Presenting the invisibility cloak!


Watching things disappear “is an amazing experience”, admits Joachim Fischer of the Karlsruhe Institute of Technology in Germany. But don’t go planning all the places you’ll sneak into or out of just yet. Unlike Harry’s famous (or infamous) invisibility cloak which is large enough to hide two or three student wizards and witches, Fischer’s cloak is small. Very, very, very small.

It’s also very, very real and being presented later this morning at the Conference on Lasers and Electro-Optics (CLEO) in Baltimore, MD, USA.

This isn’t a fashion show any more than it’s a magic show. Fischer’s invisibility cloaks are, in fact, attractive and entertaining demonstrations of the fantastic capabilities of “transformation optics”. This new area has turned modern optical design on its ear with new optical theories and nanotechnology construction methods that enable light to be manipulated in ways long considered impossible. They hold promise for dramatically improving light-based technologies from microscopes to data communications and from lenses to chip manufacturing.

At 11 a.m. EDT on 3 May, 2011, Fischer et al. will present “Three-dimensional invisibility carpet cloak at 700 nm wavelength” and describe the first-even demonstration of a three-dimensional invisibility cloak that works for visible light (red light at a wavelength of 700 nm) independent of its polarization.

Why describe it rather than demonstrate it?

Fischer’s cloak is less than half the cross-section of a human hair, too tiny for a conference room full of people to see.

The cloaks are made by direct laser writing into a polymer material. This creates an intricate structure resembling a very miniature wood-pile. The precisely varying thickness of the “logs” enables the cloak to bend light in new ways.

“If, in the future, we can halve again the log spacing of this red cloak, we could make one that would cover the entire visible spectrum,” Fischer stated.

The key to achieving the red invisibility cloak was incorporating several aspects of a diffractions-unlimited microscopy technique into the team’s 3-D direct writing process for building the cloak. The improved process dramatically increased the resolution enabling the creation of log spacings narrow enough to work in red light.

Aside from sneaking out of or around Hogwarts, the practical applications of combining transformation optics with advanced 3-D lithography (a customized version of the fabrication steps used to make microcircuits) include flat, aberration free lenses that can easily be miniaturized for use in integrated optical chips and optical “black holes” for concentrating and absorbing light. If the latter can also be used to work for visible light, they will be useful in solar cells, since 90 percent of the Sun’s energy reaches Earth as visible and near-infrared light.

The Conference on Lasers and Electro-Optics and the Quantum Electronics Laser Science Conference (QELS) are the industry’s leading events on laser science. In fact, they were where laser technology was first introduced. This year CLEO: 2011 will unite the field of lasers and electro-optics, bringing together of laser technology with content stemming from basic research to industry applications. CLEO: 2011 explores the full range of critical developments in the field showcasing significant milestones, such as the creation of red invisibility cloaks, from the laboratory to the marketplace.

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