Abstract
Ablation of copper using multipulse femtosecond laser irradiation with an 800 nm wavelength and 120-fs pulse duration is investigated theoretically. A two-temperature model, which includes dynamic optical and thermal-physical properties, is considered. The numerical results of the material thermal response obtained by varying the pulse number, the separation times between pulses and laser fluences are presented. Our results show that the increasing of pulse number with a separation time less than the thermal relaxation time can dramatically enhance the lattice temperature without a noticeable increase in ablation depth. Therefore, we suggest that the vaporization rate can be augmented in comparison to the melting rate during the same single-phase explosion at the same total fluence where a fast heat accumulation effect plays an important role for cleaner ablation during micromachining.
Highlights
As the number of applications targeted at ultrafast laser processing increases, there is even greater need to grasp the physical phenomena involved in the laser-material interaction, in order to achieve better control and quality of the patterned features
We study the thermal response of a copper metal film irradiated by a single and a burst of femtosecond laser pulses using the Temperature Model (TTM) with dynamic thermal and optical properties
This considerable enhancement of temperature is attributed to the heat accumulation effects, which can be called the Fast Thermal Accumulation Effect (FTAE) because the separation time between pulses is less than the thermal relaxation time
Summary
As the number of applications targeted at ultrafast laser processing increases, there is even greater need to grasp the physical phenomena involved in the laser-material interaction, in order to achieve better control and quality of the patterned features. They found that under the same total fluence, a laser burst with a pulse separation time of 50 ps or longer than thermal relaxation time could significantly boost the ablation rate compared to the single pulse We believe this effect may be due to a series of phase explosion processes during the irradiation with different rates of superheated liquid, because the pulse separation time is longer than the electron-phonon relaxation time. In this regard, we propose a Fast Thermal Accumulation Effect (FTAE) induced by bursts with a short interpulse separation time lower than the thermal relaxation time, which can dramatically enhance the lattice temperature within the irradiated focal volume, reducing the energy dissipation into deeper material. The numerical results of thermal response and ablation depth generated by the multipulse femtosecond laser irradiation, having different pulse numbers and separation time, are presented and discussed
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