The 2,492nd Meeting of the Society

March 22, 2024 at 8:00 PM

Powell Auditorium at the Cosmos Club

The Emerging Directed Energy Weapons

Are they finally ready to provide real military capability?

Thomas J. Karr & James Trebes

(1) Thomas J. Karr:
MITRE Corp. Chief Scientist for Sensors and Directed Energy
Consultant to the Defense Science Board and the Air Force Scientific Advisory Board
Principal Director for Directed Energy, Office of the Undersecretary of Defense (Research & Engineering), 2018-2020

(2) James Trebes:
Principal Director Directed Energy Office of the Undersecretary for Research and Development, Department of Defense, Ret.
Physics Division Leader, Lawrence Livermore National Laboratory, Ret.

Sponsored by PSW Science Member Edward Gadasu

About the Lecture

High power microwave sources first appeared prior to World War II. Lasers were invented in 1960. Both have the potential to become revolutionary military weapons. Despite major military investments by multiple nations over the last 60 years, their potential has not been realized. In the last several years both microwave and laser technology has improved considerably. This has resulted in the development, testing, and operational demonstration of numerous directed energy weapons. Directed energy weapons may be on the threshold of becoming used by multiple nations.

What are they? How do they work? What missions are they being developed for? What will be their benefits? How will they achieve useful military effects What is the United States developing? What are other countries developing? What are the major limitations? What are the key challenges that still need to be overcome before directed energy weapons become part of military arsenals?

This lecture by the two former Directors of Directed Energy Weapons for the U.S. Department of Defense will provide some answers to these questions.

Selected Reading & Media References
(1) “The New Laser Weapons,” Thomas Karr and James Trebes, Physics To-day 77 (1), 32-38 (1 January 2024);
(2) Department of Defense Directed Energy Weapons: Background and Issues for Congress, Congressional Research Service, 22 Aug 2023,
(3) Directed Energy Weapon Supply Chains: Securing the Path to the Future, NDIA/ETI, January 2024
(4) “All 11 US Super Carriers At ‘Grave Risk’, The EurAsian Times, 22 Nov 2023
(5) N. Bloembergen et al., Physics and Limitations of DEW for Missile Defense, Rev. Mod. Phys. 59, S1 (1987). A comprehensive reference on directed energy weapons still available as a downloadable PDF.
(6) “Missile Threat,” Missile Defense Project, CSIS,
(7) B. Manz, “High-power microwave systems—getting (much, much) closer to operational status,”, 24 Jan 2023
(8) T.H. Loftus et al., IEEE J. Sel. Top. Quant. Elec. 13, 487 (2007)
(9) G. D. Goodno, J.E. Rothenberg, Coherent Laser Beam Combining, A. Grignon, ed., Wiley (2013), p. 3
(10) M.D. Perry et al., “Laser containing a distributed gain medium,” US Patent 6,937,629 B2 (30 Aug 2005)
(11) W.F. Krupke, Prog. Quant. Elec. 36, 4 (2012)

About the Speaker

Thomas J. Karr
Thomas Karr is a consultant to the Defense Science Board and the Air Force Scientific Advisory Board. He is also Chief Scientist for Sensors and Directed Energy at MITRE Corporation, and he is the owner of Alamo Scientific, LLC. Previously Tom was Principal Director for Directed Energy in the OUSD/R&E, Program Manager in the DARPA Office of Strategic Technology, Director of Innovative System Solutions at Raytheon Space & Airborne Systems, among numerous other positions in research and technology development.

Tom’s research interests include national economic and military security strategy; remote sensing of the Earth and space; commercial space industry development; relativistic quantum sensing and information; laser pulse interactions with matter; and electromagnetic propagation through air, water, plasma, and nano-structured matter.

At OUSD/R&E Tom managed all DoD directed energy research, development, test and engineering. At DARPA he led the development of autonomous precision navigation systems that do not require GPS and conceived and directed the development of synthetic aperture laser radar for high-resolution imaging of deep space objects. At Lawrence Livermore National Laboratory (LLNL) he led a re-design of US “national technical means” of intelligence collection, resulting in new US intel architectures; led the development and commissioning of the first system predicting SCUD missile impact points while in flight; and discovered fundamental properties of high power laser propagation through the atmosphere, confirming all predictions by experiment. Also at LLNL he discovered a new relativistic wave equation for interacting spin-½ particles, and applied this wave equation to quarks bound into pions, revealing additional internal structure in pions beyond the standard model of colored gluons. Tom also o-founded the first US commercial radar satellite company, RDL Space Corp. He is an author on 64 publications in scientific journals and inventor on three patents.

Among many honors and awards, he received the DARPA Meritorious Public Service Medal, is an Optica Fellow, a Fellow of the Military Sensing Symposium, and a Fellow of the Society of Photo-Optical Instrumentation Engineers (SPIE). He has also held visiting fellowships at the Center for Theoretical Studies at the University of Miami, as a Joliot-Curie Fellow of the Commissariat a l’Énergie Atomique de France and the Centre d’Etudes Nucléaires Université Pierre et Marie Curie in Paris, at the Center for Theoretical Physics at the Univeristy of Miami, and twice at the University of Maryland.

Tom earned an AB in Physics at Princeton University and a PhD in Physics at the University of Maryland.

James Trebes
James Trebes is a consultant for the Office of the Under-Secretary for Defense for Research and Engineering (OUSD/RD) supporting directed energy weapons efforts, the Missile Defense Agency, and the Defense Science Board. Previously, he was Principal Physicist for Directed Energy for OUSD/RD and the Principal Director for Directed Energy for OUSD/RD. Before joining OUSD/RD Jim was with Lawrence Livermore National Laboratory for almost 40 years, where he served as a Group Leader, Division Leader for Medical Technology and Biophysics, Division Leader for Applied Physics, and Division Leader for Physics.

Jim has worked on a broad range of topics including x-ray lasers, laser fusion, nuclear weapons physics, nuclear weapons engineering, x-ray optics, x-ray imaging, space technology, detectors, biophysics, bio-detection, night vision, military special operations technology, medical technology, tomography, nuclear non-proliferation, intelligence analysis, quantum science, and conventional weapons technology.

Jim is an author on 62 scientific publications and an inventor on seven patents. Among other honors and awards he is a Fellow of the American Physical Society and served on advisory boards for both the Texas A&M Aerospace Department and the UC Berkeley Nuclear Engineering Department.

Jim earned a BS in Physics at Georgia Tech and a PhD in Physics at Yale.


On March 22nd, 2024, in the Powell Auditorium of the Cosmos Club in Washington, D.C., President Larry Millstein called the 2,492nd meeting of the Society to order at 8:08 p.m. ET. He began by welcoming attendees, thanking sponsors for their support and announcing new members. Scott Mathews then read the minutes of the previous meeting which included the lecture by Eric Cline, titled “Survival of Civilizations: After 1177 BCE”. The minutes were approved as read.

President Millstein then introduced the speakers for the evening, Thomas Karr, of MITRE Corporation, and James Trebes, of the Dept. of Defense (Ret.). Their lecture was titled “The Emerging Directed Energy Weapons: Are they finally ready to provide real military capability?”.

The two speakers alternated throughout the lecture. Karr began by indicating that the lecture would focus on laser-based weapons, with some discussion of microwave weapons, and no discussion of particle beam weapons. Karr presented an outline of the lecture, including: some history, physics, lethality, current US systems, foreign systems, and military challenges.

Trebes then discussed the physics of directed energy weapons (or DEWs), describing the variety of ways the energy beam could damage or interfere with a target, including: heating, creating fractures, spallation, shock waves, disruption in air flow, RF effects, and high electric fields. He described the potential advantages of DEWs in terms of low cost per shot and “deep magazines”. He discussed his view of the roadmap for DEWs, starting with simple, short-range systems capable of destroying UAV’s, drones, and artillery, to mid-range systems, capable of destroying cruise missiles, to complex, long-range systems capable of defeating hypersonic and ballistic missiles.

Karr then described some of the physics of DEWs. Given the focus on laser weapons, he presented graphs of the atmospheric transmission windows, indicating which lasers operated in each of the windows. He discussed the early work in the field using chemical lasers, then the semiconductor and solid-state lasers which began to appear in the 1970’s and 80’s, and the subsequent development of high-power fiber lasers, which now represent the state-of-the-art. He showed examples of diode-pumped, fiber lasers that are currently capable of generating and delivering hundreds of kilowatts of average power. He then mentioned the 22 specific DEWs systems deployed by the US for defense against “soft targets”. Karr briefly discussed the physics of combining fiber lasers, to create a more powerful beam, stating that these techniques will likely be used to create future weapons to defeat “hard targets”. He then presented some of the additional systems that need to be integrated with the laser source to create an effective weapon. These included: the power source, cooling system, beam director, target tracking, fire control, and command & control systems.

Trebes then discussed some of the physical limitations of DEWs. For laser-based systems, these include: atmospheric turbulence, thermal blooming, and self-focusing. For high power microwave systems, the primary limitation is atmospheric electrical breakdown. He presented the concept of the “Kill Chain”, describing the flow of information from long-range radar, local radar, and target tracking to the command & control center, and then to the weapon’s fire control system. Trebes then discussed “kill assessment”, and various types of kills. These included “system kills”, which result in “flaming wreckage”, and “mission kills”, which prevent mission completion. He noted that most laser weapons result in mission kills, and not system kills. He then discussed the ways in which a HPM system can get electromagnetic energy through the cracks and seams in a weapon to disrupt its electronics.

Karr then showed images of deployed DEW systems in the US military, and gave more details about each. These included the Navy ODIN (optical dazzling interdictor), the Army DE-MSHORAD (maneuvering short range air defense), the Marine CLAWS (compact laser weapons system), and the Air Force HELWS (high energy laser weapon system). He then showed images and gave details about future systems currently under development by the US military. He also showed examples of DEW systems being deployed or developed by other countries.

Both speakers then presented some of the difficulties in having the US military adopt DEWs. They discussed the fact that the Pentagon, and the warfighter in particular, do not trust these weapons systems because they are largely untested on the battlefield. They mentioned the bureaucratic hurdles associated with the “Integrated Defense Acquisition, Technology, and Logistics Life Cycle Management System”. They discussed the fact that the military has many different weapons systems that compete with DEWs. And finally, they discussed the fact that while the cost-per-shot was very low…on the second shot…these systems require considerable capital investment.

The lecture was followed by a short, collegial debate. Karr argued that each branch of the military should create a new office to direct research into DEWs. He argued that this research should be moved from the traditional research labs (ARL, NRL, AFRL) to new labs that specialize in building weapons. Trebes argued that the creation of new agencies or offices were not necessary. He argued that such “specialty organizations” would only work if the organizations were given some form of congressional mandate, forcing them to spend money on DEWs research. In the end, the two speakers agreed that they were “not that far apart”.

The lecture was followed by a Question and Answer session, however, in the interest of time, the details of the Q&A session have been omitted from the minutes.

After the question and answer period, President Millstein thanked the speakers and presented them with PSW rosettes, signed copies of the announcement of their talk, and signed copies of Volume 1 of the PSW Bulletin. He then announced speakers of up-coming lectures, made a number of housekeeping announcements, and invited guests to join the Society. He adjourned the 2492nd meeting of the society at 10:29 pm ET.

Temperature in Washington, DC: 9.4° Celsius
Weather: Cloudy
Audience in the Powell auditorium: 52
Viewers on live stream: 53 …for a total of 105 live viewers
Views of the video in the first two weeks: 946

Respectfully submitted, Scott Mathews: Recording Secretary