ADMM-inspired image reconstruction for terahertz off-axis digital holography.

Image reconstruction in off-axis terahertz digital holography is complicated due to the harsh recording conditions and the non-convexity form of the problem. In this paper, we propose an inverse problem-based reconstruction technique that jointly reconstructs the object field and the amplitude of the reference field. Regularization in the wavelet domain promotes a sparse object solution. A single objective function combining the data-fidelity and regularization terms is optimized with a dedicated algorithm based on an alternating direction method of multipliers framework. Each iteration alternates between two consecutive optimizations using projections operating on each solution and one soft thresholding operator applying to the object solution. The method is preceded by a windowing process to alleviate artifacts due to the mismatch between camera frame truncation and periodic boundary conditions assumed to implement convolution operators. Experiments demonstrate the effectiveness of the proposed method, in particular, improvements of reconstruction quality, compared to two other methods.

Serological evidence of the circulation of the Rift Valley fever virus in sheep and goats slaughtered in Yaoundé, Cameroon.

BACKGROUND: Rift Valley fever (RVF) is an emerging mosquito-borne haemorrhagic fever disease capable of causing severe outbreaks with high mortality and morbidity in human, livestock, and wildlife species, particularly in Africa. The onset of the disease in humans is often preceded by epizootic circulation in animals. Therefore, this study was conducted to investigate the seroprevalence of Rift Valley fever virus (RVFV) infection in animals slaughtered in the "Marché huitième" slaughterhouse in Yaoundé, Cameroon. METHODS: A cross-sectional study was conducted at the "Marché huitième" slaughterhouse in Yaoundé, Centre region of Cameroon in March 2020. Blood samples of two species of small ruminants (sheep and goat) were collected and processed. Serum was analysed for detection of RVFV IgG and IgM using commercial ELISA tests. RESULTS: Of the 191 ruminants tested, RVFV IgG antibodies were positive in 10 (5.2%). Regarding categorization of the population based on the species and gender, sheep and female animal had the highest seroprevalence of 6.4% (3/47) and 7.0% (8/115), respectively. All sera from IgG antibodies-positive samples were negative to IgM antibodies. CONCLUSION: This study provides evidence of the circulation of RVFV in small ruminants sold and slaughtered at the "Marché huitième" slaughterhouse in Yaoundé and highlights the need to develop a surveillance system for this virus encompassing humans, livestock, wildlife, and vectors in Cameroon.

Primary cilia control endothelial permeability by regulating expression and location of junction proteins.

AIMS: Wall shear stress (WSS) determines intracranial aneurysm (IA) development. Polycystic kidney disease (PKD) patients have a high IA incidence and risk of rupture. Dysfunction/absence of primary cilia in PKD endothelial cells (ECs) may impair mechano-transduction of WSS and favour vascular disorders. The molecular links between primary cilia dysfunction and IAs are unknown. METHODS AND RESULTS: Wild-type and primary cilia-deficient Tg737orpk/orpk arterial ECs were submitted to physiological (30 dynes/cm2) or aneurysmal (2 dynes/cm2) WSS, and unbiased transcriptomics were performed. Tg737orpk/orpk ECs displayed a fivefold increase in the number of WSS-responsive genes compared to wild-type cells. Moreover, we observed a lower trans-endothelial resistance and a higher endothelial permeability, which correlated with disorganized intercellular junctions in Tg737orpk/orpk cells. We identified ZO-1 as a central regulator of primary cilia-dependent endothelial junction integrity. Finally, clinical and histological characteristics of IAs from non-PKD and PKD patients were analysed. IAs in PKD patients were more frequently located in the middle cerebral artery (MCA) territory than in non-PKD patients. IA domes from the MCA of PKD patients appeared thinner with less collagen and reduced endothelial ZO-1 compared with IA domes from non-PKD patients. CONCLUSION: Primary cilia dampen the endothelial response to aneurysmal low WSS. In absence of primary cilia, ZO-1 expression levels are reduced, which disorganizes intercellular junctions resulting in increased endothelial permeability. This altered endothelial function may not only contribute to the severity of IA disease observed in PKD patients, but may also serve as a potential diagnostic tool to determine the vulnerability of IAs.

Robust Principal Component Thermography for Defect Detection in Composites.

Pulsed Thermography (PT) data are usually affected by noise and as such most of the research effort in the last few years has been directed towards the development of advanced signal processing methods to improve defect detection. Among the numerous techniques that have been proposed, principal component thermography (PCT)-based on principal component analysis (PCA)-is one of the most effective in terms of defect contrast enhancement and data compression. However, it is well-known that PCA can be significantly affected in the presence of corrupted data (e.g., noise and outliers). Robust PCA (RPCA) has been recently proposed as an alternative statistical method that handles noisy data more properly by decomposing the input data into a low-rank matrix and a sparse matrix. We propose to process PT data by RPCA instead of PCA in order to improve defect detectability. The performance of the resulting approach, Robust Principal Component Thermography (RPCT)-based on RPCA, was evaluated with respect to PCT-based on PCA, using a CFRP sample containing artificially produced defects. We compared results quantitatively based on two metrics, Contrast-to-Noise Ratio (CNR), for defect detection capabilities, and the Jaccard similarity coefficient, for defect segmentation potential. CNR results were on average 40% higher for RPCT than for PCT, and the Jaccard index was slightly higher for RPCT (0.7395) than for PCT (0.7010). In terms of computational time, however, PCT was 11.5 times faster than RPCT. Further investigations are needed to assess RPCT performance on a wider range of materials and to optimize computational time.

Continuous-wave terahertz reflective ptychography by oblique illumination.

Massive usage scenarios prompt the prosperity of terahertz (THz) reflective imaging methods. In this Letter, we apply ptychography to continuous-wave THz reflective imaging. Our scheme has a compact lensless layout and uses a full-field oblique-illumination recording mode. Diffraction patterns are corrected through tilted plane correction. This method can be used to retrieve the complex-valued object function and to suppress the negative effect of non-uniform illumination. The feasibility is investigated using two metal samples.

Serological and molecular investigation of hepatitis E virus in pigs reservoirs from Cameroon reveals elevated seroprevalence and presence of genotype 3.

BACKGROUND: Hepatitis E virus (HEV) is a zoonotic pathogen of which pigs have been established as reservoirs. In the present study, we investigated the presence of HEV among pigs in the Center and Littoral regions of Cameroon and performed the molecular characterization of positive strains. METHODOLOGY: A total of 453 serum and stool samples were randomly collected from pigs in slaughterhouses in Obala, Douala and Yaounde. All samples were examined for the presence of anti-HEV IgG and IgM antibodies using ELISA assays. IgM positive stool samples were tested for HEV RNA using an RT-PCR assay, followed by a nested PCR assay for sequencing and phylogenetic analysis. RESULTS: Overall, 216 samples (47.7%, 95% CI: 43.1%-52.3%) were positive for at least one of the serological markers of HEV infection. Amongst these, 21.0% were positives for anti-HEV IgM, 17.7% for anti-HEV IgG, and 9.1% for both. A total of eight stool samples (5.9%) were positive for HEV RNA by nested RT-PCR. Phylogenetic analysis showed that the retrieved sequences clustered within HEV genotype 3. CONCLUSION: This study shows a high prevalence of anti-HEV antibodies and the circulation of genotype 3 in the swine population in Cameroon. Subsequent studies will be needed to elucidate the zoonotic transmission of HEV from pigs to humans in Cameroon.

Digital Holography and 3D Imaging: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America A.

The OSA Topical Meeting on Digital Holography and 3D Imaging (DH) was held 20-23 May 2019 in Bordeaux, France. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. This year, AO and the Journal of the Optical Society of America A (JOSA A) jointly decided to have one such feature issue in each journal. This feature issue includes 46 papers in AO and 9 in JOSA A and covers a large range of topics, reflecting the rapidly expanding techniques and applications of digital holography and 3D imaging. The upcoming DH Conference (DH 2020) will be held from 22 to 26 June in Vancouver, Canada, as part of the OSA Imaging and Applied Optics Congress.

THz coherent lensless imaging.

Imaging with THz radiation has proved an important tool for both fundamental science and industrial use. Here we review a class of THz imaging implementations, named coherent lensless imaging, that reconstruct the coherent response of arbitrary samples with a minimized experimental setup based only on a coherent source and a camera. After discussing the appropriate sources and detectors to perform them, we detail the fundamental principles and implementations of THz digital holography and phase retrieval. These techniques owe a lot to imaging with different wavelengths, yet innovative concepts are also being developed in the THz range and are ready to be applied in other spectral ranges. This makes our review useful for both the THz and imaging communities, and we hope it will foster their interaction.

Digital holographic interferometry and speckle interferometry applied on objects with heterogeneous reflecting properties.

In digital holographic and speckle interferometry devoted to solid object displacement measurement, the reflecting properties of the object under study are of importance in designing the observation and laser illumination systems. In practical cases, the objects can show separate zones in which the surface property can simultaneously cause either scattering or specular reflectivity. We present strategies for dealing with both reflectivity types at a time in digital holographic and speckle interferometers. The scattered surface is illuminated with a point source whereas the specular one is illuminated by a diffuser. Both types of surfaces visible across the field-of-view give rise to a specific interferogram with gaps in between, which in turn are interpreted separately related to the sensitivity vector, the latter being defined differently for scattering and specular areas.

Digital Holography and 3D Imaging: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America A.

The OSA Topical Meeting on Digital Holography and 3D Imaging (DH) was held 20-23 May 2019 in Bordeaux, France. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. This year, AO and the Journal of the Optical Society of America A (JOSA A) jointly decided to have one such feature issue in each journal. This feature issue includes 46 papers in AO and 9 in JOSA A and covers a large range of topics, reflecting the rapidly expanding techniques and applications of digital holography and 3D imaging. The upcoming DH Conference (DH 2020) will be held from 22 to 26 June in Vancouver, Canada, as part of the OSA Imaging and Applied Optics Congress.

Iterative phase-retrieval-assisted off-axis terahertz digital holography.

In terahertz digital holography, the off-axis configuration is the appropriate choice when the investigated object is non-sparse and complex. The limitation of recording distance in the off-axis configuration restricts the imaging quality. Either low-resolution or spectra overlap can potentially occur. We propose an iterative phase-retrieval approach to improve the quality of reconstruction results obtained from an off-axis hologram. One additional capture of object wave intensity is recorded to perform iterative phase retrieval with off-axis reconstruction as the initial guess. Apodization operation can be applied to the object wave intensity capture to suppress undesired border diffraction effects. The image quality using the proposed method has been improved both from simulation and experimental verification.

Determination of vibration amplitudes from binary phase patterns obtained by phase-shifting time-averaged speckle shearing interferometry.

Speckle shearing interferometry (shearography) is a full-field strain measurement technique that can be used in vibration analysis. In our case, we apply a method that combines the time-averaging and phase-shifting techniques. It produces binary phase patterns, where the phase changes are related to the zeroes of a Bessel J0 function, typical of time-averaging. However, the contrast and resolution are better compared to traditional time-averaging. In a previous paper, we have shown that this is particularly useful in vibration testing performed under industrial conditions, because fringe patterns are noisier than in quiet laboratory environments. This paper goes a step further in proposing a processing method for estimating the vibration amplitude, for helping non-experts to identify vibration modes. Since shearography measures the spatial derivative of displacement, spatial integration is required. Prior to that, different processes like denoising, binarization, automated nodal line detection, and amplitude assignment are applied. We analyze the performance of the method on synthetic and experimental data, in the function of noise level and fringes density. Results on data acquired in an industrial environment illustrate the good performances of the proposed method.

Space mirror deformation: from thermo-mechanical measurements by speckle interferometry to optical comparison with multiphysics simulation.

Experimental testing of space optics is a mandatory process for investigating the optical performances in conditions close to reality. With the optical requirement level increasing over years, these experimental tests are increasingly expensive and time-consuming. A modeling tool would therefore be an elegant solution to avoid these drawbacks. For this purpose, a multiphysics approach has been used to predict how optics behave under thermal loads. In this paper, experimental surface deformations of a space mirror perturbed by thermal gradients are compared to multiphysics simulation results. The local displacements of the mirror surface have been measured by use of electronic speckle pattern interferometry, and the deformation itself has been calculated by subtracting the rigid body motion. After validation of the thermo-mechanical solution, experimental and numerical wavefront errors are compared.

Feature issue of digital holography and 3D imaging (DH): introduction.

The OSA Topical Meeting "Digital Holography and 3D Imaging (DH)" was held in Seattle, Washington, 13-17 July 2014. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. In this year (2014), Optics Express (OE) and AO jointly decided to have one such feature issue in each journal. The feature issue includes 27 papers and covers a large range of topics, reflecting the rapidly expanding techniques and applications of digital holography and 3D imaging. The DH meeting will continue in the future, as expected, and the next meeting is scheduled to be held on 24-28 May 2015, at Shanghai Institute of Optics and Fine Mechanics, Shanghai, China.

Real-time measurement of temperature variation during nanosecond pulsed-laser-induced contamination deposition.

In this paper, a study of heat generation during UV laser-induced contamination (LIC) and potentially resulting subsequent thermal damage are presented. This becomes increasingly interesting when optics with delicate coatings are involved. During LIC, radiation can interact with outgassing molecules, both in the gas phase and at the surface, thus triggering chemical and photo-fixation reactions. This is a major hazard, in particular for laser units operating under vacuum conditions such as in space applications. The intense photon flux not only affects the contaminant deposition rate but also alters their chemical structure, which can increase their absorption coefficient. Over cumulative irradiation shots, these molecules formed deposits that increasingly absorb photons and produce heat as a by-product of de-excitation, eventually leading to thermal damage. One could better assess the risk of the latter with the knowledge of temperature during the contamination process. For this purpose, a thermoreflectance technique is used here to estimate the temperature variation from pulse to pulse during contamination deposition through the analysis of a temperature-dependent surface reflectance signal.

Combined holography and thermography in a single sensor through image-plane holography at thermal infrared wavelengths.

Holographic interferometry in the thermal wavelengths range, combining a CO(2) laser and digital hologram recording with a microbolometer array based camera, allows simultaneously capturing temperature and surface shape information about objects. This is due to the fact that the holograms are affected by the thermal background emitted by objects at room temperature. We explain the setup and the processing of data which allows decoupling the two types of information. This natural data fusion can be advantageously used in a variety of nondestructive testing applications.

Digital holographic interferometry with CO2 lasers and diffuse illumination applied to large space reflector metrology [Invited].

Digital holographic interferometry in the long-wave infrared domain has been developed by combining a CO(2) laser and a microbolometer array. The long wavelength allows large deformation measurements, which are of interest in the case of large space reflectors undergoing thermal changes when in orbit. We review holography at such wavelengths and present some specific aspects related to this spectral range on our measurements. For the design of our digital holographic interferometer, we studied the possibility of illuminating specular objects by a reflective diffuser. We discuss the development of the interferometer and the results obtained on a representative space reflector, first in the laboratory and then during vacuum cryogenic test.

Nondestructive testing by using long-wave infrared interferometric techniques with CO2 lasers and microbolometer arrays.

We describe three different interferometric techniques (electronic speckle pattern interferometry, digital holographic interferometry, and digital shearography), using a long-wave infrared radiation produced by a CO(2) laser and recorded on a microbolometer array. Experimental results showing how these methods can be used for nondestructive testing are presented. Advantages and disadvantages of these approaches are discussed.

Performances of volume phase holographic grating for space applications: study of the radiation effect.

The special properties of volume phase holographic gratings make them promising candidates for spectrometry applications where high spectral resolution, low levels of straylight, and low polarization sensitivity are required. Therefore it is of interest to assess the maturity and suitability of volume phase holographic gratings as enabling technologies for future space missions, with demanding requirements for spectrometry. One of the main areas of research is related to grating ageing under space radiation. In the present paper, two volume grating technologies are analyzed and compared under gamma irradiation. The performances of both technologies, the photo-thermo-refractive glass and the Dichromated Gelatin, are tested on samples and assessed in the Hα and near-infrared bands. The diffraction efficiency degradation under gamma irradiation is assessed.