CC BY
21LM-PS-1
Numerical simulations of energy relaxation in molybdenum thin films upon irradiation by femtosecond and picosecond laser pulses
K. Hlinomaz1,2, Y. Levy1, T.J. Y. Derrien1, N.M. Bulgakova1
1HiLASE Centre, Institute of Physics of the Czech Academy of Sciences, Dolni Brezany, Czech Republic
2Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Department of Physical Electronics, Praha, Czech Republic
Laser processing of thin films can be employed in electronic component manufacturing and in photovoltaics [1]. However, the control of the process remains delicate due to the high number of phenomena that are taking place in the film. These are dependent on the film thickness, on the choice of substrate, and on the laser wavelength, energy and pulse duration. In addition, several modifications mechanisms can play a role in the modification of the film and/or of the substrate via oxidation [2], melting, ablation via phase explosion [3, 4] or spallation [5]. As a result, both optical and thermal phenomena are contributing to dynamics of the energy absorption, an interplay that can be addressed by numerical modeling. In particular, subtle effects such as transient change of optical properties, rapid electron excitation, thickness-dependent electron-phonon collision rate [6], and stress generation can induce important macroscopic consequences. In view of achieving a better control of laser modification of thin films, more efforts are required in the development of theoretical and numerical descriptions.
In this work, we investigate the energy absorption and subsequent melting of a thin film of molybdenum in contact with a substrate via numerical simulations. The role of the fused silica (resp. soda-lime glass) substrates was investigated for irradiation using short laser pulses of 200 fs (resp. 10 ps) duration. For this purpose a numerical code based on two-temperature model (TTM) was developed. After ensuring the energy conservation of the numerical solver, melting threshold fluences were computed and compared with experimental data on femtosecond and picosecond irradiation [7, 8]. The numerical results well repeated the experimental literature, and enable the possibility to perform further predictions. In addition, the applicability of the thin-film reflectivity model to the case of metals will be discussed.
References
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[3] N. M. Bulgakova, A. V. Bulgakov, Appl. Phys. A, 73, 199-208 (2001).
[4] M. V. Shugaev et al., in Advances in the Application of Lasers in Materials Science, Springer, 274, 107-148 (2018).
[5] C. Wu, L. V. Zhigilei, Appl. Phys. A, 114, 11-32 (2014).
[6] K. Sokolowski-Tinten et al., New J. Phys. 17, 113047 (2015).
[7] S.-S. Wellershoff et al., Appl. Phys. A 69, S99-S107 (1999).
[8] M. Domke et al, Phys. Proc. 56, 1007-1014 (2014).
