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Articles 1 - 23 of 23
Full-Text Articles in Physics
Ultrafast Laser-Induced Damage And The Influence Of Spectral Effects, Jeremy Gulley
Ultrafast Laser-Induced Damage And The Influence Of Spectral Effects, Jeremy Gulley
Jeremy R. Gulley
Numerous studies have investigated the prerequisite role of photoionization in ultrafast laser-induced damage (LID) of bulk dielectrics. This study examines the role of spectral width and instantaneous laser frequency in LID using a frequency dependent multiphoton ionization (MPI) model and numerical simulation of initially 800 nm laser pulses propagating through fused silica. Assuming a band gap of 9 eV, MPI by an 800 nm field is a six-photon process, but when the instantaneous wavelength is greater than 827 nm an additional photon is required for photoionization, reducing the probability of the event by many orders of magnitude. Simulation results suggest …
Enhanced Lunar Semidiurnal Equatorial Vertical Plasma Drifts During Sudden Stratospheric Warmings, Bela G. Fejer, B. D. Tracy, J. L. Chau
Enhanced Lunar Semidiurnal Equatorial Vertical Plasma Drifts During Sudden Stratospheric Warmings, Bela G. Fejer, B. D. Tracy, J. L. Chau
Bela G. Fejer
[1] Large scale electrodynamic and plasma density variations in the low latitude ionosphere have recently been associated with sudden stratospheric warming (SSW) events. We present average patterns of largely enhanced lunar semidiurnal equatorial vertical plasma drift perturbations during arctic winter low and high solar flux SSW events. These perturbations play a dominant role in the electrodynamic response of the low latitude ionosphere to SSWs. Our models indicate that the amplitudes of the enhanced lunar semidiurnal drifts are strongly local time and solar flux dependent, with largest values during early morning low solar flux SSW periods. These results suggest that ionospheric …
Modeling Free-Carrier Absorption And Avalanching By Ultrashort Laser Pulses, Jeremy Gulley
Modeling Free-Carrier Absorption And Avalanching By Ultrashort Laser Pulses, Jeremy Gulley
Jeremy R. Gulley
In the past decade it was demonstrated experimentally that negatively-chirped laser pulses can lower the surface LIDT for wide band-gap materials by decreasing the number of photons required for photoionization on the leading edge of the pulse. Similarly, simulations have shown that positively-chirped pulses resulting from selffocusing and self-phase modulation in bulk dielectrics can alter the onset of laser-induced material modifications by increasing the number of photons required for photoionization on the leading edge of the pulse. However, the role of multi-chromatic effects in free-carrier absorption and avalanching has yet to be addressed. In this work a frequency-selective model of …
Seasonal And Longitudinal Dependence Of Equatorialdisturbance Vertical Plasma Drifts, Bela G. Fejer, J. W. Jensen, S. Y. Su
Seasonal And Longitudinal Dependence Of Equatorialdisturbance Vertical Plasma Drifts, Bela G. Fejer, J. W. Jensen, S. Y. Su
Bela G. Fejer
[1] We used equatorial measurements from the ROCSAT-1 satellite to determine the seasonal and longitudinal dependent equatorial F region disturbance vertical plasma drifts. Following sudden increases in geomagnetic activity, the prompt penetration vertical drifts are upward during the day and downward at night, and have strong local time dependence at all seasons. The largest prompt penetration drifts near dusk and dawn occur during June solstice. The daytime disturbance dynamo drifts are small at all seasons. They are downward near dusk with largest (smallest) values during equinox (June solstice); the nighttime drifts are upward with the largest magnitudes in the postmidnight …
Quiet Time Equatorial F Region Vertical Plasma Drift Model Derived From Rocsat-1 Observations, Bela G. Fejer, J. W. Jensen, S. Y. Su
Quiet Time Equatorial F Region Vertical Plasma Drift Model Derived From Rocsat-1 Observations, Bela G. Fejer, J. W. Jensen, S. Y. Su
Bela G. Fejer
[1] We have used five years of measurements on board the ROCSAT-1 satellite to develop a detailed quiet time global empirical model for equatorial F region vertical plasma drifts. This model describes the local time, seasonal and longitudinal dependence of the vertical drifts for an altitude of 600 km under moderate and high solar flux conditions. The model results are in excellent agreement with measurements from the Jicamarca radar and also from other ground-based and in situ probes. We show that the longitudinal dependence of the daytime and nighttime vertical drifts is much stronger than reported earlier, especially during December …
Simulation And Analysis Of Ultrafast Laser Pulse Induced Plasma Generation In Dielectric Materials, Jeremy Gulley, Sebastian Winkler, William Dennis
Simulation And Analysis Of Ultrafast Laser Pulse Induced Plasma Generation In Dielectric Materials, Jeremy Gulley, Sebastian Winkler, William Dennis
Jeremy R. Gulley
Recent experiments on optical damage by ultrashort laser pulses have demonstrated that the temporal pulseshape can dramatically influence plasma generation in fused silica and sapphire. In this work a modified 3+1D nonlinear Schroedinger equation for the pulse propagation coupled to a rate equation for the plasma density in the dielectric material is used to simulate pulse propagation and plasma formation in a range of dielectric materials. We use these simulations to analyze the influence of pulse-width, pulse-shape and beam geometry on the formation of the electron plasma and hence damage in the bulk material. In particular, when possible, we simulate …
Climatology Of F Region Zonalplasma Drifts Over Jicamarca, Bela G. Fejer, J. R. Souza, A. S. Santos, A. E. Costa Pereira
Climatology Of F Region Zonalplasma Drifts Over Jicamarca, Bela G. Fejer, J. R. Souza, A. S. Santos, A. E. Costa Pereira
Bela G. Fejer
[1] We use extensive incoherent scatter radar observations made at the Jicamarca Radio Observatory between 1970 and 2003 to study and model empirically the equatorial zonal plasma drifts near the F region peak using Bernstein polynomials as base functions. Our quiet-time model results confirm that the daytime drifts are westward and are nearly season and solar cycle independent. The nighttime drifts are eastward, have larger magnitudes, and increase strongly with solar flux, particularly near equinox and December solstice. Enhanced geomagnetic activity drives small eastward perturbation drifts during the day and much larger westward disturbance drifts at night. The nighttime drift …
Magnetospheric Electric Fields And Plasma Sheet Injections To Low-Lshells During The June 4-5, 1991 Magnetic Storm: Comparison Between The Rice Convectionmodel And Observations, T. W. Garner, R. A. Wolf, R. W. Spiro, W. J. Burke, Bela G. Fejer, S. Sazykin, J. L. Roeder, M. R. Hairston
Magnetospheric Electric Fields And Plasma Sheet Injections To Low-Lshells During The June 4-5, 1991 Magnetic Storm: Comparison Between The Rice Convectionmodel And Observations, T. W. Garner, R. A. Wolf, R. W. Spiro, W. J. Burke, Bela G. Fejer, S. Sazykin, J. L. Roeder, M. R. Hairston
Bela G. Fejer
[1] The major magnetic storm of 4–5 June 1991 was well observed with the Combined Release and Radiation Experiment (CRRES) satellite in the duskside inner magnetosphere and with three Defense Meteorological Satellite Program (DMSP) spacecraft in the polar ionosphere. These observations are compared to results from the Rice Convection Model (RCM), which calculates the inner magnetospheric electric field and particle distribution self-consistently. This case study, which uses the most complete RCM runs to date, demonstrates two significant features of magnetospheric storms, the development of subauroral polarization streams (SAPS) and plasma-sheet particle injection deep into the inner magnetosphere. In particular, the …
Radar Studies Of Mid-Latitude Ionospheric Plasma Drifts, L. Scherliess, Bela G. Fejer, J. Holt, L. Goncharenko, C. Armory-Mazaudier, M. J. Buonsanto
Radar Studies Of Mid-Latitude Ionospheric Plasma Drifts, L. Scherliess, Bela G. Fejer, J. Holt, L. Goncharenko, C. Armory-Mazaudier, M. J. Buonsanto
Bela G. Fejer
We use incoherent scatter radar measurements from Millstone Hill and Saint Santin to study the midlatitude F region electrodynamic plasma drifts during geomagnetically quiet and active periods. We present initially a local time, season, and solar flux dependent analytical model of the quiet time zonal and meridional E × B drifts over these stations. We discuss, for the first time, the Saint Santin drift patterns during solar maximum. We have used these quiet time models to extract the geomagnetic perturbation drifts which were modeled as a function of the time history of the auroral electrojet indices. Our results illustrate the …
De-2 Observations Of Morningside And Eveningside Plasma Density Depletions In The Equatorial Ionosphere, M. Palmroth, H. Laakso, Bela G. Fejer, R. F. Pfaff
De-2 Observations Of Morningside And Eveningside Plasma Density Depletions In The Equatorial Ionosphere, M. Palmroth, H. Laakso, Bela G. Fejer, R. F. Pfaff
Bela G. Fejer
The occurrence of equatorial density depletions in the nightside F region ionosphere has been investigated by using observations gathered by the polar-orbiting Dynamics Explorer 2 satellite from August 1981 to February 1983. A variety of electric field/plasma drift patterns were observed within these depletions, including updrafting, downdrafting, bifurcating, converging, subsonic, and supersonic flows. The depletions, 116 events in total, are distributed over two groups: group I (eveningside depletions) consists of the events in the 1900–2300 MLT sector, and group II (morningside depletions) are the events in the 2300–0600 MLT sector. A statistical analysis reveals clear differences in the density depletion …
Effects Of The Vertical Plasma Drift Velocity On The Generation And Evolution Of Equatorial Spread F, Bela G. Fejer, L. Scherliess, E. R. De Paula
Effects Of The Vertical Plasma Drift Velocity On The Generation And Evolution Of Equatorial Spread F, Bela G. Fejer, L. Scherliess, E. R. De Paula
Bela G. Fejer
We use radar observations from the Jicamarca Observatory from 1968 to 1992 to study the effects of the F region vertical plasma drift velocity on the generation and evolution of equatorial spread F. The dependence of these irregularities on season, solar cycle, and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts. In the early night sector, the bottomside of the F layer is almost always unstable. The evolution of the unstable layer is controlled by the history of the vertical drift velocity. When the drift velocities are large enough, the …
Mid- And Low-Latitude Prompt-Penetration Ionospheric Zonalplasma Drifts, Bela G. Fejer, L. Scherliess
Mid- And Low-Latitude Prompt-Penetration Ionospheric Zonalplasma Drifts, Bela G. Fejer, L. Scherliess
Bela G. Fejer
We have used ion drift observations from the DE-2 satellite to determine the latitudinal variation and the temporal evolution of mid- and low-latitude prompt penetration zonal plasma drifts driven by magnetospheric electric fields. Our results indicate that sudden increases in convection lead to predominantly westward perturbation drifts which decrease equartorwards and have largest amplitudes in the dusk-midnight sector. The diurnal perturbation drift patterns shift to later local times with increasing storm time and decay to new quasi-equilibrium values in about 2 hours, as the ring current readjusts to the new polar cap potential. The daily and latitudinal variations and temporal …
Satellite Studies Of Mid- And Low-Latitude Ionospheric Disturbancezonal Plasma Drifts, L. Scherliess, Bela G. Fejer
Satellite Studies Of Mid- And Low-Latitude Ionospheric Disturbancezonal Plasma Drifts, L. Scherliess, Bela G. Fejer
Bela G. Fejer
We use low- and mid-latitude zonal ion drift observations from the DE-2 satellite and auroral electrojet indices to study the temporal and latitudinal variations of F-region perturbation drifts during magnetically disturbed conditions. These perturbation drifts are driven by magnetospheric and ionospheric disturbance dynamo electric fields with time constants from less than one to several hours. We determine, initially, the drift patterns due to the prompt penetration of magnetospheric electric fields and of longer lasting disturbances. In this study, we concentrate on the properties of the longer lasting perturbations which occur with latitude-dependent time delays after enhancements in the high-latitude ionospheric …
Global Equatorial Ionosphericvertical Plasma Drifts Measured By The Ae-E Satellite, Bela G. Fejer, E. R. De Paula, R. A. Heelis, W. B. Hanson
Global Equatorial Ionosphericvertical Plasma Drifts Measured By The Ae-E Satellite, Bela G. Fejer, E. R. De Paula, R. A. Heelis, W. B. Hanson
Bela G. Fejer
Ion drift meter observations from the Atmosphere Explorer E satellite during the period of January 1977 to December 1979 are used to study the dependence of equatorial (dip latitudes ≤ 7.5°) F region vertical plasma drifts (east-west electric fields) on solar activity, season, and longitude. The satellite-observed ion drifts show large day-to-day and seasonal variations. Solar cycle effects are most pronounced near the dusk sector with a large increase of the prereversal velocity enhancement from solar minimum to maximum. The diurnal, seasonal, and solar cycle dependence of the longitudinally averaged drifts are consistent with results from the Jicamarca radar except …
F-Region Plasma Drifts Over Arecibo: Solar Cycle, Seasonal And Magnetic Activityeffects, Bela G. Fejer
F-Region Plasma Drifts Over Arecibo: Solar Cycle, Seasonal And Magnetic Activityeffects, Bela G. Fejer
Bela G. Fejer
We have used Arecibo incoherent scatter measurements from 1981 to 1990 to determine the characteristics of low-latitude F region plasma drifts. The measurements show large day-to-day variability even during magnetically quiet periods. The average poleward/perpendicular plasma drifts do not change significantly with season and solar cycle except in the midnight-morning sector. The zonal drifts show clear solar cycle and seasonal effects. The afternoon-nighttime eastward drifts increase with solar flux; the westward drifts in the early morning-afternoon sector show a large increase from summer to winter but are independent of solar activity. The two perpendicular velocity components also respond differently to …
Average Vertical And Zonal F-Region Plasma Drifts Over Jicamarca, Bela G. Fejer, E. R. De Paula, S. Gonzalez, R. F. Woodman
Average Vertical And Zonal F-Region Plasma Drifts Over Jicamarca, Bela G. Fejer, E. R. De Paula, S. Gonzalez, R. F. Woodman
Bela G. Fejer
The seasonal averages of the equatorial F region vertical and zonal plasma drifts are determined using extensive incoherent scatter radar observations from Jicamarca during 1968–1988. The late afternoon and nighttime vertical and zonal drifts are strongly dependent on the 10.7-cm solar flux. We show that the evening prereversal enhancement of vertical drifts increases linearly with solar flux during equinox but tends to saturate for large fluxes during southern hemisphere winter. We examine in detail, for the first time, the seasonal variation of the zonal plasma drifts and their dependence on solar flux and magnetic activity. The seasonal effects on the …
Equatorial F-Regionvertical Plasma Drifts During Solar Maxima, Bela G. Fejer, E. R. De Paula, I. S. Batista, E. Bonelli, R. F. Woodman
Equatorial F-Regionvertical Plasma Drifts During Solar Maxima, Bela G. Fejer, E. R. De Paula, I. S. Batista, E. Bonelli, R. F. Woodman
Bela G. Fejer
Incoherent scatter radar measurements at Jicamarca are used to study the effects of large solar fluxes and magnetic activity on the F region vertical plasma drifts. The average drifts from the two last solar maxima are almost identical except in the late afternoon-early evening sector where their variations with solar flux and magnetic activity are strongly season dependent. The average evening winter (May-August) drifts appear to remain almost constant after a certain solar flux level is reached but increase with magnetic activity. The equinoctial evening drifts increase systematically with solar-flux but decrease with magnetic activity. Very large prereversal enhancement velocities, …
Electric Field And Plasmadensity Measurements In The Strongly-Driven Daytime Equatorial Electrojet: 1. The Unstablelayer And Gradient Drift Waves, R. F. Pfaff, M. C. Kelley, E. Kudeki, Bela G. Fejer, K. D. Baker
Electric Field And Plasmadensity Measurements In The Strongly-Driven Daytime Equatorial Electrojet: 1. The Unstablelayer And Gradient Drift Waves, R. F. Pfaff, M. C. Kelley, E. Kudeki, Bela G. Fejer, K. D. Baker
Bela G. Fejer
Electric field and plasma density instrumentation on board a sounding rocket launched from Punta Lobos, Peru, detected intense electrostatic waves indicative of plasma instabilities in the daytime equatorial electrojet. Simultaneous measurements taken by the Jicamarca radar showed strong 3-m type 1 electrojet echoes as well as evidence of kilometer scale horizontally propagating waves. The in situ electric field wave spectra displayed three markedly different height regions within the unstable layer: (1) a two-stream region on the topside between 103 and 111 km where the electron current was considered to be strongest, (2) a gradient drift region between 90 and 106.5 …
Electric Field And Plasmadensity Measurements In The Strongly-Driven Daytime Equatorial Electrojet: 2. Two-Streamwaves, R. F. Pfaff, M. C. Kelley, E. Kudeki, Bela G. Fejer, K. D. Baker
Electric Field And Plasmadensity Measurements In The Strongly-Driven Daytime Equatorial Electrojet: 2. Two-Streamwaves, R. F. Pfaff, M. C. Kelley, E. Kudeki, Bela G. Fejer, K. D. Baker
Bela G. Fejer
Both primary and secondary two-stream (Farley-Buneman) waves have been detected by in situ electric field and plasma density probes in the strongly driven daytime equatorial electrojet over Peru. Simultaneous Jicamarca radar observations showed strong vertical and oblique 3-m type 1 echoes, also indicative of the two-stream mechanism. The rocket data show the two-stream region on the topside of the unstable layer to be situated between 103 and 111 km where the electron current was the strongest. This region was characterized by broadband plasma oscillations extending past 1 kHz in the rocket frame. Furthermore, above 106.5 km, where the electron density …
On The Height Variation Of The Equatorial F-Region Vertical Plasmadrifts, J. E. Pingree, Bela G. Fejer
On The Height Variation Of The Equatorial F-Region Vertical Plasmadrifts, J. E. Pingree, Bela G. Fejer
Bela G. Fejer
We have used improved incoherent scatter radar measurements at the Jicamarca Radio Observatory to study the height variation of the F region vertical plasma drift velocity (driven by the zonal electric field) during moderately quiet conditions. Preliminary results indicate a nearly linear change of the vertical drift velocity with altitude between 200 and 700 km, but with considerable day-to-day variations in the value of the slope. On the average, the velocity gradients are positive in the late night and morning periods and negative during the afternoon and evening hours. Simultaneous vertical and zonal drift measurements confirm that the measured height …
Auroral E-Region Plasma Waves Andelevated Electron Temperatures, Bela G. Fejer, J. Providakes, D. T. Farley, W. E. Swartz
Auroral E-Region Plasma Waves Andelevated Electron Temperatures, Bela G. Fejer, J. Providakes, D. T. Farley, W. E. Swartz
Bela G. Fejer
We have observed 3-m auroral E region plasma waves with a high-resolution 50-MHz radar interferometer at Ithaca. During postmidnight periods of very strong magnetic activity at Ottawa (L = 3.5), the backscattered power and Doppler spectra vary rapidly with time and range and may have both mean Doppler shifts and half power widths in excess of 200 Hz (600 m/s). In addition, when the radar and magnetometer data imply that the current is approximately parallel to the radar line of sight, sharp spectral peaks corresponding to phase velocities approaching 1 km/s sometimes appear suddenly. These persist for at most several …
Electric Field And Plasma Density Measurements In The Auroral Electrojet, R. Pfaff, M. C. Kelley, Bela G. Fejer, E. Kudeki, C. W. Carlson, A. Pedersen, B. Hausler
Electric Field And Plasma Density Measurements In The Auroral Electrojet, R. Pfaff, M. C. Kelley, Bela G. Fejer, E. Kudeki, C. W. Carlson, A. Pedersen, B. Hausler
Bela G. Fejer
Intense electrostatic waves in the auroral E region have been detected simultaneously on two payloads launched in a mother-daughter configuration from Kiruna, Sweden. The data sets comprise electric field and density measurements from the ambient (dc) conditions to fluctuations as high as 50 kHz. The dc electric field measured by both payloads was 54 mV/m northwest, which corresponded to an electron drift velocity of 1080 m/s. This electric field drove two-stream waves perpendicular to both B and E observed by both spacecraft throughout an altitude region which agrees quite well with the range predicted by linear two-stream theory. The power …
Radar Interferometry: A New Technique For Studyingplasma Turbulence In The Ionosphere, D. T. Farley, H. M. Ierkic, Bela G. Fejer
Radar Interferometry: A New Technique For Studyingplasma Turbulence In The Ionosphere, D. T. Farley, H. M. Ierkic, Bela G. Fejer
Bela G. Fejer
A new radar interferometer technique has been developed and used successfully at the Jicamarca Radio Observatory in Peru to study the strong nighttime plasma turbulence in the equatorial electrojet. The technique represents a major step forward in radar probing of turbulent irregularities such as (but not limited to) those in the electrojet. In many situations it provides far more information than previous Doppler measurements. We form the cross spectrum of the backscattered signals received from approximately overhead on two antennas, separated in this case along an east-west baseline, as well as the individual power spectra. From the phase of the …