Abstract
In this dissertation, we report the experiment and results of single color and two color femtosecond ablation of Polymethylmethacrylate(PMMA). The ablation threshold of PMMA by fundamental () and second harmonic (2) of a femtosecond Ti:sapphire laser amplifier are 2.53 J/cm2 and 1.86 J/cm2 respectively. For two color ablation, we designed and built an in-line system. We studied the effect of relative phase between the two wavelengths on the ablation hole area. The pulses of two colors are overlapping in both time and spatial domain. When the polarizations of two color are parallel, the ablation hole area depends strongly on the relative phase between the fundamental and second harmonic beams. A modulation depth of (31%) in the ablated area was observed with a 2/ power ratio of 8%. This phenomenon could be explained by the dependence of ablation on multiphoton ionization rate, which is related to the synthesized waveform. We also found that when the 2/ power ratio becomes higher, the modulation depth or contrast of ablated holes becomes unclear. This characteristic could be explained as the two photon-ionization rate of the second harmonic beam of PMMA dominates over that of the fundamental beam which is due to three or four-photon ionization.