Heat Transfer in Metal Films Irradiated by Combined Nanosecond Laser Pulse and Femtosecond Pulse Train

Abstract

Heat transfer in a copper film irradiated by a femtosecond (fs) laser pulse train and by an integrated dual laser beam of a nanosecond pulse with a fspulse train was studied using the semi-classical two-temperature model. The critical point model with three Lorentzian terms was employed to characterize transient optical properties for the laser energy deposition. The effects of pulse number and separation time on the thermal response were investigated. The results showed that with the same total energy in a fs-pulse train, more pulses for shorter separation time, e.g., 1 ps, and fewer pulses for longer separation time, e.g., 100 ps, can achieve higher lattice temperature. For a dual laser beam, the lattice temperature can be increased by setting the pulse separation time as short as possible, e.g., 1 ps.

Modelling thermal energy transfer in a femtosecond pulsed laser ablation of metal using a coupled spring-mass oscillator

“…where T T l l F J = and T T e e F J = , with T F the Fermi temperature of the metal. For copper, the quantities T F , χ, and η are equal to 8.16 × 10 4 K, 377Wm −1 K −1 , and 0.139 respectively [20,21]. Figure 1(c) shows the electron thermal conductivity obtained with T l = 3000 K. The lattice thermal conductivity, is small compared to the electron thermal conductivity and is taken to be 1% of the k eq of copper [21].…”

“…Proper implementation of TTM requires the use of accurate optical and thermal properties of the material [8,[17][18][19]. For example, the optical properties are governed by the dielectric function described by the Drudecritical point model [8,13,20]. Thermal properties have complicated dependence in temperature.…”

“…Thermal properties have complicated dependence in temperature. Electron thermal conductivity are dependent to electron and lattice temperature [20,21], while electron heat capacity and electron-phonon coupling factor are dependent to electron density of states and Fermi-Dirac distributions [10,17]. These topics are complicated for undergraduate students beginning to do research in fs-PLA because they are usually encountered in advanced undergraduate or graduate-level courses.…”