Abstract
High-repetition-rate ultrafast pump-probe and terahertz spectroscopies were achieved by combining
time-stretching and time-encoding techniques. We used chirped probe pulses to map the temporal information
to the spectrum and observed its pump-induced change using a combination of a chirped fiber
Bragg grating and a photodiode. The repetition rate of the waveform acquisition is as high as 75 kHz,
which is limited by the repetition rate of the excitation laser. We applied the method to the observation
of ultrafast dynamics in the formation of laser-induced periodic surface structures (LIPSS) and laser ablation
in a phase change material, Ge2Sb2Te5 thin film. The observed pulse-to-pulse change of the ultrafast
dynamics during LIPSS formation reveals the importance of ultrafast processes for energy relaxation,
demonstrating promising capability of our proposed method.
