Abstract
Currently, laser-induced structural modifications in optical materials have been an active field of research. In this paper, we reported structural modifications in the bulk of sapphire due to picosecond (ps) laser filamentation and analyzed the ionization dynamics of the filamentation. Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material. The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track. By increasing laser energy, the length of the damage and filamentary track appeared to increase. In addition, the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations, but no increase in the filamentary zone diameter was observed with increasing laser energy.
Highlights
Over the past several decades, ultrafast laser pulses have been used for the precise and highly localized modification in various optical materials
This work aimed to investigate the ionization mechanism of picosecond laser induced filamentation in sapphire which is with high refractive index
By tightly focusing laser pulses, free carriers generation and plasma formation led to two types of structural changes in the bulk of sapphire material namely: void like structure surrounded by cracks and filamentary tracks
Summary
Over the past several decades, ultrafast laser pulses have been used for the precise and highly localized modification in various optical materials These permanent structural modifications can be used for the development of three-dimensional integrated optical devices[1,2,3,4,5]. The change in the material structure occurs as a result of the dynamical balance between self-focusing due to the nonlinear Kerr effect and self-defocusing associated with the plasma formation which is called filamentation[1,2,3,6,7,8,9,10,11]. While using ultrafast laser pulses, it is essential to understand and control the initial laser-matter interaction and resulting free electrons generation for the development of new broad and promising applications
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