And now they use just the laser beam itself to listen to distant conversations. Such a system will be able to listen to your heart beating even from a distance.
Unlike the development system described in the article, future systems won't need to use a visible laser beam to perform their magic. Instead they will use an infrared laser, invisible to the eye (but not the camera).
Some technically savvy people know that light can be used as a tool for eavesdropping: if a beam from one arm of an optical interferometer is reflected off a window, the interferometer can sense sounds—including human voices—that make the window vibrate. But not only is it hard to separate voices from other sounds sensed by the interferometer; the setup must also be very precise, and in many cases there is no window conveniently nearby.
Researchers from Bar-Ilan University (Ramat-Gan, Israel) and the Universitat de València (Burjassot, Spain) have developed a different way to sense sound remotely—one that doesn't rely on either an interferometer or a window. Instead, a single laser beam is shone on the object to be monitored (for example, a human or a cellphone) and the speckles that appear in an out-of-focus image of the object are tracked, producing information from which a spectrogram or temporal sound signal can be constructed.
Am I worried about the government listening in on my conversations? No. Well, maybe. Kinda. Oh, heck, yeah I am. But what concerns me even more is ordinary people listening in on their friends, neighbors, and adversaries. The phrase “out of earshot” could become meaningless.
I'm not sure I'm ready for anyone desiring to do so becoming privy to my private conversations. I doubt you are either.
But still, it's neat technology.