Glass board tests laser weapon energy

It is now possible to measure a laser's power and spatial energy distribution at once by directing the beam onto a reusable glass target board designed by researchers at the Georgia Tech Research Institute (GTRI). The new system will accelerate high-energy laser development and reduce the time required to make them operational for national security purposes.

Technologies for using laser energy to destroy threats at a distance have been in development for many years. High-energy lasers—one type of directed energy weapon—can be mounted on aircraft to deliver a large amount of energy to a far-away target at the speed of light, resulting in structural and incendiary damage. These lasers can be powerful enough to destroy cruise missiles, artillery projectiles, rockets and mortar rounds.

But before these weapons can be used in the field, they must be tested and evaluated. The power and energy distribution of the high-energy laser beam must be accurately measured on a target board, with high spatial and temporal resolution.

Now researchers at GTRI have developed such a system. Ultimately, the reusable target board and beam diagnostic system will help accelerate the development of such high-energy laser systems and reduce the time required to make them operational for national security purposes.

"The high-energy laser beam delivers its energy to a small spot on the target—only a couple inches in diameter—but the intensity is strong enough to melt steel," said David Roberts, senior research scientist, GTRI. "Our goal was to develop a method for determining how many watts of energy were hitting that area and how the energy distribution changed over time so that the lasers can be optimized."

GTRI teamed with Leon Glebov of OptiGrate to design and fabricate a target board that could survive high-energy laser irradiation without changing its properties or significantly affecting the beam. The researchers selected OptiGrate's handmade photo-thermo-refractive glass—a sodium-zinc-aluminum-silicate glass doped with silver, cerium and fluorine—for the target board.

"This glass is unique in that it is transparent, but also photosensitive like film so you can record holograms and other optical structures in the glass, then 'develop' them in a furnace," explained Roberts.

The researchers tweaked the optical characteristics of the glass so that the board would resist degradation and laser damage. OptiGrate also had to create a new mold to produce four-inch by four-inch pieces of the glass—a size four times larger than OptiGrate had ever made before.