Laser Doppler distance sensors using phase and frequency evaluation

The optical inspection and metrology for non-optics industry gains increasing importance. Several optical sensors are available for shape measurements of rough surfaces. However, at fast rotating objects such as turbine blades high temporal resolution is necessary, which often can not be fulfilled by commercially available sensors. The recently developed laser Doppler distance sensors allow temporal resolutions in the microsecond range. The independence of the distance measurement uncertainty to the lateral surface velocity is unique. The laser Doppler distance sensors were realized by the evaluation of the interference signal frequency as well as the interference signal phase. Both sensors have been employed for high-speed inspection.