Perhaps a UV laser diode can be used to create a discharge path.

http://docs.google.com/viewer?a=v&q=cache:cd1oegEVudgJ:handle.dtic.mil/100.2/ADA239988+uv+laser+atmospheric+ionization&hl=en&gl=us&pid=bl&srcid=ADGEESgjOl0GGEmwvQ-6ZfOro5asXjo0-nIKc63KNzA0qW3kTZDxBrIZ2_pwreI7lcj5rYjZ_5qpk9xxImm0hY5Qd6fiC3C5WElGcgLxDJ_AFiDF6Y1KkDpiGGWivkYidb6Tnz75aUDX&sig=AHIEtbSCFn_MRuuJw7Rl9wX4FKW7KigHcw

http://iopscience.iop.org/1367-2630/4/1/361/fulltext?ejredirect=migration

http://www.physlink.com/Education/AskExperts/ae289.cfm?CFID=27051700&CFTOKEN=d0f6bd9f55f01b69-99BECBE6-15C5-EE01-B9DC2C18D812B2A2

Gus
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