Virtual Ghost Imaging Principle Explored

U.S. Army Research Laboratory scientists outlined their feasibility study of virtual ghost imaging through turbulence and obscurants using Bessel beam illumination in an Applied Physics Letters paper published Feb. 10.

The three-man team became curious about how to adapt the ghost imaging principle to get light to a target through turbulence and obscurants, which would be useful for Army applications, said Physicist Ronald Meyers, quantum team lead with the Computational and Information Sciences Directorate.

They initially looked at this area of research years ago because early ghost imaging demonstrations involved static applications that were not practical for the Army, Meyers said.

The researchers received the Army Research and Development Achievement Award for outstanding research in 2009 with the first ghost image of a remote object. This time, the team, including Meyers, Keith Deacon, who is a mathematician and Arnold Tunick, a meteorologist, took a different approach.

They had been reporting findings on areas of ghost imaging that are not directly related to virtual ghost imaging. But it has all led to exploiting technology, Meyers said.

Ghost imaging, initially discovered more than 20 years ago, is a form of imaging that is computed, not seen. The imaging is based on quantum properties involving two steps - first analyzing the light source, then counting the reflected photos, Meyers said. In virtual ghost imaging there is normally one light detector instead of two. The team from ARL proposed a diffraction-free light beam as the most effective light source through turbulence.

So a key part of the uniqueness of the ARL team's recent approach is the light source - a Bessel Beam. Although there are other diffraction-free light sources, they used a Bessel beam because it is self-healing; it scatters when it hits turbulence or particulates and then reforms.

"In the military oftentimes you are not working with ideal conditions," Meyers said. "We want to duplicate that in the lab. There were actually two moments during the research when we knew it would work: when the beam went through cloudy water and when the image went through an offset aperture and reformed."

The team worked six or seven days a week collecting data, taking measurements and writing computer code as they got close to proving the principle, said Deacon, who has worked with Meyers for the last 20 years. "If you make a small error, you have to start over."

In their demonstration, the researchers compared the Bessel beam's VGI imaging capabilities with that of a Gaussian laser beam. Each time the Bessel beam produced a relatively accurate image of the letters A-R-L, but the Gaussian image was not always recognizable, Meyers said.

They found the Bessel beam insensitive to scattering of objects. Based on their findings, the method would be helpful in imaging objects through vegetation, forest or jungles, and even around corners. In the future virtual ghost imaging could be useful for special operations work in difficult environments for military surveillance.

As is the case with many laboratory projects, the quantum team's research has military implications, and other implications that could be beneficial for society, like sending red light through body tissue for example as an alternate laser source for x-rays, he said.

"We are challenged to be able to project into the future, see the basis for applications, test the ideas and adjust," Meyers said. "It's one of the best jobs you can have as a scientist."

Source: U.S. Army Research Laboratory