Directed Energy (DE) is defined for military applications as the ability to project electromagnetic energy either broadly to provide information probing of the battlespace, or in a focused manner sufficient to produce a defensive or offensive effect at militarily relevant distances within the battlespace. The military significance of Directed Energy Weapons (DEWs) has long been recognized for ability to engage at the speed of light, propagating vast distances with precision. Other benefits include potentially deep magazines, meaning the capability to fire many shots without need to physically rearm the weapon, and low cost per shot. DE can also actively probe targets and threats, i.e. laser pointers (commonly called designators), laser and radiofrequency (RF) tracking, also called radar. The final benefit worth mentioning, is the ability to cause scalable and flexible effects, to include destructive, damaging, disruptive, non-lethal, deceptive, and unattributable effects.
Today in the early 2020s, world-wide DE already plays important military roles in counter-air defense, target identification, tracking, counter intelligence search & reconnaissance (ISR), and electronic warfare (EW). U.S. military thinking on electromagnetic spectrum operations defines DE in the context of electronic attack systems designed to disrupt or degrade an adversary’s signals, deliver communications supporting cyperspace operations, or disable and destroy targets susceptible to high-energy electromagnetic radiation (U.S. Joint Chiefs’ of Staff 2020). Today there are historical definitions that delineate DE and EW weapons which are otherwise similar in function and form. Because the historical definitions are unlikely to be important 40 years in the future, in this report we considered DE and EW weapons to be synonymous, especially with respect to applications of information superiority that reply upon electromagnetic spectrum superiority to accomplish military missions.
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Although today high-energy laser equipment is proliferated worldwide, the ability to create laser effects at vast ranges, for military purposes, is still limited. Today, for reasons that we will explain further, it
is thought that two of the most militarily relevant use cases for high-energy laser weapons are i.) high- altitude (greater than 30,000 ft.) operations where the stand-off range between shooter and target is up to hundreds of kilometers, or ii.) ground- or sea-based defensive purposes.
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To understand the future technical trends in lasers system development, one must consider the drivers behind laser technology in the last 40 years. Technical trends over the next 40 years will be driven by both military and commercial interests, in addition to the lessons learned from previous laser weapon programs. Some of the lessons learned from the U.S. Airborne Laser Program, which began about 40 years ago and used gas and chemical laser architectures, were i.) the logistical footprint of a laser can create operational challenges; ii.) maximum powers in the range of Megawatts can be attained; and iii.) control of the beam is vitally important and nontrivial to achieve with highly accurate pointing. The challenges of beam control include propagation of light through potentially turbulent atmospheres, compensation of mechanical jitter from the host platform (in this case, the airplane), and C4ISR integration. Today the U.S. Air Force continues development of a high energy laser on a tactical airborne platform (Insinna 2020).
The U.S. DE community has made significant progress toward addressing the lessons learned from
early programs. Presently, the U.S. and Allied DE community uses a solid state and fiber optic laser architecture both because they learned the lessons about the logistical footprint of laser systems, and due to the industrial development and commercialization of fiber-optics and other solid-state laser technology. In fact, commercial development has revolutionized laser technology over the past 40 years. Solid state and fiber-optical approaches eliminate the need for large volumes of toxic chemicals in DE systems. Furthermore, fiber lasers can be combined to produce hundreds of kilowatts of power, with good beam quality (Anderson 2015), and have proven relevant in tactically suitable payload sizes, weights, and powers (SWAP).
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Conservatively, following trends of the past 40 years of development up until now, in the future, solid- state and fiber laser technology can be projected to achieve extremely high energy levels in the range of Megawatts over a second, high enough to reduce timelines for laser engagement to less than 1s at tactical ranges by 2060. Optimistically, 100’s of Megawatt solid state laser systems could be possible. This technical trend is bolstered by current research in laser power scaling (Sherman 2019), to reduce dwell times and/or increase range of effects. For laser weapon technologies, these advancements represent an inflection point as they reduce the timescales of engagements significantly, enabling vital missions.
Once a sufficient amount of laser energy is created, the next challenge for laser weapons lies in the ability to propagate laser energy kilometers or farther distances, through the atmosphere, to targets at range. Trends in technology development over the next 40 years will be driven by solving such challenges. The challenge includes both tracking of moving targets at high levels of accuracy from moving platforms, and
being able to control the beam both accurately and precisely. Today, lasers weapons are powerful enough for missions against soft targets such as UASs (88th Air Base Wing Public Affairs 2020, Chuter 2019) and demonstrations of counter-missile applications (88th Base Wing Public Affairs 2019). State-of-the-art beam pointing from stabilized gimbal mounts permit hundreds of nanoradian precision pointing from stationary and slowly moving platforms, while tracking fast moving objects (Kwee 2007). Microradian accuracy is currently possible on large airborne platforms. In the future, by 2060, higher pointing accuracy, approaching 100s of nanoradians, could optimistically be possible on fast moving platforms.
Invention of solutions to technical challenges will drive future trends. For example, propagating laser energy through the atmosphere, becomes challenging in poor weather or turbulence. Turbulence causes both beam wander and brightness fluctuations in
high energy lasers. Weather deleteriously effects all weapons, but poses particular problems for all optical and infrared sensors, many of which provide cues and tracking for command and control of weapon systems. Inventions over the next 40 years may prove the ability to overcome weather effects. As an example, current research focuses on ultra-short pulse lasers that promise to burn holes through fog (Rudenko 2020).
A technology that today compensates for the deleterious effects of atmospheric turbulence is adaptive optics, invented and developed nearly 40 years ago (Fugate 1991). Sophisticated adaptive optical systems can today compensate for moderate levels of turbulence and atmospheric distortions. Conceivable improvements in the engineering of optical systems, even in the most pessimistic case for technology advancement, will further improve efficiency in ability to put up to Megawatts of continuous wave laser energy on target at tactically relevant distances. Gigawatts or 100s of Megawatts of laser energy propagated at tactically relevant and longer distances, would be an optimistic technical outcome by 2060. In the atmosphere, power levels greater than a few Gigawatts would undoubtedly suffer from self-focusing effects (Nibbering, et al. 1997). U.S. DoD and Allied military utility studies have been conducted, and will continue to be conducted, to objectively determine, in conjunction with kinetic and cyber weaponry, to what degree of effectiveness DE capabilities can achieve destructive effects for specific missions and scenarios that include weather.
An easy way to avoid the issues of weather and atmospheric propagation is to deploy DEWs at high altitudes, where the earth’s atmosphere is thinner. For this reason and others, high altitude military applications of DEWs will remain important concepts into the future.
Future trends in DEW technology will follow mission needs. The “holy grail” from a military utility perspective is a DE weapon system effective enough, favorable from a SWAP perspective, and affordable enough to provide a nuclear/missile umbrella. Although a concept often associated with science fiction, in fact ground and ship-based DE defense systems effectively act like point-localized force fields against small and relatively soft targets today. Airborne and space-based DE platforms could achieve a greater area defense and multipoint defenses, for a broader coverage missile umbrella. However, these concepts require significant technical advancement by 2060 to achieve the full range of power contemplated.
Albeit significant technical advancements are required in power, and range of power specifically, in the most optimistic case it should be physically possible to design a mission relevant concept of operations that permits nanoradian beam-control accuracy while tracking missiles up to hypersonic speeds, with a fast enough command and control loop and Megawatts of laser power (for more reading on this concept see Sec 2.5 and Appendix A: Vignette 1 and Vignette 3). By 2060 a sufficiently large fleet or constellation of high-altitude DEW systems could provide a missile defense umbrella, as part of a layered defense system, if such concepts prove affordable and necessary.
