Measuring the velocity of fragments produced by high-repetition-rate nanosecond laser pulses; A Technique to visualize the fragments for laser decontamination

小菅 淳  ; 安東 航太*; 山本 恵輔*; 中嶋 隆*

Kosuge, Atsushi; Ando, Kota*; Yamamoto, Keisuke*; Nakajima, Takashi*

During laser decontamination of metal surfaces an in-situ technique to probe the dynamics of fragments far from the target is highly desired to efficiently collect them. Along this line we develop an optical technique to measure the velocity of fragments produced by high-repetition-rate nanosecond laser ablation of a metal target. By performing the laser scattering measurements at the oblique angle for the fragments at about 20-120 mm height above the stainless steel target (SUS304) during laser ablation with different pulse durations (15-200 ns) at the repetition rate of 200 kHz, we find that the fragments are classified into two velocity groups. The velocity of fast fragments is in the range of 0.1-0.7 m/s, depending on the height and pulse duration, while that for the cloud-like slow fragments is always about 0.05-0.1 m/s at any height for any pulse duration. Our results elucidate the long-term dynamics of ablated fragments during laser decontamination with a high-repetition-rate laser system.