Velocities of gas and plasmas from real time holographic interograms

A truly noninvasive measurement technique for plasma velocity has not been demonstrated. Plasma velocities have been inferred using laser Doppler anemometry or photographic analysis of the position of smoke or small particles. An alternate method based on the refractive index change created in a plasma by a gaseous probe material injected into the plasma is described. This disturbance of the refractive index can be monitored using interferometry. A multipass real time holographic interferometry system is used to follow the changes of the interferometric pattern, and the data is recorded using high speed cinematography. A transparent model of an industrial plasma torch is employed in these studies, and a number of different types of trace gas materials are used to track the plasma flow. Using a combination of multipass interferometry and a laser line absorbing gas, sufficient interferometric sensitivity is obtained to determine plasma velocities in the 100 m/s range. Based on these results, a working plasma torch is constructed. Further studies are planned using this torch and actual plasmas.