Intensified CCD Camera Research Articles

Experimental photon addition and subtraction in multi-mode and entangled optical fields.

Multiple photon addition and subtraction applied to multi-mode thermal and sub-Poissonian fields as well as twin beams are mutually compared using one experimental setup. Twin beams (TWBs) with tight spatial correlations detected by an intensified CCD camera with high spatial resolution are used to prepare the initial fields. Up to three photons are added or subtracted to arrive at the nonclassical and non-Gaussian states. Only the photon-subtracted thermal states (TSs) remain classical. In general, the experimental photon-added states exhibit greater nonclassicality and non-Gaussianity than the comparable photon-subtracted states. Once photons are added or subtracted in twin beams, both processes result in comparable properties of the obtained states owing to twin-beam photon pairing.

Gallium oxide (Ga2O3) energy dependent scintillation response to fast neutrons and flash gamma-rays.

Gallium oxide is a newly emerged ultrawide bandgap (4.9eV) semiconductor that is suitable as a combined electronics and radiation detection platform. We have experimentally demonstrated fast neutron and gamma-ray scintillation from Czochralski-grown β-Ga2O3 in a recent series (October 2023) of experiments at the unmoderated pulsed neutron spallation source located at the Los Alamos Neutron Science Center. Using the neutron time-of-flight (TOF) technique and a fast-gated intensified CCD camera, we observed energy-dependent neutron scintillation for neutron energies ranging from 1 to 400MeV, including the 14.1MeV neutron energy relevant to D-T fusion. Neutron flux is quantified and calibrated by cascading the scintillator after the fission chamber, enabling a detailed analysis of temporal and energy-dependent characteristics of the scintillation events. A pronounced scintillation signal from the spallation gamma flash with a temporal full width of half maximum of ∼4ns is indicative of the material's rapid response. Neutron energy dependent scintillation is observed using the TOF method at a 22.6-m distance from the neutron source. These results highlight the possibility of developing a Ga2O3 based fusion neutron diagnostic platform integrated with both scintillation and electronics functions on the integrated chip scale.

Time-resolved observation of 150 kHz high-power pulse burst high-frequency discharge using a high-speed video camera and an intensified charge coupled device camera

The discharge phase and time evolution of a 150 kHz high-power pulse burst discharge were observed. A vacuum chamber was constructed by connecting glass tubes on which a solenoid coil was wound. Burst pulses with a width of 1000 μs and a repetition rate of 10 Hz were applied to the solenoid coil. A high-speed video camera and an intensified CCD camera were used to record photographs of the discharges. Observation of the discharge phase using a high-speed camera showed that the discharge occurs at the time of 40 μs and propagates from the wall of the cylindrical reactor. Over time, the discharge pattern evolves, and a branched pattern appears. The number of the branches changes with time. The discharge blinks synchronize with the instantaneous power, which suggests that the discharge is generated and maintained by the electrostatic field generated by the sides of the coil. The propagation velocity calculated from downstream decreases with increasing pressure and increases with increasing power.

Generalized sub-Poissonian states of two-beam fields.

Two-beam states obtained by partial photon-number-resolving detection in one beam of a multi-mode twin beam are experimentally investigated using an intensified CCD camera. In these states, sub-Poissonian photon-number distributions in one beam are accompanied by sub-shot-noise fluctuations in the photon-number difference of both beams. Multi-mode character of the twin beam implying the beam nearly Poissonian statistics is critical for reaching sub-Poissonian photon-number distributions, which contrasts with the use of a two-mode squeezed vacuum state. Relative intensities of both nonclassical effects as they depend on the generation conditions are investigated both theoretically and experimentally using photon-number distributions of these fields. Fano factor, noise-reduction parameter, local and global nonclassicality depths, degree of photon-number coherence, mutual entropy as a non-Gaussianity quantifier, and negative quasi-distributions of integrated intensities are used to characterize these fields. Spatial photon-pair correlations as means for improving the field properties are employed. These states are appealing for quantum metrology and imaging including the virtual-state entangled-photon spectroscopy.

Nitrogen thermometry in an inductively coupled plasma torch using broadband nanosecond coherent anti-Stokes Raman scattering.

The development of atmospheric hypersonic flight and re-entry capabilities requires the characterization of the thermo-chemical state of representative test environments. This study demonstrates the usage of multiplex nanosecond N 2 coherent anti-Stokes Raman scattering (CARS) to measure temperatures in an atmospheric, high-temperature (>6000K), air plasma plume, generated by an inductively coupled plasma torch. These are some of the highest temperatures ever accessed via gas-phase CARS, to our knowledge. Temperatures of N 2 in the equilibrium plasma plume are determined via theoretical fits to measured CARS spectra. We discuss the practical implementation of CARS at very high temperatures, including the scaling of the N 2 CARS signal strength from 300 to 6700K, where the expected peak signal from the high-temperature plasma torch gases is two orders of magnitude less than commonly encountered in combustion environments. An intensified CCD camera enables single-laser-shot detection at temperatures as high as 6200K, by increasing sensitivity and providing a time gate against intense background luminosity. We also discuss the impacts of unwanted two-beam CARS contributions from outside the nominal three-beam measurement volume. We present mean axial and radial temperature profiles, as well as time-series data derived from both single-laser-shot and accumulated CARS spectra. The single-laser-shot precision is 1.7%-2.6% at temperatures of 3500 to 6200K. The presented results pave the way for the use of CARS at very high temperatures and the measurement of spatially resolved interface processes in high-enthalpy flows.

Temperature measurements inside the melting ice bead in a hot shear flow by utilizing molecular tagging thermometry technique

In the present study, we report for the first time the temperature measurements inside the melting ice bead in a hot shear flow by utilizing Molecular Tagging Thermometry (MTT) technique. A parameter study of the airflow temperature and airflow speed was carefully performed. Moreover, the melting process of an ice bead under the natural convection condition was also measured for comparisons. One CCD camera and an intensified CCD camera were used to record the ice bead melting process. The results showed that, based on the phosphorescence images, the temperature distributions within the melting ice bead could be obtained by the MTT technique. For all the cases, the average temperature within the melted water region increased gradually from an initial value of about 1.0 ℃ to a final value of approximately 4.0 ℃. Besides, the ice beads melted at a much faster rate under the forced convection conditions than that of the natural convection condition. Furthermore, when subjected to a hot shear flow, the melting time of ice bead decreased as the increase of the airflow temperature and the airflow speed. In addition, as for the cases of relatively higher airflow speed and higher airflow temperature, the vertical movement coefficient of the windward three-phase junction point was increasing at a much faster rate than that of the leeward three-phase junction point. Besides, we proposed an equation to estimate the total melting time for the ice bead under the influence of the hot shear flow. Good agreements were found between the experimental and theoretical values of the total melting time for the ice beads under different conditions.

Experimental and numerical studies on the interaction between two identical slot jet H2/CO diffusion flames

Hydrogen offers a unique opportunity in achieving a CO2-neutral future, but great challenges exist for the successful transition from conventional fossil fuels to H2, due to the great component variation and safety issues of H2 energy. The multiple-injection combustor concept effectively addresses these problems, with the merits of flexible nozzle distance satisfying the varying H2 content in the fuel and low flash-back risk comparable to diffusion flames. In such combustors, flame interaction plays an essential role in the performance of multiple-injection combustors. This work focused on the flame interaction behavior of two identical slot jet H2/CO diffusion flames. OH* chemiluminescence was captured by an intensified CCD camera and the flame temperature was measured using a type-B thermocouple. The combustion process was modeled using a Fortran flame code by incorporating the detailed thermal and transport properties as well as the chemical kinetic mechanism. With these experimental and numerical efforts, the effects of burner separating distance, fuel composition, and fuel velocity were parametrically studied. Results showed that flame interaction enables a more uniform temperature distribution. Increasing H2 content in the fuel decreases the flame length for the merged flames, but this effect is less distinguished for the merging and separated flames. In addition, flames with a higher H2 content merge more easily because of the enlarged flame radius, featured with a linear relationship between the merging distance and H2 content. When increasing the fuel flow rate, the twin flames contact and merge at farther separating distances, and this influence of fuel flow rate on flame interaction was observed to be fuel-composition-dependent. Increasing the burner separating distance lowers the flame length, which is attributed to the enhancement of CO oxidization rather than the H2 reactions. Moreover, burner separating distance plays a critical role in NO emissions, with a non-monotonical impact due to the combined effect of flame temperature and O2 concentration.

Spatial, spectral, and temporal properties of laser-induced plasma in air near an aqueous solution and comparison with ambient air

Laser-induced breakdown and subsequent plasma are produced in ambient air in the proximity of an aqueous surface using a Nd:YAG Q-switched laser at 1064 nm with a pulse width of 9 ns and a delivered focused input energy of 170 mJ. The distance between the focal point of a 10 cm convex lens and the aqueous surface is 4 mm with laser propagation perpendicular to the surface. Using an intensified CCD camera attached to a 1-m spectrometer, spatial and wavelength-resolved plasma emission data are obtained for delay times after breakdown ranging from 50 ns to 10 μs with a gate window typically 5 ns. Plasma electron density is determined by applying Lorentzian fitting and FWHM extraction to three Stark-broadened spectral lines: N II 3P-3Do multiplet (593.85 nm), Hα (656.27 nm), and the Na D doublet (589.00 and 589.59 nm). One-dimensional spatially resolved measurements of the total emission intensity and electron density are obtained by binning the camera image along the laser axis in intervals of 250 μm and are reported as a function of time from 50 ns to 10 μs. Two plasmas are ignited from a single laser pulse; one from laser breakdown at the water surface and the other a few nanoseconds later from laser-induced air breakdown at the focal point of 4 mm above the water surface. Comparisons between the evolution of the air plasma near and far from the water surface are presented along with data for the water surface plasma itself.

Spatial helicity response metric to quantify particle size and turbidity of heterogeneous media through circular polarization imaging

Backscattered circularly polarized light from turbid media consists of helicity-flipped and helicity-preserved photon sub-populations (i.e., photons of perpendicular and parallel circular handedness). Their intensities and spatial distributions are found to be acutely sensitive to average scatterer size and modestly sensitive to the scattering coefficient (medium turbidity) through an interplay of single and multiple scattering effects. Using a highly sensitive intensified-CCD camera, helicity-based images of backscattered light are captured, which, with the aid of corroborating Monte Carlo simulation images and statistics, enable (1) investigation of subsurface photonic pathways and (2) development of the novel ‘spatial helicity response’ metric to quantify average scatterer size and turbidity of tissue-like samples. An exciting potential application of this work is noninvasive early cancer detection since malignant tissues exhibit alterations in scatterer size (larger nuclei) and turbidity (increased cell density).

Stabilization of Low-NOx Hydrogen Flames on a Dual-Swirl Coaxial Injector

Abstract Hydrogen-fueled carbon-free energy is a growing prospect for the future of several industries, including the aeronautical and energy generation sectors. However, the transition to hydrogen comes with several challenges: flame stabilization due to the unique combustion properties of hydrogen compared to conventional fuels and control of nitrogen oxides (NOx) production due to the higher combustion temperature. In addition, the high flammability of hydrogen poses an increased risk of flashback in premixed configurations commonly used to generate low-NOx flames. As a consequence, research into strategies for low-NOx hydrogen combustion is developing, and several technologies are being considered for industrial use. Among these technologies, we consider here a dual swirl coaxial injector operated in nonpremixed conditions. This setup enables the stabilization of multiple types of flame structures that are parametrically investigated for their NOx emissions. The flame structure is observed using OH* chemiluminescence images collected using an intensified CCD camera equipped with a bandpass filter. Exhaust gas species mole fractions of NO, NO2, and O2 are measured using NDIR gas detectors and a paramagnetic sensor. This investigation reveals that stabilization of hydrogen-air flames on the double swirl injector is possible and that varying the flow parameters induces changes in structure that affect NOx emissions, independently of swirl level, residence time, and temperature that also play a role. The study is carried out at atmospheric pressure.

Simultaneous imaging of NO and NH in an ammonia-hydrogen-nitrogen flame using a single dye laser

This study describes a technique that utilizes a single, tunable, pulsed dye laser and two intensified CCD cameras to image NH and NO simultaneously in turbulent ammonia-hydrogen-nitrogen jet flames. The NO radical is excited at 236.214 nm in its (0,1) band, while NH is excited in its A3Π-X3Σ–(1,0) band using the residual energy of the beam at 303.545 nm, necessary to yield 236.214 nm via mixing with the fundamental of the pump laser at 1064.ßnm. Data show that it is possible to image the instantaneous structure of these turbulent flames, specifically, NH delineates the reaction zone while NO also marks the location of burnt products.

Three distinct phases of electron heating in an rf-driven atmospheric-pressure plasma jet

Cold plasma jets represent one of the most attractive and versatile plasmas, and active studies on plasma properties such as electron density (n e) and temperature (T e) have facilitated the development and implementation of plasma jets. Here we demonstrate the temporal evolution of n e and T e in a radio-frequency (rf)-driven argon plasma jet operating at atmospheric pressure. The plasma jet is driven by 5 MHz sinusoidal rf power modulated by a 50 kHz square pulse with a 75% duty ratio. A 532 nm Nd:YAG laser is applied to the plasma, and laser Thomson scattering measurements are performed using a triple-grating spectrometer coupled to an intensified CCD camera. From this investigation, we find that n e and T e vary during the pulse repetition period of 20 μs in the ranges of (2–12) × 1018 m−3 and 0.3–6.0 eV, respectively. With respect to the 5 MHz period (200 ns), T e varies with the rf oscillating field while n e remains constant. Special attention is given to three distinct electron characteristics depending on the pulse phase in the plasma jet—ionizing (on-pulse), stationary and recombining (off-pulse) states. Our measurements will be valuable for related experimental and numerical plasma research and provide further insights into the effect of rf pulsing on the electron kinetics in atmospheric-pressure plasmas.

A layer-peeling method for signal trapping correction in planar LII measurements of statistically steady flames

This work presents a layer-peeling (LP) algorithm to correct the signal trapping effect in planar laser-induced incandescence (LII) measurements of soot volume fraction. The method is based on measurements of LII signals captured by an intensified CCD camera at a series of parallel planes across a diffusion flame. A method based on presumed function (PF) of soot volume fraction is also proposed for comparison. The presented methods are numerically tested based on synthetic LII signals emitted from a simulated axisymmetric laminar diffusion flame using the CoFlame code. Numerical results showed that the LP method is able to correct the signal trapping effect, even for fairly large optical thicknesses and in a wide range of detection wavelengths. The correction decreases the relative errors induced by neglecting the trapping effect considerably. The signal trapping effect correction is less important for the determination of integrated soot quantities such as radially integrated soot volume fraction or total soot loading. Planar LII measurements were carried out and calibrated in order to test the method experimentally in a coflow flame. The LP, PF and a simplified analytical (SA) model were compared. The results indicate that the differences in soot volume fraction of 1 ppm or about 15% are obtained in zones of maximum soot loading of 6.5 ppm when the trapping effect is accounted for. Also, the LP and SA methods were found computationally efficient and accurate compared to the PF method. Although the study was performed in a canonical laminar axisymmetric flame, the proposed method can be applied to any statistically steady 3D flame.

Remote state preparation of single-photon orbital-angular-momentum lattices

Optical beams with periodic lattice structures have broadened the study of structured waves. In the present work, we generate spin-orbit entangled photon states with a lattice structure and use them in a remote state preparation protocol. We sequentially measure spatially-dependent correlation rates with an electron-multiplying intensified CCD camera and verify the successful remote preparation of spin-orbit states by performing pixel-wise quantum state tomography. Control of these novel structured waves in the quantum regime provides a method for quantum sensing and manipulation of periodic structures.

Spatial characteristics of nanosecond pulsed micro-discharges in atmospheric pressure He/H2O mixture by optical emission spectroscopy

Atmospheric pressure micro-discharges in helium gas with a mixture of 0.5% water vapor between two pin electrodes are generated with nanosecond overvoltage pulses. The temporal and spatial characteristics of the discharges are investigated by means of time-resolved imaging and optical emission spectroscopy with respect to the discharge morphology, gas temperature, electron density, and excited species. The evolution of micro-discharges is captured by intensified CCD camera and electrical properties. The gas temperature is diagnosed by a two-temperature fit to the ro-vibrational OH(A2Σ+–X2Π, 0–0) emission band and is found to remain low at 425 K during the discharge pulses. The profile of electron density performed by the Stark broadening of H α 656.1-nm and He I 667.8-nm lines is uniform across the discharge gap at the initial of discharge and reaches as high as 1023 m−3. The excited species of He, OH, and H show different spatio-temporal behaviors from each other by the measurement of their emission intensities, which are discussed qualitatively in regard of their plasma kinetics.

Imaging of OAM-entangled photon pairs in the Bessel-Gauss basis with full index control

In this paper, we directly image the orbital angular momentum (OAM) correlations, expressed in the Bessel-Gauss (BG) basis, present in quantum-entangled photon pairs produced by the process of spontaneous parametric downconversion (SPDC). We use a spatial light modulator that displays an appropriate phase mask, followed by coupling into a single-mode fiber, so as to project the signal, or heralding, photon onto a BG mode, and verify that the idler, or heralded, photon is projected non-locally as expected. In contrast with similar experiments relying on Laguerre-Gauss (LG) modes, our current experiment permits, firstly, full index control (allowing the experimenter to define both the azimuthal index ℓ s and the continuous radial index k rs , also referred to as scaling parameter). Importantly, while not resolving the radial index leaves the heralded single photon in a statistical mixture of all available radial modes, the ability to determine both indices allows us to herald single photons in a particular BG mode, described by a quantum-mechanically pure state. Our use of BG modes permits, secondly, the spatially-resolved detection of the heralded single photon, both in the near and far fields, with a time-gated intensified CCD camera, making it possible to experimentally determine both the radial and azimuthal indices of the heralded single photon. Thirdly, the fact that for BG modes the radial index (scaling parameter) is continuous makes it possible to use the scaling parameter as a continuous adjustment in quantum state engineering, for precise mode matching, or for the selection of photon-pair properties such as the spiral bandwidth, as we experimentally demonstrate. We believe that our work opens up interesting new possibilities in the field of quantum communications based on the spatial degree of freedom of photon pairs.

A hybrid plasma de-icing actuator by using SiC hydrophobic coating-based quartz glass as barrier dielectric

Aircraft icing poses a major threat to flight safety, and plasma anti-/de-icing becomes a new approach in the field of anti-/de-icing in recent years. In this paper, a surface dielectric barrier discharge (SDBD) plasma actuator with SiC hydrophobic coating-based quartz glass is designed and fabricated. Actuated by nanosecond high voltage pulse, its de-icing characteristics are explored experimentally and compared with the uncoated actuator. The results show that under the same actuation parameters, the discharge current peaks and the power consumption of SDBD are reduced with hydrophobic coating, which can be further verified by surface temperature distribution. Intensified CCD camera images indicate that after the adding of SiC coating, the discharge propagation process of SDBD does not change significantly. For both coated/uncoated actuators, two discharges occur during the voltage rise and fall phases respectively, while no discharge occurs during the pulse width phase, but the coated actuator exhibits slightly longer plasma dissipation time. Static de-icing results reveal that the instantaneous energy utilization rate of the coated actuator at 60 s of de-icing process is about 54% higher than that of the uncoated actuator, which can be explained by two aspects: one is to weaken the adverse effects of melted water on the discharge plasma to a maximum extent, and the other is to reduce the contact area between the ice accretion and the hydrophobic surface.

Laser-induced breakdown in liquid water: Influence of repeated laser pulses on plasma formation and emission

We have experimentally investigated the influence of repeated laser pulses on laser-induced breakdown (LIB) in water following a focused 1064 nm laser pulse, for repetition rates between 0.5 and 20 Hz and up to 100 pulses. LIB plasma image data are collected as a function of repetition rate and laser pulse number, using an intensified CCD camera with sub-nanosecond camera-laser timing. Each pulse induces multiple breakdowns, shockwaves, and macroscopic cavitation bubbles. These effects disappear by the time the next pulse arrives. Even so, we find that the water target retains effects from previous pulses that persist up to roughly a second and that modify subsequent LIB properties including plasma location, spatial extension, and total emission intensity. We quantify the effects by tracking the first moment of the plasma emission intensity, which we call the “center of intensity” (CoI). Three distinct reproducible repetition-rate-dependent phases are identified with repeated pulses. In particular, (1) with initial pulses, emission intensity decreases and the CoI broadens and propagates downstream from the laser focus reaching a maximum axial distance away from the focal point, (2) with additional pulses, the CoI narrows and travels back upstream toward the laser, and (3) with continued pulses, the plasma gains back a portion of the lost intensity and the CoI reaches a steady state position, not at the focal point. Two possible causal effects are highlighted; particle inclusion concentration changes and microbubbles in the laser path.

Temporal-resolved measurement using a dual light-collection for laser induced breakdown spectroscopy

Temporal-resolved measurement plays an important role in laser-induced breakdown spectroscopy (LIBS), and intensified CCD camera (ICCD) is widely applied in this field. In this work, we proposed a simple way instead of ICCD to achieve temporal-resolved detection using a dual light-collection worked with 2 CMOS cameras or 2 fiber spectrometers. In the measurement, the cameras / spectrometers were simultaneously operated under two different detection-delay with respect to the pulsed laser, and a subtraction between 2 detections was carried out as the gate width to capture evolution of the plasma morphology or the emission intensity. With aid of this method, we have successfully obtained the dynamic change of plasma and the intensity variation of LIBS signal in the regime from nanoseconds to microseconds. As a comparison, ICCD and grating-spectrometer were also employed to confirm the obtained results. It is suggested that the proposed method is a practical way for temporal-resolved imaging or spectra detection for LIBS, and the on-site application would be the prospective field for this method in future.

Heat transfer and thermoregulation within single cells revealed by transient plasmonic imaging

Summary Cells, as the basic unit of life, undergo continuous heat transfer and dissipation during their metabolism, which is related not only to fundamental cellular functions but also massive applications. Unfortunately, thus far, we still know little about the heat transfer properties at the cellular or subcellular levels. Here, we demonstrated a transient microscopic method to measure the heat transfer in single cells. The thermal conductivity of different regions within a single cell shows a wide heterogeneity, and heat transfer in the region near the cell membrane is more active than the central region. However, the median values of thermal conductivity between different individual cells are quite close. A cellular-level heat regulation that responds to environmental temperature is observed in warm-blooded humans and chickens rather than in cold-blooded bullfrogs. According to the temperature-dependent cell metabolism, we proposed a hypothesis for cellular control of heat dissipation, which might be the cellular-level foundation of body thermoregulation.