Laser microphone

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A laser microphone is a surveillance device that uses a laser beam to detect sound vibrations in a distant object. It can be used to eavesdrop with minimal chance of exposure.

The object is typically inside a room where a conversation is taking place and can be anything that can vibrate (for example, a picture on a wall) in response to the pressure waves created by noises present in the room. The object preferably has a smooth surface. The laser beam is directed into the room through a window, reflects off the object, and returns to a receiver (for example a solar panel) that converts the beam to an audio signal. The beam may also be bounced off the window itself. The minute differences in the distance traveled by the light as it reflects from the vibrating object are detected interferometrically.

The interferometer converts the variations to intensity variations, and electronics are used to convert these variations to signals that can be converted back to sound.

The director of GlobalSecurity.org, John Pike, suggested laser microphones may have been used as part of the sophisticated surveillance to determine whether Osama Bin Laden was hiding in the suspected compound in Abbottabad, Pakistan, in conjunction with spy drones, spy satellites, and other technologies.[1] Although the CIA believed that Bin Laden was hiding in the compound, it had not been able to obtain visual confirmation that he was there. There was visual intelligence gathered to determine how many people had been seen within the compound, and then laser microphones were used to demonstrate that there was someone else inside the building that had not been seen. This was done by bouncing lasers off of the glass panes in the building's windows, which would act like diaphragms to pick up voices inside. The CIA operatives could not tell what was being said, but they could distinguish individual voices from each person's unique pitch and tone. As a result, they determined that there was another person within the compound that they had not seen with visual confirmation, which led to the conclusion that Bin Laden was probably inside the compound.

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  1. ^ "CIA Used Satellites To Prep For Bin Laden Raid". National Public Radio. 2011-05-04. Retrieved 10 June 2012. Mr. PIKE:... shine a laser beam on those windows, you can detect those vibrations 

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