Experimental evidence on photo-assisted O− ion production from Al2O3 cathode in cesium sputter negative ion source. - Tarvainen, O.; Kronholm, R.; Laitinen, M.; Reponen, M.; Julin, J.; Toivanen, V.; Napari, M.; Marttinen, M.; Faircloth, D.; Koivisto, H.; Sajavaara, T. (Journal of Applied Physics, 2020)