Cascade Atom Research Articles

Microwave field sensor based on cold cesium Rydberg three-photon electromagnetically induced spectroscopy

Abstract We present the electromagnetically induced transparency (EIT) spectra of cold Rydberg four-level cascade atoms consisting of the 6S1/2 → 6P3/2 → 7S1/2 → 60P3/2 scheme. A coupling laser drives the Rydberg transition, a dressing laser couples two intermediate levels and a weak probe laser probes the EIT signal. We numerically solve the Bloch equations and investigate the dependence of the probe transmission rate signal on the coupling and dressing lasers. We find that the probe transmission rate can display an EIT or electromagnetically induced absorption (EIA) profile, depending on the Rabi frequencies of the coupling and dressing lasers. When we increase the Rabi frequency of the coupling laser and keep the Rabi frequency of the probe and dressing laser fixed, flipping of the EIA to EIT spectrum occurs at the critical coupling Rabi frequency. When we apply a microwave field coupling the transition 60P3/2 → 61S1/2, the EIT spectrum shows Autler–Townes splitting, which is employed to measure the microwave field. The theoretical measurement sensitivity can be 1.52 × 10−2 nV⋅cm−1⋅Hz−1/2 at the EIA–EIT flipping point.

Atomic-level insight into process and mechanism of ion beam machining on aluminum optical surface

Polycrystalline Al workpieces go through a complex surface atom sputtering and surface/subsurface atom diffusion throughout the ion beam machining process that plays a critical role in determining machining quality of optical mirror surfaces. Here, we leverage molecular dynamics method for the first time to reveal the machining mechanism and the polycrystalline effect of aluminum during ion beam sputtering, in term of cascade collision, atom trajectory, sputtering yield, and surface characteristic. Polycrystalline Al presents a significant low potential energy state, leading to milder cascade collision and weaker sputtering effects than monocrystalline Al during ion beam machining. The atom trajectory demonstrates irregular variation as the atom diffusion is blocked by grain boundary (GB) in polycrystalline Al, leading to the relief microstructure and poor surface quality. With incident ions increasing, the GBs are broken and atom diffusion enhancing, as well as lower subsurface defects and better finishing surface quality. The microscopic morphology evolves into gravel microstructure. Simulation results also reveal that atom diffusion will benefit from high ion concentration and low ion energy. Sputtering yield variation is more sensitive to ion energy. To acquiring better finishing surface quality of Al without influencing machining efficiency, ion concentration must be increased while the ion energy needs to be decreased appropriately but a large number of cascading collisions need to be ensured.

A cascade superradiance model

Intriguing collective spontaneous cascade emissions have recently been realized. In despite of much success, a depth understanding of the complexity is still lacking. With this motivation, a new simple cascade superradiance model is developed in this work. The existing model of identical two-level atoms is reexamined with a new insight. Temporal evolutions of average time delays and the fluctuations are introduced and the superradiance time delays are obtained in four different ways. These formulations allow to extend the two-level model to a cascade three-level model. The correlated two-mode emissions and the characteristics are discussed in detail. In the future, the correlated emissions from the collective cascade atoms may be used, for example, in quantum noise quenching.

Precise Measurement of Hyperfine Structure of Cesium 7S1/2 Excited State

We present a precise measurement of the hyperfine structure of cesium 7 S 1 / 2 excited state by employing electromagnetically induced spectroscopy (EIS) with a cesium three-level cascade ( 6 S 1 / 2 − 6 P 3 / 2 − 7 S 1 / 2 ) atom in a room temperature vapor cell. A probe laser, λ p = 852 nm, was coupled to a transition | 6 S 1 / 2 ⟩ → | 6 P 3 / 2 ⟩ , related frequency locked to the resonance hyperfine transition of | 6 S 1 / 2 ⟩ → | 6 P 3 / 2 ⟩ with a Fabry–Perot (FP) cavity and an electro-optic modulator (EOM). A coupling laser, λ c = 1470 nm, drove the | 6 P 3 / 2 ⟩ → | 7 S 1 / 2 ⟩ transition with the frequency scanned over the | 6 P 3 / 2 ⟩ → | 7 S 1 / 2 ⟩ transition line. The hyperfine level interval was extracted to be 2183.61 ± 0.50 MHz by analyzing EIS spectroscopy. The optical–optical double-resonance (OODR) spectroscopy is also presented for comparison, with the corresponding value of the hyperfine level interval being 2183.48 MHz ± 0.04 MHz, and the measured hyperfine splitting of excited 7 S 1 / 2 state is shown to be in excellent agreement with the previous work.

Evaluation of neutron radiation damage in zircaloy fuel clad of nuclear power plants: a study based on PKA and dpa calculations

During the lifetime of nuclear power plants, irradiation and mechanical interactions can cause permanent damage to their structural materials. In nuclear reactors, one of the most important of these materials is fuel clad that, in addition to its main role in transferring heat from fuel to coolant, restrains most of the radioactive fission products within its volume. In this article, neutron-induced radiation damage based on Primary Knock-on Atom (PKA) and displacement per atom (dpa) calculations are evaluated on fuel clad in Hot Fuel Assembly (HFA) in a WWER-1000 reactor core as a case study. New couplings of existing nuclear and radiation damage codes and methods are developed for dpa calculations and results are compared together and against experimental results. In the first step, the full reactor core is simulated with MCNPX code (v2.7) to determine the HFA and its relevant neutron-energy spectrum. SPECTER, SPECTRA-PKA and PTRAC card of MCNPX are then employed to evaluate the PKA spectrum under neutron bombardment. Finally, dpa calculated with the Binary Collision Approximation approach is achieved through the use of SRIM-2013 code. A MATLAB interchange program is developed to prepare and transfer the data between the mentioned codes and SRIM. Comprehensive comparisons are performed between results in terms of dpa obtained by (i) NRT calculation (NRT-dpa) (SPECTER and SPECTRA-PKA results), (ii) arc-dpa calculation (MCNPX+arc-dpa), (iii) BCA calculation (PTRAC+SRIM) and (iv) coupled calculation (SPECTRA-PKA+SRIM) (all generations of knock-on atoms and clusters are tracked in the last two methods). These comparisons reveal the portions of damage in Zircaloy due to PKAs, secondary knock-on atoms and cascade atoms, the effect of position-depended PKA and the fraction of displaced atoms that come back to their lattice positions as a result of thermal effects and annealing. Effects of elemental PKA are obtained by means of SPECTRA-PKA code and a visualization map of radiation damage in the clad is presented as an outcome of the SRIM code simulation. Results confirm that value of dpa calculated by MCNPX+arc-dpa is closer to experimental ones as the recombination effect in radiation damage is considered in this method.

Single – Photon Interference with Thermally Excited Three – Level Cascade Atoms

Single – Photon Interference with Thermally Excited Three – Level Cascade Atoms

Four Atom Efficient Enzyme Cascades for All 4-Methoxyphenyl-1,2-propanediol Isomers Including Product Crystallization Targeting High Product Concentrations and Excellent E-Factors

Atom economy and E-factor calculations are valuable tools in the sustainable process design of fine and pharmaceutical chemicals. Adjoined with the smart assembly of biocatalysts in artificial cascades, fine and pharmaceutical chemicals can be produced with high efficiency and selectivity, while also reducing the ecological footprint. In this study, all four isomers of 4-methoxyphenyl-1,2-propanediol, a potential anti-inflammatory drug, are synthesized by stereocomplementary carboligases and NADPH-dependent alcohol dehydrogenases in a one-pot, two-step cascade with isomeric purities of >99%. The consumed NADPH in the second step is regenerated by the same alcohol dehydrogenase (ADH) with an auxiliary substrate, which allows coproduct recycling into the first step to form a self-sufficient cascade and increase atom economy to 99.9%. In addition, a hydrophobic microaqueous reaction system (MARS) enabled space-time yields (STYs) of up to 165 g L–1 day–1 for the respective product isomers. The employment of t...

Investigation of dust particle removal efficiency of self-priming venturi scrubber using computational fluid dynamics

Abstract A venturi scrubber is an important element of Filtered Containment Venting System (FCVS) for the removal of aerosols in contaminated air. The present work involves computational fluid dynamics (CFD) study of dust particle removal efficiency of a venturi scrubber operating in self-priming mode using ANSYS CFX. Titanium oxide (TiO2) particles having sizes of 1 micron have been taken as dust particles. CFD methodology to simulate the venturi scrubber has been first developed. The cascade atomization and breakup (CAB) model has been used to predict deformation of water droplets, whereas the Eulerian–Lagrangian approach has been used to handle multiphase flow involving air, dust, and water. The developed methodology has been applied to simulate venturi scrubber geometry taken from the literature. Dust particle removal efficiency has been calculated for forced feed operation of venturi scrubber and found to be in good agreement with the results available in the literature. In the second part, venturi scrubber along with a tank has been modeled in CFX, and transient simulations have been performed to study self-priming phenomenon. Self-priming has been observed by plotting the velocity vector fields of water. Suction of water in the venturi scrubber occurred due to the difference between static pressure in the venturi scrubber and the hydrostatic pressure of water inside the tank. Dust particle removal efficiency has been calculated for inlet air velocities of 1 m/s and 3 m/s. It has been observed that removal efficiency is higher in case of higher inlet air velocity.

Molecular dynamics simulations of cascade damage near the Y2Ti2O7 nanocluster/ferrite interface in nanostructured ferritic alloys**Project supported by the Science Challenge Project of China (Grant No. TZ2016002) and the National Natural Science Foundation of China (Grant No. 50871057).

A comparative study of cascades in nanostructured ferritic alloys and pure Fe is performed to reveal the influence of Y2Ti2O7 nanocluster on cascades by molecular dynamics simulations. The cascades with energies of primary knock-on atom (PKA) ranging from 0.5 keV to 4.0 keV and PKA’s distances to the interface from 0 Å to 50 Å are simulated. It turns out that the Y2Ti2O7 nanocluster can absorb the kinetic energy of cascade atoms, prevent the cascade from extending and reduce the defect production significantly when the cascades overlap with the nanocluster. When the cascade affects seriously the nanocluster, the weak sub-cascade collisions are rebounded by the nanocluster and thus leave more interstitials in the matrix. On the contrary, when the cascade contacts weakly the nanocluster, the interface can pin the arrived interstitials and this leaves more vacancies in the matrix. Moreover, the results indicate that the Y2Ti2O7 nanocluster keeps stable upon the displacement cascade damage.

Entanglement formulation in the framework of electrically pumped laser cavity

We analyze electrically pumped atomic cavity coupled to a two-mode vacuum reservoirs via a single-port mirror whose open cavity contains N nondegenerate three-level cascade atoms. We carry out our analysis by putting the noise operators associated with a vacuum reservoir in normal order. It is found that unlike the mean photon number, the quadrature squeezing and the degree of entanglement do not depend on the number of atoms. This implies that the quadrature squeezing and the degree of entanglement of the cavity light do not depend on the number of photons. We have also shown that the light generated by the three-level laser is in a squeezed and entangled state, with maximum quadrature squeezing and degree of entanglement being 50%. Moreover, the mean photon number of the system in which the laser operating at threshold and above threshold does not depend on the spontaneous decay constant.

Modeling and simulation of air-assist atomizers with applications to food sprays

The Cascade Atomization and Drop Breakup (CAB) model has been developed originally for pressure atomizers. In this study, the CAB model is modified to accommodate air-assist atomization. The modifications include a change in the product drop distributions, namely, the uniform distribution used in the original CAB model is replaced with a χ-squared distribution with the same average drop size. The second modification addresses the air-assist atomization process. This process is modeled by estimating the Weber number due to the increased relative velocity caused by the air flow. Depending on the value of the Weber number this leads to a catastrophic, or a stripping (sheet-thinning), or a bag breakup. The model changes are validated with experimental data obtained from two different air-assist atomizers using an oil-in-water emulsion. The simulations were performed with a modified version of the KIVA-3 CFD code, and they showed good agreement with the experimental data.

Entanglement of Optical and Mechanical Modes Enhanced in Distant Optomechanical Systems by Atomic Coherence

We present a scheme for three-level cascade atoms to entangle various optical and mechanical modes of two coupled cavity optomechanical system. With the existence of atomic mediums, our study shows that the larger stationary macroscopic entanglement of distant optomechanical systems can be obtained and reaches the maximum at the same effective detuning. Furthermore, we find that it is insensitive to the cavity decay rate for the entanglement between the two distant movable mirrors, and between the mirror and the adjacent or the distant cavity mode, which compensates for the effects of the cavity dissipation.

Enhanced cooling of micromechanical oscillator in the atom-assisted optomechanical cavity

We investigate the two-mode optomechanical cavity coupled with the three-level cascade atom. We propose a scheme to enhance the cooling of optomechanical oscillator by introducing atomic medium. Our results show that the existence of the atom can lead to a lower effective temperature of mechanical oscillator comparing to the case without atom. The coherence of the injected atomic affects the population of the photon, which can lead to the change in the radiation pressure on the movable mirror. We also show that the cooling of the mechanical oscillator is affected by initial state of inserting atom.

디젤분무의 분열과정에 대한 수치해석 연구

High-pressure flows are ubiquitous in many industrial fields. A representative application is fuel injection using a common-rail control system in diesel engines, where the injection pressure in the injector exceeds 1000 bar. In high-speed injection, the fluid injected through the nozzle undergoes breakup owing to the interaction with the ambient gas. The breakup process influences mixture formation, which in turn influences combustion in diesel engines. Therefore, it is very important to analyze the breakup process of fuel spray. The Reitz and Diwakar model and cascade atomization and breakup (CAB) model were used in this study as sub-models for the numerical analysis of the breakup process of fuel spray. This study aims to precisely analyze the breakup process of spray and to investigate the breakup frequency of the injected fuel. Consequently, it proposes a suitable sub-model for analyzing the breakup process of a diesel spray by using CFX, a commercial CFD program.

CFD simulation of dust particle removal efficiency of a venturi scrubber in CFX

This research presents the computational fluid dynamics (CFD) simulation of dust particle removal efficiency of a venturi scrubber in ANSYS CFX. Venturi scrubber effectively encapsulates the dust particles from contaminated gas in petite droplets formed by disintegration of a liquid due to high kinetic energy of gas flowing into it. Eulerian–Lagrangian method is employed in ANSYS CFX to investigate the dust removal efficiency of a venturi scrubber for gas flow rate at 0.09, 0.115, and 0.14kgs−1 and liquid flow rate at 0.1, 0.13 and 0.16kgs−1. The hydrophobic dust particle titanium dioxide (TiO2) of diameter 1μm having density 4.23gcm−3 is used in the simulation and experimentation. Throat gas velocity, volume fraction, droplet size and removal efficiency are investigated to analyze the performance of venturi scrubber. Cascade atomization and breakup model (CAB) is used to predict the breakup of liquid in the venturi scrubber. The simulation results are verified from the experimental results of gas velocity at throat and dust removal efficiency. The simulation result predicts good with experimental results.

Non-local linear stability of ion beam eroded surfaces

Continuum theories of spontaneous pattern formation at solid surfaces during ion irradiation exist in many variants, but all of them are based upon low order gradient expansions of an underlying non-local theory and are formulated as partial differential equations. Here we reconsider the non-local theory based upon a simple Gaussian erosive crater function of Sigmund's theory of sputtering, which is also a basic ingredient of most of the existing continuum theories. We keep the full non-locality of the crater function in a linear stability analysis of a flat surface. Without gradient expansion the evolution of the height profile is governed by an integral equation. We show that low order gradient expansions may be misleading and that the bifurcation scenarios become significantly more complex, if the non-locality is taken into account. In a second step, we extend our analysis and include mass redistribution due to ion-induced drift currents of collision cascade atoms. The model is based upon results from kinetic theory and uses a simple phenomenology. Both erosion and mass redistribution share the same non-local features, as they are both caused by the collision cascade. If mass redistribution is the dominant pattern forming mechanism, we show that the resulting bifurcation scenarios may provide explanations for many of the recent, seemingly contradictory experimental results of pattern formation on Si surfaces.

Charging Phenomena During Medium Current Ion Implantation of Carbonized Photo-Resist Surface Layers

Charging phenomenon caused by ion implantation into the photo-resist has been evaluated with use of a surface potential measurement tool to clarify the mechanism of burst-like discharge of the accumulated charge in medium current implantation machines. The molecular bond of the photo-resist is cleaved by the kinetic energy of the implanted impurity ions selectively at the portion of the smallest bond energy, and cross-linking develops from this point. Bond breaking and cross-linking is accompanied by out-gassing of hydrogen released by collisions with the dopant atom and recoil cascade atoms. Finally, a carbon-rich layer with low resistance is formed on the photo-resist surface. When arsenic ions are implanted, the degraded layer of low resistance including the carbonization is being formed even under low dose (1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> or less) conditions. This is called the medium current charging phenomenon with a current of a few hundred μA. The charges are accumulated on the photo-resist, until the low resistance layer is formed on the surface of the photo-resist. When the induced voltage reaches a critical value, they rush into the open area through the layer. As a result, an explosive local melting of silicon occurs, with the critical value depending on the mask-pattern arrangement.

Entanglement of nanomechanical oscillators and two-mode fields induced by atomic coherence

We propose a scheme via three-level cascade atoms to entangle two optomechanical oscillators as well as two-mode fields. We show that two movable mirrors and two-mode fields can be entangled even for bad cavity limit. We also study entanglement of the output two-mode fields in frequency domain. The results show that the frequency of the mirror oscillation and the injected atomic coherence affect the output entanglement of the two-mode fields.

Influence of the polar angle of incidence on electronic substrate excitations in keV self-bombardment of solid silver

We present a computer simulation study on the influence of the polar angle of incidence on electronic substrate excitations in the self-sputtering of silver. For the bombardment of a silver target with 5-keV Ag atoms, we employ a standard molecular dynamics code to follow the microscopic particle dynamics within the atomic collision cascade following the primary particle impact. The transfer of kinetic energy of cascade atoms into the electronic subsystem of the metal is treated in terms of the Lindhard model of electronic stopping and an electron promotion model describing the generation of hot electrons in close binary collisions. The transport of excitation energy away from the spot of generation is treated in a diffusive manner. The calculations yield a time- and space-dependent excitation energy density E(r→,t) that can be converted into an electron temperature profile Te(r→,t). The results of our calculations show an angle-dependent duration of the initial electron temperature peak at the surface which coincides with the time the projectile needs to cross the first layer of the model crystal.

Interference between competing pathways in the interaction of three-level ladder atoms and radiation

In this paper we explore the physical origin of the transparency induced in absorbing three-level cascade atoms by the simultaneous interplay of two coherent beams of light. By utilizing the scattering technique we offer what we believe is a very convincing physical evidence for the existence, or for the absence, of quantum interference effects in the two considered ladder systems. Bare and dressed states pictures are adopted in two different field regimes when applicable. The conclusions are drawn based on the existence of different excitation pathways and their relative orders of magnitudes. The presented study includes a distinction between the Autler–Townes (AT) and electromagnetically induced transparency (EIT) phenomena.