laser produced plasma; spatial confinement; laser induced breakdown spectroscopy;PLASMA FORMATION; CENTRAL SCHEMES; ABLATION; PARTICLES; PULSES; LIBS

The spatial confinement of plasma produced by a nanosecond laser is investigated using time resolved spectroscopy, fast imaging, interferometry, and numerical computation. The dynamics of the plasma, depending on shock waves, laser power, and wall distances, are studied. Experimental results confirm that the plasma is constricted by the reflected shock associated with a temperature and density gradient. The peak laser power determines the initial plasma parameters which affect the spectral intensities and the velocity of the reflective shock waves. The wall distance determines the reflection time of the shocks, which in turn influences the time delay of the collision between the two reflective shocks. The numerical results reveal a fast propagation process surrounding the reflective shocks, which indicates that the velocity of the reflective shock wave is influenced by the density of the plasma. The maximum enhancement factor similar to 5.2 is realized at a delay time of 11.7 mu s under a pulse laser energy of 180 mJ and a wall distance of 9 mm.

Laser-induced breakdown spectroscopy; spatial confinement; signal enhancement;INDUCED BREAKDOWN SPECTROSCOPY; PULSE

In laser-induced breakdown spectroscopy (LIBS), a serious of cylindrical cavities are used to spatially confine the plasmas produced from silicon (Si) target by using a Nd: YAG laser in air. Time-resolved spectrum of Si plasma with different diameters of cylindrical spatial cavities is measured. Compared with the plasmas generated without the confined cavity, the spectral emission intensity of plasma generated with cylindrical cavity is enhanced at a certain delay time. As the diameter of cylindrical cavity increases, the spectral emission is enhanced later in time and the enhancement becomes weaker. The result shows that the presence of the confined cavity leads to an increase in the spectral emission of plasma which is attributed to compressed plasma by the reflected shockwave.