CC BY
23HiLASE-I-2
Numerical study of thermal dynamics and stress build-up in laser-induced periodic surface structures formation on metals and dielectrics
Y. Levy1, E.L. Gurevich2, N.M. Bulgakova1
1HiLASE Centre, Institute of Physics of the Czech Academy of Sciences, Dolni Brezany, Czech Republic
2Ruhr-Universitat Bochum, Applied Laser Technologies, Bochum, Germany
Laser-induced periodic surface structures (LIPSS) are believed to originate from a periodic deposition of laser energy, resulting from the interference between electromagnetic surface waves and the laser pulse itself [1]. From this periodic absorption of the laser light to the final morphology of LIPSS, different pathways of relaxation of the absorbed energy are conceivable that results in relocation of material with creation of periodic surface relief [2]. In this study, we wish to shed light on possible routes leading to the LIPSS formation.
The dynamics of temperature have been investigated numerically for the cases of irradiation of different materials by ultrashort linearly-polarized laser pulses with estimation of stress build-up. For this aim, a two-dimensional numerical code based on the two-temperature model has been developed. A modulation is introduced in the laser pulse spatial profile to reproduce the inhomogeneous deposition of energy [3] and the amplitude of the subsequent temperature modulation is followed at the surface of gold and fused silica. Change in optical properties during the laser pulse action are considered via the Drude model. In gold, dynamic optical response is conditioned by swift variation of the collision frequencies of electrons upon their heating while, in fused silica, charge-carriers excitation dynamics is simulated using the rate equation and the carrier density introduced into the optical model.
It has been found that perturbations of the temperature profile can remain substantial for several hundreds of picoseconds in the molten phase of gold in spite of its relatively high thermal conductivity. Change in optical properties also shows a significant effect on the dynamics of temperature modulation under the irradiation regimes above the material modification threshold. The thermal stresses, which can develop in the surface region of the irradiated materials, have been evaluated for our particular irradiation configuration.
References
[1] J.E. Sipe et al., Laser-induced periodic surface structure. I. Theory, Phys. Rev. B 27, 1141 (1983).
[2] S. Maragkaki et al., Wavelength dependence of picosecond laser-induced periodic surface structures on copper, Appl. Surf. Sci., 417, 88 (2017).
[3] Y. Levy et al., Relaxation dynamics of femtosecond-laser-induced temperature modulation on the surfaces of metals and semiconductors, Appl. Surf. Sci. 374, 157 (2016).
