A unified model in the pulsed laser ablation process

Abstract

In this unified model, we introduce the electron-phonon coupling time (t ie ) and laser pulse width (t p ). For long pulses, it can substitute for the traditional thermal conduction model; while for ultrashort pulses, it can substitute for the standard twotemperature model. As an example of the gold target, we get the dependence of the electron and ion temperature evolvement on the time and position by solving the thermal conduction equation using the finite-difference time-domain (FDTD) method.It is in good agreement with experimental data. We obtain the critical temperature of the onset of ablation using the Saha equation and then obtain the theoretical value of the laser ablation threshold when the laser pulse width ranges from nanosecond to femtosecond timescale, which consists well with the experimental data.With the development and the application of the ultra-short high-power laser, the effect of non-Fourier thermal conduction in pulsed laser ablation is noted as remarkable [1] . Then the two-temperature models have been established to describe the new phenomenon [2][3][4] . But for the long-pulse laser, we still adopt the traditional thermal conduction model (TCM) [5][6][7][8] . As a result, it is a complicated question that there is no model suitable for the pulse width from nanosecond to femtosecond timescale.In this paper, we present a unified model that can describe the thermal conduction phenomenon as the laser pulse width ranges from nanosecond to femtosecond timescale.As an example of the gold target, we get the dependence of the electron and ion temperature evolvement on the time and position by solving the thermal conduction equation using FDTD method. It is in good agreement with the experimental data.Many experimental and theoretical studies demonstrate the presence of two different ablation mechanisms [9] : thermal ablation and non-equilibrium ablation. If the laser pulse duration (t p ) is more than the electron-phonon coupling time, a material can go through the thermal melting and subsequent thermal phenomenon, so called thermal ablation. If the pulse width is smaller than this time (t ie ), the ablation mechanism is called non-equilibrium ablation. Usually, the electronphonon coupling time (t ie ) is several picoseconds [10,11] .When the laser irradiates the surface of the target, the electron absorbs considerable laser energy firstly because the electron mass is far smaller than the ion mass. The electron energy increases sharply. At the same time, electrons exchange energy with each other by colliding. Then the electron subsystem reaches the thermal equilibrium after tens of femtoseconds. If the laser irradiates the target, the electron subsystem continues to absorb the laser energy. And its temperature increases continually. At the same time, the ion absorbs little energy. The ion temperature is almost unchanged. It induces the tremendous difference of the temperature between the ion and the electron subsystem. Therefore, there are eigen temperature of the electron subsystems (T e ) and...

Precisely Controlled Reactive Multilayer Films with Excellent Energy Release Property for Laser-Induced Ignition

“…The RMF modulation period had a straightforward effect on the laser-induced process. A laser ignition model combining the thermal conduction and mass-diffusion reaction [2, 34] was proposed to study the effect of the modulation period of the RMFs on the laser ignition. High-temperature plasma was produced by the laser ignited RMFs.…”

“…Therefore, the chemical reaction of the RMFs further increased the temperature. The thermal equilibrium ablation process and mass-diffusion reaction mechanism were analyzed by the equations of state [2, 16, 34]. The laser-induced temperature ( T lir ) of the RMFs is given as follows: …”