A laser microphone is a
surveillance 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" is an acronym for "light amplification by stimulated emission of radiation". The ...
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 ...
vibration
Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic, such as the motion of a pendulum—or random, su ...
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 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 (; rus, Лавре́нтий Па́влович Бе́рия, Lavréntiy Pávlovich Bériya, p=ˈbʲerʲiə; ka, ლავრენტი ბერია, tr, ; – 23 December 1953) was a Georgian Bolshevik ...
, head of the
KGB, 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
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 ...
vibration
Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic, such as the motion of a pendulum—or random, su ...
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.
See also
*
Photophone
The photophone is a telecommunications device that allows transmission of speech on a beam of light. It was invented jointly by Alexander Graham Bell and his assistant Charles Sumner Tainter on February 19, 1880, at Bell's laboratory at 1325 ...
*
Passive radar
*
Laser Doppler vibrometer
A laser Doppler vibrometer (LDV) is a scientific instrument that is used to make non-contact vibration measurements of a surface. The laser beam from the LDV is directed at the surface of interest, and the vibration amplitude and frequency are ext ...
*
The Thing (listening device)
*
List of laser articles
Notes
References
* linked fro
LMJ6*
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