Characterization of kinetic energy distributions of ions in high laser irradiance via orthogonal time-of-flight mass spectrometry

The characteristics of laser ionization in low pressure background gas have been investigated through the measurement of temporal and kinetic energy distributions of Al+, Mn+, Nb+, In+, Ta+, and Bi+ produced from a disk comprised of these metallic elements. A Q-switched Nd:YAG laser was utilized with a laser beam at 532 nm of wavelength and 1.0 × 1010 W/cm2 of laser irradiance. The kinetic energy was found to be the same for all ablated species at the given pressure, regardless of the atomic mass. The plume propagation translates from a free expansion at 0.5 Pa to a collisional and shockwave-like hydrodynamic expansion at 50 Pa. A plume splitting exists at 500–1500 Pa where only the fast component can be observed with a grounded nozzle voltage. As the nozzle voltage grows up, the thermalized component with increased kinetic energy is found depending on the nozzle voltage.

► We have measured kinetic energy distributions of different elements.
► Two approaches were used for measurement: temporal profile and deflecting voltage.
► Kinetic energy distributions are the same for different species, independent of mass.
► Kinetic energy loss of ions is much smaller than the theoretical value.
► Kinetic energy of the slow component increases proportionally with nozzle voltage.