The dynamic process of intense 50 fs laser ablation of aluminum is investigated by ultrafast timeresolved microscopy. A stripe pattern preceding phase explosion is clearly seen in the shadowgraph of 1 ns time delay. Intermittent material ejections are observed within the ejected plume after 2.5 and 7 ns time delay, respectively, which may be attributed to the material response to the generation of an extremely strong thermoelastic wave. Similar processes are also recorded in the ablation of silicon and glass samples, except for the glass samples, the intermittent material ejections are not found.

The mutual transition dynamics between nonthermal and thermal dominant ablation processes is investigated in the hole-drilling and line-scribing experiments on aluminum samples with intense 50 fs to 24 ps laser pulses. It is found that a critical pulse width that separates the two different ablation regimes monotonically reduces with the increasing laser fluence. Theoretical analyses suggest that the complex interplay between photomechanical stress fragmentation and phase explosion could be responsible for these observations. A semiempirical transition law between the two ablation regimes is introduced, which is consistent with measured experimental data.

We present an experimental observation on spectrum evolution of femtosecond pulses in filamentation by introducing a hollow fiber as a probe and moving it along the filament. The results show that at a particular position of the filament, the pulse spectrum from the hollow fiber expands to its maximum, which corresponds to the shortest pulse duration existing in the filament. The influence of gas pressure on the spectrum broadening is also examined.

研究了由理想线偏振片和单轴双折射晶体波片组成的双折射滤光片倾斜放置时的二阶色散和三阶色散特性，包括波片厚度、光线入射角和光轴旋转角的变化对二阶和三阶色散的影响。 还给出了双折射滤光片的群延迟表达式，并就色散特性与GT干涉仪进行了详细比较。

The origin of the dominant pulse-shaping effects in a coupled-cavity mode-locked (CCM) KCl: Tl laser is described Inferences relating to pulse-profile detail have been deduced from spectral and temporal data that were recorded for a range of period-mismatch conditions for the main and control cavities of the CCM laser.