A Dazzling Development in Security
An SwRI-developed technology fends off intruders using an eye-safe laser
Joseph N. Mitchell is a senior research engineer in the Applied Physics Division. He specializes in developing electro-optical, laser, infrared and remote sensing systems. He has worked on a variety of programs including biometrics acquisition, industrial inspection and measurement, standoff imaging, spectroscopy, novel optical materials and in development of miniature and MEMs-based opto-mechanical devices.
The dazzler was tested outdoors at distances greater than a mile.
One application of the laser dazzler is to help determine the intent and inhibit the actions of potentially hostile individuals.
A concept illustration shows the laser dazzler in operation as it tracks an unknown vessel.
The dazzler could be used to safely disperse crowds in riot situations to reduce the risk of civilian injuries or property damage.
The dazzler uses an array of moderate power sources whose beams are designed to expand and merge into a single large beam at the system’s operating range. Spot size at the operating range is a function of distance, source divergence and lens focal length.
The dazzler was tested under daylight conditions at Fort A.P. Hill.
The laser dazzler prototype is shown in operation.
Imagine that you are captain of a small naval vessel off the coast of an unfriendly nation where other ships have been subject to harassment or attacks. It’s dusk, and it is difficult to see clearly. Suddenly, your crew spots a small fishing boat off the port side about a mile away and closing fast. You try to signal the boat, but it continues to approach. You have seen many fishermen in these waters, and now you have a decision to make: Is this just another fisherman who simply doesn’t see you, or is this an attack? A wrong decision could cost the lives of your crew, or it could create an international incident and kill innocent civilians.
A team of engineers from Southwest Research Institute (SwRI) is working on a program with the U.S. Navy to develop a technology to assess, slow and even thwart these potential threats, without harming people. The Long Range Ocular Interrupter, known informally as the “laser dazzler,” uses a high-intensity but eye-safe visible laser source to deliver a dazzling, brilliant beam to targets more than a mile away. It is used to help determine the intent of an unknown person or vessel by their response to it. It operates at multiple levels of effect, ranging from a low-intensity alert level to a glare level that would cause most people to turn away and leave the area.
If the intent of the approaching vessel appears hostile, the level of effect can be further increased to slow or even suppress an individual’s ability to take action. If the individual or vessel continues to approach, then the hostile intent is clear and a more aggressive response can be initiated.
Using light for nonlethal deterrent
The “dazzling” effect inherent in bright flashing illumination has been studied for several decades. The critical parameter is optical intensity (also referred to as power density). An “eyesafe” laser is one that has an intensity below a threshold known as the maximum permissible exposure (MPE). This level varies depending on the exposure duration and the wavelength of the light. At bright intensities below the MPE permanent damage does not occur, but temporary impairment, such as glare or flash-blindness, can degrade the ability to perform visually oriented tasks. With flash-blindness, an individual exposed to sudden changes in illumination experiences a temporary state during which nothing can be seen except an afterimage. The eye is protected from this to some degree by the natural blinkaversion response, but bright or flashing lights actually can attract the eye.
Flashing lights or images can induce further neurologic effects that may stun, or make an individual experience dizziness or be unable to act. Because the human eye is most sensitive to green light, illumination in this wavelength range produces the most “bang for the buck” and also results in the longest re-adaptation time after the illumination is removed.
The laser dazzler can be used in a wide range of operations. It can help reduce civilian casualties and keep warfighters out of harm’s way by allowing them to engage at a safe distance. Besides maritime applications, the system also can be used at roadside checkpoints, embassies and military base access points, and for crowd dispersal in riot situations to reduce injuries and property damage.
The development program for the laser dazzler has been a rapid undertaking, going from an initial study of several possible design concepts to a prototype for field evaluations in just eight months. From initial evaluations, the SwRI team developed a system design that uses an array of laser sources of low to moderate power. This has the advantages of redundancy in the event of loss or partial failure of any of the lasers, reduced cost per watt of optical power and a more distributed heat load to improve cooling. Although some early concepts involved combining the beams into a single large-output beam within the dazzler, the selected design keeps the beams separate and relies on a small amount of divergence that allows the beams to overlap at long range. The beams are aligned so that by the time they reach a certain distance, they have expanded to the desired size and are essentially fully overlapped. Keeping the beams separate enables the use of small, lightweight, low-cost optical components and provides for scalability should more lasers be required. In addition, alignment of the beams is simplified and can even be electronically controlled through small manipulations of the lenses rather than movement of the entire laser modules.
Building a dazzler
Once the general system design was developed, SwRI engineers fabricated a prototype system intended for field evaluations to prove both the feasibility of the design and determine its effectiveness. Although considerably larger and heavier than the production model, the prototype model was built to allow for quick assembly and easy troubleshooting. It was made from commercial off-the-shelf components wherever possible, allowing the SwRI team to design and assemble the prototype in less than four months. The prototype contained an active cooling system for the lasers, including thermoelectric coolers and forced air, individually adjustable lenses, a focusing mechanism for the entire lens assembly, an alignment scope and electronics to monitor and control the laser power and temperature, safety interlocks, power supplies, and strobe controls.
Characterizing the system’s performance was a significant part of the effort, using parameters such as optical power density, spot uniformity and the effects of atmospheric turbulence, among others. In addition, the team wanted to characterize the system’s performance under a range of environmental conditions. SwRI engineers conducted a series of indoor and outdoor tests at several sites, including SwRI’s headquarters in San Antonio, a three-mile range at Fort A.P. Hill in Virginia and a 1.5-mile overwater range at Dahlgren, Va. The SwRI team was able to evaluate performance in both day and night conditions in the summer heat of South Texas, during the blowing wind and dust of an approaching thunderstorm and during rain, mist and fog conditions. Although these conditions resulted in different effects on the laser beams, the dazzling effect remained effective regardless of atmospheric conditions.
With the successful demonstration of the concept, SwRI engineers have begun work on the next phase of the program: developing a production-grade system, then building several laser dazzler units for expeditionary deployment. Custom lasers are being manufactured for SwRI by a subcontractor. These will be more robust in a wide range of ambient conditions and will be able to maintain power levels even under relatively high ambient temperatures without active cooling.
SwRI will integrate these lasers into a military-grade, ruggedized package that will include control electronics, a power supply and the user controls. The dazzler system will include a number of features designed to simplify and automate its use, including a pointing and tracking system, a day/night imaging system, automatic range detection to ensure eye safety and maintain optical power levels appropriate for different targets, and dynamic control of the laser beam’s divergence and spot pattern.
Now, imagine once again you are the naval captain envisioned at the beginning. You order the laser dazzler to be deployed. Your ship’s crew points it toward the approaching boat and fires the laser at warning level. The boat continues to approach and swerves to evade the beam, but the dazzler adjusts its alignment to follow the boat’s motion. Your crew increases the laser’s intensity and activates the strobe effect. The boat slows, then turns sharply and starts heading away, eventually disappearing in the distance.
You may never find out who was in the other boat, but your own crew and vessel are safe and you didn’t have to deploy lethal force. In a few years, the use of lasers in situations such as this could be a reality as an alternative to conventional weaponry.
Questions about this article? Contact Mitchell at (210) 522-5799 or firstname.lastname@example.org..