Study on temporal and spatial distributions of Ba atoms in fluorescent lamp discharge using laser-induced florescence

A laser-induced fluorescence (LIF) technique was applied to the measurements of the temporal and spatial distributions of Ba atoms in the vicinity of the electrode of a fluorescent lamp operated at 60 Hz. Ground-state (6¹S₀) Ba atoms were excited to a 5¹P ₁ level (350.1 nm) by a frequency-doubled dye laser beam, and the subsequent fluorescence (5¹P₁-5¹D₂, 582.6 nm) was detected. Over a whole periodic time (16.67 ms), the density of the Ba atoms was found to have two peaks, and the number of Ba atoms emitted in the anode half-cycle was about twofold larger than that emitted in the cathode half-cycle. This difference between the Ba atoms emitted during the anode half-cycle and those emitted during the cathode half-cycle was studied for lamps with different gas pressures. Ba atoms were found to be emitted mainly from the hot spot of the filament electrode. It is suggested that the main factor for Ba atom emission from the electrode is not sputtering by ion bombardment but thermal evaporation.