The instantaneous measurement of both ablation front displacement and removal rate during ultrafast laser microdrilling is demonstrated by on line sensing technique based on optical feedback interferometry in both unipolar and bipolar semiconductor laser. The dependence of laser ablation dynamics on pulse duration, energy density and working pressure has been investigated, thus allowing a significant advancement of the basic understanding of the ultrafast laser-material interactions. Moreover, the detection system results high-sensitive, compact, and easily integrable in most industrial workstations, enabling the development of real-time control to improve ablation efficiency and quality of laser micro-machining processes. © 2013 The Authors.