Weinvestigatethenonlinearresponseofterahertz(THz)metamaterialperfectabsorbersconsistingofelectricsplitringresonatorsonGaAsintegratedwithapolyimidespacerandgoldgroundplane.Theseperfectabsorbersonbulksemi-insulatingGaAsarecharacterizedusinghigh-fieldTHztime-domainspectroscopy.Theresonancefrequencyredshifts20GHzandtheabsorbanceisreducedby30%astheincidentpeakfieldisincreasedfrom30to300kV/cm.ThenonlinearresponsearisesfromTHzfielddriveninterbandtransitionsandintervalleyscatteringintheGaAs.ToeliminatetheFresnellossesfromtheGaAssubstrate,wedesignandfabricateaflexiblemetamaterialsaturableperfectabsorber.Theabilitytocreatenonlinearabsorbersenablesappealingapplicationssuchasopticallimitingandself-focusing.
