Trans-timescale imaging of deep-UV femtosecond laser ablation of dielectrics with time-resolved digital holographic microscopy

We present trans-timescale imaging of femtosecond DUV laser ablation of a glass substrate, driven by linear absorption, using time-resolved digital holographic microscopy spanning from sub-picoseconds to milliseconds. This method integrates two probe branches within a pump-probe digital holographic imaging system: a femtosecond probe pulse for capturing dynamics from sub-picoseconds to nanoseconds and a nanosecond pulse for nanosecond-to-millisecond observations. To enable high-precision complex-field imaging, we developed a stable common-path interferometer, achieving milli-radian-level phase precision. Using this system, we investigated the surface processing dynamics of a BK7 glass substrate, which has an absorption edge around 300 nm, induced by a 257-nm femtosecond pump pulse. Our measurements revealed dynamic variations in amplitude and phase images across the entire timescale, enabling the observation of subtle phase changes, such as crater rim formation and thermal diffusion. This new imaging system advances the fundamental study of femtosecond DUV laser processing of glass materials across multi-timescales.