Results of an experimental investigation on the Richtmyer–Meshkov instability of a He–CO2interface are reported. A simultaneous three‐directional laser absorption technique is used to follow, at a single abscissa, the evolution of the created mixing zone before and after the interaction with the reflected shock, during the same run. CO2density profiles have been determined within both the incident and the compressed mixing zones. However, near the pure CO2, the wall boundary layer reflected shock interaction perturbs measurements and does not allow objective conclusions. ©1996 American Institute of Physics.