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“Invisibility cloak” said to be the first to work with visible light

July 28, 2011
Courtesy of the American Chemical Society
and World Science staff

For the first time, sci­en­tists have de­vised an “in­vis­i­bil­ity cloak” that hides ob­jects from de­tec­tion us­ing light vis­i­ble to hu­mans, sci­en­tists say.

Though it only works for mi­cro­scop­ic ob­jects, the new de­vice is a leap for­ward for a tech­nol­o­gy still in its “in­fan­cy,” ac­cord­ing to a re­port in the Amer­i­can Chem­i­cal So­ci­e­ty re­search jour­nal Nano Let­ters.

“This work makes ac­tu­al in­vis­i­bil­ity for the light seen by the hu­man eye pos­si­ble,” added the au­thors, Xi­ang Zhang of the Uni­vers­ity of Cal­i­for­nia, Berke­ley and col­leagues, who de­vel­oped the de­vice.

The de­vice is de­signed like a ti­ny car­pet, smooth as a mir­ror, to be laid over an ob­ject. Once in place, the bump cre­at­ed by the hid­den ob­ject van­ishes be­cause pat­terns etched in­to the ma­te­ri­al are de­signed to de­flect light in the right way to make this hap­pen.

Once a sta­ple of sci­ence fic­tion on­ly, “in­vis­i­bil­ity cloaks” are de­signed to route light waves around an ob­ject so that an un­sus­pect­ing view­er can’t see it. Most cloaks de­vel­oped so far are ex­pe­ri­men­tal de­vices made of ma­te­ri­als that can only hide things us­ing mi­cro­wave or in­fra­red waves, types of light that are not vis­i­ble to hu­mans an­y­way.

To rem­e­dy this, Zhang and col­leagues built a re­flec­tive “car­pet cloak” out of lay­ers of sil­i­con ox­ide and sil­i­con ni­tride etched in a spe­cial pat­tern. Al­though the study cloaked a mi­cro­scop­ic ob­ject roughly the width of a red blood cell, the de­vice demon­strates that it may be “ca­pable of cloak­ing any ob­ject un­derneath a re­flec­tive car­pet lay­er,” the sci­en­tists wrote.

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For the first time, scientists have devised an “invisibility cloak” that hides objects from detection using light that is visible to humans, scientists say. Though it only works for microscopic objects, the new device is a leap forward for a technology still in its “infancy,” according to a report in the American Chemical Society research journal Nano Letters. “This work makes actual invisibility for the light seen by the human eye possible,” added the authors, Xiang Zhang of the University of California, Berkeley and colleagues, who developed the device. The device is designed like a tiny carpet, smooth as a mirror, to be laid over an object. Once in place, the bump created by the hidden object vanishes because patterns etched into the material are designed to deflect light in exactly the right way to make this happen. Once a staple of science fiction only, “invisibility cloaks” are designed to route light waves around an object so that an unsuspecting viewer can’t see it. Most cloaks developed so far are experimental devices made of materials that can only hide things using microwave or infrared waves, types of light that are not visible to humans anyway. To remedy this, Zhang and colleagues built a reflective “carpet cloak” out of layers of silicon oxide and silicon nitride etched in a special pattern. Although the study cloaked a microscopic object roughly the width of a red blood cell, the device demonstrates that it may be “capable of cloaking any object underneath a reflective carpet layer,” the scientists wrote.