The invention provides a method for measuring in situ the amount of material removed by laser ablation with ultrashort laser pulses. The method relies on the geometrical information provided by the backscattered light from the ablating laser. The temporal structure of the backscattered laser light is used to provide an accurate measure for the depth of the ablated area, since the round-trip time for the short laser pulses uniquely determines the distance to the object under illumination. For femtosecond laser pulses a depth resolution of a few micrometers can be achieved. According to the invention, imaging of the backscattered light from a single ablating pulse provides all the information necessary to derive a cross-sectional profile across the ablated region.