Sorry for the clumsy title; there’s only so much space available in the title box.
What I am trying to ask is whether remote audio surveillance (of, say, a room in some distant building) is possible by examining the motion and vibration of the air molecules in the room.
Phrased differently (and I hope more clearly), let’s assume that the air molecules in a room are moving around in a random manner. Then, if people start talking in the room, the sound waves made by their speech should jostle the room’s air molecules in a way that imparts to them various non-random motions and vibrations. Presumably, these non-random motions will be a function of the sound waves created by the occupants’ conversation and, thus, in some sense ‘encode’ the conversation.
Could you not aim a laser (?laser doppler) into the ‘empty space’ of the room to detect and analyze the motion of the room’s air molecules, and thereby detect and decipher what is being said there?
You’re probably aware that lasers can be aimed at any smooth, reflecting surface in a room to capture the sound waves of what’s being spoken therein (the classic example is bouncing a laser off one of the room’s windows). But that’s old stuff. What I’m interested to know is whether you even need a smooth, reflecting surface anymore. Can you just bounce your laser off the room’s air molecules?
I doubt I’m being as clear as I would have wanted to be, but am pretty sure you’ll still get what I’m talking about.
Can it be done? Is it being done?