Ultrafast laser ablation of copper by GHz bursts
- PDF / 1,881,087 Bytes
- 7 Pages / 595.276 x 790.866 pts Page_size
- 92 Downloads / 204 Views
Ultrafast laser ablation of copper by GHz bursts Chung‑Wei Cheng1 · Jinn‑Kuen Chen2 Received: 28 March 2020 / Accepted: 24 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The ablation of copper, using a 10 GHz burst ultrafast laser with a wavelength of 1030 nm, a pulse duration of 1 ps, a variable total laser fluence, and a number of sub-pulses per burst, is investigated theoretically. A two-temperature model with an extended Lorentz–Drude model for dynamic optical properties is used to simulate the melting and ablation process. Due to the heat accumulation from the preceding pulses, multipulse laser ablation could be advantageous over a single pulse. Moreover, the ablation performance can be maximized by properly selecting the pulse number, separation time, and energy in a laser burst. The numerical result shows that the present prediction is in fairly agreement with existing experimental result. Under the same total laser fluence of 32 J/cm2, a 10 GHz burst laser with an optimized 128 sub-pulse can significantly enhance the ablation depth, 4.2 times that a single pulse does. It is found that the optimized ablation depth is a linear function of the total fluence of ultrafast laser bursts. Keywords Ultrafast laser · GHz burst · Two-temperature model
1 Introduction Ultrafast lasers have been applied in the internal modification of transparent material and surface structuring of opaque material because of their high peak power intensity [1] and minimal heat-affected zone (HAZ) [2]. The repetition rates of the ultrafast laser source usually range from kHz to MHz, and recently to GHz. When processing a metal using an ultrafast laser with a kHz repetition rate, phase explosion is one of the ablation mechanisms, and the overheated liquid metal relaxes explosively (or sputters) into a mixture of vapors that is immediately ejected from the bulk metal [3, 4]. When processing a metal by an ultrafast laser with MHz bursts, the heat accumulation effect and obvious HAZ can be found in the process since the sub-pulse separation time (1 μs for 1 MHz) is usually much shorter than the effective cooling time (i.e. tens of μs) of the metal [5].
* Chung‑Wei Cheng [email protected] 1
Department of Mechanical Engineering, National Chiao Tung University, No. 1001, Ta Hsueh Road, Hsinchu 30010, Taiwan
Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA
2
When a laser source has ultrafast GHz burst characteristics, the pulse duration and the repetition rate for the subpulses in the bursts are ultrafast (ps or fs) and GHz, respectively. Recently, numerous experiments on material ablation using ultrafast lasers with GHz bursts have been presented for metals [6–8] and silicon [9]. The sub-pulse laser fluence of each pulse considered is usually below the ablation threshold. It is interesting that the cool material ablation can occur when the separation time of the sub-pulses within a burst, e.g. 1 ns for 1 GHz, is less than the thermal relaxation t
Data Loading...
