Pump Radiation Research Articles

Exploring the Synergy of Integration: Assessing the Performance of Hydraulic Storage and Solar Power Integration in Kirkuk city

This research investigates the performance of integrated system combining of hydraulic storage and solar power in Iraq. A photovoltaic-water pumping system was designed to store solar energy in the form of water in tank at a height of 6 mm. The study evaluates the influence of solar radiation level and pumping time in determining the amount of energy stored. During clear days in March, 175 minutes was taken to pump a total of 3400 liters of water in the case of the fixed PV panel, while when using the tracker, the time is reduced to 165 minutes for filling the tank with the same quantity of water due to the increase in the pumping capacity in the case of the tracker. During a cloudy day in the same month, the same quantity of water was pumped in 230 minutes. The stored water was then utilized to generate electricity, with varying flow rates based on the desired power output .The highest produced power was obtained by 42.9 W at a 42 lit / sec water flow rate, and the lowest power obtained by 23.2 W at a minimum water flow rate of 25 lit / sec. Moreover, the system's cost-effectiveness is enhanced by employing a direct current pump which can be used without the need for the inverter or batteries. These findings provide good understanding for the integrating of the hydraulic storage and solar power systems, offering potential solutions for sustainable energy generation in Iraq.

Thermal performance of a laser-diode end-pumped Nd:YVO4 slab crystal cooled by a pair of microchannel heat sinks

Laser crystal is a key component in the all solid-state laser system. The cooling method for the laser crystal is quite critical when the pump power is high. However, due to some measurement difficulties, the surface temperature and heat dissipation pattern of the laser crystal have not been well demonstrated previously. In this work, we use a pair of novel central-jetting microchannel heat sinks (CJ-MCHSs) to cool a Nd:YVO4 slab crystal under high-power pump conditions. The surface temperature of the crystal is measured directly from its side face by using a slot barrier to filter stray light from pump radiation. The temperature distribution and local heat flux of the laser crystal are obtained. It shows that the surface temperature of the slab crystal decreases linearly along the beaming depth. At a typical pump power of 276 W, the temperature reaches 136 °C at the front face of the crystal but it is only 58 °C at the end face. The crystal's thickness affects the rate of heat dissipation. When the crystal's thickness increases from 1.0 mm to 1.5 mm, the temperature of the crystal is enhanced by about 15 °C. In the present experiments, the surface temperature of the CJ-MCHS is also monitored. The front side and back side of the CJ-MCHS show quite different temperature distribution patterns because of the non-uniform heat releasing pattern of the crystal. Comparing with a traditional macrochannel heat sink, the novel CJ-MCHS reduces the temperature gradient along the beaming direction and eliminates the unsymmetrical temperature distributions at the sides of the crystal.

ATOMIUM: Probing the inner wind of evolved O-rich stars with new, highly excited H2O and OH lines

Context. Water (H2O) and the hydroxyl radical (OH) are major constituents of the envelope of O-rich late-type stars. Transitions involving energy levels that are rotationally or vibrationally highly excited (energies ≳4000 K) have been observed in both H2O and OH. These and more recently discovered transitions can now be observed at a high sensitivity and angular resolution in the inner wind close to the stellar photosphere with the Atacama Large Millimeter/submillimeter Array (ALMA). Aims. Our goals are: (1) to identify and map the emission and absorption of H2O in several vibrational states, and of OH in Λ-doubling transitions with similar excitation energies; and (2) to determine the physical conditions and kinematics in gas layers close to the extended atmosphere in a sample of asymptotic giant branch stars (AGBs) and red supergiants (RSGs). Methods. Spectra and maps of H2O and OH lines observed in a 27 GHz aggregated bandwidth and with an angular resolution of ~0."02−1."0 were obtained at two epochs with the main ALMA array. Additional observations with the Atacama Compact Array (ACA) were used to check for time variability of water transitions. Radiative transfer models of H2O were revisited to characterize masing conditions. Up-to-date chemical models were used for comparison with the observed OH/H2O abundance ratio. Results. Ten rotational transitions of H2O with excitation energies ~4000–9000 K were observed in vibrational states up to (υ1,υ2,υ3) = (0,1,1). All but one are new detections in space, and from these we have derived accurate rest frequencies. Hyperfine split Λ-doubling transitions in υ = 0, J = 27/2 and 29/2 levels of the 2Π3/2 state, as well as J = 33/2 and 35/2 of the 2Π1/2 state of OH with excitation energies of ~4780–8900 K were also observed. Four of these transitions are new detections in space. Combining our measurements with earlier observations of OH, the υ = 0 and υ = 1 Λ-doubling frequencies have been improved. Our H2O maps show compact emission toward the central star and extensions up to twelve stellar radii or more. The 268.149 GHz emission line of water in the υ2 = 2 state is time variable, tends to be masing with dominant radiative pumping, and is widely excited in AGBs and RSGs. The widespread but weaker 262.898 GHz water line in the υ2 = 1 state also shows signs of maser emission. The OH emission is weak and quasithermally excited. Emission and absorption features of H2O and OH reveal an infall of matter and complex kinematics influenced by binarity. From the OH and H2O column densities derived with nonmasing transitions in a few sources, we obtain OH/H2O abundance ratios of ~(0.7–2.8) × 10−2.

A generalized Drude–Smith model for ultrafast pump-and-probe experiments and its application for studying of electronic dynamic properties of polycrystalline diamond

In this work, we generalize the Drude–Smith model (DSM) proposed for optical conductivity in frequency-domain to the case of ultrafast pump-and-probe experiments, where the results are measured in time-domain. The generalized DSM (GDSM) considers the optically induced electronic backscattering or localization effect, and can be utilized for studying the electronic dynamics induced by pulsed radiation field in time-domain. By applying the optical-pump and terahertz-probe (OPTP) technique via normal reflection measurement, we study the electronic dynamic properties of polycrystalline diamond (PCD) on Si substrate and examine the validity of the proposed GDSM. We find that this model can lead to a better fitting between the experimental and theoretical results and can reasonably reflect the information about time resolution of the measurement system and the energy relaxation time for free carriers in PCD. For PCD subjected to 800 nm wavelength fs laser irradiation, the effect of carrier backscattering decreases and the electronic energy relaxation time increases with increasing pump radiation fluence. We hope that the GDSM from this work can be helpful for understanding the electronic dynamics in electronic and optoelectronic materials measured by, e.g., ultrafast pump-and-probe experiments.

The Role of Ferromagnetic Layer Thickness and Substrate Material in Spintronic Emitters.

In this article, we investigate optically induced terahertz radiation in ferromagnetic FeCo layers of varying thickness on Si and SiO2 substrates. Efforts have been made to account for the influence of the substrate on the parameters of the THz radiation generated by the ferromagnetic FeCo film. The study reveals that the thickness of the ferromagnetic layer and the material of the substrate significantly affect the generation efficiency and spectral characteristics of the THz radiation. Our results also emphasize the importance of accounting for the reflection and transmission coefficients of the THz radiation when analyzing the generation process. The observed radiation features correlate with the magneto-dipole mechanism, triggered by the ultrafast demagnetization of the ferromagnetic material. This research contributes to a better understanding of THz radiation generation mechanisms in ferromagnetic films and may be useful for the further development of THz technology applications in the field of spintronics and other related areas. A key discovery of our study is the identification of a nonmonotonic relationship between the radiation amplitude and pump intensity for thin films on semiconductor substrates. This finding is particularly significant considering that thin films are predominantly used in spintronic emitters due to the characteristic absorption of THz radiation in metals.

A Laser-Printed Surface-Enhanced Photoluminescence Sensor for the Sub-Nanomolar Optical Detection of Mercury in Water

Here, we report a novel, easy-to-implement scalable single-step procedure for the fabrication of a solid-state surface-enhanced photoluminescence (SEPL) sensor via the direct femtosecond (fs) laser patterning of monocrystalline Si wafers placed under the layer of functionalizing solution simultaneously containing a metal salt precursor (AgNO3) and a photoluminescent probe (d114). Such laser processing creates periodically modulated micro- and nanostructures decorated with Ag nanoparticles on the Si surface, which effectively adsorbs and retains the photoluminescent sensor layer. The SEPL effect stimulated by the micro- and nanostructures formed on the Si surface localizing pump radiation within the near-surface layer and surface plasmons supported by the decorating Ag nanoparticles is responsible for the intense optical sensory response modulated by a small amount of analyte species. The produced SEPL sensor operating within a fluidic device was found to detect sub-nanomolar concentrations of Hg2+ in water which is two orders of magnitude lower compared to this molecular probe sensitivity in solution. The fabrication technique is upscalable, inexpensive, and flexible regarding the ability to the control surface nano-morphology, the amount and type of loading noble-metal nanoparticles, as well as the type of molecular probe. This opens up pathways for the on-demand development of various multi-functional chemosensing platforms with expanded functionality.

Quantum classical approach to spin and charge pumping and the ensuing radiation in terahertz spintronics: Example of the ultrafast light-driven Weyl antiferromagnet Mn3Sn

The interaction of a femtosecond laser pulse with magnetic materials has been intensely studied for more than two decades in order to understand ultrafast demagnetization in single magnetic layers or terahertz emission from their bilayers with nonmagnetic spin-orbit (SO) materials. However, in contrast to well-understood spin and charge pumping by dynamical magnetization in spintronic systems driven by microwaves or current injection, analogous processes in light-driven magnets and radiation emitted by them remain largely unexplained due to the multiscale nature of the problem. Here we develop a multiscale quantum-classical formalism---where conduction electrons are described by quantum master equation (QME) of the Lindblad type, classical dynamics of local magnetization is described by the Landau-Lifshitz-Gilbert (LLG) equation, and incoming light is described by classical vector potential, while outgoing electromagnetic radiation is computed using the Jefimenko equations for retarded electric and magnetic fields---and apply it to a bilayer of antiferromagnetic Weyl semimetal ${\mathrm{Mn}}_{3}\mathrm{Sn}$, hosting noncollinear local magnetization, and SO-coupled nonmagnetic material. Our $\mathrm{QME}+\mathrm{LLG}+$Jefimenko scheme makes it possible to understand how a femtosecond laser pulse directly generates spin and charge pumping and electromagnetic radiation by the ${\mathrm{Mn}}_{3}\mathrm{Sn}$ layer, including both odd and even high harmonics (of the pulse center frequency) up to order $n\ensuremath{\le}7$. The directly pumped spin current then exerts spin torque on local magnetization whose dynamics, in turn, pumps additional spin and charge currents radiating in the terahertz range. By switching on and off LLG dynamics and SO couplings, we unravel which microscopic mechanism contributes the most to emitted terahertz radiation---charge pumping by local magnetization of ${\mathrm{Mn}}_{3}\mathrm{Sn}$ in the presence of its own SO coupling is far more important than standardly assumed (for other types of magnetic layers) spin pumping and subsequent spin-to-charge conversion within the adjacent nonmagnetic SO-coupled material.

Radiative pumping of exciton-polaritons in 2D hybrid perovskites

In addition to their attractive technological applications in photovoltaics and light emitters, the perovskite family of semiconductors has recently emerged as an excellent excitonic material for fundamental studies. Specifically, the 2D hybrid organic-inorganic perovskite (HOIP) offers the added advantage of room temperature investigations owing to their large exciton binding energy. In this work, we strongly couple excitons in 2D HOIP crystals to planar microcavity photons sustaining exciton-polaritons under ambient conditions resulting in a Rabi splitting of 290 meV. Dark excitons directly pump the polariton branch along its dispersion in resonance with the Stokes shifted emission state (radiative pumping), creating a high density of polaritons at higher in-plane momentum (k||). We further probe the nonlinear polariton dispersion dynamics at varying input laser fluence, which indicates efficient polariton-polariton scattering and decay to k|| = 0 from higher k||. The observation of Stokes shift-assisted energy exchange of dark states with lower polaritons coupled with evidence of efficient polariton-polariton scattering makes 2D HOIPs an attractive platform to study exciton-polariton many-body physics and Bose-Einstein like condensation (BEC) at room temperature.

Competition between nonlinear processes excited by picosecond laser pulses in a disodium ditungstate Raman crystal for two excitation polarizations

Two nonlinear processes, namely, two-photon absorption (TPA) and stimulated Raman scattering (SRS) in Na2W2O7 crystal at a wavelength of 523.5 nm, are studied theoretically and experimentally depending on the polarization of the incident picosecond laser radiation. It was found that, due to the anisotropy of the band gap structure, the TPA coefficient at 523.5 nm strongly depends on the pump radiation polarization. For radiation along the c axis with polarization parallel to the a axis, the TPA coefficient was measured to be 1.28 cm GW−1, and no SRS process was registered. However, for polarization parallel to the b axis, no measurable TPA was detected and SRS with a gain of 6.5 cm GW−1 was observed. To the best of our knowledge, this is the first demonstration of the competition of two nonlinear processes in one crystal depending on its orientation.

Multi-frequency VLBI observations of maser lines during the 6.7 GHz maser flare in the high-mass young stellar object G24.33+0.14

Context. Recent studies have shown that 6.7 GHz methanol maser flares can be a powerful tool for verifying the mechanisms of maser production and even the specific signatures of accretion rate changes in the early stages of high-mass star formation. Aims. We characterize the spatial structure and evolution of methanol and water masers during a flare of methanol maser emission at 6.7 GHz in the high-mass young stellar object (HMYSO) G24.33+0.14. Methods. Very Long Baseline Array (VLBA) was used to image the 6.7 and 12.2 GHz methanol and 22.2 GHz water vapor masers at three epochs guided by monitoring the methanol line with the Torun 32m telescope. The 6.7 GHz maser maps were also obtained with the European VLBI Network (EVN) and Long Baseline Array (LBA) during the flare. The Wide-field Infrared Survey Explorer (WISE) data were used to find correlations between the 6.7 GHz maser and infrared (IR) fluxes. Results. The 6.7 GHz methanol maser cloudlets are distributed over ~3500 au, and the morphology of most of them is stable although their brightness varies following the course of the total flux density on a timescale of two months. The 12.2 GHz methanol maser cloudlets cover an area an order of magnitude smaller than that of 6.7 GHz emission, and both transitions emerge from the same masing gas. The 22.2 GHz maser cloudlets lie in the central region and show a systematic increase in brightness and moderate changes in size and orientation, together with the velocity drift of the strongest cloudlet during two months of the Very Long Baseline Interferometry (VLBI) observing period. Time lag estimates imply the propagation of changes in the physical conditions of the masing region with a subluminal speed (~0.3c). A tight correlation of IR (4.6 μm) and 6.7 GHz flux densities is found, supporting the radiative pumping model. Proper motion analysis does not reveal any signs of expansion or inflow of the methanol cloudlets within ~6 mas over ~10 yr. Comparison with the 230 GHz Atacama Large Millimeter Array (ALMA) data indicates that the methanol masers are distributed in the inner part of the rotating disk, whereas the 22.2 GHz emission traces the compact inner component of the bipolar outflow or a jet structure. Conclusions. The maser morphology in the target is remarkably stable over the course of the flare and is similar to the quiescent state, possibly due to less energetic accretion events that can repeat on a timescale of ~8 yr.

Noise-like Pulses as a Source of Pump Energy

This work analyses application particulars of noise-like pulses used as pulsed pump radiation for lasers (including Raman lasers) and amplifiers. The absence of a phase relationship between the electromagnetic field of the pump and that of the output laser radiation allows for a new application as a pump energy source of noise-like pulses, which may feature relatively high energy parameters. Questions related to this application are considered: configurations for noise-like pulse generation that hold a significant potential, specific aspects of amplification and compression, and characterisation of parameters of these pulses. Possibilities of the efficient application of noise-like pulses as pico- and nano-second pumping radiation are also discussed.

Ultrastrong coupling in Super Yellow polymer microcavities and development of highly efficient polariton light-emitting diodes and light-emitting transistors.

We present detailed studies on exciton-photon coupling and polariton emission based on a poly(1,4-phenylenevinylene) copolymer, Super Yellow (SY), in a series of optical microcavities and optoelectronic devices, including light-emitting diode (LED) and light-emitting transistor (LET). We show that sufficiently thick SY microcavities can generate ultrastrong coupling with Rabi splitting energies exceeding 1 eV and exhibit spectrally narrow, nearly angle-independent photoluminescence following lower polariton (LP) mode dispersion. When the microcavity is designed with matched LP low-energy state and exciton emission peak for radiative pumping, the conversion efficiency from exciton to polariton emission can reach up to 80%. By introducing appropriate injection layers in a SY microcavity and optimizing the cavity design, we further demonstrate a high-performance ultrastrongly coupled SY LED with weakly dispersive electroluminescence along LP mode and a maximum external quantum efficiency (EQE) of 2.8%. Finally, we realize an ultrastrongly coupled LET based on vertical integration of a high-mobility ZnO transistor and a SY LED in a microcavity, which enables a large switching ratio, uniform emission in the ZnO pattern, and LP mode emission with a maximum EQE of 2.4%. This vertical LET addresses the difficulties of achieving high emission performance and precisely defining the emission area in typical planar LETs, and opens up the possibility of applying various strongly coupled emitters for advanced polariton devices and high-resolution applications.

Non‐Equilibrium Bose–Einstein Condensation of Exciton‐Polaritons in Silicon Metasurfaces

AbstractExciton‐polaritons (EPs) are hybrid light–matter quasi‐particles with bosonic character formed by the strong coupling between excitons in matter and photons in optical cavities. Their hybrid character offers promising prospects for the realization of non‐equilibrium Bose–Einstein condensates (BECs), and room‐temperature BECs are possible with organic materials. However, the thresholds required to create BECs of organic EPs remain still high to allow condensation with electrical injection of carriers. One of the factors behind these high thresholds is the very short cavity lifetimes, leading to a fast EP decay and the need to inject higher exciton densities in the reservoir to form the condensate. Here a BEC of EPs in organic dyes and all‐dielectric metasurfaces at room temperature is demonstrated. By using dielectric metasurfaces that exhibit very low losses it is possible to achieve cavity lifetimes long enough to allow an efficient population of EP states via vibrational relaxation and radiative pumping. It is shown how polariton lasing or non‐equilibrium Bose–Einstein condensation is achieved in several cavities, and one of the lowest reported thresholds for BECs in organic materials is observed.

Monolithic silica fiber laser operating at 585 nm.

We report, to the best of our knowledge, the first monolithic silica fiber laser operating in the visible. The laser cavity is based on a dysprosium-doped aluminosilicate fiber bounded by a pair of fiber Bragg gratings operating at 585 nm. The yellow laser signal reaches a record output power of 147 mW. Although the pump irradiation causes photodarkening, significant reduction of the photoinduced absorption losses is demonstrated via a photobleaching process with visible light.

Gold-nanoparticles induced transition in YVO4 crystal: From saturable to reverse saturable absorption

The embedded gold (Au) nanoparticles (NPs) are synthesized inside the yttrium vanadate (YVO4) crystal by direct Au ion implantation. The formed Au nanospheres are with average diameter of ∼5 nm, generating a clear optical absorption band centered at 595 nm due to the localized surface plasmon resonance (LSPR). With the doping of Au NPs, the nonlinear optical properties of YVO4 crystal are also modified, endowing the substrate with new features. Using femtosecond open-aperture Z-scan investigation under variable laser intensities, the Au NPs-modified YVO4 exhibits saturable absorption (SA) property at moderate excitation irradiances due to the plasmonic effect of embedded Au NPs, whilst transits to reverse saturable absorption (RSA) under higher pump irradiances. As an example for practical applications, we demonstrate a 1-μm pulse laser generation utilizing Au NPs-embedded YVO4 crystal as the saturable absorber. This work suggests that ion beam synthesis of metallic NPs may be a suitable way to tailor properties of functional crystals to achieve diverse applications in optics.

Thermal load analysis and structure optimization of neutral beam injector cryosorption pump

In order to meet the high vacuum requirement of neutral beam source, cryosorption pump is used as the main pump, and the pumping performance of cryosorption pump depends on its cryogenic performance. To test and verify the feasibility of cryosorption pump steady running, modular design based on cryosorption pump, composed of 16 extraction unit in series, in a single suction unit as the research object, respectively for radiation and cryosorption pump baffle panel of the theory of heat load, and will result in finite element analysis software, the analysis of the temperature field of two structures, respectively and extraction unit structure optimization direction is put forward. The simulation results show that the normal operating temperature of the cryosorption pump can be reached under steady-state operating conditions, and the cryogenic performance of the extraction unit can be improved after the optimization of the structure, thus providing reference for the optimization of the cryogenic pump group.

Effect of Ultraviolet Radiation on Reducing Airborne Escherichia coli Carried by Poultry Litter Particles.

Airborne Escherichia coli (E. coli) originating in poultry houses can be transmitted outside poultry farms through the air, posing risks of barn-to-barn infection through airborne transmission. The objective of this study is to examine the effect of ultraviolet (UV) light on the inactivation of airborne E. coli carried by poultry dust particles under laboratory conditions. A system containing two chambers that were connected by a UV scrubber was designed in the study. In the upstream chamber of the system, airborne E. coli attached to dust particles were aerosolized by a dry aerosolization-based system. Two sets of air samplers were placed in the two chambers to collect the viable airborne E. coli. By comparing the concentration of airborne E. coli in the two chambers, the inactivation rates were calculated. The airborne E. coli inactivation rates were tested at different contact times with the aid of a vacuum pump (from 5.62 to 0.23 s of contact time) and different UV irradiance levels (of 1707 µW cm-2 and 3422 µW cm-2). The inactivation rates varied from over 99.87% and 99.95% at 5.62 s of contact time with 1707 µW cm-2 and 3422 µW cm-2 of UV irradiance to 72.90% and 86.60% at 0.23 s of contact time with 1707 µW cm-2 and 3422 µW cm-2 of UV irradiance. The designed system was able to create the average UV irradiation of 1707 µW cm-2 and 3422 µW cm-2 for one UV lamp and two UV lamps, respectively. The findings of this study may provide an understanding of the effect of UV light on the inactivation of airborne E. coli carried by dust particles and help to design an affordable mitigation system for poultry houses.

Importance of radiative pumping for the excitation of the H2O submillimeter lines in galaxies

H2O submillimeter emission is a powerful diagnostic of the molecular interstellar medium in a variety of sources, including low- and high-mass star-forming regions of the Milky Way, and from local to high-redshift galaxies. However, the excitation mechanism of these lines in galaxies has been debated, preventing a basic consensus on the physical information that H2O provides. Radiative pumping due to H2O absorption of far-infrared photons emitted by dust and collisional excitation in dense shocked gas have both been proposed to explain the H2O emission. Here we propose two basic diagnostics to distinguish between the two mechanisms: First, the ortho-H2O 321 − 212 75 μm and the para-H2O 220 − 111 101 μm rotational lines in shock-excited regions are expected to be in emission, while when radiative pumping dominates, the two far-infrared lines are expected to be in absorption. Second, the radiative pumping scenario predicts, based on the statistical equilibrium of H2O level populations, that the apparent isotropic net rate of far-infrared absorption in the 321 ← 212 (75 μm) and 220 ← 111 (101 μm) lines should be higher than or equal to the apparent isotropic net rate of submillimeter emission in the 321 → 312 (1163 GHz) and 220 → 211 (1229 GHz) lines, respectively. Applying both criteria to all 16 galaxies and several Galactic high-mass star-forming regions in which the H2O 75 μm and submillimeter lines have been observed with Herschel/PACS and SPIRE, we show that in most (extra)galactic sources, the H2O submillimeter line excitation is dominated by far-infrared pumping, combined in some cases with collisional excitation of the lowest energy levels. Based on this finding, we revisit the interpretation of the correlation between the luminosity of the H2O 988 GHz line and the source luminosity in the combined Galactic and extragalactic sample.

Origins of THz Modes and Their IR Intensities in LiNbO3

LiNbO3 crystals have been essential materials for generating freely propagating terahertz (THz) pulses among other materials because of their excellent nonlinear optical properties and high damage thresholds. However, one of their dielectric properties─the huge IR intensities of THz modes─has been impeding their practical applications. Such IR intensities produce additional contributions to the refractive index, making the phase-matching between the optical pump and THz radiation difficult. The large IR intensities also lead to strong THz absorptions, reducing the conversion coefficient. Although a couple of techniques have been applied to solve or avoid the relevant problems, a more fundamental question regarding the atomic mechanism of generating the huge IR intensities of THz modes in LiNbO3 has not been discussed so far. We performed a rigorous analysis of the nature of THz modes in terms of the contributions from the constituent atoms Li, Nb, and O using a quantitative approach originally developed in the previous studies. We further clarified the roles played by the motions of the constituent atoms in generating IR intensities by calculating the associated Born charge vectors. We revealed that the librations of the O octahedra, despite their prominent presence in some THz modes, are IR-silent motions. The translations of the O octahedra and Nb cations are the leading contributors to IR intensities, while the internal vibrations of the O octahedra play a destructive role. We propose two mechanisms for reducing the IR intensities of THz modes in LiNbO3 based on the analyzed results.

The effect of water and electron collisions in the rotational excitation of HF in comets

ABSTRACT We present the first set of rate coefficients for the rotational excitation of the 7 lowest levels of hydrogen fluoride (HF) induced by collision with water molecules, the dominant collider in cometary comas, in the 5–150 K temperature range. The calculations are performed with a quantum statistical approach from an accurate rigid rotor ab initio interaction potential. Rate coefficients for excitation of HF by electron-impact are also computed, within the Born approximation, in the 10–10 000 K temperature range. These rate coefficients are then used in a simple non-local thermodynamic equilibrium (non-LTE) model of a cometary coma that also includes solar radiative pumping and radiative decay. We investigate the range of H2O densities that lead to non-LTE populations of the rotational levels of HF. We show that to describe the excitation of HF in comets, considering collisions with both water molecules and electrons is needed as a result of the large dipole of HF.