Expansion of laser-induced plume after the passage of a counter shock wave through a background gas
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S.I. : CURRENT STATE-OF-THE-ART IN LASER ABLATION
Expansion of laser‑induced plume after the passage of a counter shock wave through a background gas Akira Higo1 · Keita Katayama1 · Hiroshi Fukuoka2 · Takehito Yoshida3 · Tamao Aoki4 · Minoru Yaga5 · Ikurou Umezu4 Received: 15 October 2019 / Accepted: 18 March 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Double-pulsed laser ablation with two targets and lasers in a background gas is a method to form nanoparticle complex. Effects of pulse delay between two lasers on plume expansion dynamics are discussed. The germanium and silicon targets were set parallel to each other and irradiated by two YAG lasers. The germanium target was irradiated followed by irradiation of the silicon target with delay time, td. We found that the expansion distance of delayed silicon plume is enhanced for 2 µs ≤ td ≤ 50 µs, compared to that when only the silicon target is irradiated. For td = 200 µs, the expansion distance of delayed silicon plume is similar to that when only the silicon target is irradiated. We discuss the expansion dynamics of the delayed silicon plume based on the effect of the density distribution induced by the primary germanium plume. Our results indicate that the effect of primary germanium plume remains up to about td = 50 µs, and it disappears by td = 200 µs. Keywords Pulsed laser ablation · Shock wave · Plume expansion · Pulsed laser deposition
1 Introduction It is well-known that the pulsed laser ablation (PLA) in a background gas is one of the dry processes to prepare nanoparticles. The predominant feature of PLA is nonequilibrium temporal and spatial evolutions of the plume. Gas-phase plume changes to nanoparticles by collisional processes during the expansion in a background gas [1, 2]. The morphology of nanoparticle aggregates deposited on the substrate varies with PLA condition due to the temporal and spatial distribution of nanoparticles in the plume [3, 4]. The double-pulsed laser ablation (D-PLA) is a method to provide a new growth field of nanoparticles induced by the collision * Ikurou Umezu umezu@konan‑u.ac.jp 1
of two plumes [5–10]. The interaction of two laser-induced plumes is also important for laser-induced breakdown spectroscopy (LIBS). The enhancement of plume intensity by the interaction of two plumes is reported [11–14], and this technique is used to increase the detection limit of LIBS. Not only in the field of pulsed laser ablation [15–18], but the collision of expanding plasma is also important in many research fields. There are extensive reports from viewpoints of laboratory simulations of astrophysical plasmas, design of inertial confinement fusion Hohlraums, and so on [19–22]. We previously observed the backward motion of the plume due to the collision with the counter shock wave when two targets are irradiated simultaneously [6]. Many of the previous researches are discussed on the collision during the simultaneous plume expansion. Collision of the plume with delay will modify the growth and aggregatio
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