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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Air resonance enhanced multiphoton ionization tagging velocimetry

Air resonance enhanced multiphoton ionization (REMPI) tagging velocimetry (ART) was demonstrated in quiescent and supersonic flows. The ART velocimetry method utilizes a wavelength tunable laser beam to resonantly ionize molecular oxygen in air and generate additional avalanche-type ionization of molecular nitrogen. The fluorescence emissions from the first negative and first positive bands of molecular nitrogen are, thus, produced and used for flow tagging. Detailed characterization of ART was conducted, including the effects of oxygen resonance to fluoresce nitrogen, nitrogen fluorescence spectrum, laser energy deposition into quiescent flow showing minimal perturbations in flow, fluorescence lifetime study at various pressures, and line tagging without breakdown. Pointwise velocity measurements within a supersonic flow from a nominal Mach 1.5 nozzle have been conducted and characterized.

Clark, Aleksander↗
NASA NTRS1990

New electronic states of NH and ND observed by resonance enhanced multiphoton ionization spectroscopy

Resonance Enhanced MultiPhoton Ionization (REMPI) spectra of NH and ND, which reveal four new electronic states are presented. Transitions from NH a 1 delta to 3s and 3p Rydberg states in both NH and ND have been observed and rotationally analyzed. The transitions were observed in the wavelength range of 258 to 288 nm. The state assignments are: e 1 pi (3s sigma) at 82857/cm, f 1 pi (3p sigma) at 86378/cm, g 1 delta (3p pi) at 88141/cm and h 1 sigma (3p pi) at 89151/cm.

Johnson, Russell D., III↗
NASA NTRS2018

Computational Study of Compact Ejector-Enhanced Resonant Pulse Combustors

Previous studies of Ejector-Enhanced Resonant Pulse Combustors considered configurations that were relatively long, making them difficult to incorporate in practical gas turbine engines. In the present study, more compact configurations are analyzed, focusing on the system pressure gain. The study shows that it is possible to reduce the length of both the pulse combustor and ejector components without compromising the device's performance. In fact, it is found that in several of the compact configurations analyzed, the system pressure gain actually increased, reaching pressure gain levels above 5%, significantly higher than those obtained in previous studies. The Rayleigh efficiency, which has been used in the past to characterize the performance of pulse combustors, is computed for several of the Ejector-Enhanced Resonant Pulse Combustor configurations. The Rayleigh efficiency is seen to correlate with both average combustor pressure and system pressure gain for a given configuration, however, it could not be used to compare different configurations.

Compact↗
DOE OSTI2024

Experimental upper bounds for resonance-enhanced entangled two-photon absorption cross section of indocyanine green

Resonant intermediate states have been proposed to increase the efficiency of entangled two-photon absorption (ETPA). Although resonance-enhanced ETPA (r-ETPA) has been demonstrated in atomic systems using bright squeezed vacuum, it has not been studied in organic molecules. We investigate for the first time r-ETPA in an organic molecular dye, indocyanine green (ICG), when excited by broadband entangled photons in near-IR. Similar to many reported virtual state mediated ETPA (v-ETPA) measurements, no r-ETPA signals are measured, with an experimental upper bound for the cross section placed at 6(±2) × 10 −23 cm 2 . In addition, the classical resonance-enhanced two-photon absorption (r-TPA) cross section of ICG at 800 nm is measured for the first time to be 20(±13) GM, where 1 GM equals 10 −50 cm 4 s, suggesting that having a resonant intermediate state does not significantly enhance two-photon processes in ICG. Furthermore, the spectrotemporally resolved emission signatures of ICG excited by entangled photons are also presented to support this conclusion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1987

Resonant enhanced multiphoton ionization studies of atomic oxygen

In resonant enhanced multiphoton ionization (REMPI), an atom absorbs several photons making a transition to a resonant intermediate state and subsequently ionizing out of it. With currently available tunable narrow-band lasers, the extreme sensitivity of REMPI to the specific arrangement of levels can be used to selectively probe minute amounts of a single species (atom) in a host of background material. Determination of the number density of atoms from the observed REMPI signal requires a knowledge of the multiphoton ionization cross sections. The REMPI of atomic oxygen was investigated through various excitation schemes that are feasible with available light sources. Using quantum defect theory (QDT) to estimate the various atomic parameters, the REMPI dynamics in atomic oxygen were studied incorporating the effects of saturation and a.c. Stark shifts. Results are presented for REMPI probabilities for excitation through various 2p(3) (4S sup o) np(3)P and 2p(3) (4S sup o) nf(3)F levels.

Dixit, S. N.↗
NASA NTRS1987

Experimental Resonance Enhanced Multiphoton Ionization (REMPI) studies of small molecules

Resonance enhanced multiphoton ionization (REMPI) utilizes tunable dye lasers to ionize an atom or molecule by first preparing an excited state by multiphoton absorption and then ionizing that state before it can decay. This process is highly selective with respect to both the initial and resonant intermediate states of the target, and it can be extremely sensitive. In addition, the products of the REMPI process can be detected as needed by analyzing the resulting electrons, ions, fluorescence, or by additional REMPI. This points to a number of exciting opportunities for both basic and applied science. On the applied side, REMPI has great potential as an ultrasensitive, highly selective detector for trace, reactive, or transient species. On the basic side, REMPI affords an unprecedented means of exploring excited state physics and chemistry at the quantum-state-specific level. An overview of current studies of excited molecular states is given to illustrate the principles and prospects of REMPI.

Dehmer, J. L.↗
DOE OSTI2022

One-dimensional air temperature measurements by air resonance enhanced multiphoton Ionization thermometry (ART)

In this work, a detailed calibration study is performed to establish non-intrusive one-dimensional (1D) rovibrational temperature measurements in unseeded air, based on air resonance enhanced multiphoton ionization thermometry (ART). ART is generated by REMPI (resonance enhanced multi-photon ionization) of molecular oxygen and subsequent avalanche ionization of molecular nitrogen in a single laser pulse. ART signal, the fluorescence from the first negative band of molecular nitrogen, is directly proportional to the 2-photon transition of molecular oxygen C 3 Π (v = 2) ← X 3 Σ (v’=0), which is used to determine temperature. Experimentally, hyperfine structures of the O 2 rotational branches with high temperature sensitivity are selectively excited through a frequency-doubled dye laser. Electron-avalanche ionization of N 2 results in the fluorescence emissions from the first negative bands of N 2 + near 390, 425, and 430nm, which are captured as a 1D line by a gated intensified camera. Post processing of the N 2 + fluorescence yields a 1D thermometry line that is representative of the air temperature. It is demonstrated that the technique provides ART fluorescence of ∼5cm in length in the unseeded air, presenting an attractive thermometry solution for high-speed wind tunnels and other ground test facilities.

42 ENGINEERING↗
NASA NTRS1991

Quantitative determination of H2, HD, and D2 internal-state distributions by (2+1) resonance-enhanced multiphoton ionization

Results are presented of an experimental study of (2+1) resonance-enhanced multiphoton ionization (REMPI) detection of H2, HD, and D2 via the E,F two-photon transition, in which the relationship between ion signals and quantum-state populations was determined by calibration against a thermal effusive source. Vibrational and rotational correction factors were obtained for 102 rovibrational levels for v-double-prime = 0, 1, and 2 and for J-double-prime ranging from 0 to 17. These correction factors make it possible to convert ion signals into relative quantum-state populations without relying on a theoretical description of the (2+1) REMPI process.

Rinnen, Klaus-Dieter↗
DOE OSTI2022

Resonance-enhanced x-ray multiple ionization of a polyatomic molecule

Extremely high charge states of atoms and molecules can be created when they are irradiated by intense x-ray pulses. At certain x-ray photon energies, electron ejection from atoms can be drastically enhanced by transient resonances created during the sequential ionization process. In this study we report on the observation of such resonance effects in a molecule, CH 3 I, and show the photon-energy-dependent shift of resonance-induced structures in ion charge state distributions. By comparing the ion charge state distribution of CH 3 I with that from ionization of atomic xenon, molecule-specific features are observed, which can be attributed to ultrafast intramolecular charge rearrangement. In addition, we experimentally demonstrate that the charge-rearrangement-enhanced x-ray ionization of molecules, previously found with hard x rays, also plays a role in the soft x-ray regime.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Resonance-Enhanced Multiphoton Ionization in the X-Ray Regime

In this work, we report on the nonlinear ionization of argon atoms in the short wavelength regime using ultraintense x rays from the European XFEL. After sequential multiphoton ionization, high charge states are obtained. For photon energies that are insufficient to directly ionize a 1s electron, a different mechanism is required to obtain ionization to Ar 17+ . We propose this occurs through a two-color process where the second harmonic of the FEL pulse resonantly excites the system via a 1s→2p transition followed by ionization by the fundamental FEL pulse, which is a type of x-ray resonance-enhanced multiphoton ionization (REMPI). This resonant phenomenon occurs not only for Ar 16+ , but also through lower charge states, where multiple ionization competes with decay lifetimes, making x-ray REMPI distinctive from conventional REMPI. With the aid of state-of-the-art theoretical calculations, we explain the effects of x-ray REMPI on the relevant ion yields and spectral profile.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Performance estimation of resonance-enhanced dual-buoy wave energy converter using coupled time-domain simulation

This article presents the modeling methodology and performance evaluation of the resonance-enhanced dual-buoy WEC (Wave Energy Converter) by HEM (hydrodynamic & electro-magnetic) fully-coupled-dynamics time-domain-simulation program. The numerical results are systematically compared with the authors’ 1/6-scale experiment. With a direct-drive linear generator, the WEC consists of dual floating cylinders and a moon-pool between the cylinders, which can utilize three resonance phenomena from moon-pool dynamics as well as heave motions of inner and outer buoys. The contact and friction between the two buoys observed in the experiment are also properly modeled in the time-domain simulation by the Coulomb-friction model. Moon-pool resonance peaks significantly exaggerated in linear potential theory are empirically adjusted through comparisons with measured values. A systematic comparative study between the simulations and experiments with and without PTO (power-take-off) is conducted, and the relative heave displacements/velocities and power outputs are well matched. Then, parametric studies are carried out with the simulation program to determine optimum generator parameters. The performance with various wave conditions is also assessed.

16 TIDAL AND WAVE POWER↗
NASA NTRS1988

(1 + 1) resonant enhanced multiphoton ionization via the A2Sigma(+) state of NO - Ionic rotational branching ratios and their intensity dependence

Rotational branching ratios resulting from the (1 + 1) resonant enhanced multiphoton ionization spectroscopy of NO via the 0-0 transition of the A-X band for the four possible branches that can be assigned as R(21.5) are explored using calculation performed in the frozen-core approximation at the Hartree-Fock level. The four different branches, of which three are distinctly different in the perturbative limit, have rather different branching ratios. The mixed R12 + Q22(21.5) branch, which is not intense and has the lowest transition energy, appears to give the best agreement with experimental branching ratio for parallel detection. The agreement is less satisfactory for perpendicular detection. Neither the effect of finite-acceptance angle of the photoelectron detector nor high intensities can explain the discrepancy.

Rudolph, H.↗
DOE OSTI2021

Coherent microwave scattering from resonance enhanced multi-photon ionization (Radar REMPI): A review

Coherent microwave scattering from laser-induced plasmas, including weakly ionized plasma, laser sparks, Multiphoton Ionization (MPI), and Resonance Enhanced Multi-Photon Ionizations (Radar REMPI) has achieved much successes in plasma, reactive and nonreactive flow diagnostics. Under illumination of microwaves (Radar), electrons inside the laser-induced plasma oscillate with the electric field of the microwave and re-radiate from the electrons forming coherent scattering. In the far-field approximation, the microwave scattering from the small volume plasma reflects the generation and evolution of unbounded electrons inside the plasma, when the microwave wavelength is much greater than the size of the plasma and the skin layer depth at the microwave frequency is larger than the size of the plasma. Laser excitation schemes, microwave detection methods, calibration of microwave scattering, and the novel applications of the technique have been significantly expanded and improved. Furthermore, this review paper summarizes physical principles, various REMPI excitation schemes for atomic and molecular species, and temperature measurements in plasma and reactive flows. Discussions on new research directions and applications are given at the end.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1987

(2 + 1) resonant enhanced multiphoton ionization of H2 via the E,F 1Sigma(+)g state

In this paper, the results of ab initio calculations of photoelectron angular distributions and vibrational branching ratios for the (2 + 1) resonant enhanced multiphoton ionization (REMPI) of H2 via the E,F 1Sigma(+)g state are reported, and these are compared with the experimental data of Anderson et al. (1984). These results show that the observed non-Franck-Condon behavior is predominantly due to the R dependence of the transition matrix elements, and to a lesser degree to the energy dependence. This work presents the first molecular REMPI study employing a correlated wave function to describe the Rydberg-valence mixing in the resonant intermediate state.

Rudolph, H.↗
NASA NTRS1988

Ionic rotational branching ratios in resonant enhanced multiphoton ionization of NO via the A2Sigma(+)(3s sigma) and D2Sigma(+)(3p sigma) states

Results are presented for the rotationally resolved photoelectron spectra resulting from a (2 + 1) one-color resonant enhanced multiphoton ionization (REMPI) of NO via the rotationally clean S21(11.5) and mixed S11(15.5) + R21(15.5) branches of the 0-0 transition in the D-X band. The calculations were done in the fixed-nuclei frozen core approximation. The resulting photoionization spectra, convoluted with a Lorentzian detection function, agree qualitatively with experimental results of Viswanathan et al. (1986) and support their conclusion that the nonspherical nature of the molecular potential creates a substantial l-mixing in the continuum, which in turn leads to the intense Delta N = 0 peak. The rather strong photoelectron energy dependence of the rotational branching ratios of the D 2Sigma(+) S21(11.5) line was investigated and compared to the weak energy dependence of the A 2Sigma(+) R22(21.5) line.

Rudolph, H.↗
NASA NTRS2016

Numerical Evaluation of an Ejector-Enhanced Resonant Pulse Combustor with a Poppet Inlet Valve and a Converging Exhaust Nozzle

A computational investigation of a pressure-gain combustor system for gas turbine applications is presented. The system consists of a valved pulse combustor and an ejector, housed within a shroud. The study focuses on two enhancements to previous models, related to the valve and ejector components. First, a new poppet inlet valve system is investigated, replacing the previously used reed valve configuration. Secondly, a new computational approach to approximating the effects of choked turbine inlet guide vanes present immediately downstream of the Ejector-Enhanced Resonant Pulse Combustor (EERPC) is investigated. Instead of specifying a back pressure at the EERPC exit boundary (as was done in previous studies) the new model adds a converging-diverging (CD) nozzle at the exit of the EERPC. The throat area of the CD nozzle can be adjusted to obtain the desired back pressure level and total mass flow rate. The results presented indicate that the new poppet valve configuration performs nearly as well as the original reed valve system, and that the addition of the CD nozzle is an effective method to approximate the exit boundary effects of a turbine present downstream of the EERPC. Furthermore, it is shown that the more acoustically reflective boundary imposed by a nozzle as compared to a constant pressure surface does not significantly affect operation or performance.

Computational Fluid Dynamics (CFD↗
DOE OSTI2026

Pattern-enhanced Resonant Soft X-ray Scattering for Operando monitoring of electrochemical solid-liquid interfaces

Unveiling interfaces at sub-nanometer scales is essential for advancing the understanding of complex chemical transformations. However, characterizing solid-liquid interfaces with high dimensional sensitivity and temporal resolution remains challenging, due to their dynamic nature and inaccessibility by conventional probes. Here we present an approach, Pattern-enhanced Resonant Soft X-ray Scattering, to overcome the challenges. Rooted in a “sample-as-optics” philosophy, this technique utilizes precisely engineered line-grating nanopatterns to modulate near-field X-ray illumination, coherently enhancing scattering signals from the line-gratings. We implement the method using Ni line-grating nanopatterns in electrochemical water oxidation. The periodic nanostructures serve as diffractive optical elements to reveal the Ni oxidation gradients and structural dynamics at the electrode-electrolyte interfaces. Finite-element simulations corroborate the observed trends by modeling variations in compositions and structures during electrocatalysis. Through integrating advanced sample design with coherent wave nature of soft X-rays, our approach opens accessible pathways to operando exploring chemical evolution and sub-nanometer dimensional variations simultaneously in electrochemical systems. This non-destructive method is efficient and element-specific, making it valuable for probing chemical and dimensional dynamics with appropriate modeling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗