The measuring principle of BOS is based on light ray deflection along density gradients normal to the lines of sight. For high precision BOS measurements in a small field of view around a micro nozzle exit a long-distance microscope (LDM), a
DMD projector, a high resolution CCD camera and evaluation software based on crosscorrelation for determining displacement vector fields have been used in the propulsion
laboratory of ESA-ESTEC in Noordwijk. The density distribution inside a micro nozzle free jet of nitrogen into a vacuum chamber has been investigated using optical
tomography for measurement data achieved with BOS