Terahertzwaves,sittinginthegapbetweenthemiddleinfraredandmillimeterwaveregions,areknownasthelastvacantareaoftheelectromagneticspectrumthathasnotquitebeenunderstoodandbroughtintoapplications.TheTerahertzregionhasbeenthefocusofresearchworldwidesinceearly1990s.Duetotheiruniquecharacteristics,Terahertztechnologieshaveawiderangeofapplications,suchashazarddetection,highspeeddatacommunications,radioastronomy,andbiomedicalimaging.