Femtosecond　laser　interference　is　a　promising　tool　for　micro-fabrication　and　micromachining　of　periodical　structures　on　the　surface　of　samples　or　inside　transparent　materials,　but　femtosecond　laser　pulses　are　very　hard　to　interfere　due　to　their　spectrum　widths　may　reach　to　several　tens　of　nanometers,　and　their　spectrum　widths　will　be　stretched　by　shorting　the　duration　according　to　the　Fourier　transform.　We　realized　two　25　fs　pulses　interference　and　encoded　micro-gratings　on　Au-Cr　thin　films　using　this　interference　pattern.　The　interference　patterns　of　two　laser　pulses　with　different　pulse　durations　in　sub-hundred　femtosecond　time　domain　were　calculated　to　explore　the　influence　of　pulse　durations　on　processing　qualities　of　encoded　micro-gratings.　The　results　show　that,　the　shorter　pulses　are　preferable　to　fabricate　micro-gratings　with　fine　resolution　on　intractable　materials,　and　longer　pulses　are　helpful　to　improve　encoding　efficiency　and　contrast　ratio　of　bright　&　dark　interfered　fringes.　The　differences　between　encoded　micro-gratings　on　Au-Cr　thin　film　using　these　interference　patterns　validated　our　analysis,　which　are　hardly　observed　when　pulse　duration　is　longer　than　100　fs　mainly　because　the　size　of　interfered　area　is　larger　than　the　focal　spots.　Moreover,　the　distance　between　two　focal　spots　also　has　been　chosen　to　identify　our　calculations,　and　the　experimental　results　are　agreement　with　the　calculations.