Web Date: April 28, 2014
Printing Holograms At Home
Holograms are a common security element on banknotes, credit cards, passports, and medicine packaging. Consumers usually can’t make their own holograms, because the images are recorded and printed with costly instruments and complex methods. Now a fast, simple holography technique could make these optical novelties affordable and easy to produce at home (ACS Photonics 2014; DOI: 10.1021/ph400149m).
Unlike traditional holography, the new technique can record holograms directly on any type of material and on curved surfaces. “We envision integrating this technology into a desktop printer so that people could print a hologram in a matter of minutes,” says Fernando da Cruz Vasconcellos, a chemical engineer at the University of Cambridge. Anyone could then include a unique hologram on business cards or create labels to personalize items.
Holograms are three-dimensional images of an object recreated from a pattern printed on a two-dimensional surface. To record the pattern, users shine laser light on the 3-D subject so that it bounces off the object and onto a transparent surface, typically a glass plate, which is coated with a light-sensitive material, such as a silver halide or photopolymer. At the same time, they shine a reference laser beam on this coated surface to create an interference pattern with the light from the object. The pattern is encoded as microscopic changes in the properties of the material. To view the hologram, another person shines a laser on the printed surface so that the encoded pattern diffracts the light and reconstructs a 3-D image of the object. The method requires specialized optical equipment and lasers, as well as chemical processing to develop the recording material. The holograms are then stamped onto flexible surfaces with an embossing tool.
With the new technique, Vasconcellos, Christopher R. Lowe, and their Cambridge colleagues can produce a hologram within a few seconds and with some common materials. They use permanent-marker ink coated on plastic as the recording medium. Ultrashort pulses of light from a common Nd:YAG laser create and engrave the interference pattern by heating up the ink and vaporizing it. The amount of ink removed depends on the light intensity at each spot in the pattern.
The technique is more flexible than conventional holography because it does not require a transparent, flat substrate. The team made holograms on bottle caps, for example. They also demonstrated holographic QR codes—a type of barcode–and a handwritten holographic signature.
“This is a delightful extension of classic optical holography,” says Daniel E. Smalley, an electrical and computer engineer at Brigham Young University. The key advantage of the new technique is that any material can be made into a hologram so long as it has a sufficiently opaque, light-absorbing layer on its surface, he says. “This opens the door for a whole host of new materials to be used as holographic substrates.”
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