The use of laser-induced fluorescence (LIF) from acetone is becoming increasingly widespread as a flow diagnostic, however, limited to measurement of low speed flowfields. In this paper, acetone planar laser-induced fluorescence (PLIF) is applied to measure the flowfield of under-expanded supersonic freejets. The field of number density taken by the present method is compared with the theoretical one obtained by CFD method. As a result, it is found that this method may be the powerful tool for measuring the density in supersonic flowfields.
