A laser microphone is a security monitoring gadget in which a laser beam is used for detecting audio vibrations across faraway targets, which are normally walls or glass of homes or offices. These devices could be applied for eavesdropping with virtually no chance of getting identified or cover getting blown.
Laser eavesdropping gadgets, it is claimed, are being used by Security and Intelligence agencies in several nations, to detect and read talks in homes and offices from distances as far as 2 miles away.
There exists a whole lot controversy and doubts concerning this, nevertheless there isn't any question that this kind of equipment are actually available.
Actually, Mr Laisk, a physicist in the Macquarie University (NSW, Australia) along with his 3rd year pupils have developed a laser snooping device and recorded discussions from a room 30 yards far which surely prove the authenticity of such sophisticated snooping gadgets.
Main Objective Behind Laser Bugs
The laser bug provides several benefits when compared to other conventional strategies.
Probably the foremost advantage is that no special devices, transmitters, or wiring has to be physically installed within the room which needs to be tracked.
Another advantage is further crucial than the first - is that the laser bug device to certain level eliminates the need for phone tapping.
How Laser Mics Work
The fundamental theory is no rocket science. Any kind of noise or sound produced within a room will result in the windows - and, to some degree, the walls, to vibrate slightly, in accordance with the sound frequency.
This impact can easily be confirmed by means of one's ear stuck on the wall, or by pressing the ears against the glass door or window.
All audible vibrations inside the room could be listened to pretty distinctly. A much more remarkable evidence is to increase the volume of a music amplifier within a compact room, when the window panes could generally be seen vibrating.
The laser microphone takes the advantage of this property, where sound inside the room being tracked causes tiny oscillations on the window glass (including the walls).
The laser beam from a laser transmitter is aimed on one of these glass window. The beam strikes upon a section of the glass window that is vibrating at the same frequency of the speech vibrations inside the room.
This gives rise to a varying displacement of the glass surface, generating a Doppler shift effect in the laser beam frequency.
The reflected beam thus turns into a frequency modulated laser beam through the vibrations of the speech inside the room.
The person monitoring the laser receives the reflected modulated laser. The modulated laser is mixed together with a sample of the original unmodulated sample laser beam, in a PIN photodiode.
The result is an output from the diode that includes a varying frequency difference between the original transmitted version and the modulated received version of the signals.
This differential signal is subsequently amplified and detected.
In Mr. Laisk's circuit, the final detector stage incorporated a special fast recovery diode for the required demodulation of the speech content from the reflected laser beam.
In more sophisticated prototypes, a double heterodyne process are often used to obtain additional gain prior to detection and demodulation. At the initial glance it might look important - to receive the reflected beam - the receiving and transmitting devices needs to be set up set up to ensure that the beam is perfectly perpendicular to the window glass surface.
However, practically it is found that this may be not necessary. Because when the laser ray hits the glass, the rays get reflected through the normal angle while some laser light get reflected in the diffused manner.
Meaning some laser energy get reflected all around. This further means that no matter from which angle the laser hits the target surface, there will always an adequate amount of stray diffused laser energy that will be reflected and captured back for the intended processing and demodulation.
And this specific technique is entirely possible even by using rather ordinary detector semiconductor parts like PIN diodes from ranges over 50 metres. If higher range is required, a lot more sensitive detectors will be necessary - perhaps working at extremely low temperatures so as to deliver an improved signal/noise ratio.
With reference to a report submitted by Dr Sydenham in his transducer series, commercially obtainable IR detector system could actually be used for sensing the sound vibrations inside a TV tower even across a 70 m of thick fog.
Equipment can be obtained from markets which only needs some modifications for applying for such snooping functions. These equipment are called Laser Velocimeters and are being ordered in vast quantities for implementation in commercial control programs. It is obvious that upgraded variations of such devices are being employed for surveillance applications.
Modulated Beam has a Wide Bandwidth
The Bandwidth of the modulated reflected laser signal can be pretty broad. With a laser beam running at maybe 1000 mm (i.e. 300 Terahertz), incident on a surface vibrating at just a few microns in a couple of kilohertz, would imply that the receiver is equipped to detect a bandwodth of nearly 1GHz for the detection!
Even in this situation, it may be easily feasible using today's technology. The level of sensitivity of such equipment is immensely high. Standard laser interferometers are now able to identify vibrations of one angstrom (10-10 metres) in fact it is documented that detection of 1/100th angstrom movements has been accomplished.
Therefore unquestionably, laser snooping is technologically achievable and these devices may be easily available in the local market with the intended features.
How to Defeat Laser Bug
As discused above, the laser bug is actually a fairly uncomplicated device. It is pretty much obvious that these are being utilized by a lot of companies - particularly by those operating in 'aggressive marketing research work - or for commercial spying as it really should be known as.
The best way to eliminate laser snooping bug is simply to make sure that no private chats ever happen within a area having an exterior wall. However due to the extreme sensitivity of such device it may be necessary that conversing in a room is done at a very low volume.
A further advanced strategy would be to set up large double glazed house windows - having the air gap between the glasses which are exposed into the outer surroundings. Additionally, the exterior panes could then be artificially energized through a white noise generator.
White noise may be furthermore forced into the air space between the two stage glass or wall layers. In a less critical application - an incredibly successful strategy could be to apply a matt black layer of paint on the exterior of the room walls. This should completely absorb the energy of the laser beam as a result inhibiting the required reflection!
Very basic products could be utilized to identify and eliminate such beams - however be aware that although the majority of commercial interferometers work with beams in the visible light spectrum, the laser snooping gadgets function within the infra-red section of the spectrum. This means that they cannot be detected with naked eye.
That said, we can still detect the the heat energy emitted from such beams pretty conveniently. Therefore, if you believe you are getting hot under the collar, who knows? Maybe several intrigued organizations could be bugging on you.