Induced evaporation of metal from an aluminum surface by a normal pulse neodymium laser

Abstract

Laser induced evaporation of material from the surface of an aluminum target in a vacuum was studied. Based on a literature examination, material removal using a normal pulse laser was judged to be more efficient than for a Q-switched laser. The experiment was conducted using a neodymium glass laser modified for normal pulse operation. The energy density was varied from 8.5x10(2) J/cm(2) where no breakdown occurred to 5x10(3) J/cm(2) where the threshold for breakdown was exceeded. The normal pulse duration was 600 µs. Analysis of the ejected material was achieved by using a Hughes Ionization Gauge placed in the path of the ejected material. Oscilloscope traces of the ionization gauge output show that the gauge "sees" what is flying past it. There is good correlation between laser radiation, plasma radiation and ionization gauge fluctuations. The ionization gauge gave distinguishable signals for ions, electrons, and neutral particles ejected from the target surface. Signal sequence was dependent on the particle velocity. By measuring the elapsed time after ejection from the surface and the target to collector distance, the first arriving neutral particle velocity was determined to be 5.2x10(4) cm/s.