March 04, 2016

US Navy plans for scaling Free electron lasers to megawatt weapon systems

There is a US Navy paper - Vision for Directed Energy and Electric Weapons In the Current and Future Navy which describes the Navy's thinking on laser weapons

Laser weapons enable delivery of scalable levels of energy at both tactically and strategically relevant distances enabling the accomplishment of new missions and generating entirely new classes of effects during naval battle engagements and on the battlefield. They also offer unique solutions to many of the most serious threats and enable safer accomplishment of hazardous missions. Compared to traditional weapons, laser weapons offer significant benefits including: non-lethal, long-range force application capabilities, lethal target effects, potentially unlimited magazines and significantly smaller logistics footprints than non-DE (directed energy) weapon systems; although some specialized support equipment will be required. Furthermore, there are advantages of reduced operational costs and lower manpower requirements because of automated battle management systems using state-of-the-art electronics.

Laser weapons destroy a target either by heating the target surface to the weakening point and causing it to fail under operating stress, or by burning through the skin to destroy underlying critical components and/or subsystems. Additionally, the laser may be used to attack energetic material in a target and cause low-order detonation, a primary destruction method. In all military applications, laser weapons, laser sensors and laser deterrence and communications systems proffer significant force multiplication and thus can enable future commanders to accomplish greater numbers of missions more effectively and in less time, consistent with Force Net and Sea Strike strategies.

In terms of weaponization, the FEL (Free electron laser) is the laser device of choice and “holy grail” for weaponization in the 2020 time frame. However, there exist many nearer-term potential naval applications for kilowatt-class solid-state laser (SSL) and high-power microwave (HPM) weapons. The development of SSLs is of particular interest to the naval aviation and to the surface naval communities, while the free electron laser is of interest to and is being developed for surface shipboard use in the “navy of the future”. HPM weapons, being developed for employment as deterrent systems will not be discussed here


Block 1 and the improved Block 1A laser weapon systems, employing unphased, ganged, single-mode fiber lasers operating at modest average power levels with a beam director of 30-50cm aperture, could be useful ranges for enhancing mission capabilities on a variety of naval platforms. Activies within these missions could include counter-rocket artillery mortar (CRAM), asymmetric threats and destroying electro-optic sensors at tactically significant ranges. The Block 1A listing would improve capabilities of Block 1 laser systems by taking advantage of updated beam control and optical technologies as they come to fruition. It is interesting to note that, in commercial applications, solid-state lasers with output power of order 5kW are used to weld and cut metals. Modularized fiber lasers, with output power up to 1 kW and capable of being ganged, are currently available commercially. Many other types of low power SSLs are currently in use in such military systems as laser pointers, sensor blinders and deception devices.



Block 2 capabilities depend on technical improvements to fiber lasers of Blocks 1 and 1A to achieve better beam quality and greater output power with improved beam control to buy greater power delivered to targets at increased range.

Blocks 3 and 4 show the long-term development paths for the free electron laser (FEL). The FEL is currently very much a research device largely in the hands of the Science and Technology (S and T) community. A truly electric laser and a fitting photon source in the context of the electric ship, it offers tunability to cope with laser propagation limitations and power throttling for a broad range of utility unavailable in any of the lasers now in use or planned for the near term.

FEL generates high-intensity laser light by utilizing the energy from unbound accelerated high-energy electrons. This technology is commonly used in the Department of Energy’s particle colliders for basic subatomic research. FEL can scale into megawatt power ranges.



Integrated Power Systems (IPS) – A Key Enabler for Electric and Directed Energy Weapons Systems

Traditional US naval vessels have dedicated and separate prime movers to drive shipboard propulsion and electrical service loads. On a typical warship, nearly 50% of the installed shipboard propulsive power (on the order of 40 MW) is only used to power the ship through the final 5 knots to a ship’s maximum flank bell. Based on a typical operational profile, a ship will only use this power less than 5% of its underway time. These propulsion prime movers are typically mechanically coupled to the propeller or water jet via a shaft and reduction gear box.

DDG-1000 is the first US warship to employ a sophisticated electrical distribution system to direct the total available installed power (approximately 80 MW) for use in both the electric propulsion motors and to support the full range of shipboard electrical loads. This system, known as the IPS, is a key enabler of a full range of novel shipboard directed energy and electric weapon systems including speed-of-light high energy laser systems and electromagnetic rail guns.




Options for adding more powerful lasers

• the Navy could design the Flight III version of the DDG-51 destroyer so that it can support an SSL with a power level of 200 kW or 300 kW or more;
• the Navy could design and procure a new destroyer as a followon or substitute for the Flight III DDG-51 that can support an SSL with a power level of 200 kW or 300 kW or more, and/or a megawatt-class FEL;
• the Navy could modify the designs of amphibious assault ships to be procured in coming years, so that they can support SSLs with power levels of 200 kW or 300 kW or more, and/or megawatt-class FELs; and
• the Navy could modify the design of the Navy’s new Ford (CVN-78) class aircraft carriers, if necessary,so that they can support SSLs with power levels of 200 kW or 300 kW or more, and/or megawatt-class FELs.


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