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Harnessing light efficiently

3M Europe : 23 April, 2003  (New Product)
By tailoring hundreds of layers of transparent polymer materials to have specific properties at the interfaces of the layers, films can be produced with reflectivity characteristics never before achieved
Ever since the first campfire, humans have sought better ways to create artificial light. But in recent years, the focus has begun shifting dramatically toward innovative ways to manage light, both natural and artificial.

3M has been a leader in optical science for the past seven decades, with a number of recent advances in light management largely resulting from an extraordinary discovery.

Until recently, physicists took for granted a limitation on the reflectivity of light. This limitation was described in 1814 by Scottish inventor David Brewster in what is known as Brewster’s Law. His “law” states that for every dielectric material (eg glass, plastics) there is an angle of light known as Brewster’s angle that produces no reflection for light having a particular polarization. Polarizing sunglasses take advantage of this principle by reducing the glare of light reflected off a surface at high angles by blocking the polarization of light preferentially reflected according to Brewster’s law. The physics discovered by Brewster led to a general belief that there were fundamental restrictions on the reflectivity of light using dielectric materials.

But 3M’s discovery demonstrates the error of these perceived restrictions posed
by “Brewster’s Law.” The company’s scientists selected materials to have specific properties in a perpendicular direction. By appropriate selection, reflectivity characteristics never before achieved can be readily obtained in 3M Multilayer Optical Films. These films can comprise as many as several hundred layers, yet are as thin as a sheet of paper.

The result is unprecedented reflectivity characteristics achieved over a wide angle. This process can produce, for example, a nonmetallic, noncorroding mirror that reflects up to 99.5 percent of visible light that hits its surface at any angle, allowing that light to be transported to distant locations at astounding intensities. Multilayered films can be structured to reflect or transmit wavelengths in the ultraviolet, visible and near-infrared portions of the spectrum, paving the way for a wide range of innovative applications that can impact our daily lives.

The first application of this technology satisfied a key demand of the fast-growing portable computer industry. 3M is able to process its multilayer films to reflect light of one polarization and transmit the other, creating a polarizer that increases the brightness of laptop computer screens. Today, this technology is used in many portable computers and handheld electronic devices, where it provides the dual benefits of easier-to-read displays and longer operation of batteries.

In addition, 3M’s reflective films do not require tedious and expensive manufacturing processes, but are compatible with mass production techniques, facilitating application to a variety of other products, such as cell phones and digital watches, achieving rapid success in the marketplace.

An especially noteworthy product approaching commercialization is 3M™ Solar Reflective Film for auto glass, a colorless optical film that reflects infrared radiation to help keep car interiors cooler in summer and conserve fuel by reducing the burden on air conditioners. Automakers in the United States, Europe and Asia are currently evaluating the film, which could be in commercial use on 2003 models.

Other promising applications include: Photonics filters for medical imaging; filters for telecommunications, which utilize Multilayer Optical Films as ultra-high efficiency reflectors; hothouse glass for enhanced horticulture and food production; light pipes for lighting building interiors; and security films that can thwart counterfeiting of passports and ID cards because of the films’ unique reflective properties.

Light Management Technology is the latest and perhaps the most dramatic development in 3M’s 70-year history in optical science. The company’s involvement in light management dates back to the 1930s, when 3M began developing glass beads for retroreflective pavement markings and traffic signs for improved highway safety. Glass beads were augmented with newer reflective technologies. Then applications broadened into safety apparel and commercial graphics.

Two decades later, light management at 3M took a huge step forward when the company found a way to make lighter and less-expensive lenses for overhead projectors by incorporating thousands of tiny grooves into a plastic surface to achieve the same light-bending properties as the traditional thick glass lens. This proved to be the origin of one of the company’s most important technology platforms – microreplication.

The company’s high performance Multilayer Optical Films were spun-off from work by 3M scientists in fields as varied as laser melting and polymer coextrusion. The result was a momentous discovery, because the technology holds the promise of changing industry.
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