Efficient metallic spintronic emitters of ultrabroadband terahertz radiation

Terahertz electromagnetic radiation is extremely useful for numerous applications such as imaging and spectroscopy. Therefore, it is highly desirable to have an efficient table-top emitter covering the 1-to-30-THz window whilst being driven by a low-cost, low-power femtosecond laser oscillator. So far, all solid-state emitters solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new terahertz source which relies on tailored fundamental spintronic and photonic phenomena in magnetic metal multilayers: ultrafast photo-induced spin currents, the inverse spin-Hall effect and a broadband Fabry-P\'erot resonance. Guided by an analytical model, such spintronic route offers unique possibilities for systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer generates ultrashort pulses fully covering the 1-to-30-THz range. Our novel source outperforms laser-oscillator-driven emitters such as ZnTe(110) crystals in terms of bandwidth, terahertz-field amplitude, flexibility, scalability and cost.Comment: 18 pages, 10 figure

Evaluating ozone depletion from very short-lived halocarbons

A new approach is needed for calculating the ozone depletion potential (ODP) of short-lived gases with mean lifetimes less than 100 days. Clearly, the ozone loss from such gases depends strongly on the location and season of emissions. It is proposed that delivery to the tropical tropopause is a surrogate for the amount of halogen entering the stratosphere. Thus 3-D global models, with accurate simulation of tropospheric chemistry and transport, can calculate the ODP specific to tropical sources (high) and high-latitude sources (low). The ODP of CH2BrCH2CH3  from this analysis ranges from 0.0002 to 0.06 depending on the location and season of emissions

Aviation Fuel Tracer Simulation: Model Intercomparison and Implications

An upper limit for aircraft-produced perturbations to aerosols and gaseous exhaust products in the upper troposphere and lower stratosphere (UT/LS) is derived using the 1992 aviation fuel tracer simulation performed by eleven global atmospheric models. Key Endings are that subsonic aircraft emissions: (1) have not be responsible for the observed water vapor trends at 40 deg N; (2) could be a significant source of soot mass near 12 km, but not at 20 km; (3) might cause a noticeable increase in the background sulfate aerosol surface area and number densities (but not mass density) near the northern mid-latitude tropopause; and (4) could provide a global, annual mean top of the atmosphere radiative forcing up to +0.006 W/sq m and -0.013 W/sq m due to emitted soot and sulfur, respectively

Stratospheric ozone in 3-D models: A simple chemistry and the cross-tropopause flux

Two simple and computationally efficient models for simulating stratospheric ozone in three-dimensional global transport models are presented. The first, linearized ozone (or Linoz), is a first-order Taylor expansion of stratospheric chemical rates in which the ozone tendency has been linearized about the local ozone mixing: ratio, temperature, and the overhead column ozone density. The second, synthetic ozone (or Synoz), is a passive, ozone-like tracer released into the stratosphere at a rate equivalent to that of the cross-tropopause ozone flux which, based on measurements and tracer-tracer correlations, we have calculated to be 475 +/- 120 Tg/Sr. Linoz and Synox ha ie been evaluated in the UC Irvine chemical transport model(CTM) with three different archived meteorological fields: the Goddard Institute for Spare Studies (GISS) general circulation model (GCM) version II', the GISS GCM version II, and merged forecast data from the European Centre forecast model (EC/Oslo). Linoz produced realistic annual, cross-tropopause fluxes of 421 Tg/yr for the GISS II' winds and 458 Tg/yr for the EC/Oslo winds; the GISS II winds produced an unrealistic flux of 790 Tg/yr. Linoz and Synoz profiles in the vicinity of the tropopause using the GISS II' and EC/Oslo winds were found to be in good agreement with observations. We conclude that either approach may be adequate for a CTM focusing on tropospheric chemistry but that Linoz can also be used for calculating ozone fields interactively with the stratospheric circulation in a GCM. A future version of Linoz will allow for evolving background concentrations of key source gases? such as CH4 and N2O, and thus be applicable for long-term climate simulations

Evaluating ozone depletion from very short-lived halocarbons

A new approach is needed for calculating the ozone depletion potential (ODP) of short-lived gases with mean lifetimes less than 100 days. Clearly, the ozone loss from such gases depends strongly on the location and season of emissions. It is proposed that delivery to the tropical tropopause is a surrogate for the amount of halogen entering the stratosphere. Thus 3-D global models, with accurate simulation of tropospheric chemistry and transport, can calculate the ODP specific to tropical sources (high) and high-latitude sources (low). The ODP of CH2BrCH2CH3  from this analysis ranges from 0.0002 to 0.06 depending on the location and season of emissions

The dry stratosphere: A limit on cometary water influx

The stratosphere accumulates the bulk of meteoric and cometary material that impacts the Earth and provides a measure of that flux. Recent models and measurements of the effective age of stratospheric air demonstrate our ability to simulate this buildup. Current observations of H2O in the stratosphere and mesosphere are consistent with an extraterrestrial source of H2O, but limit its influx to less than 2 Tg/yr. Such a flux is consistent with standard estimates but is 100 times less than the small-comet hypothesis

Excitation of the primary tropospheric chemical mode in a global three-dimensional model

Coupling of local chemical processes over the globe by atmospheric transport leads to the existence of chemical modes that are a fundamental characterization of global atmospheric chemistry and provide a true description of the atmospheric response to small changes in trace-gas emissions. Such coupled chemistry-transport modes in global tropospheric chemistry are an inherent feature of three-dimensional chemical transport models (CTMs). In CTMs these modes cannot be solved for explicitly, as they have been for the case of low-order, fully linearized systems, but they are investigated here through a series of perturbation experiments. When using meteorological fields that recycle every year, the long-lived modes are readily seen as seasonal decay patterns that e-fold each year. An important application of chemical modes is the study of how emissions of CO and NO excite perturbations to the CH4-like mode, the longest-lived (primary) mode found in tropospheric chemistry (i,e., with fixed stratospheric composition). Perturbation experiments are conducted with the University of California, Irvine, three-dimensional tropospheric CTM to identify this primary tropospheric mode and to determine its five-dimensional structure. The previous demonstrations of a long-lived chemical mode with 1.5 times the lifetime of CH4 are corroborated. The ability of emissions of CO and NO to excite this mode is then demonstrated, and a quantitative evaluation of the indirect effect of CO emissions on the greenhouse gases CH4 and tropospheric O-3 is made, showing that 100 kg of CO is equivalent to 5-6 kg of CH4 emissions