Gallium arsenide eyesafe laser rangefinder

In the past terrestrial optoelectronic distance measurement in the kilometer range was only possible by marking targets with reflector prisms or by increasing the optical output power far beyond the eyesafety limits. These requirements are unacceptable for many measurement tasks and this paper describes how they can be avoided by using a low power semiconductor laser and modern signal processing techniques. 1. DESIGN GOALS A number of manufacturers have fielded optoelectronic rangefinders which must be supported by reflector prisms mounted on the target if distances beyond 100 m are to be measured. These devices based on semiconductor lasers are very accurate (to the order of mm) and because of their low optical output power they are generally eyesafe. Devices are also available for measurements without reflector prisms (non-cooperative targets) to large distances beyond 5000 m where poor target reflectivity and atmospheric attenuation are overcome by high power output usually from an NdYAG crystal laser. The very high intensity laser radiation however is dangerous to the human eye and therefore these devices are constrained to operate under rigorous safety measures. Between these two extremes there are numerous applications where not extreme range or accuracy but eyesafety non-cooperative targets small size and low cost are of primary importance. This is the case not only for civilian applications but also for military use e. g. in force-on-force exercises or special operations. Other design goals