The objective of this study is to experimentally investigate the mixing of a transversely injected choked stream of a carrier gas carrying iodine with an oxygen cross-flow in a Chemical Oxygen Iodine Laser (COIL). The investigation was performed non-intrusively, using planar laser induced fluorescence. A frequency doubled Nd:YAG laser was used as the light source, and the images were acquired using a CCD camera. Injectant mole fraction data was reduced from these images using digital image processing. Experiments were performed for a variety of cross-flow velocities and injection pressures. A parameter called degree of unmixedness, which was defined as the ratio between the standard deviation of the image intensities and the average image intensity, was used to quantify the mixing. A mixing distance was defined as the location downstream of which the degree of unmixedness did not change by more than 10%. It is seen from the images that for the same injection pressure the mixing distance is higher for higher cross-flow velocities. It is also observed that for a given cross-flow rate, higher injection pressures lead to lower mixing distances. The mixing distances obtained were correlated using the ratio between the momentum flow rates of the injected jets and the cross-flow. The mixing distances were linearly dependent on this ratio until a value where the jets mixed almost instantaneously at the injection location. © 2000 by Muruganandam, Srihari Lakshmi, Ramesh, Viswamurthy, Sujith and Sivaram.