Sensor Plane Research Articles

Three-dimensional dynamic measurement of unstable temperature fields by multi-view single-shot phase-shifting digital holography.

A multi-view phase measurement system based on single-shot phase-shifting digital holography is proposed to dynamically obtain three-dimensional (3-D) information of an unstable temperature field. The proposed system consists of a laser, three polarization imaging cameras, and the corresponding optical components. The laser beam emitted from the laser is separated by the fibers into three pairs that contain three object beams and three reference beams. The object beams pass through the object in three different directions and interfere with the reference beams at the image sensor plane respectively. The recording of the three cameras is triggered simultaneously, which enables the phase measurement of dynamic objects from different viewpoints. We successfully measured the 3-D distributions of an unstable temperature field in the experiments with the proposed system.

Focal stack camera: depth estimation performance comparison and design exploration

The concept of focal stack cameras based on transparent sensors has been recently demonstrated, enabling depth sensing in a single exposure from a focal stack. This study investigates how the depth estimation accuracy is affected by numerous camera parameters, including aperture size, sensor resolution and number of sensor planes. We investigate the dependence of these parameters on the deep learning based depth estimation performance and make a comparison between the focal stack camera and the light field camera, thus providing guidelines for future focal stack camera design.

Deep Deconvolution of Object Information Modulated by a Refractive Lens Using Lucy-Richardson-Rosen Algorithm

A refractive lens is one of the simplest, most cost-effective and easily available imaging elements. Given a spatially incoherent illumination, a refractive lens can faithfully map every object point to an image point in the sensor plane, when the object and image distances satisfy the imaging conditions. However, static imaging is limited to the depth of focus, beyond which the point-to-point mapping can only be obtained by changing either the location of the lens, object or the imaging sensor. In this study, the depth of focus of a refractive lens in static mode has been expanded using a recently developed computational reconstruction method, Lucy-Richardson-Rosen algorithm (LRRA). The imaging process consists of three steps. In the first step, point spread functions (PSFs) were recorded along different depths and stored in the computer as PSF library. In the next step, the object intensity distribution was recorded. The LRRA was then applied to deconvolve the object information from the recorded intensity distributions during the final step. The results of LRRA were compared with two well-known reconstruction methods, namely the Lucy-Richardson algorithm and non-linear reconstruction.

Relative stopping power resolution in time-of-flight proton CT

Objective. Proton computed tomography (CT) is similar to x-ray CT but relies on protons rather than photons to form an image. In its most common operation mode, the measured quantity is the amount of energy that a proton has lost while traversing the imaged object from which a relative stopping power map can be obtained via tomographic reconstruction. To this end, a calorimeter which measures the energy deposited by protons downstream of the scanned object has been studied or implemented as energy detector in several proton CT prototypes. An alternative method is to measure the proton’s residual velocity and thus its kinetic energy via the time of flight (TOF) between at least two sensor planes. In this work, we study the RSP resolution, seen as image noise, which can be expected from TOF proton CT systems. Approach. We rely on physics models on the one hand and statistical models of the relevant uncertainties on the other to derive closed form expressions for the noise in projection images. The TOF measurement error scales with the distance between the TOF sensor planes and is reported as velocity error in ps/m. We use variance reconstruction to obtain noise maps of a water cylinder phantom given the scanner characteristics and additionally reconstruct noise maps for a calorimeter-based proton CT system as reference. We use Monte Carlo simulations to verify our model and to estimate the noise due to multiple Coulomb scattering inside the object. We also provide a comparison of TOF helium and proton CT. Main results. We find that TOF proton CT with 30 ps m−1 velocity error reaches similar image noise as a calorimeter-based proton CT system with 1% energy error (1 sigma error). A TOF proton CT system with a 50 ps m−1 velocity error produces slightly less noise than a 2% calorimeter system. Noise in a reconstructed TOF proton CT image is spatially inhomogeneous with a marked increase towards the object periphery. Our modelled noise was consistent with Monte Carlo simulated images. TOF helium CT offers lower RSP noise at equal fluence, but is less advantageous at equal imaging dose. Significance. This systematic study of image noise in TOF proton CT can serve as a guide for future developments of this alternative solution for estimating the residual energy of protons and helium ions after the scanned object.

Automatic path planning for high performance measurement by laser plane sensors

The Fourth Industrial Revolution (4IR) has led to a wide development of laser sensors and their use in inspection processes to achieve high performance is becoming more and more common. High measurement performance implies high measurement quality of surfaces in a short time. Generally, the quality is evaluated on the basis of indicators such as noise and trueness. Recently, it has been found that these indicators are mostly affected by the scanning strategy defined by two main parameters: the scanning angle and distance. Indeed, the path planning of laser sensors ensuring a high level of quality is based on the definition of the scanning strategy allowing scanning well-known surfaces with reduced noise and trueness. In this paper, an original approach for the generation of automatic path planning is proposed. The originality lies in the high performance obtained by optimizing the quality and the measurement time based on the optimal path planning. First, the laser sensor is qualified in order to evaluate the quality indicators as a function of the scanning distance and angle. Configurations that provide better quality are determined. By analyzing all laser sensor orientations held by the CMM's rotating head, a set of minimum orientations allowing high quality measurement is determined based on an optimization algorithm regarding quality, accessibility, visibility and collision detection criteria. The laser sensor path is based on the determination of the path levels in each sensor orientation. An original method is proposed to generate the optimal levels guaranteeing a high quality in terms of scanning distance. The laser sensor crossing points are then calculated in each level. An improvement of the method is proposed through the connection of levels using connection lines. Finally, collisions are studied and fixed by adding translation points. The proposed approach is applied to a part defined by its CAD model. The path is generated and executed on the CMM with a laser sensor. The measurement performance is compared to previous approaches in the literature. The methodology allows an adapted planning and can be used for automated dimensional inspection.

Study on Detection of a Small Magnetic Particle Using Thin Film Magneto-Impedance Sensor with Subjecting to Strong Normal Field

This paper deals with the detection of small magnetization using a thin film magneto-impedance sensor with subjecting to strong normal field. The sensor was made by soft magnetic amorphous thin-film with uniaxial magnetic anisotropy in the width direction of the element. It was reported that the sensor has very high sensitivity, such as pico-tesla order, when it is driven by hundreds of MHz. In this paper, a sensitive measurement method aiming for detection of a small particle or a cluster of nano-particles, having low-remanence, is proposed. The point is the application of strong normal field in the measurement area including sensor element and particle. The normal strong field is applied in the normal direction of the sensor plane in the value almost hundreds of mT. Instead of such strong normal field, the sensor keeps high sensitivity, because of the demagnetizing force in the thickness direction. A theoretical estimation for clarifying an efficiency of the method, experimental results of sensor property and sensitivity with subjecting to the normal field, and also a confirmation of detection of a small particle using the proposed method is reported. As a special mention, detection fundamentals when a applied surface normal field has a distribution and also a particle would run through in the vicinity of sensor is discussed.

R&D for compact calorimeters for e[formula omitted]e[formula omitted] colliders and their application to the LUXE experiment

The FCAL collaboration is preparing large-scale prototypes of special calorimeters to be used in the very forward region at future electron–positron colliders. Two compact calorimeters are foreseen, LumiCal and BeamCal, designed as sandwich calorimeters with very thin sensor planes to keep the Molière radius small. Silicon sensor prototypes and dedicated FE ASICs have been developed and produced for LumiCal. The ASICs have been designed to cope with the timing and dynamic range requirements. The electromagnetic calorimeters of the LUXE experiment are based on a similar technology to that developed by the FCAL collaboration. LUXE will measure the number of positrons and their energy spectrum in e-laser and γ-laser interactions or electrons in γ-laser interactions. Results of recent beam tests will be presented.

Compact LumiCal prototype tests for future e+e− colliders

The FCAL collaboration is preparing large-scale prototypes of special calorimeters to be used in the very forward region at future electron-positron colliders for instant luminosity measurement and a precise measurement of integrated luminosity and for assisting beam-tuning. LumiCal is designed as silicon-tungsten sandwich calorimeter with very thin sensor planes to keep the Molière radius small, thus facilitating the measurement of electron showers in the presence of background. Dedicated FE electronics has been developed to match the timing and dynamic range requirements. A partially instrumented prototype was investigated in a 1 to 5 GeV electron beam at the DESY II synchrotron. In the recent beam tests, a multi-plane compact prototype equipped with thin detector planes fully assembled with readout electronics were installed in 1 mm gaps between tungsten plates of one radiation length thickness. High statistics data were used to perform sensor alignment, and to measure the longitudinal and transversal shower development.

Resolution and Contrast Enhancement for Lensless Digital Holographic Microscopy and Its Application in Biomedicine

An important imaging technique in biomedicine, the conventional optical microscopy relies on relatively complicated and bulky lens and alignment mechanics. Based on the Gabor holography, the lensless digital holographic microscopy has the advantages of light weight and low cost. It has developed rapidly and received attention in many fields. However, the finite pixel size at the sensor plane limits the spatial resolution. In this study, we first review the principle of lensless digital holography, then go over some methods to improve image contrast and discuss the methods to enhance the image resolution of the lensless holographic image. Moreover, the applications of lensless digital holographic microscopy in biomedicine are reviewed. Finally, we look forward to the future development and prospect of lensless digital holographic technology.

Event-based imaging polarimeter

The design and initial experimental results from an event-based, rotating-polarizer, imaging polarimeter are presented. The speed of division-of-time imaging systems is traditionally constrained by the frame rate of the focal plane sensor and the need to sample several polarization angles during rotation. The asynchronous event reporting of event-based cameras (EBCs) frees these constraints but introduces challenges. The Stokes vectors used to describe polarization are based on irradiance, but EBCs are inherently change-detection systems that struggle to estimate irradiance. Two methods of estimating the polarization state without first recovering irradiance images are presented and compared. The DAVIS 346 sensor enables simultaneous recording of events with conventional frame-based images, enabling direct comparison of event-based polarization estimates to traditional techniques.

Interferenceless coded aperture correlation holography\xa0with\xa0point spread\xa0holograms\xa0of isolated chaotic islands for 3D imaging

Interferenceless coded aperture correlation holography (I-COACH) is an incoherent digital holographic technique with lateral and axial resolution similar to a regular lens-based imaging system. The properties of I-COACH are dictated by the shape of the system’s point response termed point spread hologram (PSH). As previously shown, chaotic PSHs which are continuous over some area on the image sensor enable the system to perform three-dimensional (3D) holographic imaging. We also showed that a PSH of an ensemble of sparse dots improves the system’s signal-to-noise ratio (SNR) but reduces the dimensionality of the imaging from three to two dimensions. In this study, we test the midway shape of PSH, an ensemble of sparse islands distributed over the sensor plane. A PSH of isolated chaotic islands improves the SNR of the system compared to continuous chaotic PSH without losing the capability to perform 3D imaging. Reconstructed images of this new system are compared with images of continuous PSH, dot-based PSH, and direct images of a lens-based system. Visibility, SNR, and the product of visibility with SNR are the parameters used in the study. We also demonstrate the imaging capability of a system with partial annular apertures. The reconstruction results have better SNR and visibility than lens-based imaging systems with the same annular apertures.

Measuring the Magnetic Field Vector of Earth

The magnetic field of Earth, Be, is an intriguing topic in the introductory physics curriculum that engages students’ curiosity and inspires numerous speculations about the nature of this phenomenon. There are several methods for measuring Earth’s magnetic field. Probably, the most widespread and visual method of measuring the field in student lab experiments utilizes a tangent galvanometer. Recently, PASCO scientific suggested to use a magnetic field sensor for this goal, in a procedure where a magnetic field sensor combined with a rotary motion sensor is rotated in a 2-D plane containing the magnetic field vector of Earth. In this case, the magnetic field detected by the magnetic field sensor is a component of the magnetic field vector oriented relative to the direction of the magnetic field sensor probe (radial component of magnetic field). This means that the detected magnetic field considered as a function of the angle of rotation of the sensor will be a sinusoidal function. The amplitude of this function is the magnitude of Earth’s magnetic field. In conducting this experiment, initially the sensor is set to zero by placing it in a Zero Gauss Chamber (mu-metal). The equipment setup of the experiment is depicted in the figure shown in Ref. 9. The described experiment requires the use of a dip needle that is a compass pivoted to move in the plane containing the magnetic field vector of Earth. The dip needle shows the dip angle θ (inclination) that Earth’s magnetic field makes with the horizontal. Besides the previously mentioned devices, this experiment requires the use of an aluminum table clamp, adjustable angle clamp, and angle indicator to ensure proper alignment of the rotary motion sensor in a 2D plane containing the magnetic field vector.

Error analysis of sparkle contrast by applying image subtraction method

AbstractMeasurement error of sparkle contrast was investigated by applying image subtraction method. The sparkle contrast was measured by changing the region of interest (ROI) and the imaging F‐number, while the measurement distance was fixed. The statistical error was dependent on the size of the ROI. It was suppressed when the ROI was over 100 × 100 LMD pixels under the condition which the intensity modulation of the image of the display matrix elements optically disappeared on the LMD sensor plane by choosing the specific combination of the effective F‐number of the imaging lens, the pitch of the display matrix element, and the optical magnification. The ratio of the intensity standard deviation of the subtracted image to that of the original image could be used as an error indicator of the statistical error by insufficient sampling points. It could also be used for analyzing the error caused by the low‐frequency intensity variations within the ROI. In case that the low‐frequency intensity variations were not eliminated from the measured sparkle pattern, the sparkle contrast kept changing with increasing the ROI. The error indicator was not converged to the certain value even if the size of the ROI was over 100 × 100 LMD pixels.

Compressive propagation with coherence.

In this Letter, we present wave propagation models of spatially partially coherent (or spatially incoherent) light to compress the computational load of forward and back propagations in inverse problems. In our model, partially coherent light is approximated as a set of random or plane wavefronts passing through spatial bandpass filters, which corresponds to an illumination pupil, and each wave coherently propagates onto a sensor plane through object space. We show that our models reduce the number of coherent propagations in inverse problems, which are essential in optical control and sensing, such as computer-generated holography (CGH) and quantitative phase imaging. We verify the proposed models by numerical and experimental demonstrations of CGH incorporating spatially partially coherent light.

Boosting background suppression in the NEXT experiment through Richardson-Lucy deconvolution

The NEXT collaboration aims to observe neutrinoless double beta decay in gaseous 136Xe using a high pressure gaseous Xe time projection chamber with signal amplification by means of electroluminescence (EL). One of the advantages of the technique is that it allows for track reconstruction making use of a sensor plane equipped with SiPMs located nearby the EL region. However, the signals recorded in the TPC are degraded by electron diffusion and spread of light produced in the EL process, limiting the potential of the detection scheme. We have recently developed an improved reconstruction procedure based on the Richardson-Lucy deconvolution [], an iterative algorithm well-known in image processing and de-blurring. Deconvolution allows reversing the smearing mechanisms in the NEXT TPC and significantly enhances the definition of reconstructed tracks. Consequently, detector performance is strongly boosted, with a five-fold improvement in background rejection demonstrated on experimental data. The algorithm application in the context of the NEXT experiment is detailed with a focus on the performance in NEXT-White, a 50 cm TPC which operated underground at Laboratorio Subterráneo de Canfranc until July 2021. The procedure applied to characterize the optical response of the chamber and obtain the point spread function that best describes the observed signals is described.

Architecture-Level Optimization on Digital Silicon Photomultipliers for Medical Imaging.

Silicon photomultipliers (SiPMs) are arrays of single-photon avalanche diodes (SPADs) connected in parallel. Analog silicon photomultipliers are built in custom technologies optimized for detection efficiency. Digital silicon photomultipliers are built in CMOS technology. Although CMOS SPADs are less sensitive, they can incorporate additional functionality at the sensor plane, which is required in some applications for an accurate detection in terms of energy, timestamp, and spatial location. This additional circuitry comprises active quenching and recharge circuits, pulse combining and counting logic, and a time-to-digital converter. This, together with the disconnection of defective SPADs, results in a reduction of the light-sensitive area. In addition, the pile-up of pulses, in space and in time, translates into additional efficiency losses that are inherent to digital SiPMs. The design of digital SiPMs must include some sort of optimization of the pixel architecture in order to maximize sensitivity. In this paper, we identify the most relevant variables that determine the influence of SPAD yield, fill factor loss, and spatial and temporal pile-up in the photon detection efficiency. An optimum of 8% is found for different pixel sizes. The potential benefits of molecular imaging of these optimized and small-sized pixels with independent timestamping capabilities are also analyzed.

Bio-inspired spectropolarimetric sensor based on tandem organic photodetectors and multi-twist liquid crystals

Simultaneous spectral and polarimetric imaging enables versatile detection and multimodal characterization of targets of interest. Current architectures incorporate a 2×2 pixel arrangement to acquire the full linear polarimetric information causing spatial sampling artifacts. Additionally, they suffer from limited spectral selectivity and high color crosstalk. Here, we demonstrate a bio-inspired spectral and polarization sensor structure based on integrating semitransparent polarization-sensitive organic photovoltaics (P-OPVs) and liquid crystal polymer (LCP) retarders in a tandem configuration. Color tuning is realized by leveraging the dynamic chromatic retardation control of LCP films, while polarization sensitivity is realized by exploiting the flexible anisotropic properties of P-OPVs. The structure is marked by its ultra-thin design and its ability to detect spectral and polarimetric contents along the same optical axis, thereby overcoming the inherent limitations associated with conventional division-of-focal plane sensors.

Multisensor data processing in dimensional metrology for collaborative measurement of a laser plane sensor combined to a touch probe

Dimensional inspection, which consists in verifying the geometric conformity of parts in terms of ISO specifications, is an essential step in the product life cycle. In recent years, new optical measurement technologies, such as laser sensors or structured light sensors, have become increasingly important. However, the quality of the data limits their expansive use for metrology applications and touch probes with CMM (Coordinate Measurement Machine) remain the reference in terms of measurement quality. On the other hand, the cooperative use of an optical system and a contact sensor presents a good solution which takes advantage of the characteristics of both systems while maintaining a quality level satisfying the requirements of metrology. However, measurement with a laser sensor and a touch probe mounted on a CMM results in two heterogeneous point clouds that must be processed before the final evaluation of specifications. This paper presents a methodology that addresses the processing of measurement data in this scenario. The proposed approach consists of four phases. In the first phase, the measurement data resulting from the laser sensor is processed to remove outliers, reduce noise and partition the point cloud. In the second phase, the point cloud resulting from both sensors are unified in a unique coordinate system. In the third phase, a fusion method is proposed to fuse the point clouds. The specifications are finally evaluated based on the fused point clouds in the fourth phase. A case study is conducted to illustrate the proposed approach with the measurement data of a test part defined by its CAD model and specifications. The results are compared with a reference inspection report obtained by a touch probe measurement system.

Biopsies vertébrales assistées par robot dans les spondylodiscites infectieuses

The use of a vertebral biopsy remains very frequently relevant in the management of patients with infectious spondylodiscitis without identified germs or vertebral metastases without identified primary cancer in order to obtain bacteriological and/or histological proof of the disease. There are few Rheumatology departments which remain completely independent in carrying out these vertebral biopsies. We describe here a technique of spinal biopsies under robotic assistance. This aims to be more precise than current techniques, more comfortable for the patient, and to reduce the average length of stay of patients hospitalized in rheumatology. The biopsy is performed in the operating room by a rheumatologist/neurosurgeon duo guided by a robot. The precision of the biopsy is based on the acquisition of three-dimensional spinal anatomy by a plane sensor scanner coupled to the robot. This technique of vertebral biopsies is easily acquired and allows the rheumatologist to be independent from the first consultation to the aetiological diagnosis, then to the treatment of infectious spondylodiscitis. This technique is however dependent on the availability of an equipped operating theater.

Model-free method for intrinsic camera parameters calibration and lens distortion correction

Although various camera calibration methods have been proposed, most of these methods cannot deliver accurate determination of the intrinsic camera parameters, because of the coupling errors existing between intrinsic and extrinsic camera parameters and the use of explicit distortion models. Here, we propose a model-free method for accurate camera calibration, which utilizes phase-shifted fringe patterns shown on a liquid crystal display (LCD) screen for estimating the intrinsic parameters of a camera and correcting lens distortion. Horizontal and vertical fringe patterns are consecutively displayed on the LCD screen, which is placed at two positions parallel to the camera sensor plane. These fringe patterns are captured by the camera from the front viewpoint for calculating the absolute phase maps. Then, the images with lens distortion can be transformed to the distortion-free images using an inverse mapping operation. Subsequently, the principal point coordinates are calculated according to the geometric imaging relationship between the positions of the two LCD screens. Finally, the focal length can be estimated using the similarity of triangles formed by the obtained principal point coordinates and the obtained phase maps at the two positions. Both simulated and real experiments are performed to verify the validity of the proposed method. The results demonstrate that this method not only successfully eliminates coupling errors but also perfectly corrects lens distortion.