Laser Microphones

Laser microphones are devices that detect sound vibrations in a distant object. As this suggests, they can be used to eavesdrop with a minimal chance of exposure. For this reason, they are common within the surveillance industry. These microphones originated from the idea of eliminating distortion from old-style microphones. Laser microphones are still in an experimental stage, but are prone to revolutionize the traditional design.

Laser Microphones: their Operation

Throughout the history, laser microphones have used a technique regarding a light beam to remotely record sounds. This dates back to around 1947, when León Theremin created the Buran Eavesdropping System. This system operated by using a low power infrared beam to detect sound vibrations in glass windows. The system worked from a distance. More importantly, its light that was not quite like a laser’s beam.

So How Do They Work?

Laser microphones operate in a quite simple manner. A stream of air filled with particles passes through a cavity located within the outer upper casing of the device. Here the sound waves received from the rear disturb the particles. When the laser beam passes through the stream, the intensity is controlled. A photosensor transforms the controlled light into an electric signal similar to the sound wave. This process removes nonlinearities, making the sound free of distortion.

Vibration to Audio

The human voice can produce sound waves in a range between 300Hz and 3400Hz. These vibrate when they are close to objects, making it possible for an analog electronic device to transform vibrations into an audio signal. Laser microphones can transform sound waves from movement to audio. This results in a laser beam reflected on a specific object. The reflection of the laser bounces as vibrations shift the surface of the vibrating object. Two steps follow: the receiver takes in the oscillating laser signal from the static location. Then, the receiver will detect the laser deflection caused by the vibrations that were initially generated from an audio signal. As a consequence, the receiver will then be able to filter and amplify the signal and transform it into audio. Through this process, a laser mic is able to reproduce the audio that induced the object’s vibration.

A laser microphone can reproduce the audio detected from a vibrating surface with high accuracy and low distortion. It can also transmit audio by using a laser-based system that captures oscillations.