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Register a new userPhoton yields from nitrogen gas and dry air excited by electrons
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In order to detect ultrahigh-energy cosmic rays (UHECR), atmospheric fluorescence light from the trajectory of the extensive air shower may be measured by mirror-photosensor systems. In this type of experiment the photon yield from electrons exciting air of various densities and temperatures is most fundamental information for estimating the primary energy of UHECR. An experiment has been undertaken using a Sr90 $beta$ source to study the pressure dependence of photon yields, and the life times of the excited states, for radiation in nitrogen and dry air. The photon yield between 300 nm and 406 nm in air excited by 0.85 MeV electrons is 3.73+-0.15 (+-14% systematic) photons per meter at 1000 hPa and 20 $^{circ}$C. The air density and temperature dependence is given for application to UHECR observations.
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Quantum coherence in quantum optics is an essential part of optical information processing and light manipulation. Alkali metal vapors, despite the numerous shortcomings, are traditionally used in quantum optics as a working medium due to convenient near-infrared excitation, strong dipole transitions and long-lived coherence. Here, we proposed and experimentally demonstrated photon retention and subsequent re-emittance with the quantum coherence in a system of coherently excited molecular nitrogen ions (N2+) which are produced using a strong 800 nm femtosecond laser pulse. Such photon retention, facilitated by quantum coherence, keeps releasing directly-unmeasurable coherent photons for tens of picoseconds, but is able to be read-out by a time-delayed femtosecond pulse centered at 1580 nm via two-photon resonant absorption, resulting in a strong radiation at 329.3 nm. We reveal a pivotal role of the excited-state population to transmit such extremely weak re-emitted photons in this system. This new finding unveils the nature of the coherent quantum control in N2+ for the potential platform for optical information storage in the remote atmosphere, and facilitates further exploration of fundamental interactions in the quantum optical platform with strong-field ionized molecules.
The air fluorescence technique is used to detect ultra-high energy cosmic rays (UHECR), and to estimate their energy. Of fundamental importance is the photon yield due to excitation by electrons, in air of various densities and temperatures. After our previous report, the experiment has been continued using a Sr90 $beta$ source to study the pressure dependence of photon yields for radiation in nitrogen and dry air. The photon yields in 15 wave bands between 300 nm and 430 nm have been determined. The total photon yield between 300 nm and 406 nm (used in most experiments) in air excited by a 0.85 MeV electron is 3.81+-0.13 (+-13 % systematics) photons per meter at 1013 hPa and 20 $^{circ}$C. The air density and temperature dependencies of 15 wave bands are given for application to UHECR observations.
The MOLLER experiment proposed at the Thomas Jefferson National Accelerator Facility plans a precision low energy determination of the weak mixing angle via the measurement of the parity-violating asymmetry in the scattering of high energy longitudinally polarized electrons from electrons bound in a liquid hydrogen target (M{o}ller scattering). A relative measure of the scattering rate is planned to be obtained by intercepting the M{o}ller scattered electrons with a circular array of thin fused silica tiles attached to air light guides, which facilitate the transport of Cherenkov photons generated within the tiles to photomultiplier tubes (PMTs). The scattered flux will also pass through the light guides of downstream tiles, generating additional Cherenkov as well as scintillation light and is a potential background. In order to estimate the rate of these backgrounds, a gas-filled tube detector was designed and deployed in an electron beam at the MAMI facility at Johannes Gutenberg University, Mainz, Germany. Described in this paper is the design of a detector to measure separately the scintillation and Cherenkov responses of gas mixtures from relativistic electrons, the results of studies of several gas mixtures with comparisons to simulations, and conclusions about the implications for the design of the MOLLER detector apparatus.
Charge transport in organic semiconductors is notoriously extremely sensitive to the presence of disorder, both intrinsic and extrinsic, especially for n-type materials. Intrinsic dynamic disorder stems from large thermal fluctuations both in intermolecular transfer integrals and (molecular) site energies in weakly interacting van der Waals solids and sources transient localization of the charge carriers. The molecular vibrations that drive transient localization typically operate at low-frequency (< a-few-hundred cm-1), which renders it difficult to assess them experimentally. Hitherto, this has prevented the identification of clear molecular design rules to control and reduce dynamic disorder. In addition, the disorder can also be extrinsic, being controlled by the gate insulator dielectric properties. Here we report on a comprehensive study of charge transport in two closely related n-type molecular organic semiconductors using a combination of temperature-dependent inelastic neutron scattering and photoelectron spectroscopy corroborated by electrical measurements, theory and simulations. We provide unambiguous evidence that ad hoc molecular design enables to free the electron charge carriers from both intrinsic and extrinsic disorder to ultimately reach band-like electron transport.
The interaction of streamers in nitrogen-oxygen mixtures such as air is studied. First, an efficient method for fully three-dimensional streamer simulations in multiprocessor machines is introduced. With its help, we find two competing mechanisms how two adjacent streamers can interact: through electrostatic repulsion and through attraction due to nonlocal photo-ionization. The non-intuitive effects of pressure and of the nitrogen-oxygen ratio are discussed. As photo-ionization is experimentally difficult to access, we finally suggest to measure it indirectly through streamer interactions.
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