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凝聚态光物理学第一页,共十四页,编辑于2023年,星期日引言:光学过程的分类,光学系数,复折射率与复介电常数,光学材料(绝缘晶体,半导体,玻璃,金属,高分子材料等),凝聚态物质光学性质的特征(对称性,电子能带,晶格振动,态密度,局域态和集体激发等),微观模型。光在凝聚态物质中传播的经典理论:光在稠密光学介质中的传播,偶极振子模型,色散理论,光学各向异性:双折射。带间吸收:带间跃迁,直接跃迁的跃迁几率,直接带隙半导体的带边吸收,间接带隙半导体的带边吸收,带边以上的带间吸收,吸收谱的测量,光探测材料与器件。激子:激子的概念,自由激子,外场中的自由激子,高密度的自由激子,弗仑克尔激子发光:固体中光的发射,带间发光,光致发光,电致发光。量子阱与量子点:量子限制结构,半导体量子阱的结构与制备,电子能级,光的吸收与激发,量子限制斯塔克效应,光发射,量子阱子的带间跃迁,Bloch振子,量子点。自由电子:Plasma反射率,自由载流子电导,金属,掺杂半导体,Plasmon。高分子材料:高分子材料简介,共轭分子的电子态,高分子光谱,芳烃共轭聚合物,有机光电子学。发光中心:电子—声子相互作用,色心,离子晶体中的顺磁杂质,固体激光器与放大器,发光材料。声子:红外活性声子,极性晶体红外反射与吸收,极化激元,极化子,非弹性光散射,声子寿命。非线性光学:非线性极化率张量,光学非线性的物理起源,二阶非线性效应,三阶非线性效应。光子晶体和光学微腔:光子能带,光子晶体的构成,光学微腔,腔量子电动力学简介。第二页,共十四页,编辑于2023年,星期日Chapter1Introduction1.1Classificationofopticalprocesses
ReflectionPropagationTransmissionOpticalmediumOpticalmediumrefractiveindex
n()=c/v()
Snell’slawabsorption~resonanceluminescence~spontaneousemissionelasticandInelasticscatteringnonlinear-opticsPropagation第三页,共十四页,编辑于2023年,星期日1.2OpticalcoefficientsCoefficientofreflectionorreflectivity(R):
R=reflectedpower/incidentpowerTransmissionortransmissivity(T):
T=transmittedpower/incidentpowerR+T=1Refractiveindex(n):Absorptioncoefficient()=-(dI/dz)/I(z);Beer’slaw:isstrongfunctionoffrequencyLuminescenceTheatomjumpstoanexcitedstatebyabsorptionofaphoton,thenrelaxestoanintermediatestate,beforere-emittingaphotonbyspontaneousemissionasitfallstothegroundstate.Thephotonemittedhasasmallerenergythantheabsorbedphoton.ThereductioninthePhotonenergyiscalledtheStokesshift.Scattering
Variationofnofthemediumonalengthscalesmallerthantheofthelight
N:thenumberofscatteringcentres/V;
S:scatteringcross-section;
=NSRayleighscattering:
第四页,共十四页,编辑于2023年,星期日1.3ThecomplexrefractiveindexanddielectricconstantComplexrefractiveindex
:extinctioncoefficientWhereComplexdielectricconstant
Therelationshipbetweentherealandimaginarypartsoftwocoefficients:For
weaklyabsorbingmedium,isverysmall,Thereflectivity(normalincidence):Inthetransparentregionofmaterial:isverysmall,and2arenegligible,onemayconsideronlytherealpartsofnand;Intheabsorptionregion,oneneedtoknowboththerealandimaginarypartsofnand.第五页,共十四页,编辑于2023年,星期日1.4Opticalmaterials1.41CrystallineinsulatorsandsemiconductorsTransparencyrange,theindexmaybetakentoberealwithnoimaginarycomponent(approximatelyconstantn=1.77)R=0.077,henceT=(1-R)2=0.85PhononabsorptionorlatticeabsorptionDuetoabsorptionbyboundelectronsFundamentalabsorptionedge,isdeterminedbythebandgap.Theopticalpropertiesofsemiconductorsaresimilartothoseofinsulators,expectthattheelectronicandphonictransitionsoccuratlongerwavelengths.Itstransparencyrangeliesoutsidethevisiblespectrum,soithasadarkMetallicappearance.第六页,共十四页,编辑于2023年,星期日1.4Opticalmaterials1.41CrystallineinsulatorsandsemiconductorsMaterialscantakeonnewpropertiesbycontrolleddopingwithopticallyactivesubstance.Transmissionspectrumofruby(rubyAl2O3With0.05%Cr3+)comparedtosapphire(pureAl2O3).Thethicknessesofthetwocrystalswere6.1mmand3.0mm,respectivelyTheprincipleofdopingopticallyactiveatomsintocolourlesshostsisemployedextensivelyinthecrystalsusedforsolidstatelasers.Atypicalexampleistherubycrystal.RubiesconsistofCr+3ionsdopedintoAl2O3.Inthenaturalcrystals,theCr+3ionsarepresentasimpurities,butinsyntheticcrystals,thedopantsaredeliberatelyintroducedincontrolledquantitiesduringthecrystalgrowthprocess.第七页,共十四页,编辑于2023年,星期日1.4Opticalmaterials
1.4.2GlassMosttypesofglassesaremadeofsilica(SiO2)withotherchemicals.Insulator,allthecharacteristicfeaturescrystallineinsulators,thetransrangefromaround200nmtobeyond2000nm;Smallabsorptionandscatteringlosses;nchangesbylessthan1%overthewholevisiblespectralregion;Chemicalsarecommonlyaddedtosilicaduringthefusionprocesstoaltertherefractiveindexandtransmissionrange;Stainedglassandcolourglassfilteraremadebyaddingsemiconductorswithgapsinvisiblespectralregion.第八页,共十四页,编辑于2023年,星期日ThemolecularmaterialsareheldtogetherbytheweakvandeWaalsbonds,whereasthemoleculesareheldtogetherbystrongcovalentbonds.Theopticalpropertiesofmaterialsaresimilartothoseoftheindividualmolecules;Saturatedcompounds:compoundswhichdonotcontainanyfreevalence(alltheelectronsaretightlyheldintheirbonds),andaretransparentinthevisible,absorbintheinfraredandultraviolet(insulatorcrystals);Conjugatedmolecules(bezeneC6H6):Theelectronsformlargedelocalizedorbitalscalledorbitalswhichspreadoutacrossthewholemolecule,thereforearelesstightlyboundthantheelectronsinsaturatedmolecules.Themoleculeswithvisibleabsorptionalsotendtoemitstronglyatvisiblefrequencies(semiconductors);Absorptionspectrumofthepolyfluorene-basedpolymersF8.ConjugatedpolymerssuchasF8luminescestronglywhenelectronsarepromotedintotheexcitedstatesofthemolecule.Thelumi-nescenceisStokesshiftedtolowerenergycomparedtoabsorption,andtypicallyoccursinthemiddleofthevisiblespectralregion.Theemissionwavelengthcanbetunedbysmallalternationtothechemicalstructureofthemolecularunitwithinthepolymers.Thepropertyhasbeenusedtodeveloporganiclightemittingdevicestocoverthefullvisiblespectralregion.1.4Opticalmaterials
1.4.4Molecular(largeorganicmolecules)Materials第九页,共十四页,编辑于2023年,星期日Whatthedifferenceisbetweencondensedmatterandatomicormolecularopticalphysics?
1.5.1Crystalsymmetry
*
longrangetranslationalorder
Electronicbands,delocalizedstates,……
*
pointgroupsymmetry
Neumann’sprinciple
Themeasurableproperty
pointgroupsymmetry
Anymacroscopicphysicalpropertymusthaveatleastthesymmetryofthecrystalstructure
Opticalanisotropy:birefringence,nonlinearopticalcoefficient……1.5Characteristicopticalphysicsinthecondensedmatter
CrystalsymmetryElectronicbandsVibronicbandsThedensityofstatesDelocalizedstatesandcollectiveexcitations第十页,共十四页,编辑于2023年,星期日
1.5.1Crystalsymmetry
Opticalanisotropy:
Liftingofdegeneracies:Degeneracycanbeliftedbyreductionofthesymmetry
1.5CharacteristicopticalphysicsinthecondensedmatterSplittingoftheenergylevelsofafreeatombythecrystalfieldeffectdeterminedbythesymmetryclassofthecrystal.ThesplittingIscausedbytheinteractionoftheorbitalsofTheatomswiththeelectricfieldsofthecry-stallineenvironment.Opticaltransitionbetweenthesecrystal-fieldspiltlevelsofenoccurinthevisibleregion,andcausethematerialtohaveeveryinterestingpropertiesthatarefoundinthefreeatoms.第十一页,共十四页,编辑于2023年,星期日
1.5.2Electronicbands
1.5CharacteristicopticalphysicsinthecondensedmatterAstheatomsarebroughtclosertogethertoformthesolid,theirouterorbitalsbegintooverlapwitheachother.Theseoverlappingorbitalsinteractstrongly,andbroadbandsareformed.Theelectronicstateswithinthebandsaredelocalizedandpossessthetranslationalinvarianceofthecrystal.Bloch’stheoremstatesthatthewavefunctions:whereuk(r)isafunctionthathastheperiodicityofthelattice.Eachelectronicbandhasadifferentenvelopefunctionuk(r)
1.5.3VibronicbandsThebandarisesfromthecouplingofdiscreteelectronicstatetoacontinuousspectrumofvibrationalmode.Thiscontrastwiththeelectronicbandthatarisesfrominteractionbetweenelectronicstatesofneighbouringatoms.第十二页,共十四页,编辑于2023年,星期日1.5.4ThedensityofstatesThisisdefinedas:NumberofstatesintherangeE
(E+dE)=g(E)dE.g(E)isworkoutinpractice:
g(E)=g(k)·dk/dE
ThiscanbeevaluatedfromknowledgeoftheE-krelationshipforelectronsorphonons.1.5.5Delocalizedstatesandcollectiveexcitationsphonon:thecollectiveexcitationoflatticevibration;exciton:formedfromdelocalizedelectronsandholesinsemiconductors;plasmon:formedfromfreeelectronsinmetalsanddopedsemiconductors;……manyopticaleffectsrelatedtothese……1.5.6Microscopicmo
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