149 research outputs found
Observations of artificial and natural optical emissions at the HAARP facility
No full textExtensive optical observations have been carried out at
the High Frequency Active Auroral Research Program (HAARP) ionospheric
heating facility since it began operations in 1999. A number of modern
optical diagnostic instruments are hosted at remote sites as well as the
main transmitter facility, which has recently been expanded from the initial
960 kW prototype configuration to its full 3.6 MW design capability.
Upgrades to optical diagnostics have allowed a number of interesting new
observations to be made at the 960 kW power level since 2004. Systematic
beam-swinging experiments generating quantifiable levels of optical emission
at various regions in the sky for the first time clearly show that emission
intensity is very sensitive to distance from the magnetic zenith, and drops
off rapidly at about 15° zenith angle in directions other than magnetic
south. High temporal resolution measurements of emissions in the 557.7 nm
green line at start-up and in short transmitter pulses demonstrate that
localized irregularities are preferentially excited in the initial seconds
of heating, with evolution into a more homogenous spot occurring over a
period of about 1 min. High-quality emission altitude profiles at both
630.0 and 557.7 nm have recently been isolated from side-looking data,
spanning an altitude extent of over 200 km, which has allowed determination
of the effective lifetime of O (1D) over an unprecedented altitude
range. An innovative automated remote imager network utilizing low-cost
mirror optics has been designed and deployed to make such measurements
routinely. Observations of natural optical emissions at the site have
revealed the common presence of highly structured but faint co-rotating
subauroral precipitation that acts to suppress excitation of artificial F
region optical emissions in areas of active precipitation. The observed
spatial modulation of artificial optical emissions by structured
precipitation is consistent with localized absorption of HF waves in the
ionospheric D layer enhanced by the energetic particle precipitation
Optical spectroscopic observations of sprites, blue jets, and elves: Inferred microphysical processes and their macrophysical implications
No full textDissertation (Ph.D.) University of Alaska Fairbanks, 2000During the past decade, several new upper atmospheric phenomena associated with thunderstorms have been discovered. The four main types of optical emissions are now called sprites, blue jets, lves, and halos. Sprites are primarily red and appear between 40--95 km altitude and last between 1--100 ms. The dominant sprite emission is the molecular nitrogen first positive band, a relatively low energy emission also observed in the red lower borders of aurorae. The total optical energy output of a bright sprite is on the order of 50 kJ. Based on spectral observations, the total vibrational and electronic energy deposited in molecular nitrogen and oxygen in the upper atmosphere is 250 MJ-1 GJ. Blue jets last hundreds of milliseconds and span altitudes 15--40 km. Spectral observations of blue jets have not been obtained to date. Elves, the third type of observed optical emissions above thunderstorms, are red emissions at altitudes 75--95 km, lasting one millisecond or less. Elves and halos are similar phenomena, but are distinct based on altitude and duration. Halos typically last 3--6 ms and occur at lower altitudes than elves. This dissertation describes the optical spectrum of sprites obtained by the University of Alaska Fairbanks during summer campaigns of 1995, 1996, and 1998, and its implication to the understanding of the electrodynamics of the middle atmosphere. The single most significant result is the determination that a typical sprite deposits up to one gigajoule into the mesosphere. These forms of electrical energy coupling from tropospheric thunderstorms into the stratosphere, mesosphere, and thermosphere/ionosphere may have critical implications for the global chemistry and energy budgets in these regions
Experimental and theoretical study of cw HF chemical laser overtone performance
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Previous issue date: 1992Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:56:35Z
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Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I OnlyThe overtone performance of the UIUC supersonic cw HF chemical laser was characterized as a function of flow rates, cavity pressure, mode volume, mirror reflectivity and method of He injection. The overtone performance was optimized by the same set of flow rates that optimized the fundamental performance. When the absorption/scattering losses of the mirrors were taken into account, an overtone efficiency of 70-90% was achieved, which is the highest reported to date. The overtone efficiency was a strong function of media saturation. There was no significant change in overtone power and efficiency as the mode volume increased. However, there were an increase in the number of lasing lines and a shift to higher J lines. Overtone performance was as sensitive to cavity pressure as fundamental performance. There was no significant change in overtone efficiency when the method of He injection was changed. Base region absorption by ground state HF has a significant effect on fundamental and overtone performance. Even with very high degrees of saturation, approximately 10% of the total power was lost when the He purge was turned off.For a laser having an extensive data base with well characterized mirrors to firmly establish the Rigrod parameters g\sb0 and I\sb{\rm sat}, the accuracy to which the mirror reflectivities can be deduced using measured mirror transmissivities, measured outcoupled power and Rigrod theory is approximately 0.07% for high reflectivity overtone mirrors. Rigrod theory shows that a higher media saturation yields a higher overall overtone efficiency, but does not necessarily yield a higher measureable power (power in the bucket). For low absorption/scattering loss overtone mirrors and a 5% penalty in outcoupled power, the intracavity flux and hence the mirror loading can be reduced by more than a factor of two when the gain length is long enough to well saturate the media.The inclusion of HF-H\sb2 multi-quantum VV transfer reactions in the ORNECL model significantly improved the prediction of the zero power gains for the H\sb2 rich UI supersonic laser. The inclusion of absorption by SF\sb{\rm x} molecules in the model significantly improved the prediction of the Fabry-Perot spectra
On the performance characteristics of multiple pass hydrogen fluoride chemical laser master oscillator/power amplifiers
No full textThe performance of a cw Hydrogen Fluoride (HF) chemical laser master oscillator with power amplifier was measured as a function of input power, the number of passes through the gain media, location of the optical axis of the input beam and oscillator/amplifier flow field match/mismatch. The amplification ratio is an inverse function of the input power (intensity) and, for maximum amplification, the peak of the intensity distribution must be matched to the peak of the zero power gain distribution in the amplifier. The measured single pass P\sb{\rm out} versus P\sb{\rm in} performance curve showed that, after a continuous increase, the difference P\sb{\rm out} \cdot P\sb{\rm in} remained almost constant over a wide range of input powers and that about one third of a device's oscillator output must be input to obtain single pass amplifier output equal to the device's oscillator performance. For two pass amplification, a substantial performance advantage was measured when the two passes overlapped at least sixty percent and filled less than eighty percent of the zero power gain zone of the amplifier. The measured two pass P\sb{\rm out} versus P\sb{\rm in} performance curve was significantly above the single pass data and showed that only one sixth of a device's oscillator output must be input to obtain two pass amplifier output equal to the device's oscillator performance.When the input beam contained time-dependent oscillations, the amplitude modulation of the output beam was reduced by a factor that equaled the amplification ratio of the amplifier; the amplifier had no effect on the period (frequency) of the oscillations of the input beam.An amplifier performance model that predicts a device's amplifier performance given the device's oscillator performance as a function of reflectivity was developed. The model was used to predict amplifier performance as a function of gain length and the number of passes through the gain media. When the amplifier performance is plotted in terms of non dimensional powers, \zeta\sb{\rm out} versus \zeta\sb{\rm in}, gain length dependent, device independent curves result. The non dimensional amplifier performance curves showed that a one meter oscillator may be able to drive as many as twelve two pass amplifiers.Made available in DSpace on 2011-05-07T13:36:21Z (GMT). No. of bitstreams: 2
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Previous issue date: 1991Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:56:52Z
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Temporal evolution of pump beam self-focusing at the High-Frequency Active Auroral Research Program
No full textOn 4 February 2005 the High-Frequency Active Auroral Research Program (HAARP) facility was operated at 2.85 MHz to produce artificial optical emissions in the ionosphere while passing through the second electron gyroharmonic. All-sky optical recordings were performed with 15 s integration, alternating between 557.7 and 630 nm. We report the first optical observations showing the temporal evolution of large-scale pump wave self-focusing in the magnetic zenith, observed in the 557.7 nm images. These clearly show that the maximum intensity was not reached after 15 s of pumping, which is unexpected since the emission delay time is <1 s, and that the optical signature had intensified in a much smaller region within the beam after 45 s of pumping. In addition, adjacent regions within the beam lost intensity. Radar measurements indicate a plasma depletion of ∼1% near the HF reflection altitude. Ray tracing of the pump wave through the plasma depletion region, which forms a concave reflecting radio wave mirror, reproduces the optical spatial morphology. A radio wave flux density gain of up to ∼30 dB may occur. In addition, the ray trace is consistent with the observed artificial optical emissions for critical plasma frequencies down to ∼0.5 MHz below the pump frequency
Experimental and theoretical study of CW hydrogen fluoride chemical laser residual fundamental gain
No full textA new technique that uses a multi-line probe beam to measure the gain on several lines simultaneously was developed. This new technique was used to measure the gains of the peak fundamental lines P\sb1 (4-9) and P\sb2(4-9) while lasing on the overtone, for three levels of media saturation. The suppression of the fundamental gains obtained at relatively high media saturation with 99.7/99.7% reflective mirrors was essentially the same as that obtained with 55% higher intracavity flux with 99.8/99.86% reflective mirrors. The gains of the low J lines P\sb1(4-6) and P\sb2(4-6) were suppressed 41% to 84%; the gains of the high J lines P\sb1(7-9) and P\sb2(7-9) were suppressed 3% to 43%. The 1 0 lines were suppressed more than the 2 1 lines. The maximum suppression occurred between 2 and 6 mm downstream from the nozzle exit plane, near the center of the 9 mm overtone beam.Simulation of the experiments with a rotational nonequilibrium computer model showed that the fundamental gains are determined by three independent mechanisms when lasing occurs on the overtone. First, overtone lasing decreases the gains of the P\sb1(J) and P\sb2(J) lines whose upper or lower levels are directly involved in P\sb{20}(J) overtone lasing. Second, overtone lasing reduces the rate at which the low J v = 2 states are populated by rotational relaxation and increases the rate at which the low J v = 0 states are populated by rotational relaxation, resulting in suppression of the low J fundamental gains whose upper or lower levels are not directly involved in overtone lasing. Third, overtone lasing reduces the rate at which the HF(0,J) and HF(1,J) states are populated by the various collisional deactivation processes.With 10% of the original rotational relaxation rate, the computer model was in reasonable agreement with the measured zero power gain profiles. The model over predicted the fundamental gain suppression () for the P\sb1(8,9) and P\sb2(8,9) lines whose upper or lower levels were directly involved in overtone lasing, and under predicted the suppression for lines P\sb1(4) and P\sb2(4,5). The model predicted the suppression for lines P\sb1(5-7) and P\sb2(6,7) reasonably well. With the original rotational relaxation rate, the model was in reasonable agreement with the measured suppression of all P\sb1(4-9) and P\sb2(4-9) lines. However, with the original RR rate, the model's agreement with the experimental zero power gain profiles was not adequate.Made available in DSpace on 2011-05-07T12:49:48Z (GMT). No. of bitstreams: 2
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Previous issue date: 1992Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:46:23Z
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Electrostatic fields in a dusty Martian environment
No full textWhile there have been several studies suggesting the possibility of electrical activity on Mars, to date there have been no measurements to search for evidence of such activity. In the absence of widespread water clouds and convective storm systems similar to those on the Earth and Jupiter, the most likely candidate for the creation of electrostatic charges and fields is triboelectric charging of dust, i.e., the friction between blown dust and the ground, and of dust particles with each other. Terrestrial experience demonstrates that electric fields 5 to 15 kV-m(exp -1) are not uncommon in dust storms and dust devils in desert regions, where the polarity varies according to the chemical composition and grain size. Simple laboratory experiments have demonstrated that modest electrostatic fields of roughly 5,000 V-m(exp -1) may be produced, along with electrical spark discharges and glow discharges, in a simulation of a dusty, turbulent Martian surface environment. While the Viking landers operated for several years with no apparent deleterious effects from electrostatic charging, this may have been at least partly due to good engineering design utilizing pre-1976 electronic circuitry to minimize the possibility of differential charging among the various system components. However, free roaming rovers, astronauts, and airborne probes may conceivably encounter an environment where electrostatic charging is a frequent occurrence, either by way of induction from a static electric field or friction with the dusty surface and atmosphere. This raises the possibility of spark discharges or current surges when subsequent contact is made with other pieces of electrical equipment, and the possibility of damage to modern microelectronic circuitry. Measurements of electrostatic fields on the surface of Mars could therefore be valuable for assessing this danger. Electric field measurements could also be useful for detecting natural discharges that originate in dust storms. This detection could be performed at distances ranging from 10s of km in the case of J-charge-like discharge signatures, to planetary distances if there exists a global electrical circuit or Schumann resonance spectrum
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