Microplasmas produced with sub-millijoule laser pulses for laser induced breakdown spectroscopy

Summary form only given, as follows. Laser induced breakdown spectroscopy (LIBS) is a powerful technique for fast determination of the chemical composition of materials based on measuring line emission from ions and neutral atoms in a transient laser produced plasma. The technique is considered almost non-destructive since only a small amount of material is ablated. In the current study we are undertaking to optimize the plasma conditions of a sub-millijoule laser produced plasma to optimize the emission of radiation for material identification and to achieve high spatial resolution on the 10 micron scale. Scaling studies have been carried out of the emission levels from metallic target materials as a function of laser pulse energy in the range of 10 to 500 microjoules and as a function of observation delay time for ultraviolet (248 nm) KrF laser pulses of 10 ns duration. Our data show that as a consequence of the smaller amount of the heated mass, time constants of the plasma emission are much shorter than the ones typically encountered in LIBS using much higher laser energies. We are currently conducting LIBS experiments with 50 ps pulses, at 248 nm in the same energy range. Few studies have looked at the scaling of plasma emission with pulse length in the picosecond regime for UV pulses. We present initial experimental results and compare these to expectations based on the scaling of the laser plasma parameters.