We investigate photo-ionization, energy deposition, plasma formation and the ultrafast optical breakdown in crystalline silicon irradiated by intense near-infrared laser pulses with duration $\tau \le$ 100 fs. The occurrence of high-intensity breakdown was established by the sudden increase of the absorbed laser energy inside the bulk, which corresponds to threshold energy fluence ${\Phi }_{th}>$ 1 J/cm${}^2$. The optical breakdown is accompanied by severe spectral broadening of the transmitted pulse. For the studied irradiation conditions, we find that the threshold fluence increases linearly with the increase of the pulse duration, while the corresponding laser intensity threshold decreases. The effect of the high plasma density on the stability of diamond lattice is also examined. For near threshold fluences, when about 5 % of valence electrons are promoted into the conduction band, the Si–Si bonds are softened and large Fermi degeneracy pressure arises (with pressure up to 100 kbar). The mechanical instability of the diamond lattice suggests that the large number of electron–hole pairs leads directly to ultrafast melting of the crystal structure.

我们研究了由具有持续时间的强近红外激光脉冲照射的晶体硅中的光电离、能量沉积、等离子体形成和超快光学击穿 $\tau \le$100 秒。高强度击穿的发生是由于体内吸收的激光能量突然增加而建立的，这对应于阈值能量注量${\Phi }_{吨H}>$ 1 焦耳/厘米${}^2$. 光学击穿伴随着传输脉冲的严重光谱展宽。对于研究的辐照条件，我们发现阈值能量密度随着脉冲持续时间的增加而线性增加，而相应的激光强度阈值降低。还研究了高等离子体密度对金刚石晶格稳定性的影响。对于接近阈值的能量密度，当大约 5% 的价电子被提升到导带时，Si-Si 键被软化并且产生大的费米简并压力（压力高达 100 kbar）。金刚石晶格的机械不稳定性表明大量电子-空穴对直接导致晶体结构的超快熔化。