Showing papers in "Proceedings of SPIE in 2021"
TL;DR: In this article, the authors present the status of the technology and of the mass production capabilities, show latest performance results, and discuss the next steps in the development of the system.
Abstract: Athena, the largest space-based x-ray telescope to be flown by the European Space Agency, uses a new modular technology to assemble its 2.5 m diameter lens. The lens will consist of several hundreds of smaller x-ray lenslets, called mirror modules, which each consist of up to 76 stacked mirror pairs. Those mirror modules are arranged in circles in a large optics structure and will focus x-ray photons with an energy of 0.5 to 10 keV at a distance of 12 m onto the detectors of Athena. The point-spread function (PSF) of the optic shall achieve a half-energy width (HEW) of 5” at an energy of 1 keV, with an effective area of about 1.4 m2, corresponding to several hundred m2 of super-polished mirrors with a roughness of about 0.3 nm and a thickness of down to 110 µm. This paper will present the status of the technology and of the mass production capabilities, show latest performance results and discuss the next steps in the development.
23 citations
TL;DR: In this paper, a set of comprehensive optical simulations were used to predict the collimation performances of the paraboloidal mirror, including the effect of surface errors obtained from metrology.
Abstract: The BEaTriX (Beam Expander Testing X-ray) facility, being completed at INAF-Brera Astronomical Observatory, will represent an important step in the acceptance roadmap of Silicon Pore Optics mirror modules, and so ensure the final angular resolution of the ATHENA X-ray telescope. Aiming at establishing the final angular resolution that can be reached and the respective fabrication/positioning tolerances, we have been dealing with a set of comprehensive optical simulations. Simulations based on wave optics were carried out to predict the collimation performances of the paraboloidal mirror, including the effect of surface errors obtained from metrology. Full-ray-tracing routines were subsequently employed to simulate the full beamline. Finally, wavefront propagation simulation allowed us assessing the sensitivity and the response of a wavefront sensor that will be utilized for the qualification of the collimated beam. We report the simulation results and the methodologies we adopted.
15 citations
TL;DR: In this article, the authors present the development and test of the collimating mirror, a paraboloid sector having an optical surface of 400 mm ´ 60 mm and sagittal radii of about 155 mm.
Abstract: The BEaTriX (Beam Expander Testing X-ray) facility under construction at INAF-Brera Astronomical Observatory aims at performing the acceptance tests of the Silicon Pore Optics mirror modules of the ATHENA (Advanced Telescope for High-ENergy Astrophysics) X-ray observatory. The facility implements a grazing-incidence collimating mirror that, together with a monochromator and a beam expander stages based on crystals, enables the full X-ray illumination of the mirror modules under test. We present the development and test of the collimating mirror, a paraboloid sector having an optical surface of 400 mm ´ 60 mm and sagittal radii of about 155 mm. The ground and lapped optics made of HOQ 310 fused quartz was corrected by bonnet polishing. In this paper, we report on the smoothing of mid-to-high spatial frequency error by pitch-tool polishing process, and on the correction of residual surface shape errors by ion-beam figuring process, both performed at INAF-Brera Astronomical Observatory. We present the X-ray test campaigns carried out on the mirror at PANTER facility, before and after coating it with a Pt layer via magnetron sputtering at DTU Space. The results provide an overview of the mirror performance in terms of angular resolution pre- and post-coating deposition.
13 citations
TL;DR: The HERMES project as discussed by the authors proposes a modular observatory of huge overall collecting area consisting in a fleet of small satellites in low orbits, with sub-microsecond time resolution and wide energy band (keV-MeV).
Abstract: Within Quantum Gravity theories, different models for space-time quantisation predict an energy dependent speed for photons. Although the predicted discrepancies are minuscule, GRB, occurring at cosmological distances, could be used to detect this signature of space-time granularity with a new concept of modular observatory of huge overall collecting area consisting in a fleet of small satellites in low orbits, with sub-microsecond time resolution and wide energy band (keV-MeV). The enormous number of collected photons will allow to effectively search these energy dependent delays. Moreover, GrailQuest will allow to perform temporal triangulation of high signal-to-noise impulsive events with arc-second positional accuracies: an extraordinary sensitive X-ray/Gamma all-sky monitor crucial for hunting the elusive electromagnetic counterparts of GW. A pathfinder of GrailQuest is already under development through the HERMES project: a fleet of six 3U cube-sats to be launched by 2021/22.
11 citations
TL;DR: The BEaTriX (Beam Expander Testing X-ray) facility at the INAF-Osservatorio Astronomico Brera (Merate, Italy) as discussed by the authors is the state-of-the-art facility for beam expansion testing of ATHENA mirror modules.
Abstract: BEaTriX (Beam Expander Testing X-ray) is the X-ray facility under construction at the INAF-Osservatorio Astronomico Brera (Merate, Italy) to prove that it is possible to perform the X-ray acceptance tests (PSF and Aeff) of the ATHENA mirror modules at the required rate and with the required accuracy. The unique optical setup makes use of a micro-focus X-ray source with anode in Titanium, a paraboloidal mirror with small radius of curvature, and a set of crystals to monochromate and expand the beam to fully illuminate the entrance pupil of the ATHENA MMs. The quality of the optical components, and their precise alignment, guarantees the production of a parallel beam at 4.51 keV, to be extended in a second phase to 1.49 keV in order to complete the acceptance requirements for the ATHENA MMs. The completion of the facility is expected to occur in July this year, while the commissioning will start in September. In this paper, we present the current status.
11 citations
TL;DR: The paper will provide an overview of most recent SPO plate designs, mirror plate production status and plan forward including reflective coating process as well as mass production developments.
Abstract: The Silicon Pore Optics (SPO) technology has been established as a new type of X-ray optics and will enable future X-ray observatories such as Athena and Arcus. SPO is being developed at cosine Research B.V. together with the European Space Agency (ESA) and academic as well as industrial partners. For Athena, about 150,000 mirror plates are required. With the technology spin-in from the semiconductor industry, mass production processes can be employed to manufacture rectangular SPO mirror plates in high quality, large quantity and at low cost. Over the last years, several aspects of the SPO mirror plates have been reviewed and undergone further developments in terms of effective area, intrinsic behavior of the mirror plates and mass production capability. The paper will provide an overview of most recent SPO plate designs, mirror plate production status and plan forward including reflective coating process as well as mass production developments.
10 citations
TL;DR: In this paper, the authors present X-ray reflectometry characterization of iridium thin films deposited on photoresist patterned silicon pore Optics plates to investigate the compatibility with the stacking process steps for the manufacturing of the Athena optics.
Abstract: The development of high-quality thin film coatings for the Athena X-ray optics is progressing, following the commissioning of an industrial scale coating facility. The assembly of silicon pore optics into mirror modules for the Athena telescope requires wet-chemical exposure of coated mirror plates to prepare bonding areas for stacking, as well as an annealing step to improve bond strength. It is therefore critical to evaluate how these post-coating processes could affect the mirror coating performance and stability.
We present X-ray reflectometry characterization of iridium thin films deposited on photoresist patterned Silicon Pore Optics plates to investigate the compatibility with the stacking process steps for the manufacturing of the Athena optics.
8 citations
TL;DR: The main scientific requirements of the mission are summarized and an overview of the updated concept, design (instruments and spacecraft) and mission profile is provided.
Abstract: THESEUS is a space mission concept, currently under Phase A study by ESA as candidate M5 mission, aiming at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. In addition to fully exploiting high-redshift GRBs for cosmology (pop-III stars, cosmic re-ionization, SFR and metallicity evolution up to the "cosmic dawn"), THESEUS will allow the identification and study of the electromagnetic counterparts to sources of gravitational waves which will be routinely detected in the late '20s / early '30s by next generation facilities like aLIGO/aVirgo, LISA, KAGRA, and Einstein Telescope (ET), as well as of most classes of X/gamma-ray transient sources, thus providing an ideal synergy with the large e.m. facilities of the near future like, e.g., LSST, ELT, TMT, SKA, CTA, ATHENA. These breakthrough scientific objectives will be achieved by an unprecedented combination of X/gamma-ray monitors, providing the capabilities of detecting and accurately localize and kind of GRBs and may classes of transient in an energy band as large as 0.1 keV - 10 MeV, with an on-board NIR telescope providing detection, localization (arcsec) and redshift measurement of the NIR counterpart. A Guest Observer programme, further improving the scientific return and community involvement is also envisaged. We summarize the main scientific requirements of the mission and provide an overview of the updated concept, design (instruments and spacecraft) and mission profile.
7 citations
TL;DR: In this article, the authors demonstrate how a laser pre-pulse improves the stability of the LWFA, and controls the evolution of the laser group and bubble velocity, which are important for determining LWFA dephasing and ultimately the electron bunch energy.
Abstract: The accelerating structure of the laser wakefield accelerator (LWFA) is dynamic and highly sensitive to the local laser and plasma properties. It can expand and contract as it responds to the evolution of the laser and plasma fields. As a result, the position of, and environment within, the LWFA bubble are usually time dependent, which is not ideal for stable acceleration. Variations can have a negative impact on electron bunch properties, and are deleterious for ion channel lasers and plasma wigglers. We demonstrate how a laser pre-pulse improves the stability of the LWFA, and controls the evolution of the laser group and bubble velocity, which are important for determining LWFA dephasing and ultimately the electron bunch energy.
6 citations
TL;DR: In this article, a spectral correction algorithm was proposed to reduce the primary spectral distortions from the raw data that arise from the detector response: charge sharing and weighting potential cross-talk, fluorescence radiation, scattering radiation, pulse pile up and incomplete charge collection.
Abstract: Photon counting imaging detectors (PCD) has paved the way for the emergence of Spectral X-ray Computed Tomography (SCT), which simultaneously measures a material’s linear attenuation coefficient (LAC) at multiple energies defined by the energy thresholds. In previous work SCT data was analysed with the SIMCAD method for material classifications. The method measures system-independent material properties such as electron density, ρe and effective atomic number, Zeff to identify materials in security applications. The method employs a spectral correction algorithm that reduce the primary spectral distortions from the raw data that arise from the detector response: charge sharing and weighting potential cross-talk, fluorescence radiation, scattering radiation, pulse pile up and incomplete charge collection. In this work, using real experimental data we analyze the influence of the spectral correction on material classification performance in security applications. We use a vectorial total variation (L∞-VTV) as a convex regularizer for image reconstruction of the spectral sinogram. This reconstruction algorithm employs a L∞ norm to penalize the violation of the inter energy bin dependency, resulting in strong coupling among energy bins. Due to the strong inter-bin correlation, L∞-VTV leads to noticeably better performance compared to bin-by-bin reconstructions including SIRT and total variation (TV) reconstruction algorithms. The image quality was evaluated with the correlation coefficient that is computed relative to ground-truth images. A positive weighting parameter defines the strength of the L∞-VTV regularization term and thus controls the trade-off between a good match to spectral sinogram data and a smooth reconstruction in both the spatial and spectral dimension. The classification accuracy both for raw and corrected data is analyzed over a set of weighting parameters. For material classification, we used 20 different materials for calibrating the SIMCAD method and 15 additional materials in the range of 6 ≤ Zeff ≤ 15 for evaluating the classification performance. We show that the correction algorithm accurately reconstructs the measured attenuation curve, and thus gives higher detection rates. We show that using the spectral correction leads to an accuracy increase of 1.6 and 3.8 times in estimating ρe and Zeff, respectively
4 citations
TL;DR: This article proposes to use a dedicated edge detection algorithm to measure LER of 2D curvilinear patterns on CD-SEM images with excellent correlation between the input roughness parameters and the measured parameters for both 1D and 2D synthetic images.
Abstract: 2D curvilinear patterns are more and more present in the lithography landscape. For the related devices, the line edge roughness (LER) is, as well as for lines and spaces, a critical figure of merit. In this article we propose to use a dedicated edge detection algorithm to measure LER of 2D curvilinear patterns on CD-SEM images. We present an original method to validate the algorithm, in the context of roughness measurement. It is based on the generation of realistic synthetic CD-SEM images with programmed roughness and a precise PSD analysis flow. We show excellent correlation (average R2 = 0.988) between the input roughness parameters and the measured parameters for both 1D and 2D synthetic images. Using synthetic images for different number of frames, the contour extraction sensitivity to noise is also explored. Finally, the methodology is successfully applied to experimental CD-SEM images for two classes of applications : photonic devices and DSA fingerprint patterns.
TL;DR: This work proposes an inverse-GAN application to embed real structural bridge detail images and incrementally edit them using learned semantic boundaries using the Interface-GAN methodology.
Abstract: Synthetic image generation using deep learning techniques like generative adversarial networks (GANS), has drastically improved since its inception. There has been significant research using human face datasets like FFHQ, and city-semantic datasets for self-driving car applications. Utilizing latent space distributions, researchers have been able to generate or edit images to exhibit specific traits in the resultant images, like face-aging. However, there has been little GAN research and datasets in the structural infrastructure domain. We propose an inverse-GAN application to embed real structural bridge detail images and incrementally edit them using learned semantic boundaries. Corrosion/non-corrosion and various steel paint colors were among the learned semantic boundaries discovered using the Interface-GAN methodology. The novel dataset used was procured from extracting hundreds of thousands of images from the Virginia Department of Transportation (VDOT) bridge inspection reports and was trained using the styleGAN2 generator. The trained model offers the ability to forecast deterioration incrementally, which is valuable to inspectors, engineers, and owners because it gives a window into the future on how and where damage may progress. As bridge inspectors typically review bridges every two years, this forecast could reinforce decisions for action or in-action.
TL;DR: In this paper, the authors quantitatively characterized and compared the performance of measurands based on moments and time windows of time-of-flight distributions of fNIRS signals.
Abstract: Time-domain fNIRS facilitates the elimination of the influence of extracerebral, systemic effects on measured signals since it contains time-of-flight information that is related to the penetration depth. Employing perturbation and MonteCarlo simulations, we quantitatively characterized and compared the performance of measurands based on moments and time windows of time-of-flight distributions. We extend our analysis to investigate whether higher moments and MellinLaplace (ML) moments promise improvements in performance. The comparison is based on spatial sensitivity profiles as well as metrics for relative contrast, contrast-to-noise ratio (CNR), depth selectivity, and the product of CNR and depth selectivity for layered absorption changes. The influence of reduced scattering coefficient, thickness of the superficial layer, and source-detector distance was analyzed. The third central moment performs similarly to variance and is worth considering for data analyzes. Higher order ML moments perform similarly to time windows and they likewise provide variable depth selectivity.
TL;DR: In this paper, a supercontinuum can be generated in bulk orientation-patterned gallium phosphide from femtosecond pulses with energies of up to 32 nJ.
Abstract: Supercontinuum generation in bulk media is not normally observed at the nJ-level pulse energies available from high-repetition-rate femtosecond oscillators. Here, we present results demonstrating how a visible supercontinuum can be produced in bulk orientation-patterned gallium phosphide from 100-MHz 1040-nm femtosecond pulses with energies of up to 32 nJ. High-order parametric gain near 550 nm, seeded by self-phase-modulated spectral sidebands, underpins this new and simple supercontinuum process which yields an output spectrum spanning from the blue/green to the red.
TL;DR: A multi-laboratory exercise was initiated with the aim of assessing and comparing diffuse optical instruments belonging to 11 partner institutions of a European level Marie Curie Consortium BitMap1 and investigating common analysis tools for the whole dataset.
Abstract: Performance assessment and standardization are indispensable for instruments of clinical relevance in general and clinical instrumentation based on photon migration/diffuse optics in particular. In this direction, a multi-laboratory exercise was initiated with the aim of assessing and comparing their performances. 29 diffuse optical instruments belonging to 11 partner institutions of a European level Marie Curie Consortium BitMap1 were considered for this exercise. The enrolled instruments covered different approaches (continuous wave, CW; frequency domain, FD; time domain, TD and spatial frequency domain imaging, SFDI) and applications (e.g. mammography, oximetry, functional imaging, tissue spectroscopy). 10 different tests from 3 well-accepted protocols, namely, the MEDPHOT2 , the BIP3 , and the nEUROPt4 protocols were chosen for the exercise and the necessary phantoms kits were circulated across labs and institutions enrolled in the study. A brief outline of the methodology of the exercise is presented here. Mainly, the design of some of the synthetic descriptors, (single numeric values used to summarize the result of a test and facilitate comparison between instruments) for some of the tests will be discussed.. Future actions of the exercise aim at deploying these measurements onto an open data repository and investigating common analysis tools for the whole dataset.
TL;DR: In this paper, the authors demonstrate images acquired by a scanning electron microscopy (SEM) to illustrate morphological changes, accumulating in particles of tin, lead and lead oxide that were subject to applied hydrogen plasma (non-EUV), leading to potential loss of adhesion of these materials to the relevant surfaces or potential defectivity outbreaks via explosive fragmentation.
Abstract: Extreme ultraviolet (EUV) lithography is a technology for high volume manufacturing (HVM) of integrated circuits. HVM defines critical specification for cleanliness of reticles (masks) used to impose a pattern on wafers. EUV-induced hydrogen plasma produced by photoionization of the H2 gas by the 13.5 nm photons plays an important role in the release and transport of particles from contaminated surfaces to the reticle. It was observed that the rate of particle deposition on the reticle in an EUV scanner scales with EUV power which in turn defines the properties of the EUV-induced plasma to increase the knowledge regarding this phenomenon. We demonstrate images, acquired by a scanning electron microscopy (SEM) to illustrate morphological changes, accumulating in particles of tin, lead and lead oxide that were subject to applied hydrogen plasma (non-EUV). These changes led to the potential loss of adhesion of these materials to the relevant surfaces or potential defectivity outbreaks via explosive fragmentation. This work proposes that the mechanical stress in particles' material lattice caused by accumulation of hydrogen bubbles under the surface plays the major role in the morphological changes observed.
TL;DR: In this paper, both healthy and malignant tissue zones of a thick formalin-fixed colon specimen were used for Mueller matrix measurements, and two more Mueller matrices from Monte Carlo simulation and tissue mimicking phantom were also evaluated, in order to assess polarimetric char- acterization and modeling of turbid media.
Abstract: Tissue polarimetry could be identified as a complementary optical and non-invasive technique to assist the gold standard histopathology analysis of tissue. In general, polarimetric diagnostics is based on tracing different polarimetric responses (including light depolarization) in tissue zones with structure altered by the benign and pre/cancerous formations. In this manuscript, both healthy and malignant tissue zones of a thick formalin-fixed colon specimen were used for Mueller matrix measurements. Additionally, two more Mueller matrices from Monte Carlo simulation and tissue mimicking phantom were also evaluated, in order to assess polarimetric char- acterization and modeling of turbid media. Symmetric decomposition algorithm of Mueller matrices developed in house was adopted to extract both polarization and depolarization properties, encoded in the Mueller matrix elements. The decomposition products allowed to reveal important information about the internal tissue struc- ture and morphology. The depolarization and polarization parameters were found to follow the particular trends that depend on a choice of parametric space.
TL;DR: The SImPOSIuM package and its collocation in ATHENA optics development framework is presented and it is presented as a good level of maturity and it offers 2 Graphical User Interfaces implementing a variety of simulation features.
Abstract: The ATHENA (Advanced Telescope for High Energy Astrophysics) X-ray observatory is the European Space Agency - selected L2 class mission, with launch scheduled in early 2030s. The observatory hosts a large X-ray telescope designed to have 5 arcseconds resolution with an effective area larger than 1.4 m2 at 1 keV. To meet these performance requirements ESA developed the Silicon Pore Optics technology: ribbed Si plates are shaped on a proper mould to copy the defined optical design and then stacked into modules. This technological solution, taking advantage of both replica process and modular implementation, is effective to populate ATHENA’s large aperture (diameter of ~2.5 m). As a result the optical pupil of an SPO will be very different than the classical nested shell one since it would be composed by a high number of small channels (about 106 channels of ~ 1 mm2 in ATHENA current design) and hence requires specific tool to be studied. To this end ESA financed the SIMPOSIuM project aimed to develop an open source, user-friendly SPOs simulation tool. The project is now at a good level of maturity and it offers 2 Graphical User Interfaces implementing a variety of simulation features. The SPORT GUI manages a full ray-tracing code and an analytical effective area calculator. The SWORDS GUI runs a SPOs diffraction effects simulator. In this paper we present the SImPOSIuM package and its collocation in ATHENA optics development framework.
TL;DR: This paper investigates to what extent CAM enables a quantitative understanding of CNN-based classification models through the creation of segmentation masks out of class activation maps, hereby targeting the use case of brain tumor classification.
Abstract: Class Activation Mapping (CAM) can be used to obtain a visual understanding of the predictions made by Convolutional Neural Networks (CNNs), facilitating qualitative insight into these neural networks when they are, for instance, used for the purpose of medical image analysis. In this paper, we investigate to what extent CAM also enables a quantitative understanding of CNN-based classification models through the creation of segmentation masks out of class activation maps, hereby targeting the use case of brain tumor classification. To that end, when a class activation map has been created for a correctly classified brain tumor, we additionally perform tumor segmentation by binarization of the aforementioned map, leveraging different methods for thresholding. In a next step, we compare this CAM-based segmentation mask to the segmentation ground truth, measuring similarity through the use of Intersection over Union (IoU). Our experimental results show that, although our CNN-based classification models have a similarly high accuracy between 86.0% and 90.8%, their generated masks are different. For example, our Modified VGG-16 model scores an mIoU of 12.2%, whereas AlexNet scores an mIoU of 2.1%. When comparing with the mIoU obtained by our U-Net-based models, which is between 66.6% and 67.3%, and where U-Net is a dedicated pixel-wise segmentation model, our experimental results point to a significant difference in terms of segmentation effectiveness. As such, the use of CAM for the purpose of proxy segmentation or as a ground truth segmentation mask generator comes with several limitations.
TL;DR: In this article, the authors simulated intra-operative US images of the brain after tumor resection surgery using GANs and found that these generated images are hardly distinguishable from real post-resection US images.
Abstract: The simulation of realistic ultrasound (US) images has many applications in image-guided surgery such as image registration, data augmentation, or educational purposes. In this paper we simulated intraoperative US images of the brain after tumor resection surgery. In a first stage, a Generative Adversarial Networks generated an US image with resection from a resection cavity map. While the cavity texture can be realistic, surrounding structures are usually not anatomically coherent. Thus, a second stage blended the generated cavity texture into a real patient-specific US image acquired before resection. A validation study on 68 images of 21 cases showed that three raters correctly identified 64% of all images. In particular, two neurosurgeons correctly labelled only 56% and 53% of the simulated images, which indicate that these synthesized images are hardly distinguishable from real post-resection US images.
TL;DR: A novel approach for segmenting the proximal femur that uses a deep convolutional neural network to produce accurate, automated, robust, and fast segmentations of the femur from CT scans is presented.
Abstract: Osteoporosis is a common bone disease that occurs when the creation of new bone does not keep up with the loss of old bone, resulting in increased fracture risk. Adults over the age of 50 are especially at risk and see their quality of life diminished because of limited mobility, which can lead to isolation and depression. We are developing a robust screening method capable of identifying individuals predisposed to hip fracture to address this clinical challenge. The method uses finite element analysis and relies on segmented computed tomography (CT) images of the hip. Presently, the segmentation of the proximal femur requires manual input, which is a tedious task, prone to human error, and severely limits the practicality of the method in a clinical context. Here we present a novel approach for segmenting the proximal femur that uses a deep convolutional neural network to produce accurate, automated, robust, and fast segmentations of the femur from CT scans. The network architecture is based on the renowned u-net, which consists of a downsampling path to extract increasingly complex features of the input patch and an upsampling path to convert the acquired low resolution image into a high resolution one. Skipped connections allow us to recover critical spatial information lost during downsampling. The model was trained on 30 manually segmented CT images and was evaluated on 200 ground truth manual segmentations. Our method delivers a mean Dice similarity coefficient (DSC) and 95th percentile Hausdorff distance (HD95) of 0.990 and 0.981 mm, respectively.
TL;DR: In this paper, the impact of annealing on the X-ray re ectance of coated mirrors relevant for the Athena mission was investigated, including single layers and bilayers.
Abstract: As part of the manufacturing process of mirror modules for the Athena X-ray telescope, Silicon Pore Optics plates are assembled into mirror module stacks. The plates that form each stack are held together by direct bonding, relying on van der Waals forces and covalent bonds for adhesion. One way to increase the strength of the covalent bonds is through annealing of the mirror stacks. It is of critical importance to the mission to ensure compatibility between the reflective coating and any post-coating processing of the plates. We present our findings of the impact of annealing on the X-ray re ectance of coated mirrors relevant for the Athena mission. These are Ir single layers, as well as Ir/B4C, Ir/SiC, and Ir/C bilayers. We investigate the effect on the performance of the coatings after annealing at atmospheric pressure and at a low vacuum using X-ray reflectometry. B4C is found to suffer degradation from annealing under atmospheric conditions but not when annealed in vacuum. All other materials investigated are robust to atmospheric annealing.
TL;DR: Volume density gratings produced by degenerate, counterpropagating laser pulses in plasma have several useful optical properties and are investigated in an investigation into creation of a transient plasma density grating that functions as a waveplate.
Abstract: Volume density gratings produced by degenerate, counterpropagating laser pulses in plasma have several useful optical properties. Here we report on one of these in an investigation into creation of a transient plasma density grating that functions as a waveplate.
TL;DR: In this paper, a simple, effective, and low-cost method is demonstrated for fabricating heat induced LPGs, as an alternative method compared to more complicated approaches that require UV lasers and hydrogen loading or CO2 lasers.
Abstract: We present recent progress on fabrication of heat induced long period gratings (LPGs) in few mode fibers for stable mode conversion between the fundamental mode LP01 to asymmetric and symmetric modes, such as LP11 and LP02. A simple, effective, and low-cost method is demonstrated for fabricating heat induced LPGs, as an alternative method compared to more complicated approaches that require UV lasers and hydrogen loading or CO2 lasers. The LPGs are written point-by-point by periodically translating and heating the fiber. The heating filament is realized by conducting electrical current through an omega shaped 0.25 mm electrical platinum wire that enclose the fiber. We expect that the physical mechanisms for the refractive index change are caused by a combination of residual stress relaxation and tapering of the fiber. A grating period down to 622 μm for coupling between the LP01 and LP02 is demonstrated, however, we believe grating periods of a few hundreds of microns are feasible.
TL;DR: A range of simulations of various aspects of telescopes are presented, capable of quantifying stray light from Compton scattering at mirror substrates, and a mechanism to include gratings for spectrometry in a telescope simulation is presented.
Abstract: AstroX is an add-on toolbox to the open source X-ray simulation software package McXtrace, which introduces Astronomical telescope optics and features to the package. Thus, enabling users to draw from the experience and developments of two communities. It may also shed further light into calibration results when measuring optics in ground based test-setups, at synchrotrons and specialized facilities. AstroX now includes a range of optical elements for Wolter class optics, extended source models, lobster eye optics, and gratings etc. Furthermore the open modular nature of McXtrace makes it fairly simple to connect to other software packages. We present a range of simulations of various aspects of telescopes: • A simulation work ow capable of quantifying stray light from Compton scattering at mirror substrates. • A study on the effect of dust contamination inside small-pore silicon pore optics. • A mechanism to include gratings for spectrometry in a telescope simulation..
TL;DR: A promising new avenue of CGH, neural holography, utilizes machine learning models in the generation of single and multi plane holograms, and has the distinct advantage that inference is performed in constant time without the need for iterative calculations of the phase SLM pattern.
Abstract: Computer Generated Holography (CGH) promises unprecedented capabilities for a variety of applications in Optics and Photonics. However, one of the biggest challenges for CGHs is the fundamental tradeoff between algorithm runtime and achieved reconstruction fidelity and efficiency while maintaining light projections at real-time frame rates. In addition, the light projection quality achieved by most CGH-modalities are rather low due to the mismatch between the optical wave propagation of the applied Spatial Light Modulator (SLM) and its simulated model. A promising new avenue of CGH, neural holography, utilizes machine learning models in the generation of single and multi plane holograms. Neural network generated holograms have the distinct advantage that inference is performed in constant time without the need for iterative calculations of the phase SLM pattern. This allows the networks to generate holograms 3-500 times faster than traditional iterative algorithms, which enables the applications dependent on real-time holography. State-of-the-art implementations of neural holography [1, 2] furthermore achieve higher accuracy than traditional iterative algorithm, when compared to target images. Applications of these SLM-encoded CGHs include all areas where a fast and parallel one- or two-photon light excitation is needed such as in Laser Material Processing, Additive Manufacturing and 3D printing, Neurophotonics and Optogenetics, Laser Image Projection and many more.
TL;DR: In this paper, a near-field potential well array with connected tiny hotspots in a large-scale was created to separate nanoparticles with sizes from 100 to 500 nm, based on the differentiated energy depths of each potential well.
Abstract: Optical tweezers are versatile tools capable to separate microparticles, yet present formidable challenges in the separation of nanoparticles smaller than 200 nm. The difficulties arise from the controversy on the requirement of a tightly focused light spot in order to create strong optical forces while a large area is kept for the sorting. To overcome this problem, we create a near-field potential well array with connected tiny hotspots in a large-scale. This can separate nanoparticles with sizes from 100 to 500 nm, based on the differentiated energy depths of each potential well. In this way, nanoparticles of 200, 300 and 500 nm can be selectively trapped in this microchannel by appropriately tuning the laser power. Our approach provides a unprecedent solution for optical trapping and separation of nanoparticles and biomolecules, so that it presents a huge potential in the physical and biomedical sciences.
TL;DR: In this article, the authors present a teaching concept which combines theory, experimental work, project management and organization to promote the students' autonomous learning, and a major part of the project was to teach the students how to develop group dynamics successfully.
Abstract: We present a teaching concept which combines theory, experimental work, project management and organization. As part of the Earth and Space Physics and Engineering education at DTU Space, a group of first year undergraduate students were given the task to design, build and test a DC magnetron sputtering system within a very limited budget and time frame. The teaching concept is designed to promote the students’ autonomous learning, and a major part of the project was to teach the students how to develop group dynamics successfully. The students successfully managed to build a direct current magnetron sputtering system wherein a plasma glow was produced. The system can be used for depositing thin film coatings, an enabling technology for numerous applications.
TL;DR: In this article, the potential of AlyGa1-yN quantum dots as DUV emitters is investigated using a stress induced growth mode transition, quantum dots (QD) are spontaneously formed on Al0.7Ga0.3N/AlN heterostructures grown on sapphire substrates by molecular beam epitaxy, and a large shift of the QD photoluminescence in the UV range is observed, going from an emission in the near UV for GaN QD down to the UVC region for Al 0.4Ga0
Abstract: Deep ultraviolet (DUV) light emitting diodes (LED) are expected to be the next generation of UV sources, offering significant advantages such as compactness, low consumption and long lifetimes. Yet, improvements of their performances are still required and the potential of AlyGa1-yN quantum dots as DUV emitters is investigated in this study. Using a stress induced growth mode transition, quantum dots (QD) are spontaneously formed on Al0.7Ga0.3N/AlN heterostructures grown on sapphire substrates by molecular beam epitaxy. By increasing the QD Al composition, a large shift of the QD photoluminescence in the UV range is observed, going from an emission in the near UV for GaN QD down to the UVC region for Al0.4Ga0.6N QD. A similar behavior is observed for electroluminescence (EL) measurements performed on LED structures and an emission ranging from the UVA (320-340 nm) down to the UVC (265-280 nm) has been obtained. The main performances of Al0.7Ga0.3N based QD LED are presented in terms of electrical and optical characteristics. In particular, the emission dependence on the input current density, including the emitted wavelength, the optical power and the external quantum efficiency are shown and discussed.
TL;DR: This work will report on the latest laser shaping GPC-modalities with temporal focusing to uniquely sculpt patterns of one- and two-photon excitations for living neural-circuits and genetically modified light-sensitive cells.
Abstract: The powerful discipline of optogenetics can be described as “the branch of biotechnology which combines genetic engineering with optics to observe and control the function of genetically targeted groups of cells with light”. Using advanced laser beam-shaping such as Generalized Phase Contrast (GPC) and derived holographic modalities makes it possible to take advantage of cutting-edge two-photon technology to develop an unprecedented ‘circuit optogenetics’ platform with both high spatio-temporal selectivity and high penetration depth without disturbing speckle-noise. We will report on the latest laser shaping GPC-modalities with temporal focusing to uniquely sculpt patterns of one- and two-photon excitations for living neural-circuits and genetically modified light-sensitive cells.