The　activation　process　of　the　GaAs　negative　electron　affinity　(NEA)　photocathode　is　now　well　known.　Activation　supplemented　by　light　illumination　has　not　yet　been　reported.　In　this　work　we　have　investigated　the　effects　of　while　light　illumination　on　the　adsorption　and　desorption　of　Cs　and　02　on　the　GaAs(110)　surface　during　various　stages　of　activation　of　the　GaAs　NEA　photocathode.　Its　effects　on　photoemission　sensitivity,　emission　stability,　and　recovery　of　impaired　photoemission　have　also　been　observed.　It　is　suggested　that　the　incident　photons　would　produce　electron-hole　pairs　on　the　GaAs　surface.　Phonons　would　be　produced　in　recombination　of　the　electrons　and　holes　thus　produced.　Based　upon　the　above　supposition,　all　the　investigated　effects　are　explained　and　discussed.　©　1989,　American　Vacuum　Society.　All　rights　reserved.