Planktonic response to light as a pollution indicator

Ecological monitoring requires sensitive and effective approaches to detecting polluting substances. One such approach involves tracking the behavioral responses of plankton that is initially adapted to normal habitat conditions. Zooplankton such as Daphnia are filter feeders that are highly sensitive to pollution. We describe how a submersible holographic camera with additional attracting lighting (at a wavelength of 532 nm) can be used to track changes of Daphnia response to light for a number of pollutants, including potassium dichromate and crude oil. Our laboratory experiments showed that the sensitivity of this method of bioanalysis is comparable to standard laboratory methods, but has the additional advantage that it can be used in real time in lakes and other water areas, and hence is more versatile than standard methods.     

太赫兹超表面计算全息

全息术是一种三维成像技术,它已经被应用于多种实际场景。随着计算机科学与技术的迅猛发展,计算全息由于其方便和灵活的特性,已经成为一种广泛应用的全息成像方法。本文回顾了我们近期基于超表面的太赫兹计算全息研究进展。其中,作为全息板的超表面展示出了超越传统光学器件的独特性能。首先,利用超表面实现了对于全息板每个像素的相位振幅同时且独立的调控,进而实现了高质量全息成像。这种新的电磁波操控能力也带来了新的全息成像效果,如利用介质超表面实现了全息像沿传播方向上的连续变化。其次,对超表面在不同偏振态下的响应进行设计,分别实现了线偏振态与频率复用、圆偏振态复用、以及基于表面波的偏振复用超表面全息术。此外,本文提出了依赖于温度变化而主动可控的超表面全息术,为今后计算全息术的设计与实现提供了新的方案,也推动了超表面在实际应用方面的发展。     

Comprehensive performance analysis of objective quality metrics for digital holography

Objective quality assessment of digital holograms has proven to be a challenging task. While prediction of perceptual quality of the recorded 3D content from the holographic wavefield is an open problem; perceptual quality assessment from content after rendering, requires a time-consuming rendering step and a multitude of possible viewports. In this research, we use 96 Fourier holograms of the recently released HoloDB database to evaluate the performance of well-known and state-of-the-art image quality metrics on digital holograms. We compare the reference holograms with their distorted versions: (i) before rendering on the real and imaginary parts of the quantized complex-wavefield, (ii) after converting Fourier to Fresnel holograms, (iii) after rendering, on the quantized amplitude of the reconstructed data, and (iv) after subsequently removing speckle noise using a Wiener filter. For every experimental track, the quality metric predictions are compared to the Mean Opinion Scores (MOS) gathered on a 2D screen, light field display and a holographic display. Additionally, a statistical analysis of the results and a discussion on the performance of the metrics are presented. The tests demonstrate that while for each test track a few quality metrics present a highly correlated performance compared to the multiple sets of available MOS, none of them demonstrates a consistently high-performance across all four test-tracks.     

数字同轴全息油液磨粒形貌检测技术的研究

提出一种基于数字同轴全息三维成像理论的油液磨损颗粒检测新技术,该技术同时具有颗粒计数、颗粒成像及形态、形貌识别分类等功能,可为基于油液分析的机械设备状态监测和磨损故障诊断提供新的检测手段.对数字同轴全息用于油液磨损颗粒检测的原理、特点及系统软硬件组成等进行了详细介绍,并进行了实验验证,实验结果证明了该技术的可行性.     

Elimination of zero-order diffraction and conjugate image in off-axis digital holography

The presence of zero-order diffraction and a conjugate image in digital holography essentially diminishes the quality of the reconstructed image. In this paper, a novel method that adopts numerical operation to eliminate the zero-order diffraction and conjugate image is presented. The whole process needs only one hologram and a complex finite impulse response (FIR) digital filter. The method of numerical elimination is simple; it filters the hologram directly in the spatial domain instead of in the frequency domain. The design of a complex finite impulse response filter is described in detail. The experimental results demonstrate that the operation can completely eliminate the zero-order diffraction and conjugate image and significantly enhance the quality of the reconstructed image.     

Model of low spatial frequency diffractive elements recorded in photopolymers during and after recording

Photopolymer are appealing materials for diffractive elements recording. Two of their properties when they are illuminated are useful for this goal: the relief surface changes and the refractive index modifications. In this paper we use a 2-dimensional model, based on direct parameter measurements, for predicting the refractive index distributions during and after illumination. We have analyzed different recording spatial frequencies for photopolymers based on PVA/Acrylamide. This model was successfully applied to different photopolymer compositions with different values of monomer diffusion and polymerization rates.     

Sequential processing of quantitative phase images for the study of cell behaviour in real‐time digital holographic microscopy

Transmitted light holographic microscopy is particularly used for quantitative phase imaging of transparent microscopic objects such as living cells. The study of the cell is based on extraction of the dynamic data on cell behaviour from the time‐lapse sequence of the phase images. However, the phase images are affected by the phase aberrations that make the analysis particularly difficult. This is because the phase deformation is prone to change during long‐term experiments. Here, we present a novel algorithm for sequential processing of living cells phase images in a time‐lapse sequence. The algorithm compensates for the deformation of a phase image using weighted least‐squares surface fitting. Moreover, it identifies and segments the individual cells in the phase image. All these procedures are performed automatically and applied immediately after obtaining every single phase image. This property of the algorithm is important for real‐time cell quantitative phase imaging and instantaneous control of the course of the experiment by playback of the recorded sequence up to actual time. Such operator's intervention is a forerunner of process automation derived from image analysis. The efficiency of the propounded algorithm is demonstrated on images of rat fibrosarcoma cells using an off‐axis holographic microscope.     

Augmented reality technology combined with three-dimensional holography to train the mental rotation ability of older adults

A decline in the cognitive ability of mental rotation causes a poor sense of spatial direction and environmental cognitive capacity. Currently, training tasks for the elderly thus affected are still presented in 2D form. However, clinical research indicates that this strategy generates a cognitive load that reduces the interest of the trainees and diminishes the effects of training. In contrast, augmented reality (AR) is a rising solution that effectively reduces cognitive load, improves the sense of spatial direction of the elderly, and helps increase interest in training. We recruited 28 elderly (age ≥ 65 years) for this study. Fourteen were randomly assigned to an active Intervention group and were given AR-based 3D hologram (AR-3DH) mental rotation training, and 14 were assigned to a group that used the traditional 2D model. Both groups took ABA-designed pre-and post-tests that required inferring the rotating shapes' states from standard mental rotation tasks. Change scores for the two groups were compared using error rates and reaction times as covariates. After six-week of training, the mental rotation ability of the Intervention group improved through the use of AR-3DH training system during the intervention phase. The practical and developmental implications of the findings are discussed.     

Influence of part material and sensor adjustment on the quality of digitised point-clouds using conoscopic holography

Conoscopic holography is an interferometric measurement technique commonly used for non-contact surfaces digitising in quality assessment, in-process inspection and reverse engineering. Among other factors, accuracy of measurements provided by this technology is influenced by the surface optical properties. Parameters such as laser power (P) or frequency of acquisition (F) are commonly used to adjust the sensor until a quality indicator of the signal acquired (Signal-to-Noise-Ratio) is maximised. Nevertheless, measurements taken under this adjusting criterion does not necessarily ensure the most accurate results from a metrological point of view. Taking this into account, the present work proposes two additional indicators to analyse the influence of sensor setting parameters on the quality of digitised point-clouds for different metals and polymers. Digitising tests have been performed on flat specimens of each material by means of a conoscopic holography sensor integrated on a Coordinate Measuring Machine. In order to meet an optimal scanning of each material, the study provides a series of recommendations about adjustment of the sensor as well as the most suitable indicator to be used in each case.     

Electron Holography Studies on Narrow Magnetic Domain Walls Observed in a Heusler Alloy Ni50Mn25Al12.5Ga12.5

Peculiar magnetic domain walls produced in Heusler alloys, which have attracted renewed interest due to their potential application to actuators and spintronic devices, are studied here using electron holography. The observations reveal unexpectedly narrow magnetic domain walls, the width of which showed perfect agreement with that of the antiphase boundaries (APB, e.g., only 3 nm). While the results can be explained by the significant depression of ferromagnetism due to the local chemical disorder, the electron phase shift indicates that ferromagnetic correlation still remains in the APB region.