Unity Efficiency Research Articles

Optimization of the design of the hard X-ray polarimeter X-Calibur

We report on the optimization of the hard X-ray polarimeter X-Calibur for a high-altitude balloon-flight in the focal plane of the InFOCμS X-ray telescope from Fort Sumner (NM) in Fall 2013. X-Calibur combines a low-Z scintillator slab to Compton-scatter photons with a high-Z Cadmium Zinc Telluride (CZT) detector assembly to photo-absorb the scattered photons. The detector makes use of the fact that polarized photons Compton scatter preferentially perpendicular to the electric field orientation. X-Calibur achieves a high detection efficiency of order unity and reaches a sensitivity close to the best theoretically possible. In this paper, we discuss the optimization of the design of the instrument based on Monte Carlo simulations of polarized and unpolarized X-ray beams and of the most important background components. We calculate the sensitivity of the polarimeter for the upcoming balloon flight from Fort Sumner and for additional longer balloon flights with higher throughput mirrors. We conclude by emphasizing that Compton polarimeters on satellite borne missions can be used down to energies of a few keV.

From A Fluorescent Chromophore in Solution to An Efficient Emitter in the Solid State

Polycyclic aromatic hydrocarbons (PAHs) normally exhibit efficient fluorescence in dilute solutions, whereas their emission is significantly quenched in the aggregated state due to the formation of π-aggregates/excimers. The rigid and planar structure of PAHs plays a positive role in terms of fluorescence in solution but a negative one in the aggregated state. To bestow PAHs a luminescent ability in the solid state, we constructed a non-coplanar PAH-substituted ethene. By using the planar PAH fluoranthene as a building block, a highly efficient solid-state emitter with a fluorescence quantum efficiency of unity in the aggregated state was obtained. OLEDs with contain the molecule as an emitter reach a luminance up to 20 520 cd m(-2) and an efficiency of 10 cd A(-1).

Single-photon frequency conversion by exploiting quantum interference

We present a scheme to achieve efficient single-photon frequency conversion by exploiting quantum interference between different transition pathways for single-photon states. As an example, we discuss the single-photon frequency-conversion process in the configuration wherein a $\ensuremath{\Lambda}$-type (Lambda-type) three-level quantum emitter is coupled to a Sagnac interferometer. It is shown that the efficiency of the frequency conversion approaches unity in the ideal case. A real-space theoretical approach and a pseudospectral numerical method are developed, which facilitate the computation for the full spatiotemporal dynamics of the scattering process.

Efficient Single-Photon Frequency Conversion Using a Sagnac Interferometer

We propose a scheme for efficient optical frequency conversion at the single-photon power level. The scheme exploits the quantum interference of single-photon states at a three-level quantum emitter coupled to a Sagnac interferometer. We show that this device can achieve single-photon frequency up- or down-conversion with near unity efficiency.

Thermoelectrically Pumped Light-Emitting Diodes Operating above Unity Efficiency

A heated semiconductor light-emitting diode at low forward bias voltage V<k(B)T/q is shown to use electrical work to pump heat from the lattice to the photon field. Here the rates of both radiative and nonradiative recombination have contributions at linear order in V. As a result the device's wall-plug (i.e., power conversion) efficiency is inversely proportional to its output power and diverges as V approaches zero. Experiments directly confirm for the first time that this behavior continues beyond the conventional limit of unity electrical-to-optical power conversion efficiency.

Design and tests of the hard X-ray polarimeter X-Calibur

X-ray polarimetry will give qualitatively new information about high-energy astrophysical sources. We designed, built and tested a hard X-ray polarimeter X-Calibur to be used in the focal plane of the InFOCμS grazing incidence hard X-ray telescope. X-Calibur combines a low-Z Compton scatterer with a CZT detector assembly to measure the polarization of 10–80keV X-rays making use of the fact that polarized photons Compton scatter preferentially perpendicular to the electric field orientation. X-Calibur achieves a high detection efficiency of order unity.

A quantitative assessment of the competition between water and anion oxidation at WO3 photoanodes in acidic aqueous electrolytes

The faradaic efficiency for O2(g) evolution at thin-film WO3 photoanodes has been evaluated in a series of acidic aqueous electrolytes. In 1.0 M H2SO4, persulfate was the predominant photoelectrochemical oxidation product, and no O2 was detected unless catalytic quantities of Ag+(aq) were added to the electrolyte. In contact with 1.0 M HClO4, dissolved O2 was observed with nearly unity faradaic efficiency, but addition of a hole scavenger, 4-cyanopyridine N-oxide, completely suppressed O2 formation. In 1.0 M HCl, Cl2(g) was the primary oxidation product. These results indicate that at WO3 photoanodes, water oxidation is dominated by oxidation of the acid anions in 1.0 M HCl, H2SO4, and HClO4, respectively.

Designing Radial Sliding Bearing Equipped with Hydrostatically Suspended Pads

Operating experience indicates that the installation of the damping bearings with the hydrostatic self generative oil film can increase the unity reliability and efficiency, reduce vibration levels, including under transient and non-stationary modes of operation, ensures a smooth transition through critical frequencies.

Organic Triplet Excited States of Gold(I) Complexes with Oligo(o- orm-phenyleneethynylene) Ligands: Conjunction of Steady-State and Time-Resolved Spectroscopic Studies on Exciton Delocalization and Emission Pathways

A series of mononuclear and binuclear gold(I) complexes containing oligo(o- or m-phenyleneethynylene) (PE) ligands, namely [PhC≡C(C(6)H(4)-1,2-C≡C)(n-1)Au(PCy(3))] (n = 2-4, 4a-c), [μ-{C≡C-(1,2-C(6)H(4)C≡C)(n)}{Au(PCy(3))}(2)] (n = 1-6, 8, 5a-g), [PhC≡C(C(6)H(4)-1,3-C≡C)(n-1)Au(PCy(3))] (n = 2-4, 6a-c), and [μ-{C≡C-(1,3-C(6)H(4)C≡C)(n)}{Au(PCy(3))}(2)] (n = 1, 2, 7a,b), were synthesized and structurally characterized. Extensive spectroscopic measurements have been performed by applying combined methods of femtosecond transient absorption (fs-TA), fs time-resolved fluorescence (fs-TRF), and nanosecond time-resolved emission (ns-TRE) coupled with steady-state absorption and emission spectroscopy at both ambient and low (77 K) temperatures to directly probe the temporal evolution of the excited states and to determine the dynamics and spectral signatures for the involved singlet (S(1)) and triplet (T(1)) excited states. The results reveal that S(1) and T(1) both feature ligand-centered electronic transitions with ππ* character associated with the phenyl and acetylene moieties. The (3)ππ* emission of the PE ligands is switched on by the attachment of [Au(PCy(3))](+) fragment(s) due to the heavy-atom effect. T(1)((3)ππ*) was found to form with nearly unity efficiency through intersystem crossing (ISC) from S(1)((1)ππ*). The ISC time constants were determined to be ∼50, 35, and 40 ps for 4b and 6a,b, respectively. Dual emission composed of fluorescence from S(1) and phosphorescence from T(1) were observed for most of the complexes except 5a and 7a, where only phosphorescence was found. The fluorescence at ambient temperature is accounted for by both the short-lived prompt fluorescence (PF) and long-lived delayed fluorescence (DF, lifetime on microsecond time scale). Explicit evidence was presented for a triplet-triplet annihilation mechanism for the generation of DF. Ligand length and substitution-dependent dynamics of T(1) are the key factors governing the dual emission character of the complexes. By extrapolation from the plot of emission energy against the PE chain length of the [Au(PCy(3))](+) complexes with oligo(o-PE) or oligo(m-PE) ligands, the triplet emission energies were estimated to be ∼530 and ∼470 nm for poly(o-PE) and poly(m-PE), respectively. Additionally, we assign the unusual red shifts of 983 cm(-1) from [PhC≡CAu(PCy(3))] (1) to [μ-{1,3-(C≡C)(2)C(6)H(4)}{Au(PCy(3))}(2)] (7a) and 462 cm(-1) from 7a to [μ(3)-{1,3,5-(C≡C)(3)C(6)H(3)}{Au(PCy(3))}(3)] (8) in the phosphorescence energies to excitonic coupling interactions between the C≡CAu(PCy(3)) arms in the triplet excited states. These complexes, together with those previously reported [Au(PCy(3))](+) complexes containing oligo(p-PE) ligands ( J. Am. Chem. Soc. 2002 , 124 , 14696 - 14706 ), form a collection of oligo(phenyleneethynylene) complexes exhibiting organic triplet emission in solution under ambient conditions. The remarkable feature of these complexes in exhibiting TTA prompted DF in conjunction with high formation efficiency of T(1)((3)ππ*) affords an opportunity for emission spectra to cover a wide range of wavelengths. This may have implication in the development of PE-based molecular materials for future optical applications.

Homogenous nucleation of sulfuric acid and water at close to atmospherically relevant conditions

Abstract. In this study the homogeneous nucleation rates in the system of sulfuric acid and water were measured by using a flow tube technique. The goal was to directly compare particle formation rates obtained from atmospheric measurements with nucleation rates of freshly nucleated particles measured with particle size magnifier (PSM) which has detection efficiency of unity for particles having mobility diameter of 1.5 nm. The gas phase sulfuric acid concentration in this study was measured with the chemical ionization mass spectrometer (CIMS), commonly used in field measurements. The wall losses of sulfuric acid were estimated from measured concentration profiles along the flow tube. The initial concentrations of sulfuric acid estimated from loss measurements ranged from 108 to 3 × 109 molecules cm−3. The nucleation rates obtained in this study cover about three orders of magnitude from 10−1 to 102 cm−3 s−1 for commercial ultrafine condensation particle counter (UCPC) TSI model 3025A and from 101 to 104 cm−3 s−1 for PSM. The nucleation rates and the slopes (dlnJ/dln [H2SO4]) show satisfactory agreement when compared to empirical kinetic and activation models and the latest atmospheric nucleation data. To the best of our knowledge, this is the first experimental work providing temperature dependent nucleation rate measurements using a high efficiency particle counter with a cut-off-size of 1.5 nm together with direct measurements of gas phase sulfuric acid concentration.

On the impact of non-sphericity and small-scale surface roughness on the optical properties of hematite aerosols

We perform a comparative modelling study to investigate how different morphological features influence the optical properties of hematite aerosols. We consider high-order Chebyshev particles as a proxy for aerosol with a small-scale surface roughness, and spheroids as a model for nonspherical aerosols with a smooth boundary surface. The modelling results are compared to those obtained for homogeneous spherical particles. It is found that for hematite particles with an absorption efficiency of order unity the difference in optical properties between spheres and spheroids disappears. For optically softer particles, such as ice particles at far-infrared wavelengths, this effect can be observed for absorption efficiencies lower than unity. The convergence of the optical properties of spheres and spheroids is caused by absorption and quenching of internal resonances inside the particles, which depend both on the imaginary part of the refractive index and on the size parameter, and to some extent on the real part of the refractive index. By contrast, small-scale surface roughness becomes the dominant morphological feature for large particles. This effect is likely to depend on the amplitude of the surface roughness, the relative significance of internal resonances, and possibly on the real part of the refractive index. The extinction cross section is rather insensitive to surface roughness, while the single-scattering albedo, asymmetry parameter, and the Mueller matrix are strongly influenced. Small-scale surface roughness reduces the backscattering cross section by up to a factor of 2–3 as compared to size-equivalent particles with a smooth boundary surface. This can have important implications for the interpretation of lidar backscattering observations.

Proposal for a Loophole-Free Bell Test with Electron Spins of Donors in Silicon

So far, all experimental tests of Bell inequalities which must be satisfied by all local realistic hidden-variable theories and are violated by quantum mechanical predictions have left at least one loophole open. We propose a feasible setup allowing for a loophole-free test of the Bell inequalities. Two electron spin qubits of donors31P in a nanoscale silicon host in different cavities 300 m apart are entangled through a bright coherent light and postselections using homodyne measurements. The electron spins are then read out randomly and independently by Alice and Bob, respectively, with unity efficiency in less than 0.7 µs by using optically induced spin to charge transduction detected by radio-frequency single electron transistor. A violation of Bell inequality larger than 37% and 18% is achievable provided that the detection accuracy is 0.99 and 0.95, respectively.

Ultrafast Dynamics of Intersystem Crossing and Resonance Energy Transfer in Er(III)−Quinolinolate Complexes

Organocomplexes with trivalent erbium are investigated by time-resolved optical spectroscopy techniques. Ultrafast time scales are reported for intraligand intersystem crossing (∼10 ps) and ligand-to-metal resonance energy transfer (∼100 ps), resulting in lanthanide-ion sensitization with nearly unity efficiency. Given the interest of erbium complexes for telecom wavelength solid-state amplifiers and emitters, the results should stimulate further theoretical investigations on radiationless transitions in such complexes.

SnO2-Based Dye-Sensitized Hybrid Solar Cells Exhibiting Near Unity Absorbed Photon-to-Electron Conversion Efficiency

Improving the solar light harvesting and photon-to-electron conversion efficiency for hybrid, organic-inorganic photovoltaics are critical challenges. Titania based solid-state hybrid solar cells are moderately efficient at converting visible photons to electrons, but major electrical losses still remain. A material based paradigm shift is required to dramatically enhance the performance of these devices. Here, we present an investigation into solid-state dye-sensitized solar cells (SDSCs) incorporating a molecular hole-transporter and mesoporous tin oxide electrodes, in place of titania usually employed. We investigate the influence of treating the surface of the SnO(2) with different oxides and find that MgO "passivated" SnO(2) electrodes demonstrate an unprecedented absorbed photon-to-electron conversion efficiency of near unity across a broad spectral range. A dual surface treatment of TiO(2) followed by MgO enables tuning of the solar cell photovoltage, fill factor, and efficiency with visible light absorbing cells delivering 3% solar-to-electrical full sun power conversion efficiency.

Photochemistry of OIO: Laboratory study and atmospheric implications

Iodine chemistry influences the oxidizing capacity of the atmosphere, principally by depleting ozone, and induces the formation of new particles in the marine boundary layer. The photochemistry of iodine dioxide (OIO) plays a key role in both these processes. Here we report that OIO photolyses in the visible (480–650 nm), yielding iodine atoms with a quantum efficiency of unity (1.07 ± 0.15). As a result, much smaller sources of iodine precursors are required to cause significant ozone depletion, which has important implications for the marine boundary layer ozone budget.

Ultrafast Studies of Charge Generation in PCBM:P3HT Blend Films following Excitation of the Fullerene PCBM

In order to better understand the limits of [6,6]phenyl C61-butyric acid methyl ester/poly(3-hexylthiophene) (PCBM:P3HT) organic solar cell device performance, ultrafast transient absorption spectroscopy has been used to probe the dynamics of charge creation in films of PCBM:P3HT following excitation of the fullerene. The time scale for splitting of the PCBM singlet excited state and “hole” transfer across the polymer−fullerene donor−acceptor interface is found to be faster than the system resolution of 250 fs and is calculated to occur with near unity efficiency. Ironically, this very quick electron transfer is discussed as being inefficient with regard to organic solar cell device power conversion efficiency as an excess amount of energy is used up in the electron transfer step.

Single-photon frequency up-conversion with multimode pumping

Efficient single-photon frequency up-conversion was demonstrated under strong multi-longitudinal-mode pump, where the incident single-photon state was converted to a superposition state after the nonlinear interaction with the multimode pump field. Through frequency summing with a sufficiently strong multimode pump at $1.06\text{ }\ensuremath{\mu}\text{m}$, a single-photon signal at $1.55\text{ }\ensuremath{\mu}\text{m}$ was up-converted to the visible replicas near $0.63\text{ }\ensuremath{\mu}\text{m}$ with a nearly unity efficiency. This may support tunable multimode photonic quantum-information interface and precise wavelength control on single-photon manipulation.

Membrane Efficiency of Shales Interacting With Water-Based and Oil-Based Muds

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 100735, "Factors Controlling the Membrane Efficiency of Shales When Interacting With Water- Based and Oil-Based Muds," by Talal M. Al-Bazali, Kuwait U.; Jianguo Zhang, SPE, Baker Atlas; and Martin E. Chenevert, SPE, and Mukul M. Sharma, SPE, U. of Texas at Austin, prepared for the 2006 SPE International Oil &amp; Gas Conference and Exhibition in China, Beijing, 5–7 December. The full-length paper presents a comprehensive set of experimental data for the membrane efficiency of four shales when interacting with different water-based muds (WBMs) and oil-based muds (OBMs). Pressure-transmission tests were used to measure the membrane efficiency using three different cations and two different anions at different concentrations (water activities). Results suggest that the membrane efficiency of shales is directly proportional to the ratio of the cation-exchange capacity to the permeability of shales. Introduction Osmosis has long been recognized as a means to extract water from a shale when the water activity of the shale is higher than that of the drilling fluid. In the absence of a hydraulic-pressure gradient, the movement of mud filtrate into shale is governed mainly by the chemical-potential difference between the pore fluid and the mud, and this results in the osmotic transport of water. However, recently it was shown that the osmotic potential generated between shale and drilling fluid is influenced greatly by the flow of ions into or out of the shale because of ionic-concentration imbalances. Therefore, the actual osmotic effect often is less than the osmotic potential. This has spurred much interest to quantify the effect of ionic flow on the osmotic potential, and that in turn has led to introducing the concept of shale membrane efficiency. Membrane efficiency describes the ability of a shale to hinder ion movement when interacting with drilling fluids. If the shale completely stops ionic flow, the shale is said to act as a perfect semipermeable membrane, with a membrane efficiency of unity. If the shale lets ions flow freely, the shale is said to act as a nonselective membrane, with a zero membrane efficiency. In this work, the membrane efficiency of shale, when interacting with WBMs and OBMs, has been estimated by use of pressure-transmission tests. The dependence of the membrane efficiency of shale onion type and concentration in the drilling fluid was explored using different cations and anions over a range of concentrations. The influence of shale permeability and cation-exchange capacity on the membrane efficiency also were investigated using four different shales. Test Description The membrane-efficiency test made use of a pressure-transmission technique where shale samples were subjected to both hydraulic and osmotic gradients during exposure to drilling fluids. The pressure drop (resultant osmotic pressure) across the shale sample was measured in response to both hydraulic- and osmotic-pressure gradients. The pressure drop then was converted to a membrane efficiency that was defined as the ratio of the pressure drop across the shale sample to the osmotic potential resulting from the differences in water activities.

Fast Spin State Initialization in a Singly Charged InAs-GaAs Quantum Dot by Optical Cooling

Quantum computation requires a continuous supply of rapidly initialized qubits for quantum error correction. Here, we demonstrate fast spin state initialization with near unity efficiency in a singly charged quantum dot by optically cooling an electron spin. The electron spin is successfully cooled from 5 to 0.06 K at a magnetic field of 0.88 T applied in Voigt geometry. The spin cooling rate is of order 10(9) s-1, which is set by the spontaneous decay rate of the excited state.

Soliton spectral tunnelling in photonic crystal fibre with sub-wavelength core defect

A numerical study of soliton spectral tunnelling in an index-guiding photonic crystal fibre with a sub-wavelength central air core defect is presented. Specifically, for a fibre design where two regions of anomalous dispersion bracket a 90 nm wide region of normal dispersion, simulations show tunnelling from 1300 to 1475 nm across the forbidden normal dispersion regime, with near unity efficiency. In addition, this effect can be exploited to obtain over a factor of two nonlinear pulse compression by interrupting propagation at the distance at which soliton tunnelling occurs.