Wehaveexperimentallystudiedthemode-lockingdynamicsofapolarization-maintainingfigure-of-eightlaserwhichhasasemiconductoropticalamplifierasgainmedium.Self-startingmode-lockingatthefundamentalrepetitionrateof18MHzisobtainedatthelasingthreshold,andfurtherincreasingthebiascurrentleadstotheprogressiveemissionofadditionalopticalpulsesineachroundtripandeventuallytomode-lockedemissionatincreasinglyhighharmonicsofthefundamentalrepetitionrate,upto2.45GHz.Theintensityautocorrelationoftheamplifiedmode-lockedpulseshasafullwidthathalf-maximumdurationof382fs,whichcorrespondstoapulsedurationof247fs.