Date: Nov 15, 2007 Author: Joe Singleton Source: MDA (
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by Joe Singleton/jsingleton@nttc.edu
Black velvet is no longer just a fabric for your painting of Elvis. Modern applications such as laser surgery might soon use black velvet to absorb radiation.
Energy Science Laboratories, Inc. (ESLI; San Diego, CA), has developed a lightweight, carbon-based velvet-lined curtain that can be affixed to a surrounding metal hull, known as a beam dump, to catch and absorb stray light and radiation emitted by a high-power laser.
Stray radiation emitted from high-power laser beams, such as the one shown here, may be further minimized by ESLI's energy-absorbing velvet curtains. The velvet-based technology is proven to suppress energy from beams with temperatures as high as 2,000ºC.
The concept of a velvet curtain emerged from a 2004 MDA SBIR Phase II contract to ESLI. The MDA project called on ESLI to design a lightweight beam dump for MDA's Airborne Laser program. Testing was conducted at the Lawrence Livermore National Laboratory, the Naval Research Laboratory, and various Army sites during the contract period that concluded in late 2006. The company is now continuing its quest to achieve an advanced technology readiness level by making the curtains available to the Defense Advanced Research Projects Agency.
ESLI's involvement in velvet-based technologies spans more than two decades, and the company holds four carbon-velvet-architecture patents. While the MDA-funded curtains are specifically designed to suppress unwanted emissions from high-yield airborne lasers, the carbon-based fabric can be used in other applications. One example with widespread use is lining telescope walls with black velvet, which would act as a stray-light suppressor. ESLI anticipates carbon-velvet curtains might someday be converted to suppress expended energy from smaller, less powerful lasers, like those used in laser surgery.
Conventional velvet is a tufted fabric, usually made from silk, cotton, or synthetic fibers, where the tufted threads are cut in evenly distributed, short, dense piles.
ESLI's velvet curtains have a unique carbon-based architecture. The material consists of short carbon fibers that stand vertically on a surface. Curtains are produced in sheets that are about 1/8-inch thick, each weighing only a few ounces per square yard. The sheets are custom-formed and fitted for a laser's beam dump. Testing of ESLI's velvet curtains has taken place in specially designed tanks filled with a water solution used for containing high-power laser energy.
ESLI makes two varieties of velvet—each with carbon fibers attached to a substrate. One velvet uses a carbon-fiber substrate (for high-power beams); the other uses a graphite substrate (for lower-intensity applications). ESLI applies a carbon-based adhesive to attach the fibers to the substrates. Both velvets produced by the company are processed at temperatures of 1,200ºC or greater.
ESLI velvets provide a significant advantage over other stray-light and radiation-suppression materials: They will not degrade under the light intensity and temperatures of high-powered lasers, said company President Timothy Knowles. The company successfully tested its velvet curtains against laser beams emitting 100 watts per square centimeter and operating at temperatures around 2,000ºC. This temperature equates to 10 times the heat that other light-suppressing materials can withstand.
Carbon velvet's ability to withstand high-energy and high-temperature environments is also beneficial in minimizing heat contamination within the beam dump. For instance, in most beam dumps, there is a threat that any substance—such as a single strand of fiber—can degrade and become detached because of the heat reflected and absorbed when the laser is fired. Such incidents could cause a detached particle to be heated to such intensity that, if it were to hit a large beam dump's observation window or the laser itself, significant damage could occur. ESLI's velvets are designed to minimize such costly and dangerous problems.
Following successful tests during the SBIR contract, ESLI now looks to market its velvet curtains to laser manufacturers as well as systems integrators involved in laser-intensive projects such as MDA's Airborne Laser program. Company officials remain hopeful that the readiness of the technology will result in new contracts and new business opportunities soon.
