Drilling of Copper Using a Dual-Pulse Femtosecond Laser

Abstract

Abstract:The drilling of copper using a dual-pulse femtosecond laser with wavelength of 800 nm, pulse duration of 120 fs and a variable pulse separation time (0.1-150 ps) is investigated theoretically. A one-dimensional two-temperature model with temperature-dependent material properties is considered, including dynamic optical properties and the thermal-physical properties. Rapid phase change and phase explosion models are incorporated to simulate the material ablation process. Numerical results show that under the same total laser fluence of 4 J/cm 2 , a dual-pulse femtosecond laser with a pulse separation time of 30-150 ps can increase the ablation depth, compared to the single pulse. The optimum pulse separation time is 85 ps. It is also demonstrated that a dual pulse with a suitable pulse separation time for different laser fluences can enhance the ablation rate by about 1.6 times.

Review on Experimental and Theoretical Investigations of Ultra-Short Pulsed Laser Ablation of Metals with Burst Pulses

“…As will be summarized in the following, both effect signal enhancement from the irradiated plume as well as the development of less deep craters are mutually dependent. Many experimental [ 7 , 8 , 14 , 16 , 19 , 57 , 58 , 59 , 66 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 ] and numerical [ 9 , 10 , 12 , 54 , 93 , 115 , 116 , 117 , 118 , 119 ] studies have been performed since the first observations about metal ablation with ultra-short double pulses were published. The following paragraphs summarize the findings to provide an overview of the effects involved in ultra-short double pulse laser ablation.…”

Ablation of Copper Metal Films by Femtosecond Laser Multipulse Irradiation

“…The numerical simulations were carried out for copper films irradiated by single and multipulse femtosecond laser irradiation with varying fluence, number of pulses and separation times. The choice of copper as a target and these specific parameters of the laser was to be able to compare our results with those available in the literature [15,16,29]. Figure 1 shows the calculated reflectivity R and absorption coefficient α, from Equations (11) and (12), as a function of temperature at an 800-nm wavelength.…”

Micromachining of Invar Foils with GHz, MHz and kHz Femtosecond Burst Modes

“…This is due to the fact that the hot area around the central peak does not have sufficient time to diffuse further into the material until the next pulse arrives, as described by Ilday et al [18]. Subsequently, this should lead to larger ablated volumes (as is predicted for the case of copper [23,35]) and a lower thermal damage threshold. However, we speculate that this situation may not always be achievable and could be material-dependent (different for melting, non-melting materials).…”

“…In addition, a train of pulses can alter the properties of the material as the sequence of pulses impinges on the sample, i.e., if the temporal separation is short enough that the heat does not diffuse away until the second pulse within the burst arrives, the heat can start to build up locally in the impinged region. In this case, given the right conditions, the reflectivity of the metal can decrease from >95% (reflection at room temperature for the first pulse) to <80% (for the trailing pulse) if two pulses are separated by~100 ps [23]. The penetration depth of light is also altered, which may reduce thermal damage and ablate more material per unit of energy [24], especially when considering deep craters.…”