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Journal of Directed Energy
Volume 4, Number 4 Summer 2012

The papers listed below constitute Volume 4, Number 4 of the Journal of Directed Energy.
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Cycling of Electrochemical Energy Storage Devices at Elevated Rates
David Wetz, Biju Shrestha, and Peter Novak, University of Texas at Arlington, and Yvonne Chen, SoftAmerica, Inc

In recent years, electrochemical energy storage devices have been developed that are more power dense than ever before. These new capabilities make them suitable for use in high-power applications, including for use as the prime power source of pulsed power and directed energy systems such as electromagnetic launchers and high-voltage Marx generators. Extremely high power cells have been developed with extremely low equivalent series resistance (ESR) values, by a number of different manufacturers. Low ESR values have significantly increased available power densities from the cells while still enabling high-energy densities to be maintained. In the case of the Saft VL5U lithium-ion battery, which has a rated energy density of 52 Wh/kg, power densities as high as 28.5 kW/kg have been demonstrated for pulse lengths as long as 200 milliseconds. Electric double-layer capacitors and hybrid capacitor-battery technologies, such as the JM Energy lithium-ion capacitor, have also been demonstrated to possess power densities as high as 5 to 7 kW/kg. In order to experimentally observe the limitations of these various types of cells, a test stand was developed at the University of Texas at Arlington that is capable of both pulsed discharging and pulsed recharging electrochemical cells at rates several times their rated C values. Development of the stand, the rationale behind the experiments, and selected results collected thus far are presented.
KEYWORDS: Pulsed power, Electrochemical energy storage, Lithium-ion battery, Lithium-ion capacitor, Electric double-layer capacitor.
PAGES 211-231

Collaborative Technology and Dynamic Air Traffic Management Expands Laser Test Operations Envelope
James Torres and Roger Hoppe, Southern Aerospace Company

There is an initiative currently underway within the Federal Aviation Administration to reform the way that Special Activity Airspace (SAA) (which will be the new name for Special Use Airspace) is scheduled and used. This initiative is called the National Special Activity Airspace Project (NSAAP). Once the NSAAP goes online, the tools and procedures developed by this project will improve the scheduling process for SAA and the responsiveness with which SAA schedule changes can be communicated and capitalized on by other system users. Some of the temporal issues cited in this article may be addressed; NSAAP will not address any of the spatial issues.
PAGES 232-244

Development of a Compact Heat Pipe Oven for Optically Pumped Alkali Laser Research
Wade L. Klennert, The Boeing Company, and Andrew J. Sandoval and David A. Hostutler, AFRL

The design for a compact heat pipe oven that is suitedfor an optically pumped alkali laser cavity is given. The design builds on conventional spectroscopic heat pipe ovens by incorporating dual cooling zones, which allows alkali laser research to be investigated in regimes previously unexplored. The development, operation, and experimental results are elucidated in great detail to allow other groups to replicate this system with minimal uncertainty.
KEYWORDS: Diode-pumped alkali laser (DPAL), Heat pipe, Metal vapor, Liquid metal, Exciplex-assisted diode-pumped alkali laser (XPAL)
PAGES 245-254

Tactical Checkpoint-Hail/Warn and Suppress/Stop
Elizabeth Mezzacappa, Charles Sheridan, Robert DeMarco, Kevin Tevis, Gladstone Reid, Kenneth Short, Nasir Jaffery, Gordon Cooke, and John Riedener, Armament Research, Development and Engineering Center, Target Behavioral Response Laboratory

Non-lethal weapons utility at tactical vehicle checkpoints was investigated during daylight conditions. Subjects drove on a course that simulated (1) a straight approach and (2) a serpentine approach to a checkpoint. Laser and multi-chromatic non-coherent (MCNC) light was evaluated for hailing and warning capabilities. Laser, MCNC light, and windshield obscuration by means of paintballs were evaluated for their suppression capabilities. Results show that the uninstructed response to the optical hail/warn devices is to continue forward motion. When the light sources were used in conjunction with auditory instructions and signs, results show that there was no significant difference between the light sources and the subjects' compliance rates. When instructions were eiven ahead of time as to the appropriate response to each of the light stimuli, fewer drivers followed the directions given in conjunction with the green laser. Suppression testing revealed that none of the stimuli was capable of inducing the driver to choose not to drive the serpentine course and none of the stimuli degraded navigational skills enough to cause contact or crashes with any barriers. There was a positive correlation between the degree of obscuration (number of paintball hits on the windshield) and the time to drive the serpentine course. The data also indicate that Warfighters should expect that at a recently or hastily established checkpoint, drivers may not understand instructions and be unsure of what to do to comply.
KEYWORDS: Non-lethal weapons, Checkpoint, Laser, Light, Driver behavior
PAGES 255-274

Extension of Reflected Laser Hazard Methodology to Ground Observer
Edward Early and George Megaloudis, TASC, Inc., and Justin Zohner, Paul Kennedy, and Robert Thomas, AFRL

A methodology to analyze reflected laser beam hazards was extended to include positions on the ground illuminated by the reflected beam. The original methodology was developed to address the need of the laser safety community for a more rigorous and accurate procedure, as compared to simplifying and overly conservative assumptions, fa determine reflected nominal ocular hazard distances to support high-energy laser field tests. The extension of this methodology considers the important case of observers on the ground exposed to the reflected laser beam. The extended methodology approach involves consideration of rays within the specularly reflected beam cone and not just the ray along the central axis used in the original methodology. At each time increment of an engagement scenario, a line on the ground is determined and exposure times and reflected irradiances are calculated at positions along this line. The set of such lines over an entire engagement scenario is used to determine both hazard regions and probabilities of injury over all positions on the ground. The relevant equations are derived, and then applied to an example engagement scenario of a ground-based laser illuminating a cylindrical target following a ballistic trajectory.
KEYWORDS: Hazard region, High-energy laser, Laser safety, Probability of injury, Reflected beam
PAGES 275-293

Beam Quality for Non-Gaussian Beams
R. Andrew Motes, Rio Rancho, New Mexico

This article describes a beam quality measure for non-Gaussian beams that is similar to power in the bucket (PIE), but bucket size is defined by the far-field central lobe size. These non-Gaussian beams include single beams and beamlet arrays. Flat-top circular, flat-top hexagonal, truncated Gaussian, and rectangular beamlet arrays are analyzed here. Methods for calculating beam quality based on this technique are demonstrated and beam quality comparisons are made of various types of beamlet arrays. The relationship between beam quality andfillfactor for these arrays is also shown. Infact, when an array's beamlets are identical and arranged in a closely packed hexagonal format, the maximum possible beam quality (as defined here) andfillfactor are the same. For truncated Gaussian beamlet arrays, we find the Gaussian beam diameter to aperture diameter ratio for maximum aperture efficiency. We then demonstrate that by varying the peak amplitude of the array's beamlets in a Gaussian fashion, one can increase the beam quality while reducing overall transmitted power. The analysis also shows that field amplitude noise in an array results in very little beam quality degradation while phase noise results in much greater degradation, and that phase noise has exactly the same effect on this beam quality definition as on Strehl ratio. Finally, we show the effects of beamlet loss on beam quality for both coherent and incoherent beam let arrays. The results of this analysis (both mathematical and numerical) demonstrate that incoherent arrays degrade more gracefully than coherent arrays. Overall, this document presents a thorough overview and tutorial for non-Gaussian beam quality and can be used as an introduction to the subject.
KEYWORDS: Beam quality, Non-Gaussian beam quality, Beamlet array, Laser arrays, Coherent beam combining, Incoherent beam combining
PAGES 294-335

Volume 4, Number 4, Journal of Directed Energy

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