1, (b) 0.25, and (c) 0.50 ms for 214 fs and 16-W average laser power. The repetition rate and dwell time affect the growth of nanotips in somewhat similar way since both control the number of laser pulses delivered to the target surface. After the breakdown of the target material

has started, it requires a certain number of pulses according to the repetition rate and dwell time to ablate the required amount Stem Cells inhibitor of target material into the plasma, as demonstrated in stages 1 to 3 in Figure 8. Before this point in time, the plume does not have enough monomers to start vapor condensation. Once the vapor condensation has started inside the plume, the vapor condensates begin to get deposited onto the hot target surface, as depicted in stage 3. If the machining is stopped little after reaching stage 3, there will not be any more incoming pulses that transfer energy to the plasma species to generate further turbulence. As a result, the plasma species start relaxing by cooling down and mixing with nitrogen gas molecules. The consequence of these phenomena will be that the pressure exerted due Smad cancer to the plasma species will be relieved and the internal pressure becomes much higher than the external pressure on the deposited plasma condensates due to the hot target surface. At the same time, the deposited condensates experience uneven cooling due to the random flow of nitrogen gas.

As a result, the deposited droplets have regions of high and low surface tension over their entire surface. As a result, the imbalance of pressure pushes the material out of the volume of deposited droplets from regions of low surface tension resulting in the formation of the stem for the nanotips, as depicted in the side figures of stage 3 in Figure 8. Figure 8 Schematic representation of the growth stages of plasma expansion and nanotips’ stem formation. The ablation mechanism somewhat changes from one repetition rate to BI 2536 chemical structure another due to the

selleck difference in threshold energy-per-pulse requirement. The incoming pulses also interact differently with plasma generated from previous pulses for each repetition rate. Thus, the nanostructures generated for even the same dwell time differ for different repetition rates, as seen in Figures 6 and 9. Figure 9 shows SEM images of the glass target irradiated with 4-, 8-, and 13-MHz repetition rates for a dwell time of 0.75 ms. For 8- and 13-MHz repetition rates, the number of nanotips produced is much less compared to 0.50 ms, as seen in Figures 6 and 7. Instead, the presence of many spherical micronanoparticles and molten droplets is observed. This phenomenon can better be understood from the stage 4 of the schematic representation depicted in Figure 8. When the irradiated spot is bombarded with too many pulses as in the case of high repetition rates and high dwell time, an excessive amount of material is added to the plasma.