Image-intensified Charge-coupled Device Research Articles

Gas Scintillation Imager With Capillary Plate

The glass capillary plate (CP) gas detector is a hole-type micropattern gas detector (MPGD) as well as a gas electron multiplier (GEM). An interesting feature of the hole-type MPGD is that since the electron multiplication takes place in each of the highly granulated holes, pixelized 2-D imaging with a high position resolution is possible. Using the CP, we have been developing a gas scintillation imager (GSI) for digital X-ray radiography, cosmic X-ray polarimetry, and neutron imaging. To realize the 2-D imaging capability, we exploit the visible and near-infrared (NIR) scintillation photons emitted from each hole upon gas excitation. This emission occurs simultaneously with electron multiplication. The readout of the scintillation photons has been carried out using an image-intensified charge-coupled device (CCD) or CMOS camera, or a cooled low-noise CCD/CMOS camera, coupled to an optical mirror or lens systems. In this article, we review the properties of the GSI as X-ray and neutron imagers and describe the outlook for future developments.

A novel, cost-effective, multi-point Thomson scattering system on the Pegasus Toroidal Experiment (invited).

A novel, cost-effective, multi-point Thomson scattering system has been designed, implemented, and operated on the Pegasus Toroidal Experiment. Leveraging advances in Nd:YAG lasers, high-efficiency volume phase holographic transmission gratings, and increased quantum-efficiency Generation 3 image-intensified charge coupled device (ICCD) cameras, the system provides Thomson spectra at eight spatial locations for a single grating/camera pair. The on-board digitization of the ICCD camera enables easy modular expansion, evidenced by recent extension from 4 to 12 plasma/background spatial location pairs. Stray light is rejected using time-of-flight methods suited to gated ICCDs, and background light is blocked during detector readout by a fast shutter. This ∼103 reduction in background light enables further expansion to up to 24 spatial locations. The implementation now provides single-shot Te(R) for ne > 5 × 1018 m-3.

Abundant bioluminescent sources of low-light intensity in the deep Mediterranean Sea and North Atlantic Ocean

Light plays a critical role in the functioning of the marine environment. In the dark ocean, bioluminescent organisms are the only visually relevant sources of light. Cameras of different sensitivities were used to compare the density of pelagic bioluminescent sources (BL) of different light intensities at a regional scale: the image-intensified charge-coupled device for deep-sea research (ICDeep), an image-intensified silicon intensifier target (ISIT) camera and a silicon intensifier target (SIT) camera. Pelagic ICDeep values were higher than ISIT measurements by a mean factor of 7.6 in the Mediterranean Sea and 3.5 in the Atlantic Ocean. Atlantic ISIT values were higher than SIT values by a mean factor of 4.5. Standardising bioluminescence measurements to the near-seafloor (0–400 m above bottom) layer, BLNSF, a logarithmic decrease with depth was observed from three independent datasets (slopes not significantly different): ISIT (Atlantic, Mediterranean), ICDeep (Mediterranean). Intercepts from ICDeep measurements were higher than ISIT measurements by a factor of 4.4. From these trends, a conversion factor to calculate benthopelagic plankton biomass from near-seafloor BLNSF density was derived. Calibration of the ICDeep enabled calculation of the minimum intensity of source visible to that camera. BLNSF sources of low-light intensity (≥1.4 × 10−7 W m−2) outnumber fourfold sources of greater intensity (>ca. 10−6 W m−2 (λpeak = 470 nm). This reveals a high abundance of low-light bioluminescent sources in the marine environment, with mean pelagic densities of 33.15 sources m−3 (Atlantic) and 6.79 sources m−3 (Mediterranean) between 500 and 1500 m depth.

Seasonal variation of deep-sea bioluminescence in the Ionian Sea

The ICDeep (Image Intensified Charge Coupled Device for Deep sea research) profiler was used to measure the density of deep bioluminescent animals (BL) through the water column in the east, west and mid-Ionian Sea and in the Algerian Basin. A west to east decrease in BL density was found. Generalized additive modelling was used to investigate seasonal variation in the east and west Ionian Sea (NESTOR and NEMO neutrino telescope sites, respectively) from BL measurements in autumn 2008 and spring 2009. A significant seasonal effect was found in the west Ionian Sea ( p<0.001), where a deep autumnal peak in BL density occurred between 500 and 2400 m. No significant seasonal variation in BL density was found in the east Ionian Sea ( p=0.07). In both spring and autumn, significant differences in BL density were found through the water column between the east and west Ionian Sea ( p<0.001).

Spatial and temporal evolution of plasma discharge in a 42-inch shadow mask plasma display panel

A new type of AC PDP with shadow mask (shadow mask PDP, SMPDP) has been presented for its effective structures with lower cost. In order to improve the image quality and reduce the cost further, a single-scan driving scheme is applied to 42-inch WXGA SMPDP. High-speed address is successfully obtained by offsetting the scan voltage from the final voltage of the ramp-down waveform. A new erase pulse is used before the sustain pulses to eliminate the misfiring. The two distinguished characters of the new driving waveform can realize 1.2 μs to 0.9 μs high speed addressing in 42-inch WXGA SMPDP prototypes. New MgO materials and the optimized process conditions provide 50 ns statistical delay time. A high speed image intensified charge coupled device (ICCD) camera and a photosensor amplifier are used to investigate the discharge of the ON and OFF cells in the reset, address, erase-before-sustain and sustain periods. The experimental results demonstrate that the stable high-speed addressing and valid sustaining can be obtained in the new driving waveforms in 42-inch WXGA SMPDP. The experimental results can help us to understand the discharge and help us to optimize the driving scheme of SMPDP.

Improved analytical modulation transfer function for image intensified charge coupled devices*

The basic problem of simulation and modeling of Image Intensified Charge Coupled Device (ICCD) is the difference between the analytical Modulation Transfer Function (MTF) formulation used in the model and the experimentally obtained MTF. An investigation into the MTF of ICCD sub-components reveal that the MTF of the Image Intensifier Tube (IIT) is the main factor in this deviation. In this study, a regulation factor for the MTF of 3^{rd} generation IITs has been developed. A commonly used MTF formulation for IITs has been modified to include a regulation factor which has helped produce more precise MTF values for the Night Vision Sight (NVS) device. The results obtained through the new formulation have been compared with the experimental results and it is revealed that the proposed formulation yields MTF values within 3% of the experimental results, on average, while the most commonly used formulation produces approximately 29.5% difference, which amounts to almost 10% improvement in analytical analysis. The analysis is then extended to other generations of IITs where similar improvements have been achieved.

Image analysis for denoising full‐field frequency‐domain fluorescence lifetime images

Video-rate fluorescence lifetime-resolved imaging microscopy (FLIM) is a quantitative imaging technique for measuring dynamic processes in biological specimens. FLIM offers valuable information in addition to simple fluorescence intensity imaging; for instance, the fluorescence lifetime is sensitive to the microenvironment of the fluorophore allowing reliable differentiation between concentration differences and dynamic quenching. Homodyne FLIM is a full-field frequency-domain technique for imaging fluorescence lifetimes at every pixel of a fluorescence image simultaneously. If a single modulation frequency is used, video-rate image acquisition is possible. Homodyne FLIM uses a gain-modulated image intensified charge-coupled device (ICCD) detector, which unfortunately is a major contribution to the noise of the measurement. Here we introduce image analysis for denoising homodyne FLIM data. The denoising routine is fast, improves the extraction of the fluorescence lifetime value(s) and increases the sensitivity and fluorescence lifetime resolving power of the FLIM instrument. The spatial resolution (especially the high spatial frequencies not related to noise) of the FLIM image is preserved, because the denoising routine does not blur or smooth the image. By eliminating the random noise known to be specific to photon noise and from the intensifier amplification, the fidelity of the spatial resolution is improved. The polar plot projection, a rapid FLIM analysis method, is used to demonstrate the effectiveness of the denoising routine with exemplary data from both physical and complex biological samples. We also suggest broader impacts of the image analysis for other fluorescence microscopy techniques (e.g. super-resolution imaging).

Negative Sustain Waveform for Improving Discharge Characteristics in AC Plasma Display Panel

The discharge characteristics produced by a negative sustain waveform were examined in comparison with those produced by a positive sustain waveform. An image-intensified charge-coupled device (ICCD) revealed that the negative sustain waveform produced a faster and stronger sustain discharge than the positive sustain waveform. Simulation results also showed that the fast and strong sustain discharge produced by the negative sustain waveform was induced due to the rapid acceleration of the negative wall charges, such as electrons, when applying the negative sustain waveform directly to the electrode with negative wall charges, such as electrons. As a result, the luminance and luminous efficiency were both improved by about 14% and 13%, respectively, with a negative sustain pulse of -180 V when compared to the results with a positive sustain waveform of 180 V.

Time-Resolving Image Analysis of Drilling of Thin Silicon Substrates with Femtosecond Laser Ablation

We have analyzed a drilling process with a femtosecond laser on a silicon surface in order to investigate the degree of the thermal effect during the dicing of a very thin silicon substrate (thickness: 50 µm). A femtosecond laser pulse (E=30–500 µJ/pulse, τ=200 fs, λ=780 nm, f=10 Hz) was focused on a thin silicon substrate using a lens with a focal length of 100 mm. An image-intensified charge-coupled device (CCD) camera with a high-speed gate of 200 ps was utilized to take images of a drilled hole during the drilling process. As a result, it was found that the smaller the pulse energy, the faster the formation of the hole. Therefore, we tried to estimate the degree of the thermal effect semi quantitatively by analyzing the rise time of the formation of the hole. By measuring the rise time in 8 kinds of metallic material, it was found that the rise time strongly correlates with the thermal conductivity in these materials. This knowledge is thought to be very important and useful for developing a dicing technique for thin silicon wafers using a femtosecond laser.

Three-dimensional emission characteristics of a plasma display panel cell

The spatio-temporal variation of infrared (IR) emission images were obtained from a real three dimensional (3-D) discharge space of a surface discharge type, alternating current plasma display panel (ac PDP) cell with the Ne-Xe (4%) 400 torr gas mixture. IR emissions were observed in each period of Address and Display Separation (ADS) driving scheme with ramp initializing waveform using an image intensified charge coupled device (ICCD) camera and the roles of each electrodes were identified.

Analysis of microdischarge characteristics induced by synchronized auxiliary address pulse based on cross-sectional infrared observation in AC plasma display panel

The microdischarge characteristics induced by an auxiliary address pulse with the synchronized application of sustain pulses are investigated based on cross-sectional infrared (IR) (823 nm) observations taken using an image-intensified charge-coupled device (ICCD) camera. The IR observations reveal that the application of an auxiliary short pulse with an optimal amplitude and width to the address electrode enhances the intensity of the IR emission. Furthermore, the cross-sectional IR observations demonstrate that the effective infrared emission region is extended toward the address electrode. In addition, a numerical analysis using a two-dimensional fluid simulation is also applied to investigate the discharge mechanism relative to the amplitude and width of the auxiliary address pulse. As a result, the improvement in the luminance and luminous efficiency was found to be caused by a face discharge between the address and the sustain (or scan) electrodes, where the face discharge plays an important role in supplying priming particles to the surface discharge and lengthening the discharge path, which in turn intensifies the surface discharge.

Tomographic fluorescence imaging in tissue phantoms: a novel reconstruction algorithm and imaging geometry

A novel image reconstruction algorithm has been developed and demonstrated for fluorescence-enhanced frequency-domain photon migration (FDPM) tomography from measurements of area illumination with modulated excitation light and area collection of emitted fluorescence light using a gain modulated image-intensified charge-coupled device (ICCD) camera. The image reconstruction problem was formulated as a nonlinear least-squares-type simple bounds constrained optimization problem based upon the penalty/modified barrier function (PMBF) method and the coupled diffusion equations. The simple bounds constraints are included in the objective function of the PMBF method and the gradient-based truncated Newton method with trust region is used to minimize the function for the large-scale problem (39919 unknowns, 2973 measurements). Three-dimensional (3-D) images of fluorescence absorption coefficients were reconstructed using the algorithm from experimental reflectance measurements under conditions of perfect and imperfect distribution of fluorophore within a single target. To our knowledge, this is the first time that targets have been reconstructed in three-dimensions from reflectance measurements with a clinically relevant phantom.

Two-dimensional imaging of ignition and soot formation processes in a diesel flame

The processes of ignition and formation of soot precursor and soot particles in a diesel spray flame achieved in a rapid compression machine (RCM) were imaged two-dimensionally using the laser sheet techniques. For the two-dimensional imaging of time and of location where ignition first occurs in a diesel spray, planar laser-induced fluorescence (PLIF) of formaldehyde was applied to a diesel spray in an RCM. Formaldehyde has been hypothesized to be one of the stable intermediate species marking the start of oxidation reactions in a transient spray under compression ignition conditions. In this study, the laser-induced fluorescence (LIF) images of the formaldehyde formed in a diesel fuel spray during the ignition process have been obtained by exciting formaldehyde with the third harmonic of a neodymium-doped yttrium aluminium garnet (Nd:YAG) laser. The LIF images of formaldehyde in a spray revealed that the time when the first fluorescence is detected is almost identical with the time when the total heat release due to low-temperature oxidation reactions equals the heat absorption by fuel vaporization in the spray. The formaldehyde level rose steadily until the high-temperature reaction phase of diesel spray ignition. At the start of this ‘hot-ignition’ phase, the formaldehyde concentration fell rapidly, thus signalling the end of the low-temperature ignition phase. Increases in the initial ambient gas temperatures advanced the hot-ignition starting time. The first hot ignition occurred in the periphery of spray head at initial ambient gas temperatures between 580 and 660 K. When the ambient gas temperature was increased to 790 K, the position of the first ignition moved to the central region of the spray head. For the investigation of soot formation processes in a diesel spray flame, simultaneous imaging of the soot precursor and soot particles in a transient spray flame in an RCM was conducted by PLIF and by planar laser-induced incandescence (PLII) techniques. The third harmonic (355 nm) and the fundamental (1064 nm) laser pulses from an Nd:YAG laser, between which a delay of 44 ns was imposed by 13.3 m of optical path difference, were used to excite LIF from the soot precursor and laser-induced incandescence (LII) from soot particles in the spray flame. The LIF and the LII were separately imaged by two image-intensified charge-coupled device cameras with identical detection wavelengths of 400 nm and bandwidths of 80 nm. The LIF from the soot precursor was mainly located in the central region of the spray flame between 40 and 55 mm (between 270 and 370 times the nozzle orifice diameter d°) from the nozzle orifice. The LII from soot particles was observed to surround the soot precursor LIF region and to extend downstream. The first appearance of the LIF from the soot precursor in the spray flame preceded the appearance of the LII from soot particles. The intensity of the LIF from the soot precursor reached its maximum immediately after rich premixed combustion. In contrast, the intensity of the LII from soot particles increased gradually and reached its maximum after the end of injection. Measured LIF spectra, of the soot precursor in the spray flame, were very broad with the peak between 430 and 460 nm.

Surface Heat Transfer Measurements Inside a Supersonic Combustor by Laser-Induced Fluorescence

A study has been conducted to measure surface temperatures inside a model rectangular supersonic combustor by the use of a nonintrusive thermal imaging system, based on the fluorescence properties of a dysprosium doped yttrium-aluminum-garnet (Dy 3+ :YAG) thermographic phosphor. In this system, the phosphor coating on the test surface is excited by a pulsed Nd:YAG laser. The resulting fluorescent emission of the temperature-sensitive 456-nm transition and that of the temperature-independent 496-nm transition are acquired by the use of a pair of image-intensified charge-coupled device cameras. The ratio of the acquired emissions is then correlated to temperature. The wind tunnel was a blowdown type that used vitiated air with nominal conditions at the entrance of the test section: M∞ =2.5, P o =5 × 10 5 N/m 2 , T o = 800 K, and Re∞/m = 9.6 x 10 6 . The fuel was hydrogen gas at room temperature, injected parallel to the tunnel through a fuel-injector slit located along the backward surface of a step. The results under hot flow conditions were compared with numerical simulations performed using a two-dimensional Navier-Stokes code with full chemistry. Temperature measurements demonstrate the feasibility of laser-induced fluorescence for surface heat transfer studies in reactive flows involving significant unsteadiness and transient phenomena.

Fluorescence-enhanced optical imaging in large tissue volumes using a gain-modulated ICCD camera

A novel image-intensified charge-coupled device (ICCD) imaging system has been developed to perform 3D fluorescence tomographic imaging in the frequency-domain using near-infrared contrast agents. The imager is unique since it (i) employs a large tissue-mimicking phantom, which is shaped and sized to resemble a female breast and part of the extended chest-wall region, and (ii) enables rapid data acquisition in the frequency-domain by using a gain-modulated ICCD camera. Diffusion model predictions are compared to experimental measurements using two different referencing schemes under two different experimental conditions of perfect and imperfect uptake of fluorescent agent into a target. From these experimental measurements, three-dimensional images of fluorescent absorption were reconstructed using a computationally efficient variant of the approximate extended Kalman filter algorithm. The current work represents the first time that 3D fluorescence-enhanced optical tomographic reconstructions have been achieved from experimental measurements of the time-dependent light propagation on a clinically relevant breast-shaped tissue phantom using a gain-modulated ICCD camera.

Detection of photoabsorption point with capillary imaging gas proportional counter

We have successfully detected the images of photoelectron tracks of 2.7and 5.9-keV X-rays utilizing a capillary imaging gas proportional counter (CIGC). The images of the photoelectron tracks were extracted by systematic analysis based on clustering of the tracks, eliminating the spurious noise cluster due to an image-intensified charge-coupled device camera. The characteristics of the images were investigated in terms of the relationship between the light yield and the area of the cluster. The extent of cluster spreading was approximately 1.3 mm on average for 2.7-keV photoelectrons. The light yield of the clusters for 5.9-keV X-rays was distributed at 74% full-width at half-maximum around a peak that is approximately two times larger than that for 2.7-keV photoelectrons. The area of the clusters for 5.9-keV X-rays was approximately 1.5 times larger than that for 2.7-keV photoelectrons. The results imply that the photoabsorption point is detectable for X-rays above 10 keV.

High-dynamic range SAXS data acquisition with an X-ray image intensifier

Data with a wide dynamic range of intensity can be collected with a pinhole high-brilliance small-angle X-ray scattering (SAXS) camera using an image-intensified charge-coupled device (CCD) detector. The point spread function (PSF) of this detector has a narrow peak with a broad low tail such that a high level of scattered intensity at small angles can cause a significant background in the detector elements at higher angles. A correction scheme for the long tail of the PSF of the detector is needed when this integrating area detector is used for measuring intensity that spans a dynamic range of four to five orders of magnitude. A procedure is described for measuring the PSF contribution by masking a small part of the detector from the scattered radiation with an absorbing material. In order to measure the PSF, it is necessary to use a high-intensity spot, which is readily achieved by using a sample that scatters strongly at small angles. Although this intensity is spread over many pixels, the sharp features in the scattering from the silica sample chosen for this study permit one to obtain simultaneously both the narrow and the broad parts of the PSF. The data are compared with the actual scattering function, which has been measured exactly with a point-geometry Bonse–Hart camera. The advantages of this procedure are discussed.

Physical phenomena in a coplanar macroscopic plasma display cell I. Infrared and visible emission

The space and time variations of the light emission in a macroscopic plasma display panel (PDP) discharge cell have been studied with an image-intensified charge-coupled device. The discharge cell is similar to a real PDP cell with a coplanar electrode configuration. The cell dimensions are on the order of 100 times larger than those of a real PDP cell and the operating pressure is about 100 times smaller. Different xenon–neon gas mixtures have been investigated. Optical filters have been used to measure infrared emission from xenon excited states 823.1 and 828.0 nm, and visible emission from neon at 640.2 nm. The measurements show that the neon visible emission occurs only above the cathode while xenon infrared emission occurs above both cathode and anode. Standing striations can be observed above the anode. The strong xenon emission above anode indicates that this region is more efficient than the cathode region in terms of ultraviolet production. The measurements are in excellent qualitative agreement with similar measurements performed in real PDP cells. However the velocity of plasma spreading above the cathode in the macrocell is significantly larger than in a real PDP cell. The interpretation of this discrepancy is given in a companion paper (part II) [J. Appl. Phys. 91, 1000 (2002)] where the experimental results are compared with results from a fluid model of the plasma.

Flux of very faint Leonid meteors observed with a 3 meter liquid mirror telescope intensified charge‐coupled device system

Abstract— We have used a 3.0 m diameter liquid mirror telescope (LMT) coupled to a microchannel plate image‐intensified charge‐coupled device (CCD) detector to study the 1999 Leonid meteor shower. This is the largest aperture optical instrument ever utilized for meteor detection. While the observing system is sensitive down to stars of +18 astronomical magnitude under optimum conditions, when corrections for meteor motion are applied the majority of the meteors collected fall in the absolute magnitude range from +5 to +10, corresponding to photometric masses from about 10−7 to 10−9 kg. This is largely due to the fact that the field of view of the LMT was only 0.28°, so that only a small portion of the luminous meteor trail was recorded. While the flux of these small (1.4 times 10−9 kg) Leonid meteors is low (on the order of one Leonid meteor per hour per square kilometer perpendicular to the Leonid), we do have clear evidence that the Leonid stream contains particles in the mass range studied here. The data showed a possibly significant peak in Leonid flux (9.3 ± 3.5) for the 1 h period from 11:00 to 12:00 u.t. 1999 November 17 (solar longitude 234.653 to 234.695, epoch 2000.0), although the main trend of these results is a broad low‐level Leonid activity. There is evidence that small meteoroids are more widely distributed in the Leonid stream, as would be expected from cometary ejection stream models. As would be expected from an extrapolation of mass distribution indices for brighter meteors, the vast majority of meteors at this size are sporadic. The LMT is a powerful detector of sporadic meteors, with an average non‐Leonid detection rate of more than 140 meteor events per hour.

Contact temperature and erosion in high-current diffuse vacuum arcs on axial magnetic field contacts

We have investigated the surface heating effects of drawn vacuum arcs for several industrial designs of axial magnetic field (AMF) contacts, using near infrared (IR) photography of the Cu-Cr arcing surfaces with an image-intensified charge-coupled device (CCD) camera and an IR pyrometer. This enables detailed contact temperature mapping immediately after a half-cycle of arc current. The very homogeneous temperature distribution observed at current zero stands in contrast to the visually nonhomogeneous high-current diffuse arc, which was studied in separately reported experiments using high-speed digital photography and arc voltage measurements. The peak temperature at current zero increased relatively linearly with the peak current I/sub P/, and reached well beyond the melting range. We combine the temperature maps with a heating model to determine the thermal sheath thickness after arcing and its dependence on I/sub P/. The results suggest that near the interruption limit of AMF contacts, the interaction of the stable high-current arc with the anode and cathode is dominated by processes induced by flowing liquid metal, which redistributes the heat input from the axially concentrated arc over most of the contact surface. Furthermore, the flow of liquid metal off the cathode and anode faces contributes to the overall contact erosion.