Abstract
Optical diagnostic techniques are routinely being used in high speed flow facilities to measure flow properties such as concentration, temperature and velocity, and thus, to study the flow physics. One such technique, tunable diode laser absorption spectroscopy (TDLAS), has proved to be particularly suitable for hostile environments such as shock tunnels and flight tests. The fundamentals, operating principle, applications and scope of the technique in high speed flow research is discussed in this review, with references to some relevant examples.