Abstract: Nozzle cooling and wall contact prevention control are included in a gaseous CRISLA apparatus, along with removable collectors, and the efficient use of one or more currently available high power lasers to produce a commercially economic isotope separation process. The wall contact prevention is accomplished with gaseous boundary layers, and a supersonic nozzle normally is used to cool and separate excitation bands of the isotopic material. Non-intermixing gaseous streams with different isotopic assays can be created in a single nozzle chamber and segmented collection chamber, which along with recirculation loops and compressors, allows a single laser system and a single nozzle system to be used to selectively excite the isotopic material while it makes multiple passes through the laser beams of the laser system until only a small fraction of the desired isotope remains to be separated. The process is especially effective in separating .sup.235 UF.sub.6 from a gaseous mixture of .sup.235 UF.sub.6 and .sup.