We present a novel technique for measurement of the temporal material modification caused by highly repeating femtosecond laser oscillator systems. Time lapse measurements show the nonlinear tissue alteration such as change of refractive index caused by a focused single femtosecond laser pulse in water within the first picoseconds till seconds. A digital-holographic system was used with either continuously or femtosecond pulsed illumination to obtain quantitative data of optical path length difference (OPL). OPL can cause following laser pulses in changing its focusing behavior. Temporal measurement of the material modification improves knowledge of medical treatment modalities such as ocular surgeries.