The inventive device (10) can be used for tissue coagulation and/or tissue ablation. It comprises at least one electrode (16) that serves for generating a spark or plasma jet and is connectable to an electric source (20) for this purpose. The probe (11) is assigned to a measuring device (24) that emits and/or receives light in the proximity of the electrode (16) and determines the distance of the probe (11) from the tissue (36) and/or the tissue temperature and/or the composition of the influenced tissue (36). Preferably the measuring device (24) is operated synchronized with pulses or pauses of the pulse-pause-modulated radio frequency voltage (UHF) of the electrode (16) in order to simultaneously carry out the desired measurements during the operation of the instrument (11) and to feedback control the operation of the instrument (11) based on the gained measurement results.
