We report on an experimental study on the formation of structures caused by surface-tension-driven instability of a molten chromium layer generated by a single KrF laser pulse of nanosecond duration. The molten metal layer is formed in a confined configuration in a 500 nm thick Cr film encapsulated between a glass substrate and a quartz cover plate. The large lateral thermal gradient ∇ Ty generates a surface tension gradient, which causes the formation of instabilities on a liquid Cr film with a very high aspect ratio, =13 000, and of a low Prandtl number of Pr∼0.01. Two types of patterns were observed, the low and high wave-number wavylike instabilities, inclined left and right with respect to the direction of ∇ Ty, respectively. As the laser energy increases from 38 to 100 mJ, the inclination angle of the waves alternates, indicating transitions between the right and left inclined structures, and vice versa. The analysis shows that the formation of inclined wavy structures occurs because the ratio W of the Rayleigh number Ra and the Marangoni number Ma (W=Ra/Ma) takes values W>1. The oscillation of inclined waves is governed by the Biot number, which decreases from the intermediate values of Bi∼49 to the low values Bi∼3-4, as the energy of the laser pulse is increased.
ASJC Scopus subject areas
- Physics and Astronomy(all)