In my recent travels to the Bay Area to talk to customers as I prepare to author our Annual Laser Market Review and Forecast for the January issue, as well as gather data for our Laser Marketplace Seminar held each year in conjunction with Photonics West, I was fortunate enough to have a meeting and enjoy a dinner at the Moss Beach Distillery (http://www.mossbeachdistillery.com). Turns out they have a ghost called "the Blue Lady" who wanders the restaurant and the beach below—a tragic tale of woe that you can read about on their website. While I didn't see her that day, it did get me thinking about the articles we've written in Laser Focus World over the years about ghost imaging and ghost reflections.
It turns out that ghostly apparitions, as unwelcome as they can be in the optics community as image spoilers, are still being studied and analyzed—and may even play a role in cloaking technology and surveillance. You can find a good overview of ghost images caused by multiple reflections in an optical system here: http://irsa.ipac.caltech.edu/data/SPITZER/docs/irac/iracinstrumenthandbook/67/. But while ghost images typically appear in an optical system due to multiple reflections within the optical path (from optics, gratings, filters), the National University of Singapore (NUS) is close to developing a useful purpose for ghost reflections: using them to 'hide' objects or create visual 'illusions' that baffle viewers.
As reported in Advanced Functional Materials, the NUS work can generate ghosts through optical scattering and artificial metallic metamaterials that cause light from an object to behave abnormally, appearing in places different from the actual location of the real object. Most metamaterial-based ghost images appear at the same location as the object, but this work enables more than one virtual ghost to appear, offering a new level of camouflage and cloaking capability. The image below shows the researchers studying the fabricated ghost device, made with specially designed metamaterials with eight concentric layers of circuit boards that cancel the original scattering signature of the object and replace it with nonexistent ghost objects.
An article in New Scientist goes beyond 2D ghost imaging to describe a 3D ghost imaging method that doesn't even require a camera. "We're actually turning a projector into a camera and a detector into a light source," says Matthew Edgar of the University of Glasgow. Using this method, his team created a 3D image of a polystyrene dummy head.
And as if ghosts weren't enough, what about orbs? You know, those circular, diffuse objects that appear in random positions (mostly in digital camera images). Some claim they are the energy signatures of spirits, while others say they are simply optical reflections caused by moisture condensation on lenses, bugs or dust particles flying by if a flash is used, or.........? Take a look at two of my own personal images of orbs. See them in the cave above the dogs and a single one just to the right of the cactus?
As much fun as it would be to give them a paranormal interpretation, orbs, says Wikipedia, are probably optical artifacts (see http://en.wikipedia.org/wiki/Orb_(optics)), and even the Southern States Paranormal Research Society debunks orbs, offering a very detailed treatment of the subject at http://ssprstn.tripod.com/id65.html and going so far as to classify them into two categories--Naturalistic Solid-Type orbs and Liquid-Based orbs. I particularly enjoyed reading the adamant message at the end of the technical discussion: "SSPRS will no longer be accepting submissions of photos of orbs, of any kind, because we have made our stand, and will continue to stand by it that orbs are not paranormal in nature. If you have read this article, please do not attempt to send us any orbs because as explained above, orbs are NOT paranormal. There are no special orbs. Sorry!"
