Search

A systematic study was conducted to understand the size and shape of nanopatterns generated on selected semiconducting (Si and Ge) and metallic (Cr, Cu, and Ag) targets under different laser pulse durations, laser energies, and number of laser pulses. The experimental results indicated that femtosecond laser pulses, compared to nanosecond laser pulses, provide lower damage thresholds to the targets but higher damage thresholds to the near field scanning optical microscope (NSOM) probes.

The effects of ionization in the energy equation of a laser induced plasma and in the jump conditions across the external shock wave are analyzed for laser ablation plume formation. Larger and higher temperature plasmas are formed at hundreds of nanoseconds after the laser pulse, when most laser energy converted to the vapor plume is in the form of ionization.

A series of synchronized fast-time resolution shadowgraph and emission images for different background gases and laser energies are used to study the phenomena occurring during nanosecond laser ablation. The quantity of vaporized mass is found to be independent of the ambient gas, but the laser energy transferred to the ambient has scaled inversely with the atomic mass of the gas.

The analysis of the laser energy coupling to a gas and the amount of vaporized mass in the vapor plume during ablation is presented. The values of background gas, the vaporized sample mass, the internal shock wave propagation within the vapor plume are determined and shown that the interaction of the internal shock wave with the sample might be one of the mechanisms including liquid sample ejection during laser ablation.

A study was made of the cooling of the laser induced vapor plume in background air and experiments were conducted over a range of laser spot sizes and energies. It was shown that for optically thin conditions, which are often valid for small vapor plumes, the variation of the surface reflectivity of the test sample had very little effect on the cooling process.