Navy Slab Solid State Lasers will scale to 300-500 Kilowatts

The Congressional Research service recently provided a Navy report of Shipboard Lasers for Surface, Air, and Missile Defense: Background and Issues for Congress.

US laser development has reached the point where lasers capable of countering certain surface and air targets at ranges of about a mile could be made ready for installation on Navy surface ships over the next few years. More powerful shipboard lasers, which could become ready for installation in subsequent years, could provide Navy surface ships with an ability to counter a wider range of surface and air targets at ranges of up to about 10 miles.

The Navy and DOD have conducted development work on three principal types of lasers for potential use on Navy surface ships—fiber solid state lasers (SSLs), slab SSLs, and free electron lasers (FELs). One fiber SSL prototype demonstrator developed by the Navy is the Laser Weapon System (LaWS). The Navy plans to install a LaWS system on the USS Ponce, a ship operating in the Persian Gulf as an interim Afloat Forward Staging Base (AFSB[I]), in the summer of 2014 to conduct continued evaluation of shipboard lasers in an operational setting. The Navy reportedly anticipates moving to a shipboard laser program of record in “the FY2018 time frame” and achieving an initial operational capability (IOC) with a shipboard laser in FY2020 or FY2021.

Northrop Slab Solid State Laser demonstrator

• Lasers with a power level of about 10 kW might be able to counter some UAVs at short range, particularly “soft” UAVs (i.e., those with design features that make them particularly susceptible to laser damage).
• Lasers with power levels in the tens of kilowatts could have more capability for countering UAVs, and could counter at least some small boats as well.
• Lasers with a power level of about 100 kW would have a greater ability for countering UAVs and small boats, as well as some capability for countering rockets, artillery, and mortars.
• Lasers with power levels in the hundreds of kilowatts could have greater ability for countering targets mentioned above, and could also counter manned aircraft and some missiles.
• Lasers with power levels in the megawatts could have greater ability for countering targets mentioned above—including supersonic ASCMs and ballistic missiles—at ranges of up to about 10 nautical miles.

Slab Solid State Lasers (Slab SSLs)
DOD has pursued multiple efforts to develop slab SSLs for military use. Among these was the Maritime Laser Demonstration (MLD), a prototype laser weapon developed as a rapid demonstration project under DOD’s Joint High Power SSL (JHPSSL) program. MLD leveraged development work on slab SSLs done elsewhere in DOD under the JHPSSL program. In March 2009, Northrop demonstrated a version of MLD that coherently combined seven slab SSLs, each with a power of about 15 kW, to create a beam with a power of about 105 kW.

Scaling up a slab laser to a total power of 300 kW is not considered to require any technological breakthroughs. Supporters of slab SSLs such as MLD believe they could eventually be scaled up further, to perhaps 600 kW. Slab SSLs are not generally viewed as easily scalable to megawatt power levels.

Free Electron Lasers (FELs)

Unlike slab SSLs, which are being developed by multiple U.S. military services, FELs are being developed within DOD solely by the Navy, in part because they would be too large to be installed on Army or Marine Corps ground vehicles or Air Force tactical aircraft, and in part because an FEL’s ability to change its wavelength so as to match atmospheric transmission sweet spots makes it particularly suited for operations in a marine environment. The basic architecture of an FEL offers a clear potential for scaling up to power levels of one or more megawatts.

A 14.7 kW FEL has been developed; it has not been moved out of a laboratory setting or fired at an operational moving target. The Office of Naval Research (ONR) had planned to follow this with the development, as an Innovative Naval Prototype (INP),35 of a 100 kW FEL; the work was scheduled to be performed during FY2010-FY2015. Developing a 100 kW FEL would reduce the risks associated with developing a megawatt-class FEL.

Because of its probable size, an FEL could not be backfitted onto existing cruisers or destroyers. Aircraft carriers and “large-deck” amphibious assault ships (i.e., LHA/LHD-type amphibious ships) might have enough room to accommodate an FEL, but existing carriers and amphibious assault ships might not have enough electrical power to support a megawatt-class FEL. In addition, because of thermal blooming and the status of carriers and amphibious assault ships as potential high-value targets, it might make more operational sense to install megawatt-class FELs on ships other than carriers or amphibious assault ships

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.