Solid-state laser weapons offer war-fighters unique capabilities for the battlefield: precision, controllability, predictability, repeatability and flexibility. These laser systems will enable Soldiers to defeat multiple threats and affect materiel targets. Each engagement, wheth-er disabling an enemy's communications antenna or causing low-order detonation of an artillery round in flight, has an average cost of $30.

During the 1970s, the Army investigated carbon dioxide lasers. But there were issues with beam transmission through the atmos-phere and difficulty focusing the beam to a small spot at the target. Both factors reduced the lasers' effectiveness. Chemical lasers provided improved performance, but the hazardous materials required to generate the laser beam posed significant risk to warfight-ers.

A safer, more efficient alternative to chemical lasers, solid-state lasers generate their beam by converting electricity into tightly fo-cused laser light. There are two main types of solid-state high-energy lasers--greater than 1 kilowatt (kW)--in development today: thin-sheet and combined-fiber lasers. Of these two, combined-fiber lasers show the greatest promise for laser weapon systems on tac-tical and combat platforms because of their efficiency in converting electrical power to power on target. The Army, working with the High Energy Laser Joint Technology Office, initiated the Robust Electric Laser Initiative (RELI) effort in 2010. Four contracts were issued under RELI. The Army retained two of the contracts and later elected to scale a combined-fiber laser, designed by Lockheed Martin Corp., to a 50-kW class power level.

FIBER LASER BASICS
A fiber laser module begins with pump laser diodes to create light energy from electrical energy. The light from the pump laser diodes is then fed into a special optical fiber where the power from a seed laser diode is amplified. (See Figure 1.)

Today's fiber laser modules are limited to a little over a kilowatt. To reach higher power levels, the individual fiber laser modules need to be combined into one beam. The Lockheed Martin design uses a spectral-beam-combining architecture whereby laser beams of different frequencies are transmitted to a grating and combined into a single beam that is transmitted out of the laser at many tens of kilowatts.

To understand the spectral-beam--combining process, imagine shining a beam of white light through a prism: The prism bends each of the frequencies differently, scattering the original beam of light into multiple beams of various colors. The spectral beam combiner does the opposite: It combines the different frequencies of each fiber laser module into a single beam. (See Figure 2.) Another beam-combining architecture, coherent-beam combining, is also being developed and matured within the high-energy laser science and technology community.

GETTING SOLUTIONS TO SOLDIERS
The Army's Indirect Fire Protection Capability, Increment 2 -- Intercept (IFPC Inc 2-I) is an acquisition program designed to pro-vide a materiel solution to protect troops from cruise missiles, unmanned aerial systems (UAS), and rockets, artillery and mortars (RAM). IFPC Inc 2-I has a Block 2 milestone decision in FY24 to add the counter-RAM capability to the program.

The U.S. Army Space and Missile Defense Command/Army Forces Strategic Command (SMDC/ARSTRAT) is developing the 100-kW High Energy Laser Tactical Vehicle Demonstrator (HEL TVD) to address the counter-RAM requirements for IFPC Inc 2-I, Block 2. The HEL TVD will be integrated on the 10-ton variant of the Family of Medium Tactical Vehicles. In FY22, the HEL TVD will demonstrate target acquisition, tracking, aimpoint selection and maintenance, to defeat selected rocket, artillery and mortar threats.

Multiple subsystems are under development for integration into the weapon system. They include laser, beam control, electrical pow-er, thermal management and fire control. The goal of the FY22 demonstration is to confirm that a pre-prototype laser system can defeat RAM threats in an environment similar to the battlefield.

To reduce risk and provide information for HEL TVD development, the Army is using its High Energy Laser Mobile Test Truck (HELMTT). The HELMTT has demonstrated laser lethality against small-caliber mortars and Group 1-2 (hobby-size) UAS using a slightly modified 10-kW commercial off-the-shelf fiber laser.

In FY14, this system underwent several proof-of-concept demonstrations, defeating small-caliber mortars and UAS. In FY16, the HELMTT was part of the Maneuver Fires Integrated Experiment (MFIX) 2016 at Fort Sill, Oklahoma, exposing the warfighter to the military utility of laser weapons. HELMTT also was used in the Joint Improvised-Threat Defeat Organization's UAS Hard-Kill Challenge in FY17. In addition to these demonstrations, the HELMTT has collected laser propagation data in a variety of environ-ments, from coasts to high deserts. These data helped anchor models used to predict laser effectiveness on the battlefield.

The 10-kW laser subsystem has been removed from the HELMTT to modify the platform for integration of the Lockheed Martin RELI 50-kW-class laser. The Army will test the 50-kW HELMTT against a variety of RAM and UAS targets in late FY18. This demonstration is designed to verify laser lethality against RAM threats for the HEL TVD effort.

To ensure that laser weapons will be lethal against assigned threats, the Army is developing vulnerability modules for RAM and UAS. The Solid State Laser Testbed on the High Energy Laser Systems Test Facility at White Sands Missile Range, New Mexico, collects lethality data for these targets. Engineers there analyze each threat to determine the best aimpoints, as well as the total laser energy required to defeat the threats. The results are threat-specific vulnerability modules in a format common across the DOD laser com-munity. Laser lethality is one of a number of areas in HEL technology development where the services and agencies work together and share data.

FINDING THE RIGHT PLATFORM
The Army has been working with industry on a concept for a high-energy laser combat platform to be used in warfighter experimen-tation. Integration of existing laser subsystems began in January 2016; within four months the Mobile Expeditionary High Energy Laser (MEHEL) participated in MFIX-16 at Fort Sill.

A 2-kW fiber laser system, integrated on a Stryker platform, was the first high-energy fiber laser on a combat vehicle. The MEHEL defeated hobby-size quadcopters and some ground targets during MFIX-16. While defeating targets shows the potential for lasers on the battlefield, the main objective of the MEHEL is to support the development of tactics, techniques and procedures and concept of operations for future laser weapons. Late in FY16, the 2-kW laser was replaced with a 5-kW fiber laser. The Army designated this new 5-kW configuration MEHEL 2.0.

In preparation for MFIX-17, contractors trained Soldiers to operate the MEHEL 2.0. During the integrated experiment, these Sol-diers shot down small fixed- and rotary-wing UAS--a first for the Army. The Army is using lessons learned from MFIX-17 to make the MEHEL easier for Soldiers to operate. MEHEL 2.0 will also be part of MFIX-18.

MULTI-MISSION HIGH ENERGY LASER
The Multi-Mission High Energy Laser (MMHEL) is a technology maturation initiative starting in FY18. Technology maturation ini-tiatives facilitate the transition of key technologies to acquisition programs. The MMHEL will be a 50-kW laser system on a Stryker, designed to reduce risk and inform requirements for the Maneuver-Short Range Air Defense objective capability. The MMHEL will undergo an operational demonstration in FY21 to validate the laser system's counter-RAM, counter-UAS, counter-battery targeting and counter-materiel capabilities.

In addition to the HEL systems developed for data collections and demonstration, the Army is conducting basic and applied research in HELs. The basic research is focused on developing technologies for next generation high-energy lasers, tracking systems and con-trol algorithms. The Mobile Beam Control System Integration Laboratory will be built to investigate, mature and verify the perfor-mance of next generation beam control technologies. This trailer-mounted laboratory will provide the ability to collect performance data on beam control components in a variety of atmospheric environments.

CONCLUSION
The Army recognizes the many advantages that HEL weapon systems may provide the warfighter and is developing HEL technologies to satisfy requirements for programs of record. High-energy laser weapons simplify logistical support, requiring only diesel fuel, which is easily converted into electricity to power the laser. High-energy laser weapons also have the flexibility to defeat or affect many different types of threats, making the laser a potential air-defense solution for maneuvering forces and forward bases. These characteristics, coupled with a low cost per shot, will provide a battlefield advantage for U.S. forces.

For more information, contact the SMDC/ARSTRAT Public Affairs Office at 256-955-3887 or 719-554-1982, or at P.O. Box 1500, Huntsville, AL 35807; or go to www.youtube.com/armysmdc.


This article is published in the January -- March 2018 Army AL&T magazine.