Intensified CCD Camera Research Articles

Dual-pass upgrade to the Thomson scattering diagnostic on the Prototype-Material Plasma Exposure eXperiment (Proto-MPEX).

The Thomson scattering (TS) diagnostic on the Prototype-Material Plasma Exposure eXperiment has been upgraded to measure electron temperature (T e ) and density (n e ) simultaneously at two axial locations. After the first pass through the vacuum vessel, the exiting laser beamline is re-collimated in the atmosphere and rerouted into the vacuum vessel for the second pass. The upgrade will help diagnose axial T e and n e gradients between the "central chamber" and the target region which are located 1 m and 2.5 m, respectively, downstream from the Helicon radio-frequency source. The TS measurements have given T e ≈ 4-15 eV and n e ≈ 2-4 × 1019 m-3 at the central chamber and T e ≈ 1-2 eV and n e ≈ 1-2 × 1019 m-3 at the target region. The upgrade also increases the number of sampling points at the target region from 3 fibers to 5 fibers, measuring 3 cm radially across the plasma column, and 25 fibers in the central chamber, radially spanning 8 cm. The intensified CCD camera is double triggered for each laser pulse in order to measure (1) the TS and laser stray light and (2) the plasma background light that contains nuisance emission lines and bremsstrahlung. Subtracting the background light from the TS photons improves the temperature and density measurements. Details of the diagnostic setup, axial and radial measurements, and areas for further optimization are discussed.

Pulse Shortening in Recirculating Planar Magnetrons

Recirculating planarmagnetron (RPM) experiments at the University of Michigan have utilized a 12-frame ultrafast intensified CCD camera to analyze the effect of plasma formation on microwave pulse duration. The RPM was driven by a −300-kV voltage pulse for 0.3–1.0 $\mu $ s, with a 0.08–0.27-T axial magnetic field. The RPM has previously demonstrated peakmicrowave powers of over 150 MW, with typical microwave pulse durations of 50–150 ns, far shorter than the available voltage pulse. To investigate possible causes of pulse shortening, the RPM was imaged with both S-band (2 GHz) and L-band (1 GHz) anodes, as well as two different cathodes with substantially different anode–cathode (AK) gap widths and end caps. It was found that a smaller AK gap produced brighter plasma and allowed for improvements in temporal resolution of the imaging configuration at the expense of larger end-loss current. Many shotsdemonstrated a direct correlationbetween intervane anode plasma formation and a sharp reduction in RF power. Anode vane plasma is formed at the axial ends of the anode, indicating field enhancement effects. Contact resistance plasma was also observed at the back of anode vane cavities. Details of plasma formation are illustrated and methods for remediating these plasmas are proposed.

Enhancing the recovery of a temporal sequence of images using joint deconvolution

In this work, we address the reconstruction of spatial patterns that are encoded in light fields associated with a series of light pulses emitted by a laser source and imaged using photon-counting cameras, with an intrinsic response significantly longer than the pulse delay. Adopting a Bayesian approach, we propose and demonstrate experimentally a novel joint temporal deconvolution algorithm taking advantage of the fact that single pulses are observed simultaneously by different pixels. Using an intensified CCD camera with a 1000-ps gate, stepped with 10-ps increments, we show the ability to resolve images that are separated by a 10-ps delay, four time better compared to standard deconvolution techniques.

Automatic detection of recoil-proton tracks and background rejection criteria in liquid scintillator-micro-capillary-array fast neutron spectrometer

We describe an analysis procedure for automatic unambiguous detection of fast-neutron-induced recoil proton tracks in a micro-capillary array filled with organic liquid scintillator. The detector is viewed by an intensified CCD camera. This imaging neutron detector possesses the capability to perform high position-resolution (few tens of μm), energy-dispersive transmission-imaging using ns-pulsed beams. However, when operated with CW or DC beams, it also features medium-quality spectroscopic capabilities for incident neutrons in the energy range 2–20 MeV.In addition to the recoil proton events which display a continuous extended track structure, the raw images exhibit complex ion-tracks from nuclear interactions of fast-neutrons in the scintillator, capillaries quartz-matrix and CCD. Moreover, as expected, one also observes a multitude of isolated scintillation spots of varying intensity (henceforth denoted ”blobs”) that originate from several different sources, such as: fragmented proton tracks, gamma-rays, heavy-ion reactions as well as events and noise that occur in the image-intensifier and CCD. In order to identify the continuous-track recoil proton events and distinguish them from all these background events, a rapid, computerized and automatic track-recognition-procedure was developed.Based on an appropriately weighted analysis of track parameters such as: length, width, area and overall light intensity, the method is capable of distinguishing a single continuous-track recoil proton from typically surrounding several thousands of background events that are found in each CCD frame.

Instantaneous imaging of ozone in a gliding arc discharge using photofragmentation laser-induced fluorescence

Ozone vapor, O3, is here visualized in a gliding arc discharge using photofragmentation laser-induced fluorescence. Ozone is imaged by first photodissociating the O3 molecule into an O radical and a vibrationally hot O2 fragment by a pump photon. Thereafter, the vibrationally excited O2 molecule absorbs a second (probe) photon that further transits the O2-molecule to an excited electronic state, and hence, fluorescence from the deexcitation process in the molecule can be detected. Both the photodissociation and excitation processes are achieved within one 248 nm KrF excimer laser pulse that is formed into a laser sheet and the fluorescence is imaged using an intensified CCD camera. The laser-induced signal in the vicinity of the plasma column formed by the gliding arc is confirmed to stem from O3 rather than plasma produced vibrationally hot O2. While both these products can be produced in plasmas a second laser pulse at 266 nm was utilized to separate the pump- from the probe-processes. Such arrangement allowed lifetime studies of vibrationally hot O2, which under these conditions were several orders of magnitude shorter than the lifetime of plasma-produced ozone.

Influence of preheating and burner geometry on modeling the attachment of laminar coflow CH4/air diffusion flames

A laminar coflow CH4/air diffusion flame was experimentally and numerically studied to elucidate the mechanism of flame attachment and the importance of preheating, thermal boundary condition at the fuel tube, and burner geometry to the flame attachment location. OH*-chemiluminescence images were captured using an intensified CCD camera. The temperature of the outer surface of fuel tube at 2 mm below the burner exit was measured using a K-type thermocouple. Detailed simulations based on five different burner wall models were conducted to investigate the influence of preheating effect and burner geometry on flame attachment. The conjugate heat transfer between the heat-conducting burner wall and the surrounding gas flows was considered in the overall flame model to account for the preheating effect without or with less ad hoc assumptions for the burner inlet conditions. The effect of different thermal boundary conditions imposed at the fuel tube on the predicted flame attachment location was investigated. Results show that it is paramount to specify the inlet location at a certain distance upstream the burner exit to model the flame attachment phenomenon. This finding can be explained in terms of the direct heating of the fuel and air streams by the flame base or the mixing process between the fuel and air streams associated with the hydrodynamics and diffusion in the vicinity of the burner rim. The thermal boundary condition at the fuel tube only slightly affects the predicted flame attachment location. The fuel decomposition occurs inside the fuel tube mainly due to preheating by the fuel tube wall and the key chemical pyrolysis process was revealed through a detailed kinetics analysis. The efflux of CH4 to the air side over the burner rim was found responsible for the flame attachment under current conditions. The flame base kernel is established around the stoichiometric mixture and its location is controlled by the thermal condition and geometry of the burner wall. The burner geometry influences the position of flame attachment on the outer surface of the fuel tube through the fuel tube heat capacity and the shape.

Electron density in surface barrier discharge emerging at argon/water interface: quantification for streamers and leaders

Optical emission spectroscopy, fast intensified CCD imaging and electrical measurements were applied to investigate the basic plasma parameters of surface barrier discharge emerging from a conductive water electrode. The discharge was generated at the triple-line interface of atmospheric pressure argon gas and conductive water solution at the fused silica dielectrics using a sinusoidal high-voltage waveform. The spectroscopic methods of atomic line broadening and molecular spectroscopy were used to determine the electron densities and the gas temperature in the active plasma. These parameters were obtained for both applied voltage polarities and resolved spatially. Two different spectral signatures were identified in the spatially resolved spectra resulting in electron densities differing by two orders of magnitude. It is shown that two discharge mechanisms take a place: the streamer and the leader one, with electron densities of 1014 and 1016 cm−3, respectively. This spectroscopic evidence is supported by the combined diagnostics of electrical current measurements and phase-resolved intensified CCD camera imaging.

Spatiotemporal evolution of the plasma from dual-pulsed laser-induced breakdown in an atmospheric air

The spatiotemporal evolution of dual-pulsed laser-induced breakdown (DPLIB) was experimentally investigated in a quiescent atmospheric air. DPLIB with time intervals between pulses of 30–100 ns and pulse energies of 10–30 mJ were compared to a single laser-induced breakdown of the same total energy. An intensified CCD camera was used to capture direct images from the onset of the breakdown until 300 ns after the breakdown. The spatial and temporal temperature and electron number density were obtained from the N II spectrum at 500 nm. With increasing laser pulse energy, the breakdown perimeter, temperature and electron number density all increase. For DPLIB, the second breakdown occurs on the outside axial edges of the first breakdown increasing the breakdown perimeter. The uneven distribution of energy to the plasma creates an uneven temperature distribution. The electron number density is increased at the edges of the DPLIB for times less than 150 ns after the first breakdown. Depending on the electron number density of the first breakdown and the focal point location of the second breakdown, the second breakdown could occur on either the near side (closest to the focusing lens) or the far side (furthest from the focusing lens) of the focal point in the axial direction of the laser beam.

Towards in-vivo assessment of fluorescence lifetime: imaging using time-gated intensified CCD camera

A novel technique for imaging of a small animal with application of time-gated intensified CCD camera was proposed. The time-resolved method based on emission of picosecond light pulses and detection of the light penetrating in tissues was applied. In this technique, the fluorescence photons, excited in the dye circulating in the tissue, that diffusely penetrate in the optically turbid medium are detected. The data acquired during measurements carried out on a rat was analyzed in order to estimate fluorescence lifetime which depends strongly on the environment in which the dye is distributed. In the lifetime estimation a special emphasis was put on compensation of influence of the instrumental response function of the setup on the measured quantity. The proposed optical system was validated in series of phantom experiments, in which estimates of fluorescence lifetime of inclusions containing indocyanine green (ICG) were obtained. ICG is a dye revealing florescence properties in near-infrared wavelength region. Images of the estimate of fluorescence lifetime of the ICG accumulated in tissues of a rat were successfully acquired around six circular spots of illumination of the diameter of 6mm. Larger lifetime values were observed in lung/heart region of the animal. Aspect of sampling rate of the fluorescence lifetime images optimization was finally discussed.

ICCD camera technology with constant illumination source and possibilities for application in multiwavelength analytical ultracentrifugation.

A new concept for multiwavelength detection in analytical ultracentrifugation is demonstrated, based on the technology of an Andor iStar intensified CCD camera and constant illumination source. The camera is coupled to an Andor Shamrock spectrograph providing a spectrometer system capable of UV/vis acquisitions with wavelengths from 190 to 790 nm. The details of the camera functions are described, and the essential operational modes demonstrated with proof of principle measurements. The Andor spectrometer system is proven to be much more sensitive than previous AUC detectors. In fact, it is so sensitive in high gain modes that signal quality is limited by photon shot-noise. Acquisition strategies are presented for detection systems working with low-light illumination sources, and the necessity of overcoming shot-noise limited signal quality is revealed. Several illumination optical concepts are tested and it is shown that when sufficient illumination is applied the detection system is capable of outperforming commercial and academic detectors previously reported in terms of signal-to-noise. A path forward for overcoming the remaining challenges is provided. The findings in this manuscript will be applicable to any type of high sensitivity detector design.

Machining behavior of additively manufactured and cast-wrought nickel-based superalloy (IN 625)

Additively manufactured (AM) and cast-wrought (CW) nickel-based superalloy (IN 625) with known processing history and quasi-static properties have been investigated for their relative machinability, in terms of tool temperature and wear, as well as machining force and chip morphology. Transparent cutting tools were used to cut tubular specimens of both materials. Visible and near infrared radiation emitted by the chip-tool interface was measured through the transparent tool using an image intensified CCD camera. A calibration procedure was used to convert this into apparent blackbody temperature from which the true temperature was inferred using literature values of emissivity of polished IN 625. Machining forces along the cutting and thrust force directions were measured using a dynamometer. Tool wear and chip morphology were characterized by measurement of tool volume loss and by scanning the chip upper side, using a 3D profilometer. It was found that during machining, AM IN 625 behaves differently from CW IN 625 of similar chemical composition. Significant differences in tool temperature, tool wear, and chip formation mechanisms were observed.

Automatic detection of recoil proton tracks and background rejection in liquid scintillator-micro-capillary-array fast neutron spectrometer

We describe results on automatic detection of fast-neutron induced recoil-proton tracks in micro-capillary bundles filled with organic liquid scintillator, viewed by an intensified CCD camera. This imaging neutron spectrometer was developed for high position-resolution (few tens of μ m) imaging and medium-quality energy spectroscopy of neutrons in the energy range 2–20 MeV. In addition to recoil proton events which display a continuous extended track structure, CCD images include also a multitude of isolated spots of varying intensity (“blobs”) that originate from several different sources, such as fragmented proton tracks, electrons from gamma-rays, short heavy-ion tracks, as well as events and noise that occur in the image intensifier and CCD. In order to identify the extended-track recoil proton events and separate them from these background events, a computerized, rapid and automatic track-recognition procedure was developed. Based on the analysis of track parameters such as: track area, light intensity, track length and width, the method is capable of distinguishing few recoil protons from the surrounding numerous background events typically found in each CCD frame.

Reaction-time-resolved measurements of laser-induced fluorescence in a shock tube with a single laser pulse.

Shock tubes allow for the study of ultra-fast gas-phase reactions on the microsecond time scale. Because the repetition rate of the experiments is low, it is crucial to gain as much information as possible from each individual measurement. While reaction-time-resolved species concentration and temperature measurements with fast absorption methods are established, conventional laser-induced fluorescence (LIF) measurements with pulsed lasers provide data only at a single reaction time. Therefore, fluorescence methods have rarely been used in shock-tube diagnostics. In this paper, a novel experimental concept is presented that allows reaction-time-resolved LIF measurements with one single laser pulse using a test section that is equipped with several optical ports. After the passage of the shock wave, the reactive mixture is excited along the center of the tube with a 266-nm laser beam directed through a window in the end wall of the shock tube. The emitted LIF signal is collected through elongated sidewall windows and focused onto the entrance slit of an imaging spectrometer coupled to an intensified CCD camera. The one-dimensional spatial resolution of the measurement translates into a reaction-time-resolved measurement while the species information can be gained from the spectral axis of the detected two-dimensional image. Anisole pyrolysis was selected as the benchmark reaction to demonstrate the new apparatus.

Electron kinetic energy and plasma emission diagnosis from femtosecond laser produced air plasmas

The characteristics of a plasma formed by a focused ultrashort laser in atmospheric-pressure air are studied with linear and circular pulses. We show that the ionization threshold for circular pulses is 1.36 times higher than for that linear pulses. Using an intensified CCD camera, we study plasma emission over seven orders of magnitude in a dynamic range. In spite of possessing a lower total ion number, plasmas produced by circular pulses are found to be brighter visible-light emitters than those produced by linear pulses of the same energy. This indicates that circular pulses produce plasmas with more electron kinetic energy than linear pulses and that kinetic energy plays a role in the optical emission intensity. The presence of high energy electrons is verified by demonstrating that a high-ionization-potential gas can be made to radiate more brightly by the addition of a low-ionization-potential gas even though the second gas lowers the achievable focal intensity.

Extraction Protocols for Individual Zebrafish's Ventricle Myosin and Skeletal Muscle Actin for In vitro Motility Assays.

The in vitro motility assay (IVMA) is a technique that enables the measurement of the interaction between actin and myosin providing a relatively simple model to understand the mechanical muscle function. For actin-myosin IVMA, myosin is immobilized in a measurement chamber, where it converts chemical energy provided by ATP hydrolysis into mechanical energy. The result is the movement of fluorescently labeled actin filaments that can be recorded microscopically and analyzed quantitatively. Resulting sliding speeds and patterns help to characterize the underlying actin-myosin interaction that can be affected by different factors such as mutations or active compounds. Additionally, modulatory actions of the regulatory proteins tropomyosin and troponin in the presence of calcium on actin-myosin interaction can be studied with the IVMA. Zebrafish is considered a suitable model organism for cardiovascular and skeletal muscle research. In this context, straightforward protocols for the isolation and use of zebrafish muscle proteins in the IVMA would provide a useful tool in molecular studies. Currently, there are no protocols available for the mentioned purpose. Therefore, we developed fast and easy protocols for characterization of zebrafish proteins in the IVMA. Our protocols enable the interested researcher to (i) isolate actin from zebrafish skeletal muscle and (ii) extract functionally intact myosin from cardiac and skeletal muscle of individual adult zebrafish. Zebrafish tail muscle actin is isolated after acetone powder preparation, polymerized, and labeled with Rhodamine-Phalloidin. Myosin from ventricles of adult zebrafish is extracted directly into IVMA flow-cells. The same extraction protocol is applicable for comparably small tissue pieces as from zebrafish tail, mouse and frog muscle. After addition of the fluorescently labeled F-actin from zebrafish—or other origin—and ATP, sliding movement can be visualized using a fluorescence microscope and an intensified CCD camera. Taken together, we introduce a method for functional analysis in zebrafish cardiac and skeletal muscle research to study mutations at the molecular level of thick or thin filament proteins. Additionally, preliminary data indicate the usefulness of the presented method to perform the IVMA with myosin extracted from muscles of other animal models.

Complex interaction of subsequent surface streamers via deposited charge: a high-resolution experimental study

The coplanar barrier discharge in synthetic air at 30 kPa pressure was studied by time-correlated single photon counting enhanced optical emission spectroscopy, far-field microscopy enhanced intensified CCD camera and sensitive current measurements. The discharge operated in a regime where two subsequent microdischarges appeared within the same voltage half-period. The electrical analysis of the barrier discharge setup enabled us to quantify charge transfer and the effective electric field development. During the second microdischarge the positive surface streamers follow the interface (triple-line) between the area of deposited charge from the previous one and the area of uncharged dielectric surface. It is shown that additional branching and flashes of surface streamers are responsible for the increased spatial complexity of the deposited surface charges at high overvoltage. A suppressed streamer propagating over the area of deposited surface charge was tracked and the evidence of surface streamer reconnection is presented. A spatiotemporal distribution (resolution of 120 ps and 100 μm) of the reduced electric field strength was obtained for both microdischarges from the recorded luminosities of the molecular nitrogen. The reduced electric field of positive streamers in the first microdischarge reached 1200 Td. For the second one, the electric field values for the streamer at the triple-line are slightly lower than that, while for the suppressed streamers are even higher.

Plume splitting and oscillatory behavior in transient plasmas generated by high-fluence laser ablation in vacuum

Abstract We present a short overview of studies performed in our research groups over the last decade on the characterization of transient plasma plumes generated by laser ablation in various temporal regimes, from nanosecond to femtosecond. New results are also presented along with this overview, both being placed in the context of similar studies performed by other investigators. Optical (fast gate intensified CCD camera imaging and space- and time-resolved emission spectroscopy) and electrical (mainly Langmuir probe) methods have been applied to experimentally explore the dynamics of the plasma plume and its constituents. Peculiar effects as plume splitting and sharpening or oscillations onset have been evidenced in vacuum at high laser fluence. New theoretical approaches have been developed to account for the experimental observations.

Improvement of lean flame stability of inverse methane/air diffusion flame by using coaxial dielectric plasma discharge actuators

Low environmental impact is a main issue in the design of novel combustion systems, as aircraft engines. In this context, the present work investigates the possibility to increase the combustion efficiency of a lean flame through the use of sinusoidally driven dielectric barrier discharge (DBD) plasma actuator. The effect of the plasma discharge on a lean non premixed methane/air flame in a Bunsen-type burner has been studied for two different configurations: the normal diffusive flame (NDF) and the inverse diffusive flame (IDF). The flame behavior was investigated by chemiluminescence imaging through an intensified CCD camera. Optical filters were installed in front of the camera, aiming to selectively record signal from the chemiluminescent species OH*, CH*, or CO2*. This allowed evaluating the changes occurring in presence of plasma actuation in term of flame emissions. It was shown that the plasma effects are significantly influenced by the burner and DBD configuration. A plasma power of approximately 25 W permitted to increase the air mass flow rate at which lean blowout appears; it rose up to 30% for low methane flow rate and up to 10% at high fuel flow rate.

Effects of H2O and CO2 diluted oxidizer on the structure and shape of laminar coflow syngas diffusion flames

The effects of up to 30% H2O and CO2 replacement of N2 in air on the structure and shape of laminar coflow syngas (COH2) diffusion flames were experimentally and numerically studied. Temperatures along the flame centerline were measured using a type-B thermocouple. The OH*-chemiluminescence and flame luminance were captured respectively by an intensified CCD camera and a CCD camera to determine the flame height and radii. The syngas diffusion flames were numerically modeled using detailed thermal and transport properties and the chemical reaction mechanism of Davis et al. (2005). Four pairs of artificial species were introduced in additional numerical calculations to isolate the chemical, thermal, transport, and radiative effects of H2O and CO2. The experimental and numerical results show that H2O and CO2 replacement of N2 in the oxidizer reduce the peak flame temperature, but they influence the flame centerline temperature distributions differently. The thermal and radiative effects of both H2O and CO2 addition decrease the flame temperatures. The chemical and transport effects of CO2 and H2O affect flame temperatures differently. H2O addition promotes the OH concentration though H+O2=O+OH and O+H2O=2OH, while CO2 addition decreases the OH concentration by suppressing those reactions. The higher concentrations of OH under H2O addition signify higher combustion intensity and hence lead to decreased flame height and radius. In contrast, the addition of CO2 suppresses flame temperature and the overall combustion process, resulting in increased flame height and radius.

Remote Raman measurements of minerals, organics, and inorganics at 430 m range.

Raman spectroscopy is a characterization technique that is able to analyze and detect water or water-bearing minerals, minerals, and organic materials that are of special interest for planetary science. Using a portable pulsed remote Raman system with a commercial 8in. (203.2mm) telescope, a frequency doubled Nd-YAG-pulsed laser, and a spectrometer equipped with an intensified CCD camera, we acquired good quality Raman spectra of various materials from a 430m standoff distance during daylight with detection times of 1-10s, in a realistic context in which both the exciting source and the detector are part of the same measurement system. Remote Raman spectra at this distance provided unambiguous detection of compounds such as water and water ice, dry ice, sulfur, sulfates, various minerals and organics, and atmospheric gases. This research work demonstrates significant improvement in the remote Raman technique as well as its suitability for solar system exploration.