凝聚態(tài)光物理學(xué)

凝聚態(tài)光物理學(xué)第1頁，課件共14頁，創(chuàng)作于2023年2月引言:光學(xué)過程的分類，光學(xué)系數(shù)，復(fù)折射率與復(fù)介電常數(shù)，光學(xué)材料(絕緣晶體，半導(dǎo)體，玻璃，金屬，高分子材料等)，凝聚態(tài)物質(zhì)光學(xué)性質(zhì)的特征(對稱性，電子能帶，晶格振動，態(tài)密度，局域態(tài)和集體激發(fā)等)，微觀模型。光在凝聚態(tài)物質(zhì)中傳播的經(jīng)典理論:光在稠密光學(xué)介質(zhì)中的傳播，偶極振子模型，色散理論，光學(xué)各向異性:雙折射。帶間吸收:帶間躍遷,直接躍遷的躍遷幾率，直接帶隙半導(dǎo)體的帶邊吸收，間接帶隙半導(dǎo)體的帶邊吸收，帶邊以上的帶間吸收，吸收譜的測量，光探測材料與器件。激子:激子的概念，自由激子，外場中的自由激子，高密度的自由激子，弗侖克爾激子發(fā)光:固體中光的發(fā)射，帶間發(fā)光，光致發(fā)光，電致發(fā)光。量子阱與量子點:量子限制結(jié)構(gòu)，半導(dǎo)體量子阱的結(jié)構(gòu)與制備，電子能級，光的吸收與激發(fā)，量子限制斯塔克效應(yīng)，光發(fā)射，量子阱子的帶間躍遷，Bloch振子，量子點。自由電子:Plasma反射率,自由載流子電導(dǎo)，金屬，摻雜半導(dǎo)體，Plasmon。高分子材料:高分子材料簡介，共軛分子的電子態(tài)，高分子光譜，芳烴共軛聚合物，有機光電子學(xué)。發(fā)光中心:電子—聲子相互作用，色心，離子晶體中的順磁雜質(zhì)，固體激光器與放大器，發(fā)光材料。聲子:紅外活性聲子，極性晶體紅外反射與吸收，極化激元，極化子，非彈性光散射，聲子壽命。非線性光學(xué):非線性極化率張量，光學(xué)非線性的物理起源，二階非線性效應(yīng)，三階非線性效應(yīng)。光子晶體和光學(xué)微腔:光子能帶，光子晶體的構(gòu)成，光學(xué)微腔，腔量子電動力學(xué)簡介。第2頁，課件共14頁，創(chuàng)作于2023年2月Chapter1Introduction1.1Classificationofopticalprocesses

ReflectionPropagationTransmissionOpticalmediumOpticalmediumrefractiveindex

n()=c/v()

Snell’slawabsorption~resonanceluminescence~spontaneousemissionelasticandInelasticscatteringnonlinear-opticsPropagation第3頁，課件共14頁，創(chuàng)作于2023年2月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4頁，課件共14頁，創(chuàng)作于2023年2月1.3ThecomplexrefractiveindexanddielectricconstantComplexrefractiveindex

:extinctioncoefficientWhereComplexdielectricconstant

Therelationshipbetweentherealandimaginarypartsoftwocoefficients:For

weaklyabsorbingmedium,isverysmall,Thereflectivity(normalincidence):Inthetransparentregionofmaterial:isverysmall,and2arenegligible,onemayconsideronlytherealpartsofnand;Intheabsorptionregion,oneneedtoknowboththerealandimaginarypartsofnand.第5頁，課件共14頁，創(chuàng)作于2023年2月1.4Opticalmaterials1.41CrystallineinsulatorsandsemiconductorsTransparencyrange,theindexmaybetakentoberealwithnoimaginarycomponent(approximatelyconstantn=1.77)R=0.077,henceT=(1-R)2=0.85PhononabsorptionorlatticeabsorptionDuetoabsorptionbyboundelectronsFundamentalabsorptionedge,isdeterminedbythebandgap.Theopticalpropertiesofsemiconductorsaresimilartothoseofinsulators,expectthattheelectronicandphonictransitionsoccuratlongerwavelengths.Itstransparencyrangeliesoutsidethevisiblespectrum,soithasadarkMetallicappearance.第6頁，課件共14頁，創(chuàng)作于2023年2月1.4Opticalmaterials1.41CrystallineinsulatorsandsemiconductorsMaterialscantakeonnewpropertiesbycontrolleddopingwithopticallyactivesubstance.Transmissionspectrumofruby(rubyAl2O3With0.05%Cr3+)comparedtosapphire(pureAl2O3).Thethicknessesofthetwocrystalswere6.1mmand3.0mm,respectivelyTheprincipleofdopingopticallyactiveatomsintocolourlesshostsisemployedextensivelyinthecrystalsusedforsolidstatelasers.Atypicalexampleistherubycrystal.RubiesconsistofCr+3ionsdopedintoAl2O3.Inthenaturalcrystals,theCr+3ionsarepresentasimpurities,butinsyntheticcrystals,thedopantsaredeliberatelyintroducedincontrolledquantitiesduringthecrystalgrowthprocess.第7頁，課件共14頁，創(chuàng)作于2023年2月1.4Opticalmaterials

1.4.2GlassMosttypesofglassesaremadeofsilica(SiO2)withotherchemicals.Insulator,allthecharacteristicfeaturescrystallineinsulators,thetransrangefromaround200nmtobeyond2000nm;Smallabsorptionandscatteringlosses;nchangesbylessthan1%overthewholevisiblespectralregion;Chemicalsarecommonlyaddedtosilicaduringthefusionprocesstoaltertherefractiveindexandtransmissionrange;Stainedglassandcolourglassfilteraremadebyaddingsemiconductorswithgapsinvisiblespectralregion.第8頁，課件共14頁，創(chuàng)作于2023年2月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9頁，課件共14頁，創(chuàng)作于2023年2月Whatthedifferenceisbetweencondensedmatterandatomicormolecularopticalphysics?

1.5.1Crystalsymmetry

*

longrangetranslationalorder

Electronicbands,delocalizedstates,……

*

pointgroupsymmetry

Neumann’sprinciple

Themeasurableproperty

pointgroupsymmetry

Anymacroscopicphysicalpropertymusthaveatleastthesymmetryofthecrystalstructure

Opticalanisotropy:birefringence,nonlinearopticalcoefficient……1.5Characteristicopticalphysicsinthecondensedmatter

CrystalsymmetryElectronicbandsVibronicbandsThedensityofstatesDelocalizedstatesandcollectiveexcitations第10頁，課件共14頁，創(chuàng)作于2023年2月

1.5.1Crystalsymmetry

Opticalanisotropy:

Liftingofdegeneracies:Degeneracycanbeliftedbyreductionofthesymmetry

1.5CharacteristicopticalphysicsinthecondensedmatterSplittingoftheenergylevelsofafreeatombythecrystalfieldeffectdeterminedbythesymmetryclassofthecrystal.ThesplittingIscausedbytheinteractionoftheorbitalsofTheatomswiththeelectricfieldsofthecry-stallineenvironment.Opticaltransitionbetweenthesecrystal-fieldspiltlevelsofenoccurinthevisibleregion,andcausethematerialtohaveeveryinterestingpropertiesthatarefoundinthefreeatoms.第11頁，課件共14頁，創(chuàng)作于2023年2月

1.5.2Electronicbands

1.5CharacteristicopticalphysicsinthecondensedmatterAstheatomsarebroughtclosertogethertoformthesolid,theirouterorbitalsbegintooverlapwitheachother.Theseoverlappingorbitalsinteractstrongly,andbroadbandsareformed.Theelectronicstateswithinthebandsaredelocalizedandpossessthetranslationalinvarianceofthecrystal.Bloch’stheoremstatesthatthewavefunctions:whereuk(r)isafunctionthathastheperiodicityofthelattice.Eachelectronicbandhasadifferentenvelopefunctionuk(r)

1.5.3VibronicbandsThebandarisesfromthecouplingofdiscreteelectronicstatetoacontinuousspectrumofvibrationalmode.Thiscontrastwiththeelectronicbandthatarisesfrominteractionbetweenelectronicstatesofneighbouringatoms.第12頁，課件共14頁，創(chuàng)作于2023年2月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