Dynamics of ripple formation on silicon surfaces by ultrashort laser pulses in subablation conditions

An investigation of ultrashort pulsed laser--induced surface modification due to conditions that result in a superheated melted liquid layer and material evaporation are considered. To describe the surface modification occurring after cooling and resolidification of the melted layer and understand the underlying physical fundamental mechanisms, a unified model is presented to account for crater and subwavelength ripple formation based on a synergy of electron excitation and capillary wave solidification. The proposed theoretical framework aims to address the laser--material interaction in subablation conditions and thus the minimal mass removal in combination with a hydrodynamics-based scenario of the crater creation and ripple formation following surface irradiation with single and multiple pulses, respectively. The development of the periodic structures is attributed to the interference of the incident wave with a surface plasmon wave. Details of the surface morphology attained are elaborated as a function of the imposed conditions, and results are tested against experimental data.