Laser attacks targeting pilots and air crews are a major concern across the world with most attacks reported to take place during take-off and landing. According to figures from the US Federal Aviation Authority, there were 6,753 laser illuminations reported in 2017. Until recently, the expense of lasers had limited their use to professional shows, but lower prices on handheld laser pointers have made this type of device widely available. They have also become easier to buy on the internet. However, these laser pointers have been cause of many aircraft accidents.
Lasers are a source of collimated, monochromatic, coherent light that can travel long distances with very little loss of intensity. This coherent property is what allows a laser to maintain a narrow, high-powered beam over long distances. This is also the cause of lasers being able to do damage to sensors, facilities, and personnel at a long range. Results of these attacks include distraction, obscuring of instruments and dials, a high probability for short-lived “flash” blindness and even permanent eye damage.
Of huge concern has been the use of military grade or ‘dazzler’ lasers, marking a serious change from the previous use of commercially available devices, and poses a far greater threat to military personnel. They have also become as tool to harass adversaries. The US accused China of pointing lasers at US military aircraft near Djibouti multiple times in the last few weeks, but Beijing has denied the allegations.
The US said there have been at least four such incidents near Djibouti, and in one of the most recent, two C-130 pilots became dizzy and saw “rings.” China opened its first overseas military base in Djibouti in 2017 and has raised concerns among American military officials about the proximity of the Chinese military installation to American forces. The Chinese have characterized the base as a logistics hub for peacekeeping and anti-piracy operations.
Lasers are also increasingly being employed both by terrorists and security agencies. The military and security agencies are using Handheld Lasers as non lethal weapons to temporarily blind terrorists and at check points for crowd control. Lasers have been used en masse against riot police in demonstrations in regions as diverse as Canada, the U.S., Ireland, Thailand, Greece, Egypt, and Italy, among others. In Seattle, WA, protesters at a WTO summit directed pointers in the field of vision of crowd-control police. In Cairo in 2013, dozens of green lasers were seen striking Egyptian military helicopters circling over Tahrir Square during large-scale gatherings, as well as directed against governmental buildings, police, and, at times, opposing protestors.
Therefore research is increasingly looking for laser protection technologies. Last year, the aircraft manufacturer Airbus announced that it was joining with Lamda Guard, a Canadian company, to test a metamaterial-based coating for cockpit windows to protect pilots in commercial aircraft from being blinded by laser pointers.
Growing threat of powerful Military lasers
The Chinese military has begun equipping its soldiers with handheld laser guns, in direct contravention of international treaties banning the use of blinding laser weapons. The official PLA Daily December 9th 2015 edition announced that Chinese soldiers are now in possession of laser guns. Since 2015, China has had at least four different kinds of blinding laser weapons: the BBQ-905 Laser Dazzler Weapon, the WJG-2002 Laser Gun, the PY132A Blinding Laser Weapon and the PY131A Blinding Laser Weapon.
The PY132A laser gun, revealed during the Chinese Police Expo in December, is designed to blind enemy sensors and cameras and intended for use against enemy vehicles and drones. International conventions like the 1998 Protocol on Blinding Laser Weapons ban the use of lasers and blinding weapons used against people.
Military forces worldwide are increasingly using lasers for many purposes including, range finding, anti-missile systems, target designation, ranging of guided munitions and the neutralizing of enemy weapon systems. Therefore soldiers and military vehicles like tanks have also become vulnerable to laser attacks. Militaries are also planning to employ laser directed energy weapons in the battlefield to neutralize rockets, UAVs and missiles.
More powerful laser beams, those that are commonly found on laser-guided munitions and long-range designators, require extreme protection against ocular injury. Other lasers require less protection due to their relatively low power. Depending on the specific laser threat, laser light absorption may range from 99.99% to 99.999% to provide the required protection, thus avoiding ocular injury.
Military Lasers can also causes damage to optical components like mirrors, fibers, nonlinear crystal materials, prisms, optical filters, optical modulators and saturable absorbers, photodetectors and SESAMs.
Therefore military forces involved in multinational operations are increasingly looking for technologies both for protection of eye as well as optical components from lasers used by both friendly and foe. Keeping pace with rapidly advancing and eminently available laser technology requires a sophisticated and pragmatic countervailing response.
Effects of Laser attacks on Pilots
The FBI has warned released public information films to warn about the effects of laser pointers, explaining how beams can blind pilots at night, with their effects intensified as light is dispersed by the cockpit windows. A laser illumination incident begins quite suddenly as the flight deck is filled with a bright light. The glare makes it difficult to concentrate on the flight instruments and can remove the crew’s visual references with the runway environment, making pilots unsure of their position relative to the runway and the ground. Green lasers, which have become increasingly more affordable, have been reported in more than 90 percent of the documented laser incidents,” says Boeing.
“Even weaker lasers could have serious consequences if pilots were distracted by the beams when landing planes: “It’s a critical point in flight, you have to have complete concentration. When it comes into the flight deck, it bounces around the walls of the cockpit,” said British Airline Pilots’ Association’s (Balpa) general secretary, Jim McAuslan.
“Dazzle will cause the eye’s response to change, making it more difficult to see other, less bright, objects. In addition, dazzle will cause the pilot to lose concentration. Laser dazzle is a particular difficulty when the pilot is undertaking a high workload, such as landing or taking off, but is also likely when the aircraft is nearer the ground, making it easier to shine a laser beam.”
Half of all pilots targeted in past year involved laser used in weaponry, says pilots’ association. Since 2004, more than 3,200 laser incidents have been reported within the United States, along with hundreds more internationally. Incidents are occurring not only in the United States but internationally as well. Reports of laser incidents have come from Australia, Canada, England, Germany, and Ireland. According to figures compiled by the Civil Aviation Authority (CAA), the number of reports of laser incidents in the UK has remained relatively constant at about four to five a day on average over the last four years.
Laser damage to eye
How a laser affects the eye depends on the wavelength of the laser, the power level, and the duration of the exposure. The visible and invisible wavelengths in a laser beam present a unique hazard to the human eye and can cause instantaneously vision disruption, distraction, disorientation, and even eye damage. The threat posed by lasers is often hidden – those in the invisible spectrum cannot be detected by the human eye and without proper protection the eyes can be severely damaged.
The human eye sensitivity peaks in the green range and perceives green 30 times brighter than red. When comparing a green and a red laser of equal power output, the green one will appear much brighter than the red. The eye’s natural defense for bright visible light is the blink response, which can take effect within a quarter of a second.
Nonvisible light can be in the wavelength range of ultraviolet (200 to 380 nanometers), near infrared (750 to 1,400 nanometers), or mid to far infrared (1,400 nanometers to 1 millimeter). Nonvisible lasers also enter the optical system and affect the eye, but they are not visible and present a different challenge: the blink response only works with visible light, so there is no natural protection for the eye when outside the visible spectrum.
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).
Laser Light can have very high optical intensities, because it is usually delivered in the form of a laser beam with small transverse dimensions, and in addition it is often generated in the form of short or even ultrashort laser pulses. Exposure to a strong laser light source can result in flash blindness and afterimages. In flash blindness, exposure to a very bright light source can deprive pilots of vision for a period of time ranging from a few seconds to a few minutes. This can be followed by afterimages, such as the yellow and purple dots seen after a flash photo. Again, these afterimages will disappear in time.
In the most serious exposures to lasers, the lens of the eye concentrates the light energy on the retina and can actually burn the retinal tissue. The human eye can compensate for small area retinal burns by looking around them, but large area retinal burns can mean permanent loss of vision for the affected area.
Laser Protection Technologies
With the continuous development of military equipment including lasers, researchers are constantly seeking to improve laser eye protection technologies. Laser lenses protect the eyes by blocking laser light either through an absorptive dye or reflective coating. The amount of laser light that is blocked at a specific wavelength is referred to as the lens’ Optical Density (OD). High OD numbers provide an order of magnitude higher protection.
Laser eye protection exists in two forms,” explains BEA Systems’ executive scientist and photonics expert Dr Mark Bray. “Coloured glass filters centred at the correct wavelength will reduce the laser light transmitted, but also cut out much of the light that the pilot wants to see, like wearing sunglasses indoors. These will reduce the overall light level by too much for a normal pilot.”
Interference filters, he says, are designed to just cut out the wavelengths required. “They have a narrow linewidth, a few nanometres, so most of the normal light is transmitted. It is, however, very angular dependent; if the laser light strikes the filter just off normal it will be transmitted, causing dazzle. The angular performance can be improved by increasing the linewidth of the filter but this in turn cuts out more of the light the pilot needs to see. So there are two competing effects.”
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.
A variety of safety glasses are available that can protect the wearer from green laser energy; however, airlines should consider the drawbacks that are associated with them. Filtering light reduces the total amount of light entering the eye, which can adversely affect normal viewing, especially at night when most laser incidents occur.
People working in hazardous environments and industries in India will soon have cost-effective goggles that can protect their eyes and improve efficiency. Bengaluru-based Hind High Vacuum (HHV) has developed a technology for high power laser safety goggles made of coated glass. There are just handful of companies with this technological capability globally, said Prasanth Sakhamuri, Managing Director.
By using these goggles, people involved in handling high precision laser equipment in research and production of hazardous material and workplaces can protect their eyes from harmful exposure. Laser Safety Goggles are available in three varieties based on the power of laser: low-power lasers need acrylic goggles, medium-power lasers need goggles made of treated glass and operating a high-power laser needs a goggle made of coated glass.
Australian Army has introduced an enhanced ballistic laser ocular protection system (BLOPS) as part of the new soldier combat ensemble that provides ballistic, environmental and laser protection to soldiers. However they provide protection against limited spectrum of common lasers (laser lenses).
Dyes and dielectric coatings for laser protection
A laser protective dye is a pigment that is added to the lens material during the injection molding process. This dye neutralizes laser threats by absorbing laser light before it can reach the eye. Laser protective dyes are widely used due to their relative low cost and ability to retain high ballistic properties. While effective, there is a drawback: lenses that protect against multiple wavelengths require the use of two or more dyes which significantly reduces the light transmission of the lens. This makes it darker and therefore less suitable for low light applications.
The dielectric coatings are made of a fine stack of layers with different reflective properties. Currently, laser protective dielectric coatings are limited in their use due to their very high cost – a lens with dielectric coatings is roughly 10 to 20 times more expensive than a lens made using laser protective dye. Dielectric coatings are also easily scratched and generally require additional anti-abrasion protection.
Aviation operating environments, mitigating low-intensity laser threat
The Naval Medical Research Unit Dayton (NAMRU-Dayton) Vision Science Lab is evaluating low-intensity threat laser eye protection (LIT-LEP) for use in aviation operating environments. Dr. Michael Reddix, senior research psychologist, and Lt. Cmdr. Micah Kinney, aerospace optometrist, are leading this joint-service initiative in response to the U.S. Coast Guard (USCG) Office of Aviation Forces’ request for assistance in mitigating the threat posed to flight safety and search and rescue operations by high-powered handheld lasers.
The LEP solution is designed to be compatible with both fixed- and rotary-wing USCG avionics. After conducting various evaluations findings demonstrated no safety of flight issues. The team completed manufacturing quality assurance, optical engineering and psychophysical evaluations, and preliminary flight simulator and ground testing. Additional evaluations included in- and out-of-cockpit color symbol discrimination, acceptable head-up display and night-vision device compatibility, and a USCG Aviation Training Center assessment and recommendation for flight acceptance testing, August–September, 2018.
Canada: CDN $3M loan to MTI to manufacture laser eye protection glasses
The Canadian federal government has provided a CDN $3M loan to Metamaterial Technologies Inc. of Halifax, to manufacture laser protection eyewear in large quantities. The company’s metaAIR eyewear uses holographic technology to reflect unwanted wavelengths of light while passing others. According to MTI founder and CEO George Palikaras, the clear glasses do not affect vision like current solutions that can be too dark or affect colors.
“What is innovative in our eyewear is that it does not affect the pilot’s vision. So when you put them on you can still see that green is green, blue is blue and red is red,” Palikaras said at a May 4 2018 press conference. In the photo below, Palikaras is wearing the glasses, which reflect some wavelengths but otherwise appear clear to the wearer. The glasses’ ability to reflect unwanted wavelengths were demonstrated by blocking 99.9% of the green light from a handheld Class 4 (> 500 milliwatts) 532 nanometer laser: Palikaras said that besides pilots, MTI has had inquiries from the navy and from train operators. He cited incidents involving trains in Germany and Switzerland.
BAE Aircraft protection system
Utilising a novel technology, BAE Systems has developed a system to block laser attacks against aircraft and their crews. Engineers at the defense and aerospace giant have developed a low-cost, lightweight system that can block dangerous laser light to protect pilots from hostile attacks.
Utilizing a novel film, the technique is selective in the way it prevents laser transmission, meaning a high level of natural light through can still pass though the canopy with minimal color distortion. As a result, pilots are protected from dangerous laser incidents with no deterioration in vision.Dr Leslie Laycock, an executive scientist at BAE Systems commented, “A series of successful trials undertaken in a laboratory environment have proven that our method is effective against a wide variety of laser wavelengths. We have been able to achieve a visible light transmission in excess of 70%.
“Our system allows the majority of the light through the protective film, without the need for pilots to wear heavily tinted industrial goggles. This allows pilots to more effectively see instruments and their surroundings, whilst simultaneously blocking the dangerous laser light.” As technology advances, the wavelength of proliferated lasers may change. Due to the adaptability of this technology, pilots will always be protected as the film can simply be upgraded and selectively tuned to combat new laser threats. The next phase of development will see experimentation and commercialisation within the public sector.
There have been significant steps taken by military and industry to counter the growing threat posed by laser attack on both military and commercial aircraft. But challenges remain, says Bray. “Among them are achieving performance for off axis incidence of laser, a high absorption at the wavelength of interest whilst keeping the transmission high elsewhere, and ensuing they work,” he says, “something not easily done given the risk to individuals if they don’t work.”
Bray says a lot of work has gone in to developing products that protect pilots from this form of attack; now much of the challenge is about developing the frames to house the filters. BAE has developed a filter that Bray says cuts out all laser power and works at three well known wavelengths simultaneously, whilst providing over 70% normal transmission. He explains that the system has additional features that improve the performance for off axis beams, adding: “The filter is designed to operate at different angles by curving the filter the angular performance is improved.”
Technologies of the future include tunable laser protection to counteract the threat of tunable lasers (lasers which can change their operational wavelength) and to protect against multiple laser threats simultaneously. Also being explored are optical switches and limiters that activate only in the presence of specific laser wavelengths. This allows the protection to stay completely clear until laser protection is needed and allows for excellent visible light transmission.
Protection against Multi wavelength Lasers
U.S. Army Tank Automotive Research, Development and Engineering Center (TARDEC), has developed a new optical system to protect soldiers using magnified direct-view optics, such as gunner’s primary sights on battle tanks, against eye-damaging Multi wavelength lasers.
The filters which are used to block single wavelength lasers are ineffective against wavelength-diverse lasers, unless they block the entire visible spectrum. The new technology incorporates laser-protection cells at the focal planes, where a laser threat’s energy is focused, that absorb and disperse the laser energy, weakening the light and distributing it over a larger area of the retina to minimize eyesight damage.
The system was tested against a multiple wavelength laser system developed by the U.S. Army Research Laboratory’s Survivability/Lethality Analysis Directorate (SLAD) which simulated “a worst-case, visible laser threat” in terms of its energy, pulse width, beam size and divergence.”
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