GAS-DYNAMIC EFFECTS OF THE INTERACTION BETWEEN A PULSED LASER-ABLATION PLUME AND THE AMBIENT GAS - ANALOGY WITH AN UNDEREXPANDED JET

The expansion of a laser-ablation plume into different ambient gases i s investigated theoretically using a two-fluid gas-dynamic model and e xperimentally with time-of-flight mass spectrometry. Both calculations and measurements, performed for laser ablation of YBa2Cu3O7-x in oxyg en or noble gases, reveal an oscillatory behaviour of plume expansion dynamics which is strongly dependent on the molecular weight of the am bient gas. Simple gas-dynamic considerations based on the analogy betw een an ablation plume and a supersonic underexpanded gaseous jet are f ound to explain a number of the effects of the interaction between the plume and the background gas. The effect of plume focusing observed p reviously at fairly high pressures of various ambient gases is reasona bly described using the phenomenology of the underexpanded jet. The an alogy also predicts vortex formation at the plume periphery.