Linear　polarization　effects　on　laser　drilling　were　investigated　by　the　use　of　a　picosecond　laser　system.　It　was　observed　that　the　exit　shapes　of　stainless　steel　were　placed　perpendicular　to　the　direction　of　polarization.　According　to　theoretical　analysis,　the　main　factor　that　determines　the　exit　hole　shape　is　the　difference　between　R　(s)　and　R　(p).　When　this　gap　is　large　enough,　the　bulges　on　the　exit　hole　will　be　easily　observed.　Inversely,　when　the　gap　is　small,　bulges　can　be　barely　spotted　on　the　exit　hole.　This　is　further　confirmed　by　comparative　experiment　and　calculation　conducted　on　a　copper　sheet.　(C)　2013　The　Japan　Society　of　Applied　Physics