MoS_2,MoSe_2andWSe_2thinflakeswerefabricatedbythestandardmicromechanicalcleavageprocedures.ThethicknessandtheopticalcontrastoftheatomicthindichalcogenideflakesonSiO_2/Sisubstratesweremeasuredbyatomicforcemicroscopy(AFM)andspectroscopicellipsometer.Arapidandnondestructivemethodbyusingreflectionspectrawasproposedtoidentifythelayernumberof2DlayeredtransitionmetaldichalcogenidesonSiO_2(275nm)/Sisubstrates.Thecontrastspectraof2DnanosheetswithdifferentlayernumbersareinagreementwiththeoreticalcalculationsbasedonFresnel'slaw,indicatingthatthismethodprovidesanunambiguousandnondestructivecontrastspectrafingerprintforidentifyingsingle-andfew-layeredtransitionmetaldichalcogenides.Theresultswillgreatlyhelpinfundamentalresearchandapplication.
