CCD Array Detector Research Articles

High efficiency microcolumnar Lu2O3:Eu scintillator thin film for hard X-ray microtomography

We have developed microstructured Lu2O3:Eu scintillator films capable of providing spatial resolution on the order of micrometers for hard X-ray imaging. In addition to their extraordinary resolution, Lu2O3:Eu films simultaneously provide high absorption efficiency for 20 to 100 keV X-rays, and bright 610 nm emission, with intensity rivalling that of the brightest known scintillators. At present, high spatial resolution of such a magnitude is achieved using ultra-thin scintillators measuring only about 1 to 5 μm in thickness, which limits absorption efficiency to ~3% for 12 keV X-rays and less than 0.1% for 20 to 100 keV X-rays, resulting in excessive measurement time and exposure to the specimen. Lu2O3:Eu would significantly improve that (99.9% @12 keV and 30% @ 70 keV). Important properties and features of our Lu2O3:Eu scintillator material, fabricated by our electron-beam physical vapour deposition (EB-PVD) process, combines superior density of 9.5 g/cm3, microcolumnar structure emitting 48000 photons/MeV whose wavelength is an ideal match for the underlying CCD detector array. We grew thin films measuring 5–50μm in thickness as well as covering areas up to 5 × 5 cm2 which can be a suitable basis for microtomography, digital radiography as well as CT and hard X-ray Micro-Tomography (XMT).

Lensfree On-chip Tomographic Microscopy Employing Multi-angle Illumination and Pixel Super-resolution

Tomographic imaging has been a widely used tool in medicine as it can provide three-dimensional (3D) structural information regarding objects of different size scales. In micrometer and millimeter scales, optical microscopy modalities find increasing use owing to the non-ionizing nature of visible light, and the availability of a rich set of illumination sources (such as lasers and light-emitting-diodes) and detection elements (such as large format CCD and CMOS detector-arrays). Among the recently developed optical tomographic microscopy modalities, one can include optical coherence tomography, optical diffraction tomography, optical projection tomography and light-sheet microscopy. 1-6 These platforms provide sectional imaging of cells, microorganisms and model animals such as C. elegans, zebrafish and mouse embryos. Existing 3D optical imagers generally have relatively bulky and complex architectures, limiting the availability of these equipments to advanced laboratories, and impeding their integration with lab-on-a-chip platforms and microfluidic chips. To provide an alternative tomographic microscope, we recently developed lensfree optical tomography (LOT) as a high-throughput, compact and cost-effective optical tomography modality. 7 LOT discards the use of lenses and bulky optical components, and instead relies on multi-angle illumination and digital computation to achieve depth-resolved imaging of micro-objects over a large imaging volume. LOT can image biological specimen at a spatial resolution of <1 μm x <1 μm x <3 μm in the x, y and z dimensions, respectively, over a large imaging volume of 15-100 mm3, and can be particularly useful for lab-on-a-chip platforms.

Lensfree On-chip Tomographic Microscopy Employing Multi-angle Illumination and Pixel Super-resolution

Tomographic imaging has been a widely used tool in medicine as it can provide three-dimensional (3D) structural information regarding objects of different size scales. In micrometer and millimeter scales, optical microscopy modalities find increasing use owing to the non-ionizing nature of visible light, and the availability of a rich set of illumination sources (such as lasers and light-emitting-diodes) and detection elements (such as large format CCD and CMOS detector-arrays). Among the recently developed optical tomographic microscopy modalities, one can include optical coherence tomography, optical diffraction tomography, optical projection tomography and light-sheet microscopy. These platforms provide sectional imaging of cells, microorganisms and model animals such as C. elegans, zebrafish and mouse embryos. Existing 3D optical imagers generally have relatively bulky and complex architectures, limiting the availability of these equipments to advanced laboratories, and impeding their integration with lab-on-a-chip platforms and microfluidic chips. To provide an alternative tomographic microscope, we recently developed lensfree optical tomography (LOT) as a high-throughput, compact and cost-effective optical tomography modality. LOT discards the use of lenses and bulky optical components, and instead relies on multi-angle illumination and digital computation to achieve depth-resolved imaging of micro-objects over a large imaging volume. LOT can image biological specimen at a spatial resolution of <1 μm x <1 μm x <3 μm in the x, y and z dimensions, respectively, over a large imaging volume of 15-100 mm(3), and can be particularly useful for lab-on-a-chip platforms.

CdSe-ZnS quantum dots as temperature sensors during thermal coagulation of bovine serum albumin (BSA) solder

Laser tissue soldering (LTS) has variously interesting applications such as wound closure, anastomosis of blood vessels, and sealing corneal wounds. Since tissue properties such as optical absorption or thermal conductivity may differ, temperature control is essential to obtain full coagulation and to minimize thermal side effects. In this article, a non-invasive technique is proposed for temperature sensing by using CdSe-ZnS quantum dots (QDs) dissolved in protein solder, namely bovine serum albumin (BSA). The temperature measurement is conducted by monitoring the change in the photoluminescence spectra of the QDs. It is shown that the peak emission wavelength of about 653 nm of CdSe-ZnS QDs shifts linearly in a temperature range from 30 °C to 70 °C, with a coefficient of 0.153 nm °C−1 with increasing temperature. The wavelength shift can be determined by applying a small spectrometer with a CCD-array detector. The uncertainty associated with this method is estimated to be less than 6 °C in temperature. As the temperature increases, the measured signal strength initially remains constant and then falls off abruptly when exceeding 55 °C. The signal drop correlates with a phase change from a clear, low-scattering protein solution to strong-scattering solid material.

The Application of Linear Variable Filter to Improve the Resolution of Micro Spectrometer Systems

Using a linear variable filter in front of photo-detector array such as CCD or CMOS detector array, we could minimize the impact of stray light and improve the resolution of micro spectrometers. Unfortunately, this method could not exhibit the spectral resolution of a parallel filter in the same way, because the transmitted beam from a linear variable filter has broadening. The broadening becomes limited in the linear variable filter for high-resolution spectral systems. In this study, through theoretical analysis of the focused beam and the experiments, we developed a method to improve the resolution of micro spectrometer. This method was useful for practical engineering applications.

Laser ablation-miniature mass spectrometer for elemental and isotopic analysis of rocks

A laser ablation-miniature mass spectrometer (LA-MMS) for the chemical and isotopic measurement of rocks and minerals is described. In the LA-MMS method, neutral atoms ablated by a pulsed laser are led into an electron impact ionization source, where they are ionized by a 70 eV electron beam. This results in a secondary ion pulse typically 10-100 μs wide, compared to the original 5-10 ns laser pulse duration. Ions of different masses are then spatially dispersed along the focal plane of the magnetic sector of the miniature mass spectrometer (MMS) and measured in parallel by a modified CCD array detector capable of detecting ions directly. Compared to conventional scanning techniques, simultaneous measurement of the ion pulse along the focal plane effectively offers a 100% duty cycle over a wide mass range. LA-MMS offers a more quantitative assessment of elemental composition than techniques that detect ions directly generated by the ablation process because the latter can be strongly influenced by matrix effects that vary with the structure and geometry of the surface, the wavelength of the laser beam, and the not well characterized ionization efficiencies of the elements in the process. The above problems attendant to the direct ion analysis has been minimized in the LA-MMS by analyzing the ablated neutral species after their post-ionization by electron impaction. These neutral species are much more abundant than the directly ablated ions in the ablated vapor plume and are, therefore, expected to be characteristic of the chemical composition of the solid. Also, the electron impact ionization of elements is well studied and their ionization cross sections are known and easy to find in databases. Currently, the LA-MMS limit of detection is 0.4 wt.%. Here we describe LA-MMS elemental composition measurements of various minerals including microcline, lepidolite, anorthoclase, and USGS BCR-2G samples. The measurements of high precision isotopic ratios including (41)K/(39)K (0.077 ± 0.004) and (29)Si/(28)Si (0.052 ± 0.006) in these minerals by LA-MMS are also described. The LA-MMS has been developed as a prototype instrument system for space applications for geochemical and geochronological measurements on the surface of extraterrestrial bodies.

Improved multiple-pass Raman spectrometer

An improved Raman gain spectrometer for flame measurements of gas temperature and species concentrations is described. This instrument uses a multiple-pass optical cell to enhance the incident light intensity in the measurement volume. The Raman signal is 83 times larger than from a single pass, and the Raman signal-to-noise ratio (SNR) in room-temperature air of 153 is an improvement over that from a single-pass cell by a factor of 9.3 when the cell is operated with 100 passes and the signal is integrated over 20 laser shots. The SNR improvement with the multipass cell is even higher for flame measurements at atmospheric pressure, because detector readout noise is more significant for single-pass measurements when the gas density is lower. Raman scattering is collected and dispersed in a spectrograph with a transmission grating and recorded with a fast gated CCD array detector to help eliminate flame interferences. The instrument is used to record spontaneous Raman spectra from N(2), CO(2), O(2), and CO in a methane-air flame. Curve fits of the recorded Raman spectra to detailed simulations of nitrogen spectra are used to determine the flame temperature from the shapes of the spectral signatures and from the ratio of the total intensities of the Stokes and anti-Stokes signals. The temperatures measured are in good agreement with radiation-corrected thermocouple measurements for a range of equivalence ratios.

Comparison between laser-induced photoemissions and phototransmission of hard tissues using fibre-coupled Nd:YAG and Er3+-doped fibre lasers

During pulsed laser irradiation of dental enamel, laser-induced photoemissions result from the laser-tissue interaction through mechanisms including fluorescence and plasma formation. Fluorescence induced by non-ablative laser light interaction has been used in tissue diagnosis, but the photoemission signal accompanying higher power ablative processes may also be used to provide real-time monitoring of the laser-tissue interaction. The spectral characteristics of the photoemission signals from normal and carious tooth enamel induced by two different pulsed lasers were examined. The radiation sources compared were a high-power extra-long Q-switched Nd:YAG laser operating at a wavelength of 1,066 nm giving pulses (with pulse durations in the range 200-250 μs) in the near infrared and a free-running Er(3+)-doped ZBLAN fibre laser operating at a wavelength near 3 μm with similar pulse durations in the mid-infrared region. The photoemission spectra produced during pulsed laser irradiation of enamel samples were recorded using a high-resolution spectrometer with a CCD array detector that enabled an optical resolution as high as 0.02 nm (FWHM). The spectral and time-dependence of the laser-induced photoemission due to thermal emission and plasma formation were detected during pulsed laser irradiation of hard tissues and were used to distinguish between normal and carious teeth. The use of these effects to distinguish between hard and soft biological tissues during photothermal ablation with a pulsed Nd:YAG laser or an Er fibre laser appears feasible. The real-time spectrally resolved phototransmission spectrum produced during pulsed Nd:YAG laser irradiation of human tooth enamel samples was recorded, with a (normalized) relative transmission coefficient of 1 (100%) for normal teeth and 0.6 (60%) for the carious teeth. The photoemission signal accompanying ablative events may also be used to provide real-time monitoring of the laser-tissue interaction.

Quantification of light reflectance spectroscopy and its application: Determination of hemodynamics on the rat spinal cord and brain induced by electrical stimulation

Two quantification methods for light reflectance spectroscopy (LRS) were developed and validated to determine absolute and relative values of hemodynamic parameters and light scattering, followed by a specific application using in vivo animal experiments. A single-channel LRS system consisted of a light source, CCD-array detector, and a computer along with a bifurcated, 2-mm-diameter optical probe; this system was utilized to perform laboratory tissue phantoms for validation of the algorithms. In the animal study, a multi-channel, multisite approach was used to measure several reflectance spectra from rat brain and spinal cord on both the ipsi-lateral and contra-lateral sides, using thin 800-μm-diameter optic probes. The neuro-hemodynamic changes were induced by 10-V electrical stimulation in rat hind paw. The LRS data of the animals were analyzed using both absolute and relative methods. The results show that the relative method is computation-efficient and offers a quick estimation of changes in oxy-hemoglobin concentration for real-time monitoring. The absolute quantification method, on the other hand, provides us with an accurate computational tool to calculate absolute values of oxy-, deoxy-, total hemoglobin concentrations, and light scattering coefficients. We also observe that the hemodynamic responses in rat spinal cord were delayed with a few seconds and have an overall broader full width at half maximum, as compared to those from rat somatosensory cortex. LRS as a measurement system provides a robust method for studying local hemodynamic changes and a potential technique to investigate hemo-neural mechanisms in pain processing.

Measurement of residual wedge angle of a high optical quality transparent parallel plate with a multipass optical configuration

A new technique of wedge angle measurement of a transparent nearly parallel plate (PP) is presented. In this technique, the single-pass angular deviation suffered by a pair of mutually parallel, laterally separated pencil beams is enhanced by using a multipass cavity formed with two right-angle prisms. The resultant angular deflection is converted to linear deviation by means of a Fourier transform lens (FTL), which focuses the pencil beams on to its focal plane. A two-dimensional CCD detector array placed at the focal plane of the FTL measures the linear shift of the intensity centroid (IC) of the resulting Young's fringes formed due to the superposition of the laterally separated pencil beams. The wedge angle is determined from the measured value of the linear shift of the IC due to the PP.

Monitoring of all hydrogen isotopologues at tritium laboratory Karlsruhe using Raman spectroscopy

We have recorded Raman spectra for all hydrogen isotopologues, using a CW Nd:YVO4 laser (5 W output power at 532 nm) and a high-throughput (f/1.8) spectrograph coupled to a Peltier-cooled (200 K) CCD-array detector (512 × 2048 pixels). A (static) gas cell was used in all measurements. We investigated (i) “pure” fillings of the homonuclear isotopologues H2, D2, and T2; (ii) equilibrated binary fillings of H2 + D2, H2 + T2, and D2 + T2, thus providing the heteronuclear isotopologues HD, HT, and DT in a controlled manner; and (iii) general mixtures containing all isotopologues at varying concentration levels. Cell fillings within the total pressure range 13–985 mbar were studied, in order to determine the dynamic range of the Raman system and the detection limits for all isotopologues. Spectra were recorded for an accumulation period of 1000 s. The preliminary data evaluation was based on simple peak-height analysis of the ro-vibrational Q1-branches, yielding 3σ measurement sensitivities of 5 × 10−3, 7 × 10−3, and 25 × 10−3 mbar for the tritium-containing isotopologues T2, DT, and HT, respectively. These three isotopologues are the relevant ones for the KATRIN experiment and in the ITER fusion fuel cycle. While the measurement reported here were carried out with static-gas fillings, the cells are also ready for use with flowing-gas samples.

Improved sensitivity gas detection by spontaneous Raman scattering

Accurate, real-time measurement of the dilute constituents of a gaseous mixture poses a significant challenge usually relegated to mass spectrometry. Here, spontaneous Raman backscattering is used to detect low pressure molecular gases. Rapid detection of gases in the approximately 100 parts in 10(6) (ppm) range is described. Improved sensitivity is brought about by use of a hollow-core, photonic bandgap fiber gas cell in the backscattering configuration to increase collection efficiency and an image-plane aperture to greatly reduce silica-Raman background noise. Spatial and spectral properties of the silica noise were examined with a two-dimensional CCD detector array.

Label-Free Protein Detection via Gold Nanoparticles and Localized Surface Plasmon Resonance

Protein plays key role in cellular processes and diseases diagnosis [1-3]. This paper reports a label-free detection of proteins through localized surface plasmon resonance (LSPR) and realized Au nanoparticles (AuNPs) immobilized on glass slide. Glass slide is first sonicated with 5% v/v glassware detergent in ultrapure water for 30 mins, and then in ultrapure water for another 30 mins. A 5% v/v aminopropyltriethoxysilane (APTES) solution in ultrapure water is prepared and the glass slide is immersed in the 5% v/v APTES solution for 20 mins. The glass slide is sonicated for 60 mins in ultrapure water. The purpose of the sonication is to remove the multi-layers of APTES which are formed on the glass surface. The silanized glass slide is immersed in AuNPs solution for 40 mins. Finally, the protein solution is added on the surface of the slide. The surface absorption of proteins induces a significant difference of environmental refractive index around the AuNPs. The shift in the wavelength of the LSPR spectra is very sensitive to the change in the surface refractive index of the nanoparticles. The shifts in the LSPR spectra are primarily determined by the volatility and refractive indices of the protein species. In this paper, the LSPR-nanobiosensor is designed and fabricated. The LSPR band responses are measured by a real-time UV–vis spectrometer with a CCD array detector. The response time of the protein–LSPR spectrum is less than 3 seconds and the response is reversible and reproducible.

Spectral measurements of large particles by flow cytometry

Flow cytometers designed to analyze large particles are enabling new applications in biology and chemistry. Similarly, flow spectroscopy approaches are extending the capabilities of the flow cytometry platform. Here, we report on the adaptation of a commercial large particle analyzer to measure fluorescence and Raman spectra of individual particles at high speeds. We modified a Union Biometrica COPAS Plus instrument to allow red excitation and optical fiber-based light collection and spectral analysis using a spectrograph and CCD array detector. These modifications did not compromise the ability of the instrument to resolve different sized particles based on their extinction and time of flight signals. The modified instrument has the sensitivity and spectral resolution to measure the fluorescence and Raman signals from individual particles with signal integration times of 10 usec. The high speed spectral analysis of individual particles in flow will enable new applications in biological and chemical analyses.

Action-Spectra of Electrochromic Voltage-Sensitive Dyes in an Intact Excitable Tissue

Voltage-sensitive dyes VSDs provide a spatially resolved optical read-out of electrical signals in excitable tissues. Several com- mon fluorescent VSDs display electrochromic shifts of their emission spectra, making them suitable candidates for ratiometric measure- ments of transmembrane voltages. These advantages of VSDs are tem- pered by tissue-specific shifts to their fluorescence emission. In addi- tion, the optimal electrochromic dye response occurs in wavelength bands distinct from the dye's maximal resting emission. This spectrum can undergo tissue-specific shifts as well. We have devel- oped a technique for in situ measurements of the action spectra of VSDs in intact excitable tissues. Fluorescence emission spectra of VSDs during action-potential depolarization were obtained within a single sweep of a spectrophotometer equipped with a change-coupled device CCD array detector. To resolve the subtle electrochromic shifts in voltage-induced dye emission, fluorescence emission spectra measured right before and during field-induced action-potential de- polarization were averaged over about 100 trials. Removing white- noise contributions from the spectrometer's CCD detector/amplifier via low-pass filtering in Fourier space, the action spectra of all dyes could be readily determined. © 2008 Society of Photo-Optical Instrumentation En-

Analysis of the Modulation Transfer Function Spectral Variation in Different Detector Arrays by Means of Speckle Patterns

Today, CCD and CMOS detector arrays present excellent features in imaging systems. To investigate the suitability of each technology according to various applications, in this work we have comparatively studied the quality of the images provided by different cameras. To this end we have used the speckle method to determine the modulation transfer function (MTF) at different wavelengths of the visible spectrum for the detectors of a low-cost CCD video camera and of two scientific cameras (CCD and CMOS). For both the low-cost CCD and the scientific CMOS detectors, the differences between the MTF curves intensify as the spatial frequency augments, while the MTF decreases as the wavelength increases. For the scientific CCD detector, the MTF spectral behavior does not show this trend, and the differences between the MTF curves corresponding to extreme wavelengths are not expected to be significant, as opposed to what appears for the scientific CMOS detector.

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.

Improved aperture for modulation transfer function measurement of detector arrays beyond the Nyquist frequency

The design of an aperture for the generation of laser speckle with a flat power spectrum covering a wide band of the measurement spatial-frequency range is presented. This aperture allows for the measurement of modulation transfer function (MTF) from zero to twice the Nyquist frequency of a two-dimensional detector array. This design mitigates many of the measurement problems inherent in other aperture designs. The MTF measurement of a CCD detector array is used to demonstrate the measurement technique and illustrate the advantages of the new aperture design.

800 nm WDM Interrogation System for Strain, Temperature, and Refractive Index Sensing Based on Tilted Fiber Bragg Grating

A low-cost high-resolution wavelength-division-multiplexing (WDM) interrogation system operating around 800 nm region with operational bandwidth up to 60 nm and resolution of 12.7 pm utilizing a tilted fiber Bragg grating (TFBG) and a CCD-array detector has been implemented. The system has been evaluated for interrogating fiber Bragg grating based strain, temperature sensors, giving sensitivities of 0.59 pm/muepsiv and 5.6 pm/degC, which are in good agreement with previously reported values. Furthermore, the system has been utilized to detect the refractive index change of sample liquids, demonstrating a capability of measuring index change as small as 10-5. In addition, the vectorial expression of phase match condition and fabrication of TFBG have been discussed.

Label-free Optical Detection of Molecular Interactions by Molecular Interferometric Imaging

Abstract Molecular interferometric imaging (MI2) is a label-free optical biosensor that combines common-path interferometry with shot-noise limited characteristics of a CCD array detector to detect protein binding to surfaces. In the metrology limit, it has achieved roughness-limited surface height resolution of 15 pm per 0.4 micron pixel, corresponding to a scaling mass sensitivity of 7 fg/mm, and a molecular resolution of about 15 IgG molecules per pixel. We have applied MI2 to detect cytokine interleukin-5 at a concentration detection limit of 50 pg/mL with a sandwich immunoassay. Real-time binding assays with MI2 enable the study of reaction kinetics, with a scaling mass sensitivity of 2 pg/mm under 7x magnification. Real-time MI2 measurements of anti-rabbit IgG against rabbit IgG were compared with results from surface plasmon resonance, with identical association rate constants at 5x103 M-1sec-1.