Nearly all lenses, whether natural, like the lens in your eye, or man-made, such as in a camera or microscope, are curved, which limits the amount of light that enters. But, using a spray-on technology, a team of researchers made an advancement in flat lens technology that could revolutionize the way optical lenses are made and used.

A sample object placed on a flat slab of the ultraviolet metamaterial, when illuminated with UV light (purple), is projected as a 3D image floating in free space on the other side of the slab. Here a ring-shaped opening in an opaque sheet on the left of the slab is replicated in light on the right. (Credit: Lezec/NIST)

Scientists working at the National Institute of Standards and Technology (NIST) have demonstrated for the first time a new type of lens that bends and focuses ultraviolet (UV) light in such an unusual way that it can create ghostly, 3D images of objects that float in free space. They say that the easy-to-build lens could lead to improved photolithography, nanoscale manipulation and manufacturing, even high-resolution 3D imaging, and more.

The new lens is formed from a flat slab of metamaterial with special characteristics that cause light to flow backward—a counterintuitive situation in which waves and energy travel in opposite directions, creating a negative refractive index. A negative-index flat lens like this also has been predicted to enable the transfer of image details substantially smaller than the wavelength of light and create higher-resolution images than are possible with lenses made of positive-index materials such as glass.

The new metamaterial consists of sandwiched alternating nanometer-thick layers of silver and titanium dioxide, and the lens has a focal length of about half a millionth of a meter, which is challenging to achieve with conventional refractive optics such as glass lenses. They say that the metamaterial can be turned on and off using higher frequency light as a switch, allowing the flat lens to also act as a shutter with no moving parts.