INVESTIGATION OF LASER SPUTTERING OF IRON AT LOW FLUENCE USING RESONANCE IONIZATION MASS-SPECTROMETRY

Emission of neutral and ionized Fe atoms induced by N2 laser irradiati on (lambda=337 nm) of iron targets was investigated for laser fluences ranging from the sputtering threshold (a few tens mJ/cm2) up to 320 m J/cm2. The unique sensitivity of resonance ionization mass spectrometr y permitted to identify the laser-sputtered neutral particles, to stud y their velocity distribution and excitation state, and to measure the laser-sputtering yield at a very low emission level (100 Fe atoms rem oved per laser shot). In this soft ablation mode, it appears that the sputtered atoms carry direct information on the primary mechanisms inv olved in the laser sputtering of an iron surface. The present study co rroborates a thermal process in which the laser beam acts as a pulsed heat source. Energy characteristics of the emitted neutral atoms refle ct rather well the thermal state of the surface, the atom temperature increasing from the ambient at threshold to melting and boiling temper atures for growing laser energies.