Protecting Eyes from Lasers

The U. S. Army Research Laboratory‘s Survivability/Lethality Analysis Directorate is applying its unique expertise in the technical performance and vulnerabilities of optical systems in order to optimize a laser-protection device for the gunner’s primary sight on the M1A2 tank.

The latest result of a five-year collaboration with the device’s developers at the Tank Automotive Research, Development and Engineering Center is SLAD’s development of a laser system to emulate a worst-case threat so TARDEC can ensure its design meets even that tall order.

A large, one-of-a-kind laser was purchased commercially and is used to pump the SLAD threat emulator. (Photo courtesy of ARL/SLAD/Released)

This custom laser was designed by SLAD to mimic the same type of wavelength-diverse laser that Soldiers could encounter on the battlefield. (Photo courtesy of ARL/SLAD/Released)

TARDEC’s device is designed to protect from threat lasers when soldiers are using magnified direct-view optics, like the gunner’s sight on a main battle tank. Though many threat lasers operate at a single wavelength and their beams can thus be blocked with filters, some lasers can operate at a number of different wavelengths. Trying to defeat such wavelength-diverse lasers by means of filtering would require blocking the entire visible spectrum, an obvious non-starter.

But these lasers can inflict serious damage on a soldier’s eye and may also damage a gunner’s sight or other such optics. And, although they are not yet prevalent on today’s battlefield, there are indications that they will become more common.

So if filters aren’t the answer, how can you protect against wavelength-diverse lasers?

Programs like this one highlight SLAD’s forward focus on survivability of soldiers in the Army of the future.  “As the threat evolves, at some point our soldiers will likely encounter lasers that are wavelength diverse and very dangerous,” explained Norman Comer, SLAD physicist and team leader at the Electro-Optical Vulnerability Analysis Facility, or EOVAF, at located at White Sands Missile Range in New Mexico.

“Our primary concern is to protect soldiers from eye damage and blindness, but it is also our goal to give soldiers an advantage in the field by being able to defeat these kinds of threats.”

To do so, TARDEC developed a system that incorporates into the direct-view optics so-called laser-protection cells at the focal planes, which is where the energy from a laser threat is focused. The cells both absorb and disperse the energy from the laser so that the portion that reaches the back of the soldier’s eye is attenuated and distributed over a much larger area in the retina, and therefore is much less damaging to the soldier’s eyesight.

To test TARDEC’s prototype in a field environment, SLAD used its threat emulators. For tackling part of the problem, SLAD could use a lower-power laser at the EOVAF’s laser range to test the prototype at short range.

However, to mimic what soldiers could encounter on the battlefield, SLAD also needed to test the prototype at a longer, stand-off range. So for the past two years, SLAD has been developing a new emulator, this one a threat-level laser system representing a worst-case, visible-laser threat operating at tactical range.

“This threat emulator is based on a large laser custom built for us by a laser manufacturer,” said Comer.

“We use this custom laser to ‘pump’ a dye laser, which we developed in house. Together, they mimic a wavelength-diverse laser. The final output is designed to simulate the postulated threat in terms of its energy, pulse width, beam size, and divergence.”

Comer indicated that SLAD will use this long-range emulator to test the eye-protection device at the EOVAF during the summer of 2014.

A large, one-of-a-kind laser was purchased commercially and is used to pump the SLAD threat emulator. (Photo courtesy of ARL/SLAD?released)

A large, one-of-a-kind laser was purchased commercially and is used to pump the SLAD threat emulator. (Photo courtesy of ARL/SLAD?released)

In addition to its test capabilities, SLAD also applied to this program its capabilities in measurement and modeling. SLAD developed a mathematical characterization that predicts a protection cell’s optical cross-section signature based on the size and concentration of particles inside the cell.

Taking TARDEC’s device into the lab, Comer and colleagues then measured the origin and magnitude of its OCS and found that the signature arises from multiple scatters and not from the more-typical single reflection from standard focal planes such as glass reticles and detectors.

This information will help TARDEC determine not only the degree to which inserting these laser-protection devices will increase the OCS signature but also how any resulting increase in the sight’s detectability would degrade survivability.

The EOVAF is the Army’s premier facility for laser-vulnerability evaluations. SLAD uses it to evaluate optical systems prior to fielding and support the development of prototype laser-hardening devices.

“We want our colleagues to know how we use this facility and our expertise to best serve our customers and ensure their needs are met,” said Comer.

Story and information provided by the Army Research Lab
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