Laser interferometry: streaked shadowgraphy and Schlieren imaging

Optical diagnostics are extensively used to probe plasmas because they do not perturb the measured medium. Among them, the measurements of the refractive index and its variations give direct access to the electronic density, its gradients and the hydrodynamics of the plasma. Schlieren and shadowgraphy show qualitatively the density gradients and can even give quantitative information if certain conditions are fulfulled, in particular symmetry. Laser interferometry gives a very precise density measurement in a cylindrical plasma. Time resolution is achieved either using ultra-short laser pulses or using a streak camera. The authors illustrate such methods, describing some optical diagnostics of a laser produced plasma. (Auth.)