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Experimental investigation is essential to improve the understanding of aerospace flows. During the last years, effort has been put on the development of optical diagnostics capable of imaging or yielding data from the flow in a nonintrusive way. The application of some of these techniques to supersonic and hypersonic flows can be highly challenging due to the high velocity, strong gradients, and restricted optical access generally encountered. Widely used qualitative and semiquantitative optical flow diagnostics are shadowgraph, schlieren, and interferometry. Laser-based techniques such as laser Doppler anemometry and particle image velocimetry are well established for investigation of supersonic flows, but as yet their use in hypersonic flows has been limited. Other relevant measurement techniques include particle tracking velocimetry, Doppler global velocimetry, laser-two-focus anemometry, background oriented schlieren and laser induced fluorescence methods. This paper reviews the development of these and further optical measurement techniques and their application to supersonic and hypersonic aerospace flows in recent years. [ABSTRACT FROM AUTHOR]