Lasers and Trains

A laser is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emission of photons. The term laser originated as an acronym for Light Amplification by Stimulated Emission of Radiation. The emitted laser light is notable for its high degree of spatial and temporal coherence, unattainable using other technologies. Laser systems can be used to implement highly precise and ultra-fast measuring processes. Railway measuring technology has a huge worldwide need here. One prerequisite for its use is that nobody is damaged or suffers irritations by the laser. Dr. Heinrich Höfler and Dipl.-Ing. Harald Wölfelschneider from the Fraunhofer Institute for Physical Measurement Techniques IPM in Freiburg have worked with their team to develop a 3D laser scanner. It can be used outdoors without hesitation. Extremely fast and precise, it is able to spatially measure and monitor the position of the contact wire or the track from a train traveling at up to 100 kilometers (62 mph) per hour. If the scanner is stationary, it can capture passing trains and check for loads that might have slipped. When lasers were invented in 1960, they were called "a solution looking for a problem".  Since then, they have become ubiquitous, finding utility in thousands of highly varied applications in every section of modern society, including consumer electronics, information technology, science, medicine, industry, law enforcement, entertainment, and the military. The first use of lasers in the daily lives of the general population was the supermarket bar code scanner, introduced in 1974. The laser disk player, introduced in 1978, was the first successful consumer product to include a laser but the compact disc player was the first laser-equipped device to become common, beginning in 1982 followed shortly by laser printers. Heinrich Höfler stated how their application works: "We send off a laser beam and wait until it returns. We measure the time in between and that tells us how far away an object is." The difficult part is capturing the returning beam. Often, only very little light comes back and what is more, the transmitted light beam is back in an extremely short space of time. The solution: A kind of slow motion. The laser beam is very rapidly switched on and off — modulated, as scientists would put it. The time shift of this modulation wave can be determined more quickly and precisely than is possible with a single laser pulse. The system measures, by default, one million times per second. "For Deutsche Bundesbahn (German Railway), we equipped a measurement train that scans the surroundings of the test track, using several laser beams and which delivers, taking four million measurements per second, a 3D image of what it scans", explains Harald Wölfelschneider. That allows even small obstacles and constrictions to be detected, or we can plan the route via which a heavy load can best be transported to its destination. Another field of train application is the measuring of passing trains. This requires the scanner to be permanently mounted, which, however, does increase the chance of someone looking into the laser beam for a longer period. To make the scanner safe for the human eye, the researchers had to develop a new wavelength range: infrared, which is harmless for our eyes. The consequence being that the entire system had to be fully reconfigured. The laser system has already been marketed and used successfully all over the world for rail traffic safety. Not only fast and precise, this system is also highly robust.