
April 24, 2014 17:29 PSP Book - 9in x 6in 03-Rashid-A.-Ganeev-c03
Low-Order Harmonic Generation in Nanosecond Laser Ablation Plasmas 75
the TH generation at longer delays. The reason for choosing inert
gases with increasing atomic size is to evidence the influence of
the collision diameter in the aggregation of species. The larger
size of Xe atoms favors the probability of collisions and therefore
the aggregation, resulting in a higher TH signal enhancement in
comparison with that observed under Kr. On the contrary, this
signal enhancement at longer delays due to the presence of heavier
particles was not observed under helium atmosphere (not shown).