Femtosecond Ablation Dynamics Observed with Terahertz Radiation

Pulse-to-pulse time-domain waveforms of terahertz radiation emitted during laser ablation process were observed using a highly sensitive single-shot terahertz spectrometer using an echelon mirror. We observed the terahertz radiation with the peak electric field strength of 10 V/cm and found that the amplitude and the carrier-envelope phase (CEP) of the emitted terahertz pulses vary with increasing the excitation fluence. Because the changes of the waveforms are observed in the fluence range around the ablation threshold, we conclude that the terahertz radiation reflects the emission dynamics of electrons and ions from the surface. The results suggest that terahertz radiation is an important diagnostic to monitor the initial process of laser ablation.