Ablation suppression of a titanium surface interacting with a two-color double-pulse femtosecond laser beam

The suppression of ablation rate on a titanium surface irradiated by a double-pulse beam with a two-color laser was experimentally investigated with time delays of Delta t = 0-700 ps. The double pulse beam consists of 800 nm with 150 fs pulse and 400 nm with > 150 fs pulse. The fundamental-pulse fluence F-800 is kept below the ablation threshold (F-800th = 0.108 J/cm(2)), while the second harmonic pulse fluence F-400 is above the ablation threshold (F-400th = 0.090 J/cm(2)). The ablation rate of titanium is clearly suppressed to 2.39 nm per pair with a time delay of Delta t = 200 ps. This ablation rate corresponds to one-third of the 7.3 nm/pulse for only the first pulse beam, but it corresponds to about one-half of the one-color double-pulse irradiation. Ablation suppression with a two-color double-pulse beam is more pronounced compared to that for a one-color double pulse beam, which may be due to the shorter optical penetration length of the first pulse.