Intensified CCD Camera Research Articles

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.

Laser-induced optical breakdown spectroscopy of polymer materials based on evaluation of molecular emission bands

Laser-induced breakdown spectroscopy (LIBS) for composition analysis of polymer materials results in optical spectra containing atomic and ionic emission lines as well as molecular emission bands. In the present work, the molecular bands are analyzed to obtain spectroscopic information about the plasma state in an effort to quantify the content of different elements in the polymers. Polyethylene (PE) and a rubber material from tire production are investigated employing 157nmF2 laser and 532nm Nd:YAG laser ablation in nitrogen and argon gas background or in air. The optical detection reaches from ultraviolet (UV) over the visible (VIS) to the near infrared (NIR) spectral range. In the UV/VIS range, intense molecular emissions, C2 Swan and CN violet bands, are measured with an Echelle spectrometer equipped with an intensified CCD camera. The measured molecular emission spectra can be fitted by vibrational-rotational transitions by open access programs and data sets with good agreement between measured and fitted spectra. The fits allow determining vibrational-rotational temperatures. A comparison to electronic temperatures Te derived earlier from atomic carbon vacuum-UV (VUV) emission lines show differences, which can be related to different locations of the atomic and molecular species in the expanding plasma plume. In the NIR spectral region, we also observe the CN red bands with a conventional CDD Czerny Turner spectrometer. The emission of the three strong atomic sulfur lines between 920 and 925nm is overlapped by these bands. Fitting of the CN red bands allows a separation of both spectral contributions. This makes a quantitative evaluation of sulfur contents in the start material in the order of 1wt% feasible.

Seeded and unseeded helical modes in magnetized, non-imploding cylindrical liner-plasmas

In this research, we generated helical instability modes using unseeded and kink-seeded, non-imploding liner-plasmas at the 1 MA Linear Transformer Driver facility at the University of Michigan in order to determine the effects of externally applied, axial magnetic fields. In order to minimize the coupling of sausage and helical modes to the magneto Rayleigh-Taylor instability, the 400 nm-thick aluminum liners were placed directly around straight-cylindrical (unseeded) or threaded-cylindrical (kink-seeded) support structures to prevent implosion. The evolution of the instabilities was imaged using a combination of laser shadowgraphy and visible self-emission, collected by a 12-frame fast intensified CCD camera. With no axial magnetic field, the unseeded liners developed an azimuthally correlated m = 0 sausage instability (m is the azimuthal mode number). Applying a small external axial magnetic field of 1.1 T (compared to peak azimuthal field of 30 T) generated a smaller amplitude, helically oriented instability structure that is interpreted as an m = +2 helical mode. The kink-seeded liners showed highly developed helical structures growing at the seeded wavelength of λ = 1.27 mm. It was found that the direction of the axial magnetic field played an important role in determining the overall stabilization effects; modes with helices spiraling in the opposite direction of the global magnetic field showed the strongest stabilization. Finally, the Weis-Zhang analytic theory [Weis et al., Phys. Plasmas 22, 032706 (2015)] is used to calculate sausage and helical growth rates for experimental parameters in order to study the effects of axial magnetic fields.

Highly Sensitive Detection of Catalase Modified Magnetic Nanoparticle Using Signal-Off ECL Imaging of Multichamber Electrode

Introduction Electrochemiluminescence (ECL) is the chemical luminescence reaction catalyzed by electrochemically active species. In the case of luminol-based ECL, the oxidation of luminol at the electrode and the reactive oxygen species (ROS) as coreactant result in excited intermediate and the release of photon upon relaxation. ECL is used in immunoassay and nucleic acid studies for its advantages such as low background and requiring no external light source. Many of these studies use H2O2 as target or coreactant since many biologically relevant events involve H2O2 and the results are often analyzed by the increase in ECL intensity. Particularly, many enzyme-based ECL that targets H2O2 are reported to date. In this study, catalase enzyme was used to take advantage of its fast turnover rate. However, use of enzymes are sometimes troublesome due to spontaneous reaction upon mixture containing enzyme and its substrate. We addressed this issue by generating substrate for enzyme that utilizes oxygen derivatives at electrode surface by oxygen reduction reaction (ORR). Also, magnetic nanoparticles are used for collection of target species to electrode proximity to elicit concentration effect. Therefore, combination of ORR-ECL and magnetic nanoparticles provide powerful tool for highly sensitive detection system. In this study, we report signal-off ECL using enzyme modified magnetic beads and electro-generated substrate reaction on a small volume multi-chamber screen printed electrode. Materials and Method Catalase enzyme was coupled to NHS modified magnetic nanoparticle (φ200 nm, Tamagawa Seiki) and the absorption spectra and enzyme activity of catalase modified magnetic nanoparticle (CAT-MB) were evaluated using spectroscopic method. For ECL measurement, screen printed electrode with 73 chambers (diameter 200 μm x height 10 μm) was used to limit the reaction volume to about 300 pL. Chambers were filled with solution containing CAT-MB and luminol and magnetic nanoparticles were attracted to the electrode surface using external magnet. Cover glass was placed on top of the electrode chip to cover the chambers to prevent diffusion of enclosed species. The substrate for catalase was electro-generated at the electrode surface. Constant negative potential was applied during the pretreatment time thereby generating ROS. ECL of chambers were recorded with image intensifier and electron magnifying CCD camera mounted on upright microscope. The enclosed catalase enzymes catalyzed H2O2 thus diminish of ECL intensity was observed with increasing magnetic particle concentrations. Electro-generation of ROS species on electrode surface was evaluated with various conditions including electrode pretreatment potential and pretreatment time to control the amount of ROS formed. Results and Discussion Spectroscopic characterization revealed absorbance peak shift from 280 nm to 220 nm from free catalase in aqueous phase to CAT-MB, respectively. Enzyme activity of CAT-MB was found to be lowered by factor of 10 compared to calculated value and the detection limit of CAT-MB was 0.2 μg/mL. The reduced enzyme activity was attributed to the structural modification of catalase molecule during the modification process. ROS electro-generation conditions were investigated by changing the pretreatment potential and time. Starting potential of CV sweep was changed from -1000 to 0 mV with 100 mV interval and the observed ECL intensity showed exponential reduction as the starting potential moved to more positive. Pretreatment time of 20 to 60 seconds were tested at various pretreatment potential and the ECL imaging at -500 mV showed clear difference in brightness at different pretreatment time conditions. The effect of bare magnetic nanoparticles and the use of external magnet on ECL response was also tested. Quantitative ECL imaging analysis using different concentrations of CAT-MB showed that this system can detect 1 ng/mL of magnetic nanoparticle on a multi-chamber chip, and each chamber was estimated to contain average of 5 magnetic nanoparticles. Conclusion In summary, this study successfully developed highly sensitive enzyme modified magnetic particle detection system using the combination of small volume multi-chamber electrode and magnet nanoparticles. Detection was conducted by observing the reduction of ECL signal caused by decomposition of H2O2 electro-generated at the electrode surface by catalase modified on the magnetic nanoparticles enclosed in small chambers. Difference in ECL signal with few nanoparticles as low as average of 5 magnetic nanoparticles in a chamber was detected.

Narrow band flame emission from dieseline and diesel spray combustion in a constant volume combustion chamber

In this paper, spray combustion of diesel (No. 2) and diesel-gasoline blend (dieseline: 80% diesel and 20% gasoline by volume) were investigated in an optically accessible constant volume combustion chamber. Effects of ambient conditions on flame emissions were studied. Ambient oxygen concentration was varied from 12% to 21% and three ambient temperatures were selected: 800K, 1000K and 1200K. An intensified CCD camera coupled with bandpass filters was employed to capture the quasi-steady state flame emissions at 430nm and 470nm bands. Under non-sooting conditions, the narrow-band flame emissions at 430nm and 470nm can be used as indicators of CH∗ (methylidyne) and HCHO∗ (formaldehyde), respectively. The lift-off length was measured by imaging the OH∗ chemiluminescence at 310nm. Flame emission structure and intensity distribution were compared between dieseline and diesel at wavelength bands. Flame emission images show that both narrow band emissions become shorter, thinner and stronger with higher oxygen concentration and higher ambient temperature for both fuels. Areas of weak intensity are observed at the flame periphery and the upstream for both fuels under all ambient conditions. Average flame emission intensity and area were calculated for 430nm and 470nm narrow-band emissions. At a lower ambient temperature the average intensity increases with increasing ambient oxygen concentration. However, at the 1200K ambient temperature condition, the average intensity is not increasing monotonically for both fuels. For most of the conditions, diesel has a stronger average flame emission intensity than dieseline for the 430nm band, and similar phenomena can be observed for the 470nm band with 800K and 1200K ambient temperatures. However, for the 1000K ambient temperature cases, dieseline has stronger average flame emission intensities than diesel for all oxygen concentrations at 470nm band. Flame emissions for the two bands have a smaller average emission area under higher ambient oxygen concentration and temperature for both fuels, while dieseline has a slightly larger average flame emission area than diesel for most cases. The experimental findings were further analyzed and discussed based on an empirical model of the distributions of air and fuel. Both experiment results and theoretical model show that dieseline has wider 430 nm and 470 nm band emissions than diesel under all conditions.

Self-quenching in toluene LIF

Toluene is frequently used as laser-induced fluorescence (LIF) tracer for visualizing mixing processes, for example, in internal combustion engines. The signal evaluation relies on a linear dependence of the LIF signal on tracer concentration – which is not present in many practically relevant cases. This paper presents an investigation of the dependence of the LIF signal intensities on the toluene concentration, revealing a non-linear signal response already at concentrations approximately ten times below those given by the room-temperature vapor pressure. Toluene was vaporized in a mass-flow controlled evaporator and investigated in a free jet. Nitrogen was used as bath gas with a variable addition of oxygen. After excitation at 266nm, an intensified CCD camera recorded the spectrally filtered fluorescence. In separate experiments, the effective fluorescence lifetime upon picosecond UV-laser excitation was determined. The results indicate that the fluorescence lifetime decreases with increasing tracer concentration due to self-quenching. Results from imaging and fluorescence lifetime measurements are consistent. The investigation reveals that the self-quenching of toluene is dominated by collisions with excited-state toluene molecules, which causes an additional dependence of the magnitude of self-quenching on the laser fluence.

Preliminary energy-filtering neutron imaging with time-of-flight method on PKUNIFTY: A compact accelerator based neutron imaging facility at Peking University

Peking University Neutron Imaging Facility (PKUNIFTY) works on an accelerator–based neutron source with a repetition period of 10ms and pulse duration of 0.4ms, which has a rather low Cd ratio. To improve the effective Cd ratio and thus improve the detection capability of the facility, energy-filtering neutron imaging was realized with the intensified CCD camera and time-of-flight (TOF) method. Time structure of the pulsed neutron source was firstly simulated with Geant4, and the simulation result was evaluated with experiment. Both simulation and experiment results indicated that fast neutrons and epithermal neutrons were concentrated in the first 0.8ms of each pulse period; meanwhile in the period of 0.8–2.0ms only thermal neutrons existed. Based on this result, neutron images with and without energy filtering were acquired respectively, and it showed that detection capability of PKUNIFTY was improved with setting the exposure interval as 0.8–2.0ms, especially for materials with strong moderating capability.

A time-resolved imaging and electrical study on a high current atmospheric pressure spark discharge

We present a time-resolved imaging and electrical study of an atmospheric pressure spark discharge. The conditions of the present study are those used for nanoparticle generation in spark discharge generator setups. The oscillatory bipolar spark discharge was generated between two identical Cu electrodes in different configurations (cylindrical flat-end or tipped-end geometries, electrode gap from 0.5 to 4 mm), in a controlled co-axial N2 flow, and was supplied by a high voltage capacitor. Imaging data with nanosecond time resolution were collected using an intensified CCD camera. This data were used to study the time evolution of plasma morphology, total light emission intensity, and the rate of plasma expansion. High voltage and high current probes were employed to collect electrical data about the discharge. The electrical data recorded allowed, among others, the calculation of the equivalent resistance and inductance of the circuit, estimations for the energy dissipated in the spark gap. By combining imaging and electrical data, observations could be made about the correlation of the evolution of total emitted light and the dissipated power. It was also observed that the distribution of light emission of the plasma in the spark gap is uneven, as it exhibits a “hot spot” with an oscillating position in the axial direction, in correlation with the high voltage waveform. The initial expansion rate of the cylindrical plasma front was found to be supersonic; thus, the discharge releases a strong shockwave. Finally, the results on equivalent resistance and channel expansion are comparable to those of unipolar arcs. This shows the spark discharge has a similar behavior to the arc regime during the conductive phase and until the current oscillations stop.

Monte Carlo simulation of a very high resolution thermal neutron detector composed of glass scintillator microfibers

In order to develop a high spatial resolution (micron level) thermal neutron detector, a detector assembly composed of cerium doped lithium glass microfibers, each with a diameter of 1μm, is proposed, where the neutron absorption location is reconstructed from the observed charged particle products that result from neutron absorption. To suppress the cross talk of the scintillation light, each scintillating fiber is surrounded by air-filled glass capillaries with the same diameter as the fiber. This pattern is repeated to form a bulk microfiber detector. On one end, the surface of the detector is painted with a thin optical reflector to increase the light collection efficiency at the other end. Then the scintillation light emitted by any neutron interaction is transmitted to one end, magnified, and recorded by an intensified CCD camera. A simulation based on the Geant4 toolkit was developed to model this detector. All the relevant physics processes including neutron interaction, scintillation, and optical boundary behaviors are simulated. This simulation was first validated through measurements of neutron response from lithium glass cylinders. With good expected light collection, an algorithm based upon the features inherent to alpha and triton particle tracks is proposed to reconstruct the neutron reaction position in the glass fiber array. Given a 1μm fiber diameter and 0.1mm detector thickness, the neutron spatial resolution is expected to reach σ∼1μm with a Gaussian fit in each lateral dimension. The detection efficiency was estimated to be 3.7% for a glass fiber assembly with thickness of 0.1mm. When the detector thickness increases from 0.1mm to 1mm, the position resolution is not expected to vary much, while the detection efficiency is expected to increase by about a factor of ten.

Laser-induced breakdown spectroscopy on metallic samples at very low temperature in different ambient gas pressures

Analysis of metals at very low temperature adopting laser-induced breakdown spectroscopy (LIBS) is greatly beneficial in space exploration expeditions and in some important industrial applications. In the present work, the effect of very low sample temperature on the spectral emission intensity of laser-induced plasma under both atmospheric pressure and vacuum has been studied for different bronze alloy samples. The sample was cooled down to liquid nitrogen (LN) temperature 77K in a special vacuum chamber. Laser-induced plasma has been produced onto the sample surface using the fundamental wavelength of Nd:YAG laser. The optical emission from the plasma is collected by an optical fiber and analyzed by an echelle spectrometer combined with an intensified CCD camera. The integrated intensities of certain spectral emission lines of Cu, Pb, Sn, and Zn have been estimated from the obtained LIBS spectra and compared with that measured at room temperature. The laser-induced plasma parameters (electron number density Ne and electron temperature Te) were investigated at room and liquid nitrogen temperatures for both atmospheric pressure and vacuum ambient conditions. The results suggest that reducing the sample temperature leads to decrease in the emission line intensities under both environments. Plasma parameters were found to decrease at atmospheric pressure but increased under vacuum conditions.

Coherent optical transients observed in rubidium atomic line filtered Doppler velocimetry experiments

We report the first successful results from our novel Rubidium Atomic Line Filtered (RALF) Doppler velocimetry apparatus, along with unanticipated oscillatory signals due to coherent optical transients generated within pure Rb vapor cells. RALF is a high-velocity and high-acceleration extension of the well-known Doppler Global Velocimetry (DGV) technique for constructing multi-dimensional flow velocity vector maps in aerodynamics experiments [H. Komine, U.S. Patent No. 4,919,536 (24 April 1990)]. RALF exploits the frequency dependence of pressure-broadened Rb atom optical absorptions in a heated Rb/N2 gas cell to encode the Doppler shift of reflected near-resonant (λ0 ≈ 780.24 nm) laser light onto the intensity transmitted by the cell. The present RALF apparatus combines fiber optic and free-space components and was built to determine suitable operating conditions and performance parameters for the Rb/N2 gas cells. It yields single-spot velocities of thin laser-driven-flyer test surfaces and incorporates a simultaneous Photonic Doppler Velocimetry (PDV) channel [Strand et al., Rev. Sci. Instrum. 77, 083108 (2006)] for validation of the RALF results, which we demonstrate here over the v = 0 to 1 km/s range. Both RALF and DGV presume the vapor cells to be simple Beer's Law optical absorbers, so we were quite surprised to observe oscillatory signals in experiments employing low pressure pure Rb vapor cells. We interpret these oscillations as interference between the Doppler shifted reflected light and the Free Induction Decay (FID) coherent optical transient produced within the pure Rb cells at the original laser frequency; this is confirmed by direct comparison of the PDV and FID signals. We attribute the different behaviors of the Rb/N2 vs. Rb gas cells to efficient dephasing of the atomic/optical coherences by Rb-N2 collisions. The minimum necessary N2 buffer gas density ≈0.3 amagat translates into a smallest useful velocity range of 0 to 2 km/s, which can readily be extended to cover the 0 to 10 km/s range, and beyond. The recognition that coherent optical transients can be produced within low pressure vapor cells during velocimetry experiments may offer new insights into some quantitative discrepancies reported in earlier DGV studies. Future plans include “line-RALF” experiments with streak camera detection, and two-dimensional surface velocity mapping using pulsed laser illumination and/or gated intensified CCD camera detection.

Real-time imaging of spin-to-orbital angular momentum hybrid remote state preparation

Quantum teleportation is a process in which an unknown quantum state is transferred between two spatially separated subspaces of a bipartite quantum system which share an entangled state and communicate classically. In the case of photonic states, this process is probabilistic due to the impossibility of performing a two-particle complete Bell state analysis with linear optics. In order to achieve a deterministic teleportation scheme, harnessing other degrees of freedom of a single particle, rather than a third particle, has been proposed. Indeed, this leads to a novel type of deterministic teleportation scheme, the so-called hybrid teleportation. Here we report the first realization of photonic hybrid quantum teleportation from spin-to-orbital angular momentum degrees of freedom. In our scheme, the polarization state of photon A is transferred to orbital angular momentum of photon B. The teleported states are visualized in real-time by means of an intensified CCD camera. The quality of teleported states is verified by performing quantum state tomography, which confirms an average fidelity higher than 99.4%. We believe this experiment paves the route towards a novel way of quantum communication in which encryption and decryption are carried out in naturally different Hilbert spaces, and therefore may provide means of enhancing security.

Raman Spectroscopic Techniques for Planetary Exploration: Detecting Microorganisms through Minerals

Raman spectroscopy can provide highly specific chemical fingerprints of inorganic and organic materials and is therefore expected to play a significant role in interplanetary missions, especially for the search for life elsewhere in our solar system. A major challenge will be the unambiguous detection of low levels of biomarkers on a mineral background. In addition, these biomarkers may not be present at the surface but rather inside or underneath minerals. Strong scattering may prevent focusing deeper into the sample. In this paper, we report the detection of carotenoid-containing microorganisms behind mineral layers using time-resolved Raman spectroscopy (TRRS). Two extremophiles, the bacterium Deinococcus radiodurans and the cyanobacterium Chroococcidiopsis, were detected through translucent and transparent minerals using 440 nm excitation under resonance conditions to selectively enhance the detection of carotenoids. Using 3 ps laser pulses and a 250 ps gated intensified CCD camera provided depth selectivity for the subsurface microorganisms over the mineral surface layer and in addition lowered the contribution of the fluorescent background. Raman spectra of both organisms could be detected through 5 mm of translucent calcite or 20 mm of transparent halite. Multilayered mineral samples were used to further test the applied method. A separate tunable laser setup for resonance Raman and a commercial confocal Raman microscope, both with continuous (non-gated) detection, were used for comparison. This study demonstrates the capabilities of TRRS for the depth-selective analysis through scattering samples, which could be used in future planetary exploration to detect microorganisms or biomarkers within or behind minerals.

Evaluating the Performance of Time-Gated Live-Cell Microscopy with Lanthanide Probes

Probes and biosensors that incorporate luminescent Tb(III) or Eu(III) complexes are promising for cellular imaging because time-gated microscopes can detect their long-lifetime (approximately milliseconds) emission without interference from short-lifetime (approximately nanoseconds) fluorescence background. Moreover, the discrete, narrow emission bands of Tb(III) complexes make them uniquely suited for multiplexed imaging applications because they can serve as Förster resonance energy transfer (FRET) donors to two or more differently colored acceptors. However, lanthanide complexes have low photon emission rates that can limit the image signal/noise ratio, which has a square-root dependence on photon counts. This work describes the performance of a wide-field, time-gated microscope with respect to its ability to image Tb(III) luminescence and Tb(III)-mediated FRET in cultured mammalian cells. The system employed a UV-emitting LED for low-power, pulsed excitation and an intensified CCD camera for gated detection. Exposure times of ∼1 s were needed to collect 5–25 photons per pixel from cells that contained micromolar concentrations of a Tb(III) complex. The observed photon counts matched those predicted by a theoretical model that incorporated the photophysical properties of the Tb(III) probe and the instrument’s light-collection characteristics. Despite low photon counts, images of Tb(III)/green fluorescent protein FRET with a signal/noise ratio ≥ 7 were acquired, and a 90% change in the ratiometric FRET signal was measured. This study shows that the sensitivity and precision of lanthanide-based cellular microscopy can approach that of conventional FRET microscopy with fluorescent proteins. The results should encourage further development of lanthanide biosensors that can measure analyte concentration, enzyme activation, and protein-protein interactions in live cells.

Ablation plume structure and dynamics in ambient gas observed by laser-induced fluorescence imaging spectroscopy

The dynamic behavior of an ablation plume in ambient gas has been investigated by laser-induced fluorescence imaging spectroscopy. The second harmonic beam from an Nd:YAG laser (0.5–6J/cm2) was focused on a sintered oxide pellet or a metal chip of gadolinium. The produced plume was subsequently intersected with a sheet-shaped UV beam from a dye laser so that time-resolved fluorescence images were acquired with an intensified CCD camera at various delay times. The obtained cross-sectional images of the plume indicate that the ablated ground state atoms and ions of gadolinium accumulate in a hemispherical contact layer between the plume and the ambient gas, and a cavity containing a smaller density of ablated species is formed near the center of the plume. At earlier expansion stage, another luminous component also expands in the cavity so that it coalesces into the hemispherical layer. The splitting and coalescence for atomic plume occur later than those for ionic plume. Furthermore, the hemispherical layer of neutral atoms appears later than that of ions; however, the locations of the layers are nearly identical. This coincidence of the appearance locations of the layers strongly suggests that the neutral atoms in the hemispherical layer are produced as a consequence of three-body recombination of ions through collisions with gas atoms. The obtained knowledge regarding plume expansion dynamics and detailed plume structure is useful for optimizing the experimental conditions for ablation-based spectroscopic analysis.

Gated Luminescence Imaging of Silicon Nanoparticles.

The luminescence lifetime of nanocrystalline silicon is typically on the order of microseconds, significantly longer than the nanosecond lifetimes exhibited by fluorescent molecules naturally present in cells and tissues. Time-gated imaging, where the image is acquired at a time after termination of an excitation pulse, allows discrimination of a silicon nanoparticle probe from these endogenous signals. Because of the microsecond time scale for silicon emission, time-gated imaging is relatively simple to implement for this biocompatible and nontoxic probe. Here a time-gated system with ∼10 ns resolution is described, using an intensified CCD camera and pulsed LED or laser excitation sources. The method is demonstrated by tracking the fate of mesoporous silicon nanoparticles containing the tumor-targeting peptide iRGD, administered by retro-orbital injection into live mice. Imaging of such systemically administered nanoparticles in vivo is particularly challenging because of the low concentration of probe in the targeted tissues and relatively high background signals from tissue autofluorescence. Contrast improvements of >100-fold (relative to steady-state imaging) is demonstrated in the targeted tissues.

Impact of plasma dynamics on equivalence ratio measurements by laser-induced breakdown spectroscopy

The systematic errors introduced by triggering a USB spectrometer for laser-induced breakdown spectroscopy equivalence ratio measurements are studied. We analyze the temporal behavior of laser-induced plasma in a nonreacting methane/air mixture and investigate the influence of the dynamics on equivalence ratio measurements with gated and ungated detection. For use of gated detectors, optimal delay times were found to be between 500 and 2000 ns to allow effective suppression of interferences while maintaining sufficient signal-to-noise levels. Good precision was found for short and long exposure time intervals when an intensified CCD camera was employed. On the other hand, the jitter of an externally triggered ungated spectrometer leads to high uncertainties. Running the ungated spectrometer freely, the single-shot uncertainty can be reduced by more than 1 order of magnitude.

Time-resolved spectra of solar simulators employing metal halide and xenon arc lamps

The time-resolved spectra of the irradiation emitted from solar simulators employing the two types of high-intensity discharge arc lamps that are commonly used in solar simulators, i.e. metal halide (here 6kW) and xenon arc (here 5kW) lamps, are reported. The lamp emission was recorded by a fast-response photodiode, which reveals that the amplitude of oscillating irradiation intensity from the metal halide lamp is approximately 60% of the peak intensity, while its oscillation frequency is twice of the frequency of the AC power supply, here 100Hz. The irradiation of the xenon arc lamp is powered by a modulated DC supply to oscillate at 300Hz, with an amplitude that is found to be only approximately 9% that of the peak intensity. An intensified CCD camera, which was coupled with a spectrometer operating in a range of 350–900nm, was synchronized with the lamp to provide phase-resolved spectra. The irradiation from the xenon arc lamp was found to be spectrally stable with time; while that from the metal halide lamp varies significantly throughout oscillation cycle, especially at the shorter-wavelengths of below 550nm. All spectra were calibrated to reveal that the time-averaged spectrum of the simulator with a metal halide lamp matches the solar spectrum significantly better than does that from a xenon arc lamp. The reflecting surface of polished ellipsoidal reflector was found to reduce the intensity of selected frequency bands by up to 10%, while that from both the polished ellipsoidal reflector and conical concentrator was found to reduce the intensity in selected frequency bands by up to 20%.

The importance of corona generation and leader formation during laser filament guided discharges in air

Images taken with an intensified CCD camera show the dynamics during filament guided discharge events. The images reveal that filament initiated corona plays a role in the presented results. Furthermore, the images show the formation of leaders, propagating and eventually bridging the gap between the high voltage (HV) electrodes. Analysis of the images and comparison to oscilloscope traces of voltage and current dynamics reveal the origin of the delay between the filament and HV discharge and allows for a probability of discharge analysis.

INFLUENCE OF SUBSTRATE THICKNESS ON DIFFUSE COPLANAR SURFACE BARRIER DISCHARGE PROPERTIES

In presented work the influence of dielectric barrier thickness on the parameters of Diffuse Coplanar Surface Barrier Discharge was investigated. The discharge was operated at atmospheric pressure laboratory air. The electrical parameters of the system were studied both experimentally and using numerical simulations. The discharge pattern was studied as well using intensified CCD camera.