The underexpanded sonic jet issued from an axisymmetric convergent nozzle are experimentally investigated in which the nozzle is operated at a pressure ratio of 4.0 to produce a Mach disk in the jet plume. Multidirectional rainbow schlieren pictures of the jet acquired by rotating the nozzle about its longitudinal axis in equal angular intervals are utilized to reconstruct the jet three-dimensional density fields with both of the Abel inversion and convolution back-projection algorithms. The

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... e structure of the free-jet with a Mach disk in the first shock-cell is distinctly displayed with a two-dimensional density contour plot including the jet centerline and isopycnic surface representation for the jet 3D density field. Furthermore, the jet centerline density profile obtained from the present rainbow schlieren is quantitatively compared with that from the background oriented schlieren performed by ONERA in the past.