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Robert D. Loper

Bio: Robert D. Loper is an academic researcher from Air Force Institute of Technology. The author has contributed to research in topics: Laser beam quality & Space weather. The author has an hindex of 4, co-authored 10 publications receiving 41 citations. Previous affiliations of Robert D. Loper include National Center for Atmospheric Research.

Papers
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01 Mar 2013
TL;DR: In this paper, the authors used the Baranger model to compute collisional broadening and shift of the D1 and D2 spectral lines of M + Ng, where M = K, Rb, Cs and Ng = He, Ne, Ar, using scattering phase shift differences which are calculated from scattering matrix elements.
Abstract: : The Baranger model is used to compute collisional broadening and shift of the D1 and D2 spectral lines of M + Ng, where M = K, Rb, Cs and Ng = He, Ne, Ar, using scattering phase shift differences which are calculated from scattering matrix elements. Scattering matrix elements are calculated using the Channel Packet Method where the collisions are treated non-adiabatically and include spin-orbit and Coriolis couplings. Non-adiabatic wavepacket dynamics are determined using the split-operator method together with a unitary transformation between adiabatic and diabatic representations. Scattering phase shift differences are thermally weighted and integrated over energies ranging from E = 0 Hartree up to E = 0.0075 Hartree and averaged over values of total angular momentum that range from J = 0.5 up to J = 400.5. Phase shifts are extrapolated linearly to provide an approximate extension of the energy regime up to E = 0.012 Hartree. Broadening and shift coefficients are obtained for temperatures ranging from T = 100 K up to T = 800 K and compared with experiment. Predictions from this research find application in laser physics and specifically with improvement of total power output of Optically Pumped Alkali Laser systems.

15 citations

Journal ArticleDOI
TL;DR: In this paper, the performance of a 100kW Rb-He diode pumped alkali laser system is predicted, including power scaling, optical efficiency, and beam quality, and a transverse flow geometry with longitudinal diode pumping produces a nonlinear temperature profile in the flow direction.
Abstract: The performance of a 100 kW Rb–He diode pumped alkali laser system is predicted, including power scaling, optical efficiency, and beam quality. A transverse flow geometry with longitudinal diode pumping produces a nonlinear temperature profile in the flow direction, with temperature increasing by 124 K for a 0.5 m/s flow rate and a 30 kW/cm2 pump intensity. The optical-to-optical efficiency is 70%, and the tilt-corrected Strehl is 0.545 for this slow flow, 45 ms residence time design. By increasing the flow speed to 15 m/s (1.5 ms residence time), the efficiency is improved to 82%, and the laminar flow beam quality is near the diffraction limit, Strehl>0.99. Beam quality is adversely affected at higher helium pressure for the slow flow conditions.

10 citations

Journal ArticleDOI
TL;DR: In this paper, the impact of a Carrington-class coronal mass ejection (CME) from the Sun was examined and the Drake equation was used to estimate the number of intelligent extraterrestrial species in our galaxy.
Abstract: The Drake equation is a calculation providing an upper bound on the likely number of intelligent species in our galaxy. In order to reconcile a potentially high occurrence of intelligent extraterrestrial species with the current non-observation of them, we frequently resort to some Great Filter which represents some inevitable, cataclysmic fate (such as nuclear war, pandemic, or asteroid impact) that tends to await enough worlds to negate the expectation that the galaxy ought to be teeming with intelligent life. This paper is intended to examine one potential Great Filter for electronic-based civilizations, the impact of a Carrington-class coronal mass ejection (CME) from the Sun. Carrington-class CMEs are classified as "once in a century" events caused by our Sun; this appears to place a time limit, following the development of a civilization dependent on electronic devices, either for hardening electronics against the geomagnetically induced currents that result from CMEs or for beginning interplanetary colonization.

6 citations

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TL;DR: In this article, the photospheric magnetic field during solar flares within a large HMI dataset (May 2010 through September 2019) was analyzed and compared to identify and compare trends in the different categories of flare strengths and determine indications of the physical phenomena taking place.

5 citations

Journal ArticleDOI
TL;DR: In this paper, the authors use the Baranger model to compute collisional broadening and shift rates for the D1 and D2 spectral lines of M + Ng, where M = K, Rb, Cs and Ng = He, Ne, Ar. They find that predicted broadening rates compare well with experiment, but shift rates are predicted poorly by this model because they are extremely sensitive to the nearasymptotic behavior of the potential energy surfaces.
Abstract: We use the Baranger model to compute collisional broadening and shift rates for the D1 and D2 spectral lines of M + Ng, where M = K, Rb, Cs and Ng = He, Ne, Ar. Scattering matrix elements are calculated using the channel packet method, and non-adiabatic wavepacket dynamics are determined using the split-operator method together with a unitary transformation between adiabatic and diabatic representations. Scattering phase shift differences are weighted thermally and are integrated over temperatures ranging from 100 K to 800 K. We find that predicted broadening rates compare well with experiment, but shift rates are predicted poorly by this model because they are extremely sensitive to the near-asymptotic behavior of the potential energy surfaces.

3 citations


Cited by
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Journal Article
TL;DR: The space weather storm of late May 1967 has been of mostly fading academic interest as discussed by the authors, although it has been listed as one of the most significant events of the last 80 years.
Abstract: Although listed as one of the most significant events of the last 80 years, the space weather storm of late May 1967 has been of mostly fading academic interest. The storm made its initial mark with a colossal solar radio burst causing radio interference at frequencies between 0.01 and 9.0 GHz and near-simultaneous disruptions of dayside radio communication by intense fluxes of ionizing solar X-rays. Aspects of military control and communication were immediately challenged. Within hours a solar energetic particle event disrupted high-frequency communication in the polar cap. Subsequently, record-setting geomagnetic and ionospheric storms compounded the disruptions. We explain how the May 1967 storm was nearly one with ultimate societal impact, were it not for the nascent efforts of the United States Air Force in expanding its terrestrial weather monitoring-analysis-warning-prediction efforts into the realm of space weather forecasting. An important and long-lasting outcome of this storm was more formal Department of Defense-support for current-day space weather forecasting. This story develops during the rapid rise of solar cycle 20 and the intense Cold War in the latter half of the twentieth century. We detail the events of late May 1967 in the intersecting categories of solar-terrestrial interactions and the political-military backdrop of the Cold War. This was one of the “Great Storms” of the twentieth century, despite the apparent lack of large geomagnetically induced currents. Radio disruptions like those discussed here warrant the attention of today's radio-reliant, cellular-phone and satellite-navigation enabled world.

56 citations

Journal ArticleDOI
TL;DR: In this article, the Anderson-Talman theory was compared to line shape predictions for the Rb D1 (5 S 1/2 2 + 2 ) and D2 ( 5 S 1 / 2 2 ↔ 5 P 1/ 2 2 ) transitions with 4He and 3He collisions at pressures of 500-15,000 ǫ and temperatures of 333-533 K.
Abstract: Line shapes for the Rb D1 ( 5 S 1 / 2 2 ↔ 5 P 1 / 2 2 ) and D2 ( 5 S 1 / 2 2 ↔ 5 P 3 / 2 2 ) transitions with 4He and 3He collisions at pressures of 500–15,000 Torr and temperatures of 333–533 K have been experimentally observed and compared to predictions from the Anderson–Talman theory. The ground X Σ 1 / 2 + 2 and excited A Π 1 / 2 2 , A Π 3 / 2 2 , and B Σ 1 / 2 + 2 potential energy surfaces required for the line shape predictions have been calculated using a one-electron pseudo-potential technique. The observed collision induced shift rates for 4He are dramatically higher for the D1 line, 4.60±0.12 MHz/Torr, than the D2 line, 0.20±0.14 MHz/Torr. The asymmetry is somewhat larger for the D1 line and has the same sign as the shifting rate. The 3He broadening rate for the D2 line is 4% larger than the 4He rate, and 14% higher for the D1 line, reflecting the higher relative speed. The calculated broadening rates are systematically larger than the observed rates by 1.1–3.2 MHz/Torr and agree within 14%. The primary focus of the current work is to characterize the high pressure line shapes, focusing on the non-Lorentzian features far from line center. In the far wing, the cross-section decreases by more than 4 orders of magnitude, with a broad, secondary maximum in the D2 line near 735 nm. The potentials do not require empirical modification to provide excellent quantitative agreement with the observations. The dipole moment variation and absorption Boltzmann factor is critical to obtaining strong agreement in the wings.

22 citations