Combating Infrared Threats on the Battlefield
There have been several news headlines lately about offenders pointing commercial lasers at helicopters or police personnel, temporarily blinding and distracting them. An increasing number of “laser assault” incidents have led to tougher penalties with fines and jail time in various countries. The lasers typically used in these attacks operate in the visible light spectrum; therefore, these lasers can be blocked by special absorbing optical dyes contained in special laser defense eyewear.
On the battlefield, however, modern military equipment and enemy threats utilize lasers that operate in the infrared (IR) spectrum to harm pilots and ground forces. It’s difficult to detect these invisible lasers, and a more sophisticated technology is required to block lasers at the IR wavelengths. Many military operations occur at night, requiring warfighters to wear night vision goggles (NVGs). Soldiers and pilots wearing NVG’s need protection from friendly forces’ IR aiming and pointing lasers as well as threat IR lasers. Protecting warfighters from laser eye damage requires systems designers who have knowledge of the specific wavelengths so they can design systems that block or reflect the specific wavelength of the laser while maximizing the transmission of light at the wavelength needed for operation of the system.
Laser Interference Filters
The eighties saw development of the first laser interference filters (LIF) for U.S. Army NVGs as a countermeasure to jamming and damage. The challenge was to create a coating that could block harmful laser wavelengths, while allowing transmission of visible and NIR light for warfighters to successfully perform their missions. A unique dieletric coating was created that protected night vision devices from laser damaging IR aiming and pointing lasers used by U.S. forces and our allies. Today, LIFs are a standard protective feature on U.S. military-grade night vision systems. Over 1.2 million LIFs have been used extensively in military operations around the world, including in Iraq and Afghanistan.
New Approaches for Advanced Laser Eye Protection
Processes, materials and systems have advanced over the years and VIAVI is now collaborating on new approaches for laser eye protection. A proprietary, load-locked, magnetron sputtering coating chamber, known as UCP, produces notch filters and broadband IR blocking filters that are of the highest quality in the industry.
UCP relies upon a very precise and stable deposition process, enabled by a unique internal geometry as well as a load lock feature. This combination of attributes, along with a low coating temperature in UCP, enables precision LEP coatings on plastic polycarbonate lenses customarily used for ballistic eyewear.
UCP coatings may be several tens of microns thick and are very clear, in the visible range, and dense. Coating geometry optimization within the UCP chamber produces low haze, high uniformity coatings over curved surfaces. Companies like Gentex Corporation, a global leader in personal protection for defense forces, use these dielectric coatings to produce specialized spectacles and visors for use by U.S. military aviators, providing them with the highest levels of protection against IR lasers. Gentex was recently awarded a U.S. Navy contract for laser eye protection spectacles for pilots.
“Superior dielectric coating capability provides a crystal-clear filter, which is instrumental in helping Gentex provide a fully compliant, multiple wavelength protection spectacle design for the Navy,” says John Cueva, Technical Director of Optics for Gentex Corporation.
With newer laser eye protection solutions and normalized costs, every solider on the field could eventually have advanced laser eye protection to protect their vision while maintaining maximum situational awareness and effectiveness to complete their missions.
Sensor Protection for Defense Systems
Sensor protection is another emerging area where laser notch filters are making a significant impact. With the proliferation of laser weapons and advanced sensor technology in weapons platforms, it is important for the military to find solutions to combat enemy lasers. Enemy lasers can render satellites, airplanes, drones and ground vehicles ineffective by damaging sensors. It is essential for coatings to block or redirect damaging laser light away from sensitive components within these systems, while maximizing transmission of non-threat, i.e. in-band wavelengths of light needed for human (visible) or sensor (typically IR) detection, thus facilitating improved signal to noise ratio at the critical sensors.
Intelligence Surveillance and Reconnaissance (ISR) system designers need coatings that protect sensors from threat lasers while maximizing the in-band transmission to the sensors. Military grade sensor systems, particularly those found in satellite or aircraft payloads, are complex and comprised of numerous optical elements. ISR designers can prevent or mitigate laser damage to expensive detectors by carefully designing laser protection coatings for multiple optical elements in the complex optical systems.
The level of protection that an optical filter provides at each element of the system is known as the Optical Density (OD). The OD for the overall system – the level of protection against the laser found at the sensor – is the sum of the respective ODs at each optical element found in a series. A high optical density is achieved by filtering a small amount of laser energy at each optical element with manufacturable, reasonably thin optical coatings.
Lasers and coating systems have advanced significantly in recent years. New advances promise less harm to both personnel and valuable equipment.
Narrower and steeper notch filters: Laser rejection filters are designed to block one or more designated wavelengths while providing the highest possible transmittance at the unblocked wavelengths. It is possible to produce very narrow band rejection filters, known as notch filters, using state of the art manufacturing capabilities in the UCP coating chamber. Notch filters reflect a narrow band in the center of a defined wavelength zone while transmitting adjacent bands at both longer and shorter wavelengths. As laser notch filters advance for defense systems, the ability to control the thickness of the deposited coating layers has led to narrower and steeper notch filters, resulting in increased laser protection and improved transmission of in-band light.
Multi-notch IR coatings: There are many types of lasers operating at different wavelengths and military sensor systems often require optical coatings with multiple laser notches. Technologists, defense systems integrators and the Department of Defense (DOD) are exploring material sets and filter designs that could simultaneously protect against multiple enemy lasers, ranging from the visible to the long-wavelength infrared spectrum (LWIR). They are working on manufacturable designs that protect against laser threats without impeding the transmission of the optics at the key sensor wavelengths.
This article was written by Shawn Cullen, Product Line Manager, Defense & Aerospace, VIAVI Solutions Optical Security and Performance Products (OSP) (Santa Rosa, CA). For more information, visit here .