Improving the beam pointing and intensity stability of the third harmonic generated in air filament

Third harmonic generation (THG) by laser filamentation in gases is immune to the damage threshold and phase matching limit for UV and EUV pulse generation. Here, we report on the jitter measurements of the beam pointing and the intensity of the THG through filamentation with different repetition rates in air. The THG jitters are stronger at the high repetition rates (1 kHz) filaments. A technique of applying an external DC electric field on the filament was found to suppress the jitters. The beam pointing and intensity jitters of the 1 kHz THG from laser filament in air were reduced by about 1 fold with the extreme external electric field electric field applied on the filament. This technique provides a way to generate a stable, high repetition rate UV and EUV sources.