Trans-timescale complex optical electric-field imaging for femtosecond laser processing of dielectric materials

We present time-resolved complex optical electric-field imaging of femtosecond laser ablation, covering ten orders of magnitude in timescales, from sub-picoseconds to milliseconds. This method integrates two probe branches in a pump-probe digital holographic imaging system: a femtosecond probe pulse for measuring dynamics from sub-picosecond to nanosecond and a nanosecond pulse from nanosecond to millisecond. We developed a stable common-path interferometer for complex-field imaging, achieving a phase precision of 1.5 mrad. Using this system, we investigated the surface processing dynamics of a BK7 glass substrate induced by a 257-nm femtosecond pump pulse. Our measurements revealed dynamic variations in amplitude and phase images over the entire timescale, allowing observation of subtle phase changes such as crater rim formation and thermal diffusion. This new imaging system advances the study of laser material processing across multi-timescales.