How do directed energy weapons work?

Directed energy weapons (DEWs) use electromagnetic (EM) energy, such as high-energy lasers (HELs), high-powered microwaves (HPMs), or high-power millimeter waves (HPMMs), to degrade or destroy targets. Sometimes, sound waves are included in the DEW category. This article focuses on EM DEWs.

EM DEWs have several advantages compared with traditional munitions, including:

Speed: EM energy travels at the speed of light, almost instantaneously striking the target.
Stealth: EM energy travels silently, usually with invisible or nearly invisible beams that are hard to detect.
Precision: EM energy can be highly focused and deliver precise energy levels for lethal and non-lethal applications.

Cost is an important aspect of EM DEWs. They are touted to have a much lower cost per shot than traditional weapons like missiles. However, the cost of EM DEW systems can be significantly higher than that of traditional munitions. Still, the overall lifetime operational cost can be less for EM DEWs.

HELs offer superior precision compared with microwave and millimeter-wave weapons. They can even hit specific points on a target. In contrast, millimeter waves can hit multiple targets simultaneously, and microwaves can disrupt electronics over a larger area with a wide beam (Figure 1). The lack of precision of HPM and HPMM weapons can result in unintended collateral damage.

HELs

HELs are typically based on a solid-state laser (SSL) instead of a liquid or gas medium. Semiconductor lasers like laser diodes are also solid-state devices but are in a different category — SSLs use a solid, transparent material doped with ions to create a laser.

There are several options for building HELs, including:

Neodymium:yttrium-aluminum-garnet (Nd: YAG) that operates at 1020 nm.
Titanium-doped sapphire that can be tuned from about 660 to 1080 nm.
Alexandrite is also tunable, but over a narrower range of about 700 to 820 nm, and produces higher-energy pulses than titanium-sapphire lasers.

Nd: YAG and Alexandrite lasers are used in current HEL DEW designs, and titanium-doped sapphire lasers are being explored for future DEW applications. HEL DEWs can produce continuous or pulsed outputs (Figure 2).

Figure 2. SSL-based HEL DEWs can produce highly focused and powerful beams. (Image: *U.S. Naval Institute*)

In addition to the laser, there are several key components in a HEL-based DEW, including:

Beam director: optical components that focus the laser beam and compensate for atmospheric disturbances.
Power source: generator and energy storage systems supporting the system’s power requirements.
Cooling systems: thermal management is crucial for the sustained operation of HELs.

Gas lasers, such as chemical and CO2 lasers, are also being considered for DEWs. Gas lasers can achieve high power outputs, but they are more complex to operate and maintain than SSLs and have limitations on beam quality and stability.

HPMM weapons

HPMM DEWs have wavelengths between 1 and 10 mm and can affect multiple targets simultaneously. These weapons are also called active denial systems (ADS). The mm waves penetrate the skin to about 0.4 mm, exiting the water and fat molecules and causing a burning sensation. The sensation stops when the HPMM beam is removed.

An ADS is a non-lethal weapon and heats the skin to about 44 °C. First-degree burns occur at about 51 °C and second-degree burns at about 58 °C. These weapons are being designed for crowd control and to incapacitate enemy personnel. Challenges with deploying HPMM DEWs include:

Effectiveness is lower at longer distances and in adverse atmospheric conditions.
Collateral damage can result from the relatively wide beam.
Ineffective against shielded targets.

HPMs

HPMs are used to disable and destroy electronics like those used in communication systems or drones. They are useful in urban environments and can impact multiple targets simultaneously. HPM effectiveness depends on the ability to deliver the needed energy level and is impacted by the distance to the target and the dwell time on the target. Other factors that can limit the effectiveness of HPM include:

Adverse atmospheric conditions can reduce the ability to deliver a focused energy beam.
Shielding can protect targets from the effects of HPM.
HPMs operate better when the line of sight is unobstructed.

Summary

EM-based DEWs are bringing new capabilities to the battle field. They can be used to destroy equipment or incapacitate enemy personnel. And they can do it at a lower cost than traditional weapons like missiles.