The sputtering of polymer films with 248 or 308 nm laser pulses causes two groups of particles to be emitted. Light particles are emitted more rapidly and escape to form a shock wave. Heavy particles are emitted more slowly and under some conditions are impeded by the light ones, expand sideways, and leave debris on the target surface. Debris formation can be understood from ordinary gas dynamics where it is equivalent to recondensation beyond the bombarded spot. This is shown by numerical solution of the flow equations.