Everyday Use of Laser
In everyday life we're more or less surrounded by laser applications. Carpenters use laser instead of spirit levels, hunters use laser instead of ordinary telescopic sights and most likely, you use laser when you listen to music.
A DVD player contains a laser that is used not because it produces a parallel beam, but rather because the light emerges from a tiny point, which enables it to be focused on the different layers of the disc. By moving the lens sideways - laterally, it is possible to reach areas farther in or out on the disc. By moving the lens along the beam - longitudinally, different depths can be reached in the disc. The information, ones and zeros, is stored in several layers, and only one layer is to be read at a time. Every point on a particular layer is read during every revolution of the disc.
In order to make room for a lot of information on every disc, the beam has to be focused on as small an area as possible. This cannot be done with any other light source than a laser.
Today this area has been reduced to about half a square micrometer, which yields 2 megabits or 0,25 MB(yte) per mm2.
Laser pointers are made from inexpensive semiconductor lasers that together with a lens produce a parallel beam of light that can be used to make a bright spot to point with. Their range is very large. If one points at a surface 200 meters (220 yards) distant in the dark, a person standing close to the object being pointed at will have no trouble seeing the shining spot (of course, someone else has to hold the laser). On the other hand, the one holding the pointer will have difficulty seeing the spot. The eternal question of range has more to do with the light's behavior on its way back to the sender than with the length of the beam.
Laser sights for rifles and guns can be based on several different principles. Some send a laser beam parallel to the trajectory so that the point of impact becomes visible. This method exposes the marksman. Some project a red dot inside a telescopic sight (instead of cross hairs). In both cases, the dot can be produced with a ring around it.
Speed Measurement Using Laser
The method the police use to measure car speed is based on a laser signal that is sent towards the target. This beam bounces back and is mixed with light that has not hit the car. The result is an oscillation - the same as when you tune a guitar - with higher frequency (more treble) the faster the target moves.
The speed has to be measured straight from the front or from the back. If it is measured at an angle, the speed is underrated. This means that you cannot get false values that are too high.
The measurement is dependent on the car having something that reflects well. The license plate is perfect, as are different types of reflecting objects. Fogged surfaces are okay, but reduce the maximum distance.
Laser Distance Meter
The primary users of laser distance meters today are surveyors and constructors, but the car industry is catching on. Least spectacular is the so-called parking assistance that helps the driver to estimate the distance to the car behind when parking. A more recent application measures the distance to the car in front of the driver when driving on highways or other roads. You simply lock in the distance to the car in front of you in order to maintain that distance. This makes driving more efficient and faster as long as it all works. This kind of laser is found in most robots with mechanical vision.
Optical Loudspeaker Cable
Any amplifier of worth nowadays has an optical cable for transmission to the loudspeakers. The advantage of this method is that it is insensitive to interference from electromagnetic fields, that is interference from electronic devices and radio transmitters such as cell phones. The light source used as a transmitter is a small laser semiconductor. All equipment using optic cable uses the same standard. For example, the maximum bit rate for broadband applications is today 50-100 times higher using optics, but the potential ratio is 10,000 times.
First published 19 December 2002
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