Distance measurement according to the light detection and ranging (LiDAR) principle is one of the oldest applications for lasers. One of the most well-known applications in everyday life is "radar speed guns,” which the police use to catch speeding motorists. For industrial applications, however, more powerful components are required.
LiDAR systems operate on the principle of optical time-of-flight (ToF) measurement: a pulsed laser diode emits a short light pulse. The emitted light propagates until it is reflected by an obstacle and returns to the source. There the pulse is detected by an avalanche photodiode. The distance between the light source and the reflecting obstacle can be calculated from the time that has elapsed between the emission of the light pulse and its return.
The first LiDAR applications were used by NASA just a few years after the invention of the laser. However, the technology did not become suitable for mass production until the late 1980s when small, efficient emitters became available with the development of the first semiconductor pulse laser diodes (PLDs).
Now laser distance measurement is used in a wide range of applications:
When transporting large, heavy goods, several independent cranes often have to work as a common system. It is imperative that both cranes run absolutely parallel to each other at all times to prevent the load from swaying. LiDAR-supported systems register even the smallest deviations and automatically adjust the running speeds of the cranes to each other.
A constantly growing area of application is autonomous driving. While transport and cleaning robots with LiDAR-based navigation are already being used on factory floors and living rooms, it will be some time before the technology becomes established in road traffic. In these applications, pulsed laser diodes (PLDs) are usually used which emit in the near infrared range (NIR) with a wavelength of typically 905 nm. Although this means that the beam itself is not visible, it prevents damage to the eyes when the pulse width is small. Depending on the application, the optical power ranges from a few tens of watts to several kW.
Three-dimensional surface profiles can be created using laser beams emitted from aircraft and satellites. As early as 1971, NASA used a flashlamp-pumped ruby laser to measure the lunar surface as part of the Apollo 15 mission.1 Recently, with the help of LiDAR, archaeologists have succeeded in discovering the remains of ancient Mayan buildings under the dense cover of leaves in the Central American rainforest.