Introduction – The innovation of making an object invisible was admired as the magic trick but we do can find an object that is completely opaque or you can say transparent. The Researchers from TU Wien (Vienna), together with colleagues from Greece and the USA, have now succeeded with a new idea for a cloaking technology. A completely opaque material is illuminated from above with a unique wave pattern with the effect that light waves from the left can now move through the material without any obstruction. The effect or result surprisingly brings up completely new possibilities for active disguise. The idea can be practiced to different kinds of waves, like it is experimented in way that it should work with sound waves just as well as with light waves. Experiments are already in the planning process, which will be considered in future as anew project.
Process – “Complex materials such as a sugar cube are opaque, because light waves inside them are scattered multiple times,” says Professor Stefan Rotter (TU Wien). “A light wave can enter and exit the object, but will never proceed through the medium on a straight line. Instead, it is distributed into all possible directions”.
For long years many different attempts have been made to deceive this kind of scattering, creating a “cloak of invisibility.” Rare materials have been worked out, for example, which are able to escort light waves around an object. Alternatively, also they have performed experiments with objects that can emit light. When an electronic display dispatched out exactly the same light as it absorbs in the back, it can appear invisible, at least when looked at in the right angle.
Approach – At TU Wien a more essential approach has now been selected. “We did not want to reroute the light waves, nor did we want to restore them with additional displays. Our goal was to guide the original light wave through the object, as if the object was not there at all,” says Andre Brandstötter, one of the authors of the study. “This sounds strange, but with certain materials and using our special wave technology, it is indeed possible.”
The Laser Material – The team at TU Wien has delivered years working on optically active materials, which are adopted for building lasers. To make the laser shine, energy has to be provided by means of a pump beam. Otherwise, the laser material acts just like any other material that absorbs a part of the incident light. “The crucial point is to pump energy into the material in a spatially tailored way such that light is amplified in exactly the right places, while allowing for absorption at other parts of the material,” says Professor Konstantinos Makris from the University of Crete (previously TU Wien). To get this, a beam with exactly the right pattern has to be projected onto the material from above like from a standard video projector, except with much higher resolution.
If this pattern correlates to the inner irregularities of the material, which usually distributes the light, then the projection from the above can effectively switch off the distribution, and another beam of light travelling through the material from one side can pass without any hindrance, distributed or loss.