Silicon Charge-coupled Device Research Articles

Short-wavelength-infrared upconversion edge enhancement imaging based on a Laguerre-Gaussian composite vortex filter

Edge-enhanced imaging by spiral phase contrast has proven instrumental in revealing phase or amplitude gradients of an object, with notable applications spanning feature extraction, target recognition, and biomedical fields. However, systems deploying spiral phase plates encounter limitations in phase mask modulation, hindering the characterization of the modulation function during image reconstruction. To address this need, we propose and demonstrate an innovative nonlinear reconstruction method using a Laguerre-Gaussian composite vortex filter, which modulates the spectrum of the target. The involved nonlinear process spectrally transforms the incident short-wavelength-infrared (SWIR) signal from 1550 to 864 nm, subsequently captured by a silicon charge-coupled device. Compared with conventional schemes, our novel filtering method effectively suppresses the diffraction noise, significantly enhancing image contrast and resolution. By loading specific phase holograms on the spatial light modulator, bright-field imaging, isotropic, amplitude-controlled anisotropic, and directional second-order edge-enhanced imaging are realized. Anticipated applications for the proposed SWIR edge-enhanced imaging system encompass domains such as artificial intelligence recognition, deep tissue medical diagnostics, and non-destructive defect inspection. These applications underscore the valuable potential of our cutting-edge methodology in furthering both scientific exploration and practical implementations.

Analysis of radiation damage in silicon charge-coupled devices used for dark matter searches

Nuclear recoils in crystal detectors generate radiation damage in the form of crystal defects that can be measured in scientific-grade CCDs as local hot spots of leakage current stimulated by temperature increases in the devices. In this proceeding, we use a neutron source to generate defects in DAMIC-M CCDs, and using increases in leakage current at different temperatures, we demonstrate a procedure for identifying crystal defects in the CCDs of the DAMIC-M experiment. This is the first time that individual defects generated from nuclear recoils have been studied. This technique could be used to distinguish nuclear recoils from electron recoils in some energy ranges, which would improve the ability of CCD detectors to search for weakly interacting dark matter.

High-efficiency narrow-band green-emitting Tb-doped fluorosilicate glass for X-ray detectors

High-efficiency scintillators for radiation detections are urgently desired in many fields such as nondestructive inspection, medical imaging, and space exploration. Nowadays, commercial scintillators still face challenges of costly and time-consuming fabrication techniques and restricted size. Here, we present a high-efficient narrow-band green-emitting Tb3+-doped fluorosilicate (SF) glass scintillator with manufacturing of large size and low cost. Its emission (530–565 nm, ∼58% photons of total) highly superimposes with the peak sensitivity wavelength (∼550 nm) of silicon photomultipliers or charge-coupled device detectors. Moreover, owing to the particularly designed glass matrix, the photoluminescence (PL) quantum yield (QY) reaches up to 83%, which is high compared with other reported Tb3+-doped scintillators. The high PLQY combined with negligible self-absorption (400–800 nm) enables the high scintillation relative integral area (171% relative to commercial Bi4Ge3O12 single crystal). Therefore, the Tb3+-doped SF glass will be one of the promising alternatives for scintillator-based indirect-type X-ray detectors.

Infrared Clinical Enamel Crack Detector Based on Silicon CCD and Its Application: A High-Quality and Low-Cost Option.

Enamel cracks generated in the anterior teeth not only affect the function but also the aesthetics of the teeth. Chair-side tooth enamel crack detection is essential for clinicians to formulate treatment plans and prevent related dental disease. This study aimed to develop a dental imaging system using a near-IR light source to detect enamel cracks and to investigate the relationship between anterior enamel cracks and age in vivo. A total of 68 subjects were divided into three groups according to their age: young, middle, and elderly. Near-infrared radiation of 850 nm was used to identify enamel cracks in anterior teeth. The results of the quantitative examination showed that the number of enamel cracks on the teeth increased considerably with age. For the qualitative examination, the results indicated that there was no significant relationship between the severity of the enamel cracks and age. So, it can be concluded that the prevalence of anterior cracked tooth increased significantly with age in the young and middle age. The length of the anterior enamel cracks tended to increase with age too; however, this result was not significant. The silicon charge-coupled device (CCD) with a wavelength of 850 nm has a good performance in the detection of enamel cracks and has very good clinical practicability.

Features of images of water, ice, snow, objects and a human formed by a hybrid television camera in the near-infrared range

Recently, television cameras operating in the near-infrared range have become increasingly widespread. The advantage of shooting in the short wave infrared range is the ability to observe objects in low light and difficult weather conditions. Such cameras can use hybrid sensors that consist of an infrared photocathode and an electron-sensitive matrix based on silicon in a single vacuum volume. The paper investigates the capabilities of one of the latest samples of a similar camera, created at JSC “NRI Electron”. The images of a human, water, ice, snow and other objects in the wavelength range of 0.95–1.7 microns have been analyzed. The images were taken using a television camera based on a hybrid television infrared sensor, which consists of a photocathode and a silicon charge-coupled device in proximity range to each other in a single vacuum volume. Illumination of the objects in the near-infrared range was produced by a continuous spectrum lamp with a maximum of the detected radiation at a wavelength of 1.55 μm. The authors compared the images obtained in the near-infrared range with the ones obtained in the visible region. An explanation is given for the differences between snow images and water and ice images in the near-infrared range. As an example, the difference in light transmission between the surfaces of materials for diving equipment, such as coated and open cell neoprene, is demonstrated. Due to a significant contrast shown in the near-infrared range by images of various objects on the surface of water and ice, it is possible to create an effective system for searching objects on the water. The paper discusses the advantages of the proposed visual search system compared to other systems, including passive systems and the ones operating in the MWIR and LWIR. The research outlined the prospects of using the new camera for building an effective search system for objects and people on water surfaces

Constructing a background model for DAMIC CCDs

The DAMIC Collaboration uses fully-depleted silicon charge-coupled devices to search for low mass dark matter particles. We present a new analysis of backgrounds in the DAMIC at SNOLAB detector, which is used to construct a background model for an ongoing WIMP search analysis. The formation of this background model reveals new radioactive background components, the presence of which has since been experimentally confirmed. This background model additionally informs how best to proceed in meeting the lower background constraints of the DAMIC-M detector.

DAMIC-M experiment: Thick, silicon CCDs to search for light dark matter

This report presents an overview of the unconventional use of charge-coupled devices (CCDs) to search for Dark Matter (DM). The DArk Matter in CCDs (DAMIC Experiment) employs the bulk silicon of thick, fully-depleted CCDs as a target for ionization signals produced by interations of particle dark matter from the galactic halo. The DAMIC collaboration has engaged in an extensive campaign of characterization efforts to understand the response of these CCDs to low-energy nuclear recoils and their unique capabilities, including the use of high spatial resolution for both the rejection and study of backgrounds. The preliminary results of DAMIC prove the performance of the detector, provide measurements of the background contamination and demonstrate the potentiality for DM searches, with only ∼40 grams of detector mass. The next phase of the experiment, DAMIC-M (DArk Matter in CCDs at Modane), will consist of a kg-sized detector, implementing the most massive CCDs ever built. These CCDs will feature sub-electron noise and will be deployed in a low-radioactivity environment at the Laboratoire Souterrain de Modane in France.

Nesting box imager: Contact-free, real-time measurement of activity, surface body temperature, and respiratory rate applied to hibernating mouse models.

Noncontact methods to measure animal activity and physiology are necessary to monitor undisturbed states such as hibernation. Although some noncontact measurement systems are commercially available, they are often incompatible with realistic habitats, which feature freely moving animals in small, cluttered environments. A growing market of single-board computers, microcontrollers, and inexpensive sensors has made it possible to assemble bespoke integrated sensor systems at significantly lower price points. Herein, we describe a custom-built nesting box imager (NBI) that uses a single-board computer (Raspberry Pi) with a passive infrared (IR) motion sensor, silicon charge-coupled device (CCD), and IR camera CCD to monitor the activity, surface body temperature, and respiratory rate of the meadow jumping mouse during hibernation cycles. The data are logged up to 12 samples per minute and postprocessed using custom Matlab scripts. The entire unit can be built at a price point below US$400, which will be drastically reduced as IR (thermal) arrays are integrated into more consumer electronics and become less expensive.

Suppressing the influence of charge-coupled device vertical blooming on the measurement of laser beam quality factor (M2) of a near-infrared laser.

In this paper, a new method, which is based on reconstructing the original intensity distribution of a laser with images captured by a charge-coupled device (CCD) in two orthogonal directions, is proposed for suppressing the influence of CCD vertical blooming on the measurement of the laser beam quality factor (M2). A simplified theoretical model for the distribution of CCD blooming is also proposed. With the proposed method and model, the influence of CCD vertical blooming on the measurement of M2 is simulated. The experimental results demonstrate that the new method can be an effective means to measure the M2 of a near-infrared laser with a silicon CCD camera. The proposed method can be applied to a beam quality analyzer in order to suppress the influence of blooming on the measurement of M2.

Single-silicon CCD-CMOS platform for multi-spectral detection from terahertz to x-rays.

Charge-coupled devices (CCDs) are a well-established imaging technology in the visible and x-ray frequency ranges. However, the small quantum photon energies of terahertz radiation have hindered the use of this mature semiconductor technological platform in this frequency range, leaving terahertz imaging totally dependent on low-resolution bolometer technologies. Recently, it has been shown that silicon CCDs can detect terahertz photons at a high field, but the detection sensitivity is limited. Here we show that silicon, complementary metal-oxide-semiconductor (CMOS) technology offers enhanced detection sensitivity of almost two orders of magnitude, compared to CCDs. Our findings allow us to extend the low-frequency terahertz cutoff to less than 2THz, nearly closing the technological gap with electronic imagers operating up to 1THz. Furthermore, with the silicon CCD/CMOS technology being sensitive to mid-infrared (mid-IR) and the x-ray ranges, we introduce silicon as a single detector platform from 1EHz to 2THz. This overcomes the present challenge in spatially overlapping a terahertz/mid-IR pump and x-ray probe radiation at facilities such as free electron lasers, synchrotron, and laser-based x-ray sources.

Angular sensitivity of modeled scientific silicon charge-coupled devices to initial electron direction

Previously, scientific silicon charge-coupled devices (CCDs) with 10.5-μm pixel pitch and a thick (650μm), fully depleted bulk have been used to measure gamma-ray-induced fast electrons and demonstrate electron track Compton imaging. A model of the response of this CCD was also developed and benchmarked to experiment using Monte Carlo electron tracks.We now examine the trade-off in pixel pitch and electronic noise. We extend our CCD response model to different pixel pitch and readout noise per pixel, including pixel pitch of 2.5μm, 5μm, 10.5μm, 20μm, and 40μm, and readout noise from 0eV/pixel to 2keV/pixel for 10.5μm pixel pitch. The CCD images generated by this model using simulated electron tracks are processed by our trajectory reconstruction algorithm. The performance of the reconstruction algorithm defines the expected angular sensitivity as a function of electron energy, CCD pixel pitch, and readout noise per pixel.Results show that our existing pixel pitch of 10.5μm is near optimal for our approach, because smaller pixels add little new information but are subject to greater statistical noise.In addition, we measured the readout noise per pixel for two different device temperatures in order to estimate the effect of temperature on the reconstruction algorithm performance, although the readout is not optimized for higher temperatures. The noise in our device at 240K increases the FWHM of angular measurement error by no more than a factor of 2, from 26° to 49° FWHM for electrons between 425keV and 480keV. Therefore, a CCD could be used for electron-track-based imaging in a Peltier-cooled device.

High-performing nonlinear visualization of terahertz radiation on a silicon charge-coupled device.

Photoinduced electron transitions can lead to significant changes of the macroscopic electronic properties in semiconductors. This principle is responsible for the detection of light with charge-coupled devices. Their spectral sensitivity is limited by the semiconductor bandgap which has restricted their visualization capabilities to the optical, ultraviolet, and X-ray regimes. The absence of an imaging device in the low frequency terahertz range has severely hampered the advance of terahertz imaging applications in the past. Here we introduce a high-performing imaging concept to the terahertz range. On the basis of a silicon charge-coupled device we visualize 5–13 THz radiation with photon energy under 2% of the sensor's band-gap energy. The unprecedented small pitch and large number of pixels allow the visualization of complex terahertz radiation patterns in real time and with high spatial detail. This advance will have a great impact on a wide range of terahertz imaging disciplines.

Measurement of radioactive contamination in the high-resistivity silicon CCDs of the DAMIC experiment

We present measurements of radioactive contamination in the high-resistivity silicon charge-coupled devices (CCDs) used by the DAMIC experiment to search for dark matter particles. Novel analysis methods, which exploit the unique spatial resolution of CCDs, were developed to identify α and β particles. Uranium and thorium contamination in the CCD bulk was measured through α spectroscopy, with an upper limit on the 238U (232Th) decay rate of 5 (15) kg−1 d−1 at 95% CL. We also searched for pairs of spatially correlated electron tracks separated in time by up to tens of days, as expected from 32Si –32P or 210Pb –210Bi sequences of β decays. The decay rate of 32Si was found to be 80+110−65 kg−1 d−1 (95% CI). An upper limit of ∼35 kg−1 d−1 (95% CL) on the 210Pb decay rate was obtained independently by α spectroscopy and the β decay sequence search. These levels of radioactive contamination are sufficiently low for the successful operation of CCDs in the forthcoming 100 g DAMIC detector.

Extraction efficiency enhancement of single InAs quantum dot emission through light scattering on the Au nanoparticles

Single semiconductor quantum dots (QDs) have been considered as the promising solid-state single photon sources. To obtain bright quantum sources, the key issue is to enhance extraction efficiency of the QD emission, which is challenging since QDs normally emit isotropically in a high refractive index material. In this article, we investigate the influence of Au nanoparticles on the QD photoluminescence (PL) extraction efficiency based on the techniques of optically positioned QDs and single QD emission detection. The InAs QD samples studied are grown using the molecular beam epitaxy on a (001) GaAs substrate. The sample consists of, in sequence, a 200 nm GaAs buffer layer, a 100 nm AlAs sacrificed layer, a 30 nm GaAs, a QD layer, and a 100 nm GaAs cap layer. The QD sample is mounted in a cryostat cooled down to 5 K, and excited by illumination of a 640 nm diode laser (CW or pulsed with a repetition frequency of 80 MHz). Excitation laser beam is focused to an approximately 2 μm spot on the sample using a microscope objective (NA : 0.5) which is mounted on a nanocube XYZ piezo nanopositioning stage with a scanning range of 100×100×100 μm3. The QD PL is collected using the same objective and measured using a 0.5 m focal length monochromator equipped with a silicon charge-coupled device (CCD). The PL decay measurements are performed using a silicon avalanche photodiode (APD) and a time-correlated single-photon counting (TCSPC) board.#br#In order to study the influence of different environments surrounding the QDs on the spontaneous emission rate and the extraction efficiency, the same QD emissions are measured under the conditions that: (1) A typical QD is at first chosen and optically positioned and then its emission is measured. (2) A GaAs layer containing the QDs is lifted off from the as-grown sample by an AlAs sacrificed layer and placed on the Au film with or without Au nanoparticles. (3) Optical measurements are carried out to obtain the QD emission intensity. This technique enables us to compare the same QD emission intensity for the as-grown QD sample, which is placed on the Au film or on the Au nanoparticles.#br#In summary, it is found that the measured QD emission intensity increases up to 6 times that of the original for the QD placed on the Au nanoparticles, otherwise it is only doubled for the QD placed on the Au film. The time-resolved PL measurements show that the QDs have nearly the same decay time for the QDs in different environments, implying that the QD spontaneous emission rate has not been changed. Therefore, the enhanced PL is due to the increase of extraction efficiency. The physical mechanism underlying the Au nanoparticles-induced PL enhancement is attributed to the trapped QD emission light within the sample and scattered again by Au nanoparticles and collected by the microscopy objective.

The Impact of Silicon CCD Photon Spread on Quantitative Analyses of Luminescence Images

Commercial and R&D photoluminescence imaging systems commonly employ indirect bandgap silicon charge-coupled device (CCD) imaging sensors. Silicon is a weak absorber of the near-infrared band-to-band emission of silicon, and significant lateral spreading of the luminescence signal can occur within the sensor. Uncorrected, this effect reduces image contrast, introduces artificial signal gradients, and limits the minimum feature size for which accurate quantitative measurements can be derived. Empirical quantification of the spreading effect defined in terms of the point-spread function (PSF) for the imaging apparatus allows for postprocessing deconvolution, which quantitatively improves image accuracy and contrast. Assessment of the impact of a photon spread indicates that signal smear under commonly occurring high contrast ratio scenarios is sufficient to warrant the application of deconvolution to improve the accuracy of quantitative data in calibrated luminescence images. With a carefully defined PSF, corrections to within ± 10% of the true signal ratio for small-area features can be achieved. Short-pass filtering provides partial correction of the photon spread with the advantage of reduced experimental complexity but, nonetheless, with limitations on the minimum feature size for which accurate signal ratios can be measured.

An Assessment of the Bias Dependence of Displacement Damage Effects and Annealing in Silicon Charge Coupled Devices

The dependence of displacement damage effects in silicon charge coupled devices on the bias conditions during proton irradiation has been assessed. The devices have been fully characterized for dark signal increase, charge transfer degradation and the generation of random telegraph signals. A 5 to 10% higher degradation rate for all these parameters has been seen when unbiased during irradiation, under conditions typically used for a proton irradiation campaign, compared with the case when operating the devices during the irradiation. Room temperature annealing has been investigated and shows a bias dependence for all parameters tested. A reverse annealing behavior of bulk dark signal and random telegraph signals following illumination is reported for the first time. Both the annealing and reverse annealing observations may, in part, be attributed to the behavior of the trivacancy.

The performance of Hydrogenated Amorphous Silicon Charge Coupled Devices

The performance of Hydrogenated Amorphous Silicon Charge Coupled Devices

Active DLP Hyperspectral Illumination: A Noninvasive, in Vivo, System Characterization Visualizing Tissue Oxygenation at Near Video Rates

We report use of a novel hyperspectral imaging system utilizing digital light processing (DLP) technology to noninvasively visualize in vivo tissue oxygenation during surgical procedures. The system's novelty resides in its method of illuminating tissue with precisely predetermined continuous complex spectra. The Texas Instruments digital micromirror device, DMD, chip consisting of 768 by 1024 mirrors, each 16 μm square, can be switched between two positions at 12.5 kHz. Switching the appropriate mirrors controls the intensity of light illuminating the tissue as a function of wavelength, active spectral illumination. Meaning, the tissue can be illuminated with a different spectrum of light within 80 μs. Precisely, predetermined spectral illumination penetrates into patient tissue, its chemical composition augments the spectral properties of the light, and its reflected spectra are detected and digitized at each pixel detector of a silicon charge-coupled device, CCD. Using complex spectral illumination, digital signal processing and chemometric methods produce chemically relevant images at near video rates. Specific to this work, tissue is illuminated spectrally with light spanning the visible electromagnetic spectrum (380 to 780 nm). Spectrophotometric images are detected and processed visualizing the percentage of oxyhemoglobin at each pixel detector and presented continuously, in real time, at 3 images per second. As a proof of principle application, kidneys of four live anesthetized pigs were imaged before, during, and after renal vascular occlusion. DLP Hyperspectral Imaging with active spectral illumination detected a 64.73 ± 1.5% drop in the oxygenation of hemoglobin within 30 s of renal arterial occlusion. Producing chemically encoded images at near video rate, time-resolved hyperspectral imaging facilitates monitoring renal blood flow during animal surgery and holds considerable promise for doing the same during human surgical interventions.

Electrode level Monte Carlo model of radiation damage effects on astronomical CCDs

Current optical space telescopes rely upon silicon Charge Coupled Devices (CCDs) to detect and image the incoming photons. The performance of a CCD detector depends on its ability to transfer electrons through the silicon efficiently, so that the signal from every pixel may be read out through a single amplifier. This process of electron transfer is highly susceptible to the effects of solar proton damage (or non-ionizing radiation damage). This is because charged particles passing through the CCD displace silicon atoms, introducing energy levels into the semi-conductor bandgap which act as localized electron traps. The reduction in Charge Transfer Efficiency (CTE) leads to signal loss and image smearing. The European Space Agency's astrometric Gaia mission will make extensive use of CCDs to create the most complete and accurate stereoscopic map to date of the Milky Way. In the context of the Gaia mission CTE is referred to with the complementary quantity Charge Transfer Inefficiency (CTI = 1-CTE). CTI is an extremely important issue that threatens Gaia's performances. We present here a detailed Monte Carlo model which has been developed to simulate the operation of a damaged CCD at the pixel electrode level. This model implements a new approach to both the charge density distribution within a pixel and the charge capture and release probabilities, which allows the reproduction of CTI effects on a variety of measurements for a large signal level range in particular for signals of the order of a few electrons. A running version of the model as well as a brief documentation and a few examples are readily available at http://www.strw.leidenuniv.nl/~prodhomme/cemga.php as part of the CEMGA java package (CTI Effects Models for Gaia).

Optical and IR applications in astronomy and astrophysics

The set comprising silicon charge-coupled devices, low band-gap infrared arrays and bolometer arrays provide astronomers with position-sensitive photon detectors from the X-ray to the sub-mm. In recent years the most significant advances have occurred in the near-infrared part of the spectrum because not only have the detector formats caught up with those of charge-coupled device (CCDs) but also because the advent of adaptive optics (AO) has meant that the very largest telescopes can achieve their diffraction limit in the near-infrared. Thus infrared cameras, spectrometers and hybrid instruments that measure spatial and spectral information simultaneously are now commanding the greatest attention on telescopes from 6.5 to 10 m in effective aperture. Scientific applications of these new infrared instruments span everything from the search for nearby solar systems to the orbital motions of stars about the massive black hole at the center of the Milky Way, and studies of the first galaxies to form in the high redshift Universe. Background, principles and applications of infrared array detectors to astronomy and astrophysics will be discussed with particular emphasis on work at the W.M. Keck 10-m telescope on Mauna Kea, Hawaii.