Through　femtosecond　laser　single-pulse　experiments,　we　investigated　the　influence　of　polarization　directions　(0°,　45°,　90°,　and　135°)　on　the　damage　threshold　of　x-cut　lithium　niobate　(LN)　crystals.　We　found　that　the　material　damage　threshold　exhibited　considerable　polarization　dependence,　with　the　damage　threshold　along　the　90°　polarization　direction　being　lower　than　those　in　other　polarization　directions.　Through　first-principles　calculations,　we　confirmed　that　tunneling　ionization　caused　by　the　femtosecond　laser　mainly　breaks　Nb—O　bonds.　Along　the　incident　polarization　angle　of　90°,　more　number　of　Nb—O　bonds　are　easily　broken,　thereby　reducing　the　damage　threshold　in　that　polarization　direction.　This　study　contributes　to　an　in-depth　understanding　of　the　ablation　of　ultrafast　lasers　on　LN　crystal　surfaces　and　has　an　important　reference　value　for　the　laser　preparation　of　functional　devices　on　LN　crystal　surfaces.　©　2024　Universitat　zu　Koln.　All　rights　reserved.