CC BY
17LM-O-18
Picosecond-laser-induced damage and ablation of gold in water: Effects of the water layer thickness
O. Gatsa1, A. V. Bulgakov12
1-HiLASE Centre, Institute of Physics of the Czech Academy of Sciences, Za Radnici 828, 25241 Dolni
Brezany, Czech Republic
2- S.S. Kutateladze Institute of Thermophysics SB RAS, Lavrentyev ave. 1, 630090 Novosibirsk, Russia
oleksandr.gatsa@hilase. cz
Pulsed laser ablation in liquids (PLAL) is a very attractive technique for surface nanostructuring allowing fabrication of surface structures for various materials in a simple and controllable way at low laser fluences [1]. PLAL is also considered as an efficient promising alternative to the chemical methc for synthesis of colloidal nanoparticles [2] The PLAL process is very complicated and its understanding is a key step in optimization of applications of the technique. Laser-induced damage and ablation thresholds (DTs and ATs) are important parameters offering references for modeling. However, the threshold determination for PLAL conditions is not as straightforward as for the air environment and , e.g., for gold, the literature provides contradictory data for the thresholds, both higher and lower than the corresponding air values [3-5].
In this work, we have investigated damage and ablation of gold irradiated in water by picosecond pulses of a PHAROS laser (1030-nm wavelength, 6 ps pulse duration). The size and morphology of the irradiation spots produced under single -shot and multi-shot irradiation conditions are analyzed using microscopy methods and the DTs and ATs are determinedThe main attention is paid to the effect of thi thickness of the water layer (in the range 2-30 mm) and the results are compared with those obtained ii air (Fig. 1). The DTs and ATs in water are found to be lower than the corresponding values in air (app. 1.2 and 1.9 J/cm2, respectively) being weakly dependent on the water depth. It is demonstrated thatself-focusing of the laser beam during its propagation in water plays an important role under the considered conditions even at low fluences, near the DT, and its contribution increases with the water layer thickness. It is also found that at a relatively high fluence, in the range of 6-10 J/cm2 (depending on the water depth), there is an abrupt change in the ablation regime resulting in a strong decrease of the damage area and in a decrease of the ablation area as compared to the air behavior. This threshold-like transition to a different ablation regime is explained by manifestation of another non -linear effect, scattering of the laser beam by plasma produced due to the optical water breakdown. Influences of the surface reflectivity change of the target immersed in water and of the cavitation bu bble on ps -laser-induced damage and ablation of gold in water are discussed.
Fig. 1. Optical images of spots on the gold surface produced by single ps-laser pulses in air (a) and in water of the depth of 5 mm (b) and 20 mm (c) at a peak fluence at the surface of 3 J/cm2. The damage (outer) and ablation (inner) regions are clearly seen.
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