Dependence of silicon ablation regimes on fluence during ultrafast laser irradiation

Abstract

Models and experiments were developed to study femtosecond laser ablation of silicon using 800 nm, 40 fs pulses with fluences ranging from 0.5 to 35 J/cm 2 . At low fluences, ablation was found to occur due to bubble formation and splashing within the melt layer. At higher fluences, it was found that the ablation depth exceeded the melt layer depth due to shockwave ablation. The variation in ion flux and ion velocity was also studied both experimentally and theoretically. It was found that the variation in ion flux is mainly dependent on the variation in the average charge state, with only a small variation in the total number of ions above ∼1.5 J/cm 2 . Comparisons between the theoretical and experimental ion flux showed that higher charge state ions received greater portion of the laser energy compared with lower charge state ions.

Characteristics of Ions Emission from Ultrashort Laser Produced Plasma

“…This is followed by a second regime at a higher laser fluence (> 4 J/cm 2 ), described by a slow ion flux increase rate. The trend in the ion flux is in a good agreement with previous experiements2122. It should be emphasized that the IC signal is sensitive to the charge not to the number of ions.…”

“…The maximum ion charge, Q max , that can be ejected from a target can be estimated by assuming that all atoms, n i , lie in a volume defined by laser spot size on target, S , and depth defined by optical skin depth, l s , given by 21 where ω pe , ω, and v eff are electron plasma frequency, laser frequency and effective collision frequency, respectively, will be ionized. So Q max can be expressed as 22. The ion emission was found to follow certain angular distribution given by equation 42324.…”

Особенности Наноструктурирования Поверхности Кремния В Результате Ее Сверхбыстрого Нагрева Фемтосекундным Лазерным Импульсом В Воде

“…При этом линейная зависимость глубины абляционного кратера, полученного на воздухе (рис. 2, а), от плотности энергии в диапазоне F 0 = 0.2−1.9 J/cm 2 ранее также наблюдалась в работах [14][15][16]. На рис.…”