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Journal of Directed Energy
Papers to be Published

The papers listed below, if any, will be published in an upcoming issue of the Journal of Directed Energy. If you wish to reference these works, include the authors and title, plus "Journal of Directed Energy, forthcoming"'.
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Integration Readiness Assessment Tools for Streamlining Technology Development through Transition
Sean Ross, Acquisition Science, Technology, and Engineering

Technology readiness level only tells a part of the system maturation story. As technologies are developed to become part of systems designed to meet operational needs, there are also integration and manufacturing issues to consider. This paper outlines tools that have been developed to capture and measure the system readiness level that incorporates a broader view of system maturity..
KEYWORDS: System engineering, Integration readiness, System readiness

Evaporation and Beam Profile Measurements on an Irradiated Water Drop
Timothy E. Tracey and Cody J. Brownell; U.S. Naval Academy

This work investigates the interaction of a high energy laser and single water drops. The drop thermodynamics and optical propagation of the laser are coupled through the absorption-dependent vaporization process. An analytical model of absorption and rapid evaporation for small aqueous aerosols is extended for use with large drops. Experimentally, a high energy infrared laser is used to irradiate single drops of water, and the drop shape and size as well as the transmitted beam profile are measured. The drop is levitated using an ultrasonic levitator, where the drop is held in place by the pressure from a standing sound wave. Drop size and composition are varied, along with the incident laser power. Experimental data are used to validate findings from the analytical model, and to show the effects of drop size, composition, and irradiance on evaporation rate. An overall energy balance for the drop is discussed, and the relative magnitude of absorption, transmission, and reflection are estimated from the data. Several qualitative observations are used to suggest areas for further work.
KEYWORDS: Raindrop, Vaporization, HEL, Imaging

Jittered Uniform Annular Beams
Charles J. Albers, Jr., Radiance Technologies

The effect of jitter is analytically determined on the time-averaged focal-plane irradiance distribution due to a uniform circular annular beam in the transmitting aperture. It is assumed that the time average can be replaced by the ensemble average and the pointing angles are sufficiently small making the usual small-angle approximations valid. The integrand for determining the ensemble-averaged irradiance is not separable, but the expression for the ensemble-averaged irradiance has been reduced to an integral of a function of three variables that is amenable to numerical evaluation. For a given outer beam diameter and obscuration, it is found that the power in the bucket is well fit by an expression similar to that for an ideal Gaussian beam but with two parameters instead of one. The first parameter is similar to conventional beam quality while the second accounts for wide-angle dispersion of the beam in the focal plane. The parameters are weakly dependent on jitter.
KEYWORDS:Diffraction, Jitter, Annular beams, Beam quality, Power in the bucket

Laser Communication as a Secure, High-Bandwidth Airborne Communication Link
Lester Begg and David Robie; General Atomics

As airborne intelligence, surveillance, and reconnaissance (ISR) payloads become more capable and operating environments become more contested, assured ISR backhaul from airborne nodes will become challenged. Lasercomm provides a solution to these challenges. General Atomics Aeronautical Systems, Inc. (GA-ASI) is developing an airborne laser communication terminal, capable of bi-directional, secure communications to/from an MQ-9 Reaper unmanned aerial vehicle (UAV). A description of the world-wide lasercomm geo-synchronous satellite (GEOSAT) constellation, being deployed by Airbus Defence and Space, is presented. This paper describes how ISR data collected by multiple UAVs can be transmitted to an overhead GEOSAT(s), and relayed to anywhere in the world with minimal latency. An outline of the stepping-stone, build, and test progression of the GA-ASI Airborne Laser Communication System (ALCOS) demonstration program is provided.
KEYWORDS: Laser communication, Anti-jam, Low probability of detection, Low probability of intercept, Data rates, GEOCOM

To Be Published, Journal of Directed Energy

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Last updated: 2 April 2018