Birge Hopfield Research Articles

Far ultraviolet mirrors for aurora imaging: design and fabrication.

The emission lines of 140-180nm are auroral bands of N 2 Lyman-Birge-Hopfield, and they have been imaging targets of many satellites that need reflective mirrors. To obtain good imaging quality, the mirrors also should have excellent out-of-band reflection suppression as well as high reflectance at working wavelengths. We designed and fabricated non-periodic multilayer L a F 3/M g F 2 mirrors with working wave bands of 140-160nm and 160-180nm, respectively. We used a match design method and deep search method to design the multilayer. Our work has been utilized in the new wide-field auroral imager of China, and the application of these notch mirrors with excellent out-of-band suppression reduces the utilization of corresponding transmissive filters in the optical system of space payload. Furthermore, our work provides new routes for the design of other reflective mirrors in the far ultraviolet region.

The Electronic Kinetics of Molecular Nitrogen and Molecular Oxygen in the Earth’s Middle Atmosphere during the GLE Events of Solar Cycle 23

Based on models of the electronic kinetics of triplet and singlet states of molecular nitrogen andsinglet states of molecular oxygen for the Earth’s middle atmosphere, we calculated the intensity profiles ofthe bands of the first and second positive N2 systems, the Lyman–Birge–Hopfield N2 bands, and the infraredO2 bands in the case of precipitation of high-energy protons during the GLE65, GLE67, GLE69, and GLE70events of solar cycle 23. Calculations have shown that almost over the entire interval of altitudes of 20–80 km,there is a significant contribution from the processes of quenching some electronically excited states of N2and O2 during molecular collisions. The kinetics of O2 singlet states at the altitudes of the middle atmosphereduring proton precipitation is considered taking into account both direct excitation by high-energy particlesand intermolecular processes of electron excitation transfer

Triplet state harvesting and search for forbidden transition intensity in the nitrogen molecule.

Triplet excited states of the N2 molecule play an important role in electric discharges through air or liquid nitrogen accompanied by various afterglows. In the rarefied upper atmosphere, they produce aurora borealis and participate in other energy-transfer processes connected with atmospheric photochemistry and nightglow. In this work, we present spin-orbit coupling calculations of the intensity of various forbidden transitions, including the prediction of the electric dipole transition moment of the new band, which is strongly prohibited by the (+|-) selection rule, the new spin-induced magnetic transition, magnetic and electric quadrupole transitions for the B3Πg Wilkinson band, and the Lyman-Birge-Hopfield a1Πg ← X1Σg transition. Also, two other far-UV singlet-singlet quadrupole transitions are calculated for the first time, namely, the Dressler-Lutz a"1Σg +-X1Σg + and the less studied z1Δg-X1Σg + weak transitions.

Far-ultraviolet airglow remote sensing measurements on Feng Yun 3-D meteorological satellite

Abstract. The Ionospheric Photometer (IPM) is carried on the Feng Yun 3-D (FY3D) meteorological satellite, which allows for the measurement of far-ultraviolet (FUV) airglow radiation in the thermosphere. IPM is a compact and high-sensitivity nadir-viewing FUV remote sensing instrument. It monitors 135.6 nm emission in the nightside thermosphere and 135.6 nm and N2 Lyman–Birge–Hopfield (LBH) emissions in the dayside thermosphere that can be used to invert the peak electron density of the F2 layer (NmF2) at night and the O/N2 ratio in the daytime, respectively. Preliminary observations show that the IPM could monitor the global structure of the equatorial ionization anomaly (EIA) structure around 02:00 LT using atomic oxygen (OI) 135.6 nm nightglow. It could also identify the reduction of O/N2 in the high-latitude region during the geomagnetic storm of 26 August 2018. The IPM-derived NmF2 agrees well with that observed by four ionosonde stations along 120∘ E with a standard deviation of 26.67 %. Initial results demonstrate that the performance of IPM meets the design requirements and therefore can be used to study the thermosphere and ionosphere in the future.

A Study of the Luminescence of the Lyman–Birge–Hopfield Bands in the Atmospheres of the Earth and Titan

A Study of the Luminescence of the Lyman–Birge–Hopfield Bands in the Atmospheres of the Earth and Titan

Deriving column-integrated thermospheric temperature with the N<sub>2</sub> Lyman–Birge–Hopfield (2,0) band

Abstract. This paper presents a new technique to derive thermospheric temperature from space-based disk observations of far ultraviolet airglow. The technique, guided by findings from principal component analysis of synthetic daytime Lyman–Birge–Hopfield (LBH) disk emissions, uses a ratio of the emissions in two spectral channels that together span the LBH (2,0) band to determine the change in band shape with respect to a change in the rotational temperature of N2. The two-channel-ratio approach limits representativeness and measurement error by only requiring measurement of the relative magnitudes between two spectral channels and not radiometrically calibrated intensities, simplifying the forward model from a full radiative transfer model to a vibrational–rotational band model. It is shown that the derived temperature should be interpreted as a column-integrated property as opposed to a temperature at a specified altitude without utilization of a priori information of the thermospheric temperature profile. The two-channel-ratio approach is demonstrated using NASA GOLD Level 1C disk emission data for the period of 2–8 November 2018 during which a moderate geomagnetic storm has occurred. Due to the lack of independent thermospheric temperature observations, the efficacy of the approach is validated through comparisons of the column-integrated temperature derived from GOLD Level 1C data with the GOLD Level 2 temperature product as well as temperatures from first principle and empirical models. The storm-time thermospheric response manifested in the column-integrated temperature is also shown to corroborate well with hemispherically integrated Joule heating rates, ESA SWARM mass density at 460 km, and GOLD Level 2 column O/N2 ratio.

Auroral ionospheric E region parameters obtained from satellite- based far-ultraviolet and ground-based ionosonde observations – effects of proton precipitation

Abstract. Coincident auroral far-ultraviolet (FUV) and ground-based ionosonde observations are compared for the purpose of determining whether auroral FUV remote sensing algorithms that assume pure electron precipitation are biased in the presence of proton precipitation. Auroral particle transport and optical emission models, such as the Boltzmann 3-Constituent (B3C) model, predict that maximum E region electron density (NmE) values derived from auroral Lyman–Birge–Hopfield (LBH) emissions, assuming electron precipitation, will be biased by up to ∼20 % (high) for pure proton aurora, while comparisons between LBH radiances and radiances derived from in situ particle flux observations (i.e., Knight et al., 2008, 2012) indicate that the bias associated with proton aurora should be much larger. Surprisingly, in the comparisons with ionosonde observations described here, no bias associated with proton aurora is found in FUV-derived auroral NmE, which means that auroral FUV remote sensing methods for NmE are more accurate in the presence of proton precipitation than was suggested in the aforementioned earlier works. Possible explanations for the discrepancy with the earlier results are discussed.

Luminescence of Lyman–Birge–Hopfield Bands of N2 in the Earth’s Atmosphere during the Precipitation of High-Energy Electrons

The luminescence intensity profiles of Lyman–Birge–Hopfield bands of molecular nitrogen have been calculated for the precipitation into the Earth’s atmosphere of electrons with energies of 10 keV to 10 MeV. With an increase in the energy of electrons penetrating the atmosphere, there is an increase in the contribution of the quenching of the a1Πg N2 state in molecular collisions. This leads to a reduced ratio of the integral luminescence intensities of the Lyman–Birge–Hopfield ultraviolet bands and the second positive system upon an energy increase in high-energy electrons precipitating into the atmosphere.

Modeling of extreme ultraviolet emissions from nonthermal gas discharges in air: the b(1) − X(0) band of molecular nitrogen

We model the (v′ = 1, v″ = 0) band of the Birge–Hopfield I band system of molecular nitrogen, N2, i.e. , emitted by nonthermal gas discharges in low pressure air. In particular, we calculate the rate of electron impact excitation of N2, which is thermally equilibrated at room temperature, to rotational levels J′ < 31 of N2(b1Πu, v′ = 1, J′). Subsequently, we calculate the intensity of emission lines resulting from radiative transitions from the aforementioned rotational levels to . Predissociation is the only nonradiative channel considered for the decay of N2(b1Πu, v′ = 1, J′) levels.

Experimental study of the dynamics of fast gas heating in a low-pressure DC discharge in nitrogen

This paper discusses the experimental studies of the gas heating dynamics of a low-pressure DC discharge in nitrogen. The time evolution of the discharge current, the electric field, and the gas temperature in the positive column of a pulsed DC discharge in nitrogen for a gas pressure of 1.5 Torr and a current density of 0.1–6 A cm−2 were measured. The gas temperature in the discharge was equal to the rotational temperature in the and metastable electronic states of nitrogen. The rotational temperature in the state was found from the spectra of the first positive system of N2, which were recorded by using intracavity laser absorption spectroscopy. The rotational temperature in the state was determined from the VUV emission spectra of the Lyman–Birge–Hopfield system of N2. The gas temperatures obtained by these two spectroscopic methods were in good agreement. It was found that two phases with different gas heating rates exist during a discharge pulse. In the first phase, the gas heating was relatively slow. With increasing current density, the duration of the first heating phase decreased from 150 μs at 0.2 A cm−2 to 10 μs at 2.5 A cm−2. In the second phase, fast gas heating occurred. The gas heating rate in the second phase increased with increasing discharge current, and was equal to 10 K μs−1 for a current density of about 2 A cm−2. The relation between the rate of the fast heating and the density of deposited power obeyed a power law. In 300 μs, the gas was heated in the discharge up to about 400, 1500, and 3000 K for current densities of 0.2, 1, and 2.5 A cm−2, respectively. These experimental data can be the basis for verification of kinetic models for gas heating dynamics in a low-pressure discharge in nitrogen.

Photoionization capable, extreme and vacuum ultraviolet emission in developing low temperature plasmas in air

Experimental observation of photoionization capable extreme ultraviolet and vacuum ultraviolet emission from nanosecond timescale, developing low temperature plasmas (i.e. streamer discharges) in atmospheric air is presented. Applying short high voltage pulses enabled the observation of the onset of plasma formation exclusively by removing the external excitation before spark development was achieved. Contrary to the common assumption that radiative transitions from the b (Birge–Hopfield I) and b (Birge–Hopfield II) singlet states of N2 are the primary contributors to photoionization events, these results indicate that radiative transitions from the c (Carroll–Yoshino) singlet state of N2 are dominant in developing low temperature plasmas in air. In addition to c transitions, photoionization capable transitions from atomic and singly ionized atomic oxygen were also observed. The inclusion of c transitions into a statistical photoionization model coupled with a fluid model enabled streamer growth in the simulation of positive streamers.

Production of [formula omitted] Vegard–Kaplan and Lyman–Birge–Hopfield emissions on Pluto

We have developed a model to calculate the emission intensities of various vibrational transitions of N2 triplet band and Lyman–Birge–Hopfield (LBH) band emissions in the dayglow of Pluto for solar minimum, moderate, and maximum conditions. The calculated overhead intensities of Vegard–Kaplan (A3Σu+–X1Σg+), First Positive (B3Πg–A3Σu+), Second Positive (C3Πu–B3Πg), Wu–Benesch (W3Δu–B3Πg), Reverse First Positive, and LBH (a1Πg–X1Σg+) bands of N2 are 17 (74), 14.8 (64), 2.4 (10.8), 2.9 (12.7), 2.9 (12.5), and 2.3 (10) R, respectively, for solar minimum (maximum) condition. We have predicted the overhead and limb intensities of VK (150–190nm) and LBH (120–190nm) bands of N2 on Pluto for the New Horizons (NH) flyby condition that can be observed by ALICE: the ultraviolet imaging spectrograph also know as P-ALICE. The predicted limb intensities of VK and LBH bands peak at radial distance of ∼2000km with the value of about 5 (13) and 9.5 (22) R for solar zenith angle 60° (0°), respectively. We have also calculated overhead and limb intensities of few prominent transition of CO Fourth Positive bands for NH flyby condition.

Electric and spectroscopic analysis of a pure nitrogen mono-filamentary dielectric barrier discharge (MF-DBD) at 760 Torr

Mono-filamentary dielectric barrier discharge (MF-DBD), occurring within 1 mm gap of atmospheric pressure pure nitrogen and operating with a sinusoidal electric supply at about 8 kHz, is studied in this paper. A thorough electrical analysis allows experimental determination of the ignition and extinction voltages, respectively (15 750 ± 50) V and (2097 ± 7) V, the injected energy (158 ± 2) J and charge (17.22 ± 0.22) nC in a single filament. The mean axial reduced electric field is equal to (644 ± 2) Td at ignition. An empirical technique is proposed to evaluate these discharge parameters by avoiding bulky calculations. Optical emission spectroscopic measurements of the vacuum ultraviolet (VUV), ultraviolet (UV), visible and near infrared (IR) emissions are presented and discussed. Two atomic nitrogen lines attributed to the decay of the N[2s2p23s 2P] triplet towards N[2s22p3 2D°] level are observed at 150 and 175 nm, together with the Lyman–Birge–Hopfield system in the VUV range. The second positive system (N2[C 3Πu] → N 2[B 3Πg]) dominates the UV and visible-blue spectra. The (0–0) transition of the first negative system peaking at 391.4 nm, the first positive system and the Herman IR transitions are also present. Both our VUV and near IR spectra are consistent with recently reported results in hollow cathode and cylindrical DBDs. The electrical and spectroscopic experimental results reported here are useful for ongoing and forthcoming modelling of filamentary nitrogen dielectric barrier discharges.

Vacuum UV and UV spectroscopy of a N2–Ar mixture discharge created by an RF helical coupling device

Optical emission spectroscopy in vacuum ultraviolet and UV spectral ranges is applied to study densities, and vibrational and rotational temperatures of the N2 molecule in a nitrogen–argon (0–95% Ar) plasma sustained at a pressure of 400 Pa by a helical cavity supplied with a power of 28 W and an excitation frequency of 27 MHz. The spatial investigation of all emission systems from UV to NIR shows a minimum situated in the middle of the helical structure and two maxima located at the positions where the RF power is transmitted to the gas and at the end of the helix. The minimum was deepest for emission of the first positive (1+) nitrogen system. This hollow shaped density profile due to the presence of a non-linear phenomenon in the discharge is constant whatever the gas composition. The emissions related to Lyman–Birge–Hopfield and the second positive (2+) systems of molecular nitrogen, and N(2P) atoms, are analyzed versus the Ar percentage. Additionally, the NO(A 2Σ+ → X 2Π) and OH(A 2Σ+ → X 2Π) emission systems coming from impurities are investigated. All the densities of the considered species increase with Ar amount. The rotational and vibrational temperatures of the emitter species are determined through the comparison between experimental and simulated spectra. In the case of a N2 discharge, all the rotational temperatures deduced through the nitrogen emission systems are equal and can be assimilated to the gas temperature. With the increase in the Ar amount, only the rotational temperature obtained from the 1+ system is close to the gas temperature. The rotational and vibrational temperatures related to the NO(A 2Σ+) species are constant whatever the gas composition. The vibrational distribution function of N2(a 1Πg) state presents a Boltzmann law with a vibrational temperature in the range 5600–8000 K (±1000 K) for the N2–x% Ar mixture with x < 75%. When the Ar percentage increases above this limit, we observe strong deviations from the Boltzmann law and no temperature can be deduced. Some kinetic considerations, where the nitrogen and argon metastables play an important role, are discussed to explain the strong dependence of the temperatures and density species toward the Ar amount in the gas mixture.

Lyman–Birge–Hopfield emissions from electron-impact excited N2

Relative electron-impact-induced emission cross sections for the a 1Πg (v′ = 3)–X 1Σ+g (v″ = 0) and a 1Πg (v′ = 2)–X 1Σ+g (v″ = 0) transitions are presented. Critical comparison is made with existing cross sections showing significant discrepancy with the widely accepted excitation function of Ajello and Shemansky (1985 J. Geophys. Res. 90 9845–61) at energies below ∼80 eV. A series of extensive measurements are presented that were performed to rule out any possible systematic or random errors in the present experimental apparatus and methodology. These efforts lead to the conclusion that the current measurements are robustly reproducible and, thus, should supplant the LBH cross-section shape of Ajello and Shemansky (1985 J. Geophys. Res. 90 9845–61).

Air plasma kinetics under the influence of sprites

A full time-dependent kinetic study is presented for the main microscopic collisional and radiative processes underlying the optical flashes associated with an impulsive (τ = 5 µs) discharge in the form of a single sprite streamer passing through an air region of the mesosphere at three different altitudes (63, 68 and 78 km). The kinetic formalism developed includes the coupling of the rate equations of each of the different species considered (electrons, ions, atoms and molecules) with the Boltzmann transport equation so that, in this way, all the kinetics is self-consistent, although, in the present approach, the electrodynamics (no Poisson equation is considered) is not coupled. The chemical model set up for air plasmas includes more than 75 species and almost 500 reactions. In addition, a complete set of reactions (more than 110) has been considered to take into account the possible impact of including H2O (humid chemistry) in the generated air plasmas. This study also considers the vibrational kinetics of N2 and CO2 and explicitly evaluates the optical emissions associated with a number of excited states of N2, O2, O in the visible, CO2 in the infrared (IR) and ultraviolet (UV) emissions of sprite streamers due to the N2 Lyman–Birge–Hopfield (LBH) and the NO-γ band systems. All the calculations are conducted for midnight conditions in mid-latitude regions (+38°N) and 0° longitude, using as initial values for the neutral species those provided by the latest version of the Whole Atmosphere Community Climate Model (WACCM). According to our calculations, the impact of 4 ppm of H2O is only slightly visible in at 68 and 78 km while it strongly affects the behaviour of the anion at all the altitudes investigated. The local enhancement of NOx predicted by the present model varies with the altitude. At 68 km, the concentrations of NO and NO2 increase by about one order of magnitude while that of NO3 exhibits a remarkable growth of up to almost three orders of magnitude. The variation of the O3 density predicted by the model in the sprite streamer head is negligible in all the altitudes investigated. The analysis of the time dependence of the electron distribution function (EDF) in the sprite plasma during the pulse reveals that the EDF transient is quite fast, reaching its ‘steady’ values during the pulse in less than 100 ns (much shorter than streamer head lifetimes). In addition, the calculated EDF during the pulse and in the afterglow is far from being Maxwellian, especially for energetic electrons (with ε > 30 eV). Finally, the evaluation of the mid-latitude nighttime electrical conductivity of air plasmas under the influence of a single sprite event reveals an increase of up to four orders of magnitude (at 68 km) above its measured background level of at an altitude of ∼70 km. This sudden increase in the electrical conductivity lasts for 100 ms (at 68 km), being shorter (∼1 ms) and longer (1 s) at 63 km and 78 km, respectively. The total power delivered by the streamer head of a single sprite event has been estimated to be approximately 1677 W (at 78 km), 230 kW (at 68 km) and 78 MW (at 63 km).

EUV resonance fluorescence of the c′ 4→ X (0, v″) and b′→ X (1, v″) transitions of N 2

Extreme ultraviolet (EUV) resonance fluorescence of the (0, v″) bands of the c′ 4 1Σ u +→ X 1Σ g + and the (1, v″) bands of the b′ 1Σ u +→ X 1Σ g + transitions of N 2 has been observed by photon excitation of N 2 in the vicinity of 95.8 nm. The integrated fluorescence intensities of the c′ 4→ X (0, v″) emission become saturated at N 2 pressures higher than ∼0.16 mTorr. The emission features in the spectral region between 105 and 130 nm become progressively significant as the N 2 pressure is increased. The (1, v″) progression for v″ up to 11 of the b′→ X transition and two progressions of the Lyman–Birge–Hopfield (LBH) system have been identified. The multiple scattering processes apparently cause significant reduction in the c′ 4→ X (0,0) emission rates. The present results may be useful in the explanation of the weak c′ 4→ X (0,0) fluorescence as well as the significant c′ 4→ X (0, v″) features in the dayglow of the Earth observed by the Far Ultraviolet Spectroscopic Explorer.

An empirical Kp-dependent global auroral model based on TIMED/GUVI FUV data

In this paper, a new empirical formulation of the mean energy and energy flux of precipitating electrons in the auroral oval is presented. Global far ultraviolet (FUV) observations by Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Global Ultraviolet Imager (GUVI) (N 2 Lyman–Birge–Hopfield small (LBHS) 140.0–150.0 nm and Lyman–Birge–Hopfield long (LBHL) 165.0–180.0 nm) are used to estimate the mean energy (Eo) and energy flux ( Q) of precipitating electrons based on an auroral model (Boltzman Three Constituent—B3C) and airglow model (Atmospheric Ultraviolet Radiance Integrated Code—AURIC). For the first time, a FUV-based and Kp-dependent model of global auroral products (Eo, Q) was developed using 4 years (2002–2005) of GUVI data and Epstein function fitting. This FUV-based model covers all Kp ranges (0–9). Due to the large spatial coverage of FUV auroral images, the FUV measurements lead to a more consistent estimation of the auroral hemispheric power. The model described here will be useful in a number of applications: global ionosphere/thermosphere simulations, space weather forecasting and nowcasting, and global ionospheric models.

Contributions of diatomic molecular electronic systems to heated air radiation

A spectroscopic database has been constructed for all the contributing electronic systems of air diatomic molecules for elevated temperatures (up to 15,000 K ). The electronic systems which have been investigated are N 2 first- and second-positive, Birge–Hopfield 1 and 2, Carroll–Yoshino, Worley and Worley–Jenkins, N 2 + Meinel, first- and second-negative, O 2 Schumann–Runge and NO γ,β,δ,ε,γ′,β′,11,000 A ̊ and infrared. The RKR potentials have been reconstructed in order to calculate the vibrational wavefunctions, and the electronic-vibrational part of line intensities has been computed with up-to-date ab-initio electronic transition moment functions. The results of our calculated vibrational band strengths are in good agreement with the available measurements. The positions and intensities of the rotational lines have been determined in intermediate a/b Hund's coupling case with up-to-date molecular constants, and the lambda doubling has been resolved when related parameters were available in the literature. Absorption spectra and the optically thin radiation source strengths of the studied electronic systems are presented and discussed in terms of their comparative contribution to emission and absorption.

Coincident ultraviolet imager and energetic particle sensor observations of the continuous electron aurora

Coincident observations in the continuous electron aurora by the ultraviolet (UV) imager on the Polar BEAR satellite and the energetic particle detector on the DMSP satellite have been examined for agreement in the energy deposition rates and the location of the equatorward auroral boundary. The energy deposition rates and the boundary location are important parameters for magnetospheric, thermospheric, and ionospheric models. Energetic particle sensors provide an accurate measurement of these quantities, but only along the path of the satellite. Two coincidences from January–February of 1987, when the Polar BEAR satellite collected UV images of the aurora at 136 nm (primarily O 5S o) and 160 nm (N 2 Lyman–Birge–Hopfield bands) while the DMSP satellite measured the electron fluxes, are discussed. For both the energy deposition rates and the boundary location, the UV and energetic particle measurements are in acceptable agreement.