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Journal of Directed Energy
Volume 3, Number 3 Winter 2009

The papers listed below constitute Volume 3, Number 3 of the Journal of Directed Energy. Print copies of issues of the Journal of Directed Energy are available through the online store..
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Capability Assessment of the High-Energy Laser Liquid Area Defense System (HELLADS)
Ryan S. Ponack, 14 AF/A9 and J.O.Miller, Air Force Institute of Technology

High-energy Laser (HEL) technology continues to improve, and its planned place in the battlefield is ever evolving. The Defense Advance Research Projects Agency (DARPA)-envisioned HEL Liquid Laser Area Defense System (HELLADS) has two main advantages over any HEL predecessor. One, the configuration is small and light enough to be carried on more tactical aircraft such as fighters. Two, the thermal management greatly increases HEL firepower by increasing dwell time on target. To assess HELLADS operational capabilities, the test community has been challenged with how to effectively examine the advantages and limitations in a cost-effective manner. Where field testing is infeasible, modeling and simulation emerges as a relatively low-cost and robust assessment tool. Specifically, this research effort focuses on the assessment of operational capabilities for a yet-to-be-developed HEL weapon system patterned after HELLADS. An Air Force Standard Analysis Toolkit mission-level model, the Extended Air Defense Simulation Model (EADSIM), is used in this study along with the HEL End-to-End Operational Simulation (HELEEOS) to model atmospheric propagation. Of particular interest is the investigation of the envisioned HELLADS operational envelope and the potential advantages it offers over other HEL systems. Scenarios are developed to represent the homeland defense arena in which HELLADS is envisioned to operate.
KEYWORDS: Computer simulation, High-energy laser, Liquid laser, Mission-level combat modeling
PAGES 193-211

Diagnostic Array for Characterizing Narrow-Band High-Power Microwave Sources
P.D.Coleman, Sandia National Laboratory; and C.W.Woods and G.S.Nelson, Air Force Research Laboratory

Accurate characterization of radiated antenna patterns is critical to successfully developing high-power microwave (HPM) sources. Accurately measuring the intense fields and radiation patterns of these dynamic sources is a difficult task. This paper details the design and operation of a 31-element, time-resolved diagnostic array that has been used in the development of various HPM sources.
KEYWORDS: Antenna, Diagnostic, Array, HPM
PAGES 213-221

Broad-Spectrum Optical Turbulence Assessments from Climatological Temperature, Pressure, Humidity, and Wind
Steven T. Fiorino, Richard J. Bartell, Matthew J. Krizo, Brandon T. McClung, J. Jean Cohen, Robb M. Randall, and Salvatore J. Cusumano; Air Force Institute of Technology

The effects of optical turbulence on high-energy laser propagation have been well documented. The optical turbulence is typically characterized using the index of refraction structure parameter, Cn2. The value and three-dimensional variation of Cn2 can be accurately diagnosed for the surface boundary layer (lowest 50 m of the atmosphere) from values of temperature, pressure, humidity, and wind velocity using meteorological similarity theory. Examples of such similarity theory Cn2 calculators include the Tunick model for overland applications and the Navy Surface Layer Optical Turbulence (NSLOT) model for ocean scenarios. Both the Tunick and NSLOT models are limited in their applicability to relatively small portions of the spectrum in the visible and infrared; generally they are valid from 400 to 3,000 nm and from 7.8 to 19 microm. This study expands the valid spectral range of the Tunick Cn2 model to 400 nm-8.6 m, continuously. This is accomplished by adapting the Tunick model for use with the Air Force Institute of Technology Center for Directed Energy HELEEOS (High Energy Laser End-to-End Operational Simulation) and LEEDR (Laser Environmental Effects Definition and Reference) models. The derived Cn2 values can be wavelength tuned and compared to scintillometer and radar measurements of Cn2
KEYWORDS: Anomalous dispersion, Atmospheric effects, NSLOT model, Optical turbulence, Surface layer, Tunick model
PAGES 223-238

Ablative Polymeric Materials for Near-Infrared High-Energy Laser Beam Diagnostics
Christopher T. Lloyd, Robert F. Cozzens, and Collin J. Bright, Naval Research Laboratory; and D. Jason (Jake) Sames, Larry K. Myers, and Peter D. Kazunas, The Electro-Optics Center

One-micron lasers are of high interest for industrial and military applications fueled by recent developments in fiber lasers. There exists a large gap in data collection for the ablation of polymeric materials with near-infrared (IR) lasers. It is necessary to understand how and why chemical structural properties such as aromaticity, heteroatomic content, and degree of cross-linking affect near-IR ablation of polymers, as well as thermal stability and optical properties. More so, properties such as these are useful for determining which polymers are best suited for laser beam diagnostic measurements. Polymers such as clear Plexiglas have been used as beam diagnostic materials at 10.6 microm. in the past. Identification of two commercial polymers was made for laser beam profiling and diagnostic purposes at near-IR wavelengths. Differences in ablation and beam diagnostics using carbon black-loaded plastics were observed. Several synthesized and commercial polymeric materials were irradiated with a 10-kW, 1.07- microm. fiber laser, and corresponding ablation energies were obtained. Ablation energies are dependent on the molecular structure of polymers, especially aromatic and heteroatomic character and thermal degradation processes. This study was aimed at understanding how near-IR radiation ablates polymers and to evaluate different polymers for use as potential irradiance diagnostic tools (witness plates).
KEYWORDS: Carbon black, HEL irradiation, Irradiance diagnostics, 1.07 micrometer fiber laser, Polymer ablation
PAGES 239-256

Measurements of Improved ElectricOIL Performance, Gain, and Laser Power
J.W.Zimmerman, G.F.Benavides, and B.S.Woodard, University of Illinois at Urbana-Champaign; D.L.Carroll, A.D.Palla, and J.T.Verdeyen, CU Aerospace; and W.C.Solomon, University of Illinois at Urbana-Champaign

Ongoing experiments have led to continued improvements in the electric oxygen-iodine laser (ElectricOIL) system that significantly increased the performance, gain, and laser power output. Experimental investigations utilize radio-frequency discharges in O2/He/NO mixtures in the pressure range of 30-60 torr. The goal of these investigations was maximization of both the yield and flow rate (power flux) of O2(a1delta) in order to produce favorable conditions for subsequent gain and lasing in our ElectricOIL system. Numerous measurements of O2(a1?), oxygen atoms and discharge excited states are made to characterize the discharge. A gain of 0.22% cm-1 was measured with a corresponding outcoupled power of 28 W. Modeling with the BLAZE-IV code is in good agreement with data and helps to guide our understanding of the complex hybrid laser system.
KEYWORDS: ElectricOIL, Oxygen-iodine laser, Singlet oxygen
PAGES 257-275

Finite Element Analysis and Dynamic Simulation of Target Thermal Response to High-Energy Lasing
Christopher Larson, Clay Canning, Gunnar Tamm, and John Hartke, United States Military Academy

High-energy laser (HEL) systems on the order of 100 kW are under development to neutralize stationary and mobile targets. Modeling the thermal response of the target will identify both requirements for the laser system and means to protect the target against such laser systems. Analytical solutions are limited, and computational solutions are accurate only if they consider boundary conditions and material properties varying with time, temperature, and location. A transient three-dimensional finite element solution has been developed that employs dynamic simulation techniques. Stationary and mobile targets are evaluated under loading by a continuous-wave laser with various beam profiles, with particular attention to mortar rounds in flight. Results from the target thermal model support complementary analyses of the 100-kW HEL system completed at the U.S. Military Academy.
KEYWORDS: Finite element, Heat transfer, High-energy laser
PAGES 276-288

Volume 3, Number 3, Journal of Directed Energy

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