Silicon CCD Research Articles

Spatial Narrowing of Two-Photon Imaging in a Silicon CCD Camera

Imaging based on nonlinear two-photon absorption can offer an attractive alternative for the traditional one-photon imaging scheme with many potential benefits of imaging resolution, speed, and ability to image through scattering media. Here we experimentally demonstrate a direct imaging scheme based on two-photon absorption in the conventional silicon CCD camera and observe a spatial narrowing effect in its imaging. This technique, compared with its one-photon counterpart, exhibits a better imaging resolution and signal-to-noise ratio, thanks to the nonlinear nature of the two-photon absorption process. This nonlinear imaging scheme opens up an avenue for rapid real-time and high-resolution imaging through scattering media like rain, fog, and biomedical samples.

Silver nanoparticle aggregates: Wavelength dependence of their SERS properties in the first transparency window of biological tissues

Silver nanoparticle aggregates are very common substrates for surface enhanced Raman scattering (SERS) due to their simplicity of preparation and good optical enhancement. In this paper, their SERS properties are investigated from 680 to 920 nm, region that spans most of the first transparency window of biological tissues.Our experiments show that the SERS enhancement extends as far as 920 nm, without a significant wavelength dependence: the observed very broad optical response has been interpreted with the formation of large sized aggregates, possibly possessing a partial fractal character. On the other hand, the SERS signal, normalized by the laser power and by the integration time, quickly diminishes from 680 to 920 nm. This happens because the SERS signal depends on the enhancement but also on the instrument sensitivity and on the molecular cross section: for dispersive Raman instruments equipped with silicon CCD detectors and for non resonant molecules, these two parameters tend to diminish towards longer excitation wavelengths.The relevance of these results is twofold. a) Simple silver nanoparticle aggregates are good plasmonic substrates in most of the spectral region in which biological tissues present low absorption. b) The enhancement of the substrate and the normalized SERS signal (that is related to the limit of detection) are not necessarily correlated: they carry complementary pieces of information, both needed for properly designing a SERS experiment.

Development of an Economical, Linear CCD Based Spectrometer

Spectrometry provides vital information about the composition of electromagnetic radiation by measuring wavelengths of light over a wide range of the electromagnetic spectrum. In this work, design and construction of an economical linear CCD spectrometer and a computer application is presented. A sample of the light source travelling through an optical fiber enters the device and the spectrum produced by a diffraction grating is projected on a linear CCD detector. The data is sampled using a 10-bit ADC to the microcontroller memory and finally transferred to the computer via a full speed USB connection. In the computer, the data is digitally processed and displayed through a graphical user interface with several useful functionalities. The device is sensitive to electromagnetic waves of wavelengths ranging from 400 to 800 nm, which is decided by the sensitivity of the silicon CCD detector. The device performs in par with commercially available handheld spectrometers and is equipped with wavelength and amplitude calibration capabilities.

In-flight calibration system of imaging x-ray polarimetry explorer

The NASA/ASI Imaging X-ray Polarimetry Explorer, which will be launched in 2021, will be the first instrument to perform spatially resolved X-ray polarimetry on several astronomical sources in the 2-8 keV energy band. These measurements are made possible owing to the use of a gas pixel detector (GPD) at the focus of three X-ray telescopes. The GPD allows simultaneous measurements of the interaction point, energy, arrival time, and polarization angle of detected X-ray photons. The increase in sensitivity, achieved 40 years ago, for imaging and spectroscopy with the Einstein satellite will thus be extended to X-ray polarimetry for the first time. The characteristics of gas multiplication detectors are subject to changes over time. Because the GPD is a novel instrument, it is particularly important to verify its performance and stability during its mission lifetime. For this purpose, the spacecraft hosts a filter and calibration set (FCS), which includes both polarized and unpolarized calibration sources for performing in-flight calibration of the instruments. In this study, we present the design of the flight models of the FCS and the first measurements obtained using silicon drift detectors and CCD cameras, as well as those obtained in thermal vacuum with the flight units of the GPD. We show that the calibration sources successfully assess and verify the functionality of the GPD and validate its scientific results in orbit; this improves our knowledge of the behavior of these detectors in X-ray polarimetry.

Broadband THz to NIR up-converter for photon-type THz imaging

High performance terahertz imaging devices have drawn wide attention due to their significant application in healthcare, security of food and medicine, and nondestructive inspection, as well as national security applications. Here we demonstrate a broadband terahertz photon-type up-conversion imaging device, operating around the liquid helium temperature, based on the gallium arsenide homojunction interfacial workfunction internal photoemission (HIWIP)-detector-LED up-converter and silicon CCD. Such an imaging device achieves broadband response in 4.2–20 THz and can absorb the normal incident light. The peak responsivity is 0.5 AW−1. The light emitting diode leads to a 72.5% external quantum efficiency improvement compared with the one widely used in conventional up-conversion devices. A peak up-conversion efficiency of 1.14 × 10−2 is realized and the optimal noise equivalent power is 29.1 pWHz−1/2. The up-conversion imaging for a 1000 K blackbody pin-hole is demonstrated. This work provides a different imaging scheme in the terahertz band.

Compact self-illuminated image upconversion system based on intracavity second-harmonic generation.

We present an image upconversion system based on intracavity Type II second-harmonic generation to create an image in the visible spectrum of a target illuminated by an infrared laser. The system has the novelty of being self-illuminated. It uses some fractional leaking power of the infrared laser to illuminate a target located in the object focal plane of the system, and to couple back a created infrared target image to an intracavity nonlinear crystal, where it mixes with the cavity laser beam to obtain a second-harmonic image, visible with a silicon CCD camera. For a proof of concept, we have built a system based on a diode-pumped Nd3+:YVO4 continuous-wave (cw) laser and an intracavity KTP crystal to upconvert 1342nm target images to 671nm. The upconverted cw power allowed us to capture real-time video in a standard nonintensified CCD camera, with 2.5W of a diode pump.

Observation of galactic cosmic ray spallation events from the SoHO mission 20-yr operation of LASCO

A shower of secondary Cosmic Ray (CR) particles is produced at high altitudes in the Earth's atmosphere, so the primordial Galactic Cosmic Rays (GCRs) are never directly measured outside the Earth magnetosphere and atmosphere. They approach the Earth and other planets in the complex pattern of rigidity's dependence, generally excluded by the magnetosphere. GCRs revealed by images of single nuclear reactions also called spallation events are described here. Such an event was seen on Nov. 29, 2015 using a unique LASCO C3 space coronagraph routine image taken during the Solar and Heliospheric Observatory (SoHO) mission observing uninterruptedly at the Lagrangian L1 point. The spallation signature of a GCR identified well outside the Earth's magnetosphere is obtained for the 1st time. The resulting image includes different diverging linear "tracks" of varying intensity, leading to a single pixel, this frame identifies the site on the silicon CCD chip of the coronagraph camera. There was no solar flare reported at that time, nor Coronal Mass Ejection (CME) and no evidence of optical debris around the spacecraft. More examples of smaller CR events have been discovered through the 20 years of continuous observations from SoHO. This is the first spallation event from a CR, recorded outside the Earth's magnetosphere. We evaluate the probable energy of these events suggesting a plausible galactic source. Key words: Sun: Galactic Cosmic Rays, Solar Energetic Particles, Heliosphere.

Upconversion imaging using short-wave infrared picosecond pulses.

To the best of our knowledge, we present the first demonstration of short-wavelength infrared image upconversion that employs intense picosecond signal and pump beams. We use a fiber laser that emits a signal beam at 1877nm and a pump beam at 1550 nm-both with a pulse width of 1ps and a pulse repetition rate of 21.7MHz. Due to synchronization of high peak-power pulses, efficient upconversion is achieved in a single-pass setup that employs a bulk lithium niobate crystal. Optimizing the temporal overlap of the pulses for high upconversion efficiency enables us to exploit a relatively large pump beam diameter to upconvert a wider range of signal spatial frequencies in the crystal. The 1877nm signal is converted into 849 nm-enabling an image to be acquired by a silicon CCD camera. The measured size of the smallest resolvable element of this imaging system is consistent with the value predicted by an improved model that considers the combined image blurring effect due to finite pump beam size, thick nonlinear crystal, and polychromatic infrared illumination.

Upconversion imaging using an all-fiber supercontinuum source.

In this Letter, the first demonstration, to the best of our knowledge, of pulsed upconversion imaging using supercontinuum light is presented. A mid-infrared (IR) imaging system was built by combining a mid-IR supercontinuum source emitting between 1.8 and 2.6 μm with upconversion detection. The infrared signal is used to probe a sample and mixed with a synchronized 1550 nm laser pulse inside a lithium niobate (LiNbO3) crystal. The signal is thus upconverted to the 860-970 nm range and acquired on a standard silicon CCD array at a rate of 22 frames per second. In our implementation, spatial features in the sample plane as small as 55 μm could be resolved.

Cesium hafnium chloride: A high light yield, non-hygroscopic cubic crystal scintillator for gamma spectroscopy

We report on the scintillation properties of Cs2HfCl6 (cesium hafnium chloride or CHC) as an example of a little-known class of non-hygroscopic compounds having the generic cubic crystal structure of K2PtCl6. The crystals are easily growable from the melt using the Bridgman method with minimal precursor treatments or purification. CHC scintillation is centered at 400 nm, with a principal decay time of 4.37 μs and a light yield of up to 54 000 photons/MeV when measured using a silicon CCD photodetector. The light yield is the highest ever reported for an undoped crystal, and CHC also exhibits excellent light yield nonproportionality. These desirable properties allowed us to build and test CHC gamma-ray spectrometers providing energy resolution of 3.3% at 662 keV.

Backside spectroscopic photon emission microscopy using intensified silicon CCD

A typical solution for backside analysis of photon emissions from semiconductor integrated circuits has been the InGaAs detector. It takes advantage of the transparency of the silicon material to wavelengths within its spectral sensitivity regime. However, it has been recently demonstrated that light spectral information extraction is more reliable when using silicon CCDs (SiCCDs) assisted by proper backside bulk Si thinning of the device. In this paper we demonstrate further improvement of the photon emission spectrum acquisition using the solid-state intensified silicon CCD (SI-CCD). Using the presented solution it is possible to significantly reduce the analysis time, expand the detectable spectral regime as well as improve the spectral wavelength resolution.

Quantification of bioactive gentiopicroside in the medicinal plant Gentiana scabra Bunge using near infrared spectroscopy

Near infrared (NIR) spectroscopy was employed to perform a quantitative analysis of gentiopicroside, the bioactive component of the medicinal plant Gentiana scabra Bunge. Modified partial least squares regression (MPLSR) and stepwise multiple linear regression (SMLR) calibration models were built using 94 plant tissue culture samples and 136 grown plant samples, respectively, over the full wavelength range (400–2498 nm) and the silicon charge-coupled-device (CCD) sensing band (400–1098 nm). For tissue culture, the smoothing, first-derivative MPLSR model can produce the best effect [calibration set (Rc) = 0.868, standard error of calibration (SEC) = 0.606%, standard error of validation (SEV) = 0.862%] in the wavelength ranges of 900–1000, 1200–1300, and 1600–1700 nm. By contrast, for grown plant samples, the smoothing, second-derivative MPLSR model can produce the best effect (Rc = 0.944, SEC = 0.502%, SEV = 0.685%) in the wavelength ranges of 400–500, 1100–1200, 1600–1800, and 2200–2300 nm. With the silicon CCD sensing band, the smoothing, second-derivative, four-wavelength (670, 786, 474, and 826 nm) SMLR model showed best predictability (Rc = 0.860, SEC = 0.775%, SEV = 0.848%). This study successfully built spectral calibration models for determining gentiopicroside content at different growth stages of G. scabra Bunge. The specific wavelengths selected within the silicon CCD sensing band can be used in combination with multispectral imaging as a powerful tool for monitoring or inspecting the quality of G. scabra Bunge during cultivation.

Short-Wave near Infrared Spectrometry of Back Scattering and Transmission of Light by Milk for Multi-Component Analysis

Quality and authenticity of milk are usually defined by the content and composition of fat, proteins, total solids, somatic cells and other established indicators. Along with traditional reference methods for quantitative analysis, the use of near infrared (NIR) spectrometers and multivariate modelling is becoming more widely utilised. It would be useful to apply a spectrometer with a linear silicon CCD array as a rapid, portable and rather cheap supervising device. However, milk is a multiphase disperse system which includes a rough disperse phase of somatic cells and fatty globules, a thin phase of casein and whey proteins particles and the molecular solutions of lactose, salts, vitamins etc. in water. The scattering of incident light by particles of milk affect the signal of an NIR spectrometer significantly. The calibration of a spectrometer can be improved by considering the distinction between scattering by fatty globules and casein micelles. For this purpose, it is attractive to use the anisotropy of scattering by rough particles, in particular, by fatty globules. The comparative results for calibration models constructed with transmission and back scattering spectra of milk are presented in this paper. The spectra were acquired with a new two-channel short wave NIR spectrometer. Restored drinking milk has been modelled with a set of calibration samples, since the difference in the optical properties due to the globules and the micelles is significant and also because the reliable quality control of drinking milk using a simple spectrometer is a relevant practical problem. PLS models were constructed for the prediction of fat and protein and also of the fat-free total solids which serve as an indicator of authenticity for drinking milk. The results obtained demonstrate that a large reductions in errors is possible. The SEP value of not more than 0.08% wt was achieved when predicting the fat content of milk using a calibration based on the difference spectra of transmission and backscattering compared with a SEP of 0.21% wt for the model using transmission spectra only. For protein determination, the SEP was reduced from 0.25% wt to 0.12% wt if the calibration was based on the spectra of backscattering rather than on transmission.

On the method of photoluminescence spectral intensity ratio imaging of silicon bricks: Advances and limitations

Spectral photoluminescence imaging is able to provide quantitative bulk lifetime and doping images if applied on silicon bricks or thick silicon wafers. A comprehensive study of this new method addresses previously reported artefacts in low lifetime regions and provides a more complete understanding of the technique. Spectrally resolved photoluminescence measurements show that luminescence originating from sub band gap defects does not cause those artefacts. Rather, we find that optical light spreading within the silicon CCD is responsible for most of the distortion in image contrast and introduce a method to measure and remove this spreading via image deconvolution. Alternatively, image blur can be reduced systematically by using an InGaAs camera. Results of modelling this alternative camera type and experiments are shown and discussed in comparison. In addition to eliminating the blur effects, we find a superior accuracy for lifetimes above 100 μs with significantly shorter, but dark noise limited exposure times.

Atomically precise surface engineering of silicon CCDs for enhanced UV quantum efficiency

The authors report here on a new technique, combining the atomic precision of molecular beam epitaxy and atomic layer deposition, to fabricate back illuminated silicon CCD detectors that demonstrate world record detector quantum efficiency (>50%) in the near and far ultraviolet (155–300 nm). This report describes in detail the unique surface engineering approaches used and demonstrates the robustness of detector performance that is obtained by achieving atomic level precision at key steps in the fabrication process. The characterization, materials, and devices produced in this effort will be presented along with comparison to other approaches.

Color separation enhancement of pixn diodes by optimizing absorption regions of a-SiGe:H/a-SiC:H alloys and using a low reflective Al-doped ZnO cathode

ABSTRACTSecurity imaging systems working with crystalline silicon CCD or CMOS detectors are not able to distinguish colorimetrically between a large number of dangerous chemical substances, for example whitish powders [1]. In order to offer an alternative to expensive and destructive chemical methods of analysis, we developed optimized hydrogenated amorphous silicon (a-Si:H) multicolor photodiodes with different spectral response characteristics for a reliable, fast, cheap and non-destructive identification of potentially dangerous substances. Experimental optical, C-V and I-V studies were performed to explore the effect of combining linear graded a‑SiC:H-/a‑SiGe:H layers with low-reflective ZnO:Al back-contacts. Typically, a-Si:H with profiled energy gaps can be found in tandem solar cells to optimize the collection of incoming photons [2,3]. We determined the absorption coefficients of a group of a-SiC:H and a-SiGe:H graded and non-graded layers to calculate the penetration depth of photons at different energies into the device structure. Knowing the indices of absorption, refraction and extinction, it is possible to engineer diodes in such a way that accumulations of charge carriers are generated precisely at varying device depths. Common chromium back reflectors avoid a sharp falling edge of the sensitivity towards longer wavelengths and lead to interference fringes in the spectral response [4]. By combining linear graded absorption zones and ZnO:Al back contacts, we designed an optimized device with a highly precise adjustment of the spectral sensitivity reaching from 420 nm to 560 nm and reduced interference fringes at a very low reverse bias voltage of maximum -2.5 V. Similar three terminal devices allow a shift from 440 nm to 630 nm, however, at a much higher reverse bias of -11 V at 560 nm [4]. Present research efforts concentrate on the development of fast and high dynamic front illumination device structures which ensure a continuous narrow-band shift of the spectral photosensitivity and an optimum adaption to a predetermined light source-/sample measurement configuration.

Ultrabroadband detection of a mid-IR continuum by chirped-pulse upconversion

Ultrabroadband mid-IR continuum pulses can be detected on a single-shot basis using chirped-pulse upconversion. Converting the mid-IR pulse to the visible reduces the fractional bandwidth and enables use of a silicon CCD camera. Removing the cross-phase modulation of the chirped pulse results in 1 cm(-1) resolution over a 600 cm(-1) detected bandwidth.

Measuring absorptive two-dimensional infrared spectra using chirped-pulse upconversion detection

Chirped-pulse upconversion (CPU) enables the detection of mid-infrared spectra using a silicon CCD camera by sum-frequency mixing a mid-IR field with a highly chirped near-IR (800 nm) field. Although the substantial chirp limits the spectral broadening and phase distortions caused by the inherent cross-phase modulation, the exquisite phase fidelity needed to measure a fully absorptive two-dimensional IR spectrum demands the correction of the phase distortions. We demonstrate how to correct all of the phase distortions involved in recording an absorptive 2DIR spectrum including delay stage calibrations as well as the requisite nonlinear signals. Besides the extra experimental step of the upconversion process itself, the phase correction procedure requires only the knowledge of the spectral or temporal phase of the chirped pulse. The method is demonstrated in a metal carbonyl complex, Mn2(CO)10, in n-hexane and methanol solvents showing that the method operates well in cases of both homogeneous and inhomogeneous broadening.

Focus on photonics and biomedical optics

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Effect of fruit moving speed on predicting soluble solids content of ‘Cuiguan’ pears ( Pomaceae pyrifolia Nakai cv. Cuiguan) using PLS and LS-SVM regression

Visible (Vis)/near infrared (NIR) spectroscopy is an excellent technique for non-destructive fruit quality assessment. This research was focused on evaluating the use of Vis/NIR spectroscopy for measuring soluble solids content (SSC) of intact ‘Cuiguan’ pears ( Pomaceae pyrifolia Nakai cv. Cuiguan) on-line. Also, the effect of fruit moving speed on SSC measurements was investigated. Diffuse transmission spectra were collected using a fiber spectrometer equipped with a 3648-element linear silicon CCD array detector in the wavelength range of 345–1040 nm, and all sample spectra were collected three times at different fruit moving speeds of 0.3 m s −1, 0.5 m s −1 and 0.7 m s −1. Spectral pre-processing such as derivative, standard normal variate transformation (SNV) and multiplicative scatter correction (MSC) was used before calibration. Partial least squares (PLS) and least squares support vector machines (LS-SVM) were used to develop calibration models for SSC. The results show that fruit moving speed has few effects on spectra and model performance at a fruit moving speed of 0.3–0.7 m s −1. At 0.5 m s −1, the best model for SSC was PLS regression coupled with original spectra, its coefficient of determination ( R 2) and root mean square error of prediction (RMSEP) being 0.916% and 0.530%, respectively.