Inthispaper,theangularspreadoftheSAWbeamdiffractedbyBragggrating,denotedbyδθ1,isana-lysedbasedontheequationsofthedeflectionangleandthedeflectioneffciency.AparameterδθBisde-finedtoreferto"Braggangularspectrumwidth"ofthegrating.Theimportanceofthisparameterindis-tinguishingtheangularspreadrangeofthedeflectedbeamfordifferentregimesisdiscussedaswell.Itisshowfromtheanalysisthatifthespreadangleoftheincidentbeamlabelledwithδθincislargethanthe"Braggwitdthoftheangularspectrum"ofthegrating,thespreadangleδθ1ofthedeflectedbeamwillequaltoδθB;butiftheangularpergenceoftheincidentbeamislessthanδθB,thenδθ1=δθincExperimentally,fourkindsofsampleswithdifferentconfigurationsareinvestigatedbyopticalmethod,twoofwhichoperateintheregimeofδθinc<<δθBandtheotherscorrespondtothecaseintheregimeofδθinc>>δθB.Thewidthsoftheangularspreadoftheinciden
