Time-harmonic electromagnetic fields in chiral medium

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1、1.INTRODUCTIONAtthebeginningofthelastcentury,thephenomenonofopticalactivityincertainbiologicalandmineralsubstanceswasdiscoveredindependentlybyArago[1811]andBiot[1812,1815,1817].Condensedmattertheorieswerestillinembryonicstagesatthattime.Assuch,itisremarkablethatPasteur[1848,1850]interpretedBlot'sob

2、servationsbyimaginingthatthearrangementofatomswithinanopticallyactivematerialisasymmetricinhavinganon-superposablemirrorimage;i.e.,thisarrangementishandedorchiral.AnothertwentyoddyearshadtoelapseforPasteurtobevindicatedbythesimultaneousproposalsofthetetravalentcarbonatombyvan'tHoff[1874]andLeBel[18

3、74].Notonlydidthesediscoveriesrequiretheidentificationofthatpropertyoftheopticallyactivesubstanceswhichcausesrotationofpolarizedlight,buttheyalsoforcedthethenscientificestablishmenttoenquiremorevigorouslyintothenatureoflight.In1819,Fresnel[1866]hadbeenabletoshowthattheeffectsofpolarizedlightcouldbe

4、explainedbythehypothesisthatlightwasatransversewave.Withadvancesinelectromagneticfieldtheorywhichprovedthatlightwasindeedanelectromagneticwave,thefieldofstereochemistryexpandedradicallyandhasprovidedinsightsintothestructureofmoleculesand,indeed,intothenatureoflife.Foraninterestinghistoricaldevelopm

5、entofthisareainthe19thcentury,arecentreviewbyApplequist[1987]isrecommended.Achiralmediumischaracterizedbyeitheraleft-handednessoraright-handednessinitsmicrostructure.Asaresult,inachiralmediumleft-andright-circularlypolarized(LCPandRCP)fieldspropagatewithdifferentphasevelocities:thefieldwiththelatte

6、rpolarizationtravelingthrougharight-handedmediumfasterthantheleft-circularlypolarizedfield,andviceversa.Opticalactivity,whichisexhibitedbyamultitudeoforganicmoleculesatopticalfrequencies,isamanifestationofthenativechiralityofthesemolecules[Eyringetal1944;Charney1979;Barron1982].Thetwinphenomenaofci

7、rculardichroism(CD)andopticalrotatorydispersion(ORD)areobservedwhenalinearly-polarizedplanewavetravelsthroughasuspensionofchiralmolecules.ORDreferstotherotationoftheplaneofpolarizationofthetransmittedplanew