LASER TRIGGERING OF ELECTRIC BREAKDOWN IN LIQUIDS

Electric breakdown in semihomogeneous geometries has been studied in n -hexane and transformer oil using a laser triggering method for fields far below the spontaneous breakdown field. The method uses a laser-pr oduced plasma to initiate the breakdown. Strong self focusing in the l iquids was limited by increasing the numerical aperture of the laser b eam to > 0.20 prior to focusing. Electrical breakdown could be trigger ed at fields as low as 50 kV/cm in transformer oil and 25 kV/cm for n- hexane. The time lags are between 30 and 200 mus, depending on voltage , liquid, and gap size. Current and light emission measurements of the prebreakdown phenomena are presented and a model for the triggering p rocess is proposed.