large DOF, makes 3D dynamic imaging through scattering media possible.