Laser Doppler velocimetry using powerful solid-state light sources

Opto-electronic measurement techniques are well established in fluid flow investigations. Their advantages are that they are non-intrusive, provide highly accurate measurement data and have fast response times. Laser Doppler velocimetry (LDV) is one of the most important methods for velocity measurements with high spatial and temporal resolution. Diode lasers and diode-pumped solid-state lasers as well as glass fibres and micro-optics are employed to an increasing extent. Particularly, the development of solid-state lasers proceeds rapidly. New lasers with improved properties such as high-power fundamental-mode emission make it possible to develop enhanced LDV sensor heads. This may open up new fields of application, for example in medicine and aerospace technology. The aim of this review is to describe the present state-of-the-art in LDV and to demonstrate how new laser concepts can still contribute to the development of new, improved LDV sensors. For that purpose, solid-state lasers such as diode lasers and diode-pumped solid-state lasers are introduced, and concepts of communication engineering for accomplishing directional multi-component velocity measurements are discussed. Also, velocity measurements with high spatial resolution are reported. A conclusive overview of applications and an outlook on future challenges are outlined.