Spatial chirp induced by the misaligned gratings and mirrors in a parallel grating pair pulse stretcher can significantly affect the performance of the output pulses. Firstly, a detailed analysis about the spatial chirp of the stretched pulses caused by the misalignments has been carried out using the ray tracing simulation method. According to the simulation results, an adjustment procedure has been summarized to accurately calibrate these misalignments. The proposed method has been successfully applied in a home-made chirped pulse stretcher. By measuring the output pulse with an imaging spectrometer, the results show the stretched pulse has a good linear temporal chirp and little spatial chirp, which demonstrates the good adjustment of the stretcher.

A single pulse diffraction method to probe the plasma column evolution of the air ionization induced by the femtosecond laser pulse has been proposed. By utilizing a linearly chirped pulse as the probe light, the spatiotemporal evolution spectrum of the plasma column can be acquired in a single measurement. A method based on the Fresnel diffraction integral is proposed to extract the evolution of the phase shift after the probe light is crossing through the plasma column. Results show that the plasma expands rapidly within 7 ps due to the ionization, and then reaches a steady state with a diameter of about 80 μm with the pump pulse energy of 1 mJ. Furtherly, the temporal profile of the free electron density and the refractive index in the plasma region were determined using the corresponding physical models. The single-shot method can be expected to broaden the way for detecting the dynamics of the femtosecond laser-induced plasma.

The shock etalon method with normal incidence is an effective method to extract the shocked dynamic parameters of transparent materials. In order to eliminate the sample surface reflection, additional efforts on the sample preparation are usually introduced, which may limit the application of the method. Here, we proposed a Brewster incidence method to carry out the shock compression experiment on transparent materials. By utilizing the p-polarized light as the probe pulse at Brewster incidence, the sample surface reflection can be directly eliminated, which consequently simplified the experiment preparations. The errors of the proposed method have been evaluated using a set of virtual experiments. The results show that the shocked dynamic parameters can be accurately and robustly retrieved even when the nominal refractive index of the sample deviates 0.01 from its true value, or the incident angle bias 0.33° from the Brewster angle. Finally, a set of shock compression experiments on a polycarbonate film sample are carried out, and shocked dynamic parameters, such as shock velocity, particle velocity, and shocked refractive index, are successfully measured, for demonstration.