A laser microphone is a

surveillance Surveillance is the monitoring of behavior, many activities, or information for the purpose of information gathering, influencing, managing, or directing. This can include observation from a distance by means of electronic equipment, such as ...

device that uses a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...

beam to detect

sound In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the br ...

vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

s 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 should have a smooth surface for the beam to be reflected accurately. The laser beam is directed into the room through a window, reflects off the object, and returns to a receiver 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.

History

The technique of using a light beam to remotely record sound probably originated with

Léon Theremin Lev Sergeyevich Termen ( 18963 November 1993), better known as Leon Theremin, was a Russian inventor, most famous for his invention of the theremin, one of the first electronic musical instruments and the first to be mass-produced. He also worke ...

in the Soviet Union at or before 1947, when he developed and used the ''Buran'' eavesdropping system. Galeyev This worked by using a low power infrared beam (not a laser) from a distance to detect the sound vibrations in the glass windows. Glinsky 261

Lavrentiy Beria Lavrentiy Pavlovich Beria ka, ლავრენტი პავლეს ძე ბერია} ''Lavrenti Pavles dze Beria'' ( – 23 December 1953) was a Soviet politician and one of the longest-serving and most influential of Joseph ...

, head of the

KGB The Committee for State Security (, ), abbreviated as KGB (, ; ) was the main security agency of the Soviet Union from 1954 to 1991. It was the direct successor of preceding Soviet secret police agencies including the Cheka, Joint State Polit ...

, had used this Buran device to spy on the U.S., British, and French embassies in Moscow. On 25 August 2009, was issued for a device that uses a laser beam and smoke or vapor to detect

s in free air ("Particulate Flow Detection Microphone based on a laser-photocell pair with a moving stream of smoke or vapor in the laser beam's path"). Sound pressure waves cause disturbances in the smoke that in turn cause variations in the amount of laser light reaching the photo detector. A prototype of the device was demonstrated at the 127th Audio Engineering Society convention in New York City from 9 through 12 October 2009.

Notes

References

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*

External links

(archived fro

, Gearwire
New Mic Proof of Concept
David M. Schwartz
Smoke and Laser Mic Prototype Two Demo
David M. Schwartz {{DEFAULTSORT:Laser Microphone Optical devices Microphones Surveillance Covert listening devices Inventions by Léon Theremin

History

See also

Notes

References

External links