In an electrode combination for a radiation head for the generation of electromagnetic radiation comprising an anode means having a tip end component and a cathode means, the tip end component comprising a material able to facilitate, in response to a predetermined pulse voltage applied between the anode means and cathode means, the generation of electromagnetic radiation, the improvement wherein the electrode combination comprises a trigger electrode, the tip end component, the cathode means and the trigger electrode being spaced apart from each other by a respective predetermined distance.