- A simple, one-dimensional leak flow tube model was used to calculate the effect of mixing on the performance of chemical oxygen-iodine lasers (COIL). Both the maximum gain and the characteristic length of the iodine dissociation are shown to be nonmonotonic functions of the iodine flow rate, nI 2. The maximum nI 2 for which lasing is possible is less than 1-2% of the oxygen flow rate. This is in agreement with experimental data and is not explained by models assuming premixed flows. The present model was applied to calculations of the performance of supersonic COILs.