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LightSca*eringbySmallPar3cles
MinZhongApr.2nd.2010
Outline
• Backgroundintroduc3on• Theory• Applica3on• Reference
PHY4422 2Lightsca*eringbySmallPar3cles
Haveyouseenanylightscatteringphenomenadaily?
Source:myskymom.com
AerosolandClimateChange
• Aerosol:suspendedpar3clesinatmosphere
• Size:typicalrange0.01~100um• Source:nature(90%)andhumanac3vi3es(10%)
PHY4422 Lightsca*eringwithPar3cles 3
Source:nasa.org
Introduc3on
AerosolandClimateChange
PHY4422 Lightsca*eringwithPar3cles 4
Source:sciencedaily.com
• Aerosolcanabsorborsca*ersunlight,warmingeffectandcoolingeffect
• Theuncertaintyofaerosolmakesthetotales3matesolarge
• Aerosolisthekeytoclimatechange
Introduc3on
Interac3onbetweenlightandpar3cle
PHY4422 Lightsca*eringwithPar3cles 5
• Elas&csca(eringThewavelengthofthesca*eringisthesameasthatoftheincidentlight
• Inelas&csca(eringTheemi*edlighthasawavelengthdifferentfromthatoftheincidentlight
Reflec3onλ0
Incidentlightλ0
RamanλR
FluorescenceλF
Refrac3onλ0
Thermalemissionλj
Par3cle
Sca*eringλ0
Absorp3on
Fortheinterac3onofsolarradia3onwithatmosphericaerosols,elas3clightsca*eringistheprocessofinterest.
Introduc3on
PHY4422 Lightsca*eringwithPar3cles 6
Elas3cLightSca*ering
• RayleighSca*ering– Spherical,small,non‐absorbing,.
• MieSca*ering– Spherical,absorbing/non‐absorbing,nosizebound.
LordRayleigh GustavMieSource:Nobelprize.org
Introduc3on
LightSca*ering
PHY4422 Lightsca*eringwithPar3cles 7
• Redirec3onofEMwavewhenencountersanobstacleornon‐homogeneity(Sca*eringAerosol).
• ItisNOTasimplebounceofPhoton.Hahn,D.W.etal
Introduc3on
LightSca*ering
PHY4422 Lightsca*eringwithPar3cles 8
Threeparametersthatgovernthesca*ering:
1.Wavelengthλofincidentlight2.Sizeofthepar3cle,sizeparameter
3.thepar3cleop3calpropertyrela3vetothesurroundingmedium,refrac0veindex
CriteriaforRayleighRegimex<<1,or|m|x<<1
Introduc3on
RayleighTheory
PHY4422 Lightsca*eringwithPar3cles 9
Theory
Assump&on:par3cleissmallcomparedtothewavelengthsothattheelectricfieldinsidethepar3cleduetoEMwaveisuniform.
Source:wikimedia
Auniformelectricfiledinsidethepar3cle
Hi
Ei
CoordinategeometryforRayleighandMiesca*ering,
Source:ipac.caltech.edu
Rayleightheorydescribesthesca*eringofelectromagne3cradia3onbysmallsphericalpar3clesbasedonthedipolemoment �
PHY4422 Lightsca*eringwithPar3cles 10
RayleighTheory
p:dipolemomenta:par3cleradiusE0:incidentelectricfieldε:electricconstant
Source:MKerker
Incidentoscilla3onelectricfiled:inducedoscilla3ondipolemoment
Accelera3ngchargescanemitradiatetheoscilla3ondipoleswillradiateatthesamefrequencyastheappliedfieldinallthedirec3on
Bluesky
Theory
Bluesky&RedSunsets
PHY4422 Lightsca*eringwithPar3cles 11
• Day3meskylooksblueonaclearday• Theskylooksredatsunriseandsunset
Bluelightissca*eredmoreefficientlythanred
Why?
h*p://www.forbrf.lth.se/
Applica3on
Miesca*ering�
PHY4422 Lightsca*eringwithPar3cles 12
Mietheorydescribesthesca*eringandabsorp3onofelectromagne3cradia3onbysphericalpar3clesthroughsolvingtheMaxwellequa3ons �
KeyAssump*ons �
i)Par3cleisasphere;ii)Par3cleishomogeneous(thereforeitischaracterizedbyasinglerefrac&veindexm=n‐ikatagivenwavelength);�
Solu3onofMiesca*ering
PHY4422 Lightsca*eringwithPar3cles 13
Intensi3esofsca*eringradia3on Crosssec3ons
Fortunately,therearesomepeoplewhoenjoysolvingtheseequa3onsandsepngupcomputerprogramstocalculatetheresults.
OverviewofMiesca(eringsolu&onforspheres:
• BeginwithMaxwell’sequa3ons• Deriveawaveequa3oninsphericalpolarcoordinates
• Provideboundarycondi3onsatsurfaceofasphere
• Solvethepar3aldifferen3alwaveequa3onfordependenceonr,θ, φ.
MieSca*eringCode
PHY4422 Lightsca*eringwithPar3cles 14
Year Name Authors Language Short description
1983 BHMIE Craig F. Bohren Matlab, Fortran Mie solution by a homogeneous
sphere
2002 MiePlot Philip Laven VB Solution for a number of wavelength
2003 Mie single Gareth Thomas IDL Solution for both single and populations of particle with
log-normal PSD
CodeforMiesca(eringbyasinglesphere
Year Name Authors Language Short description
1993 IFCS Thomas Kaiser Fortran Compute the scattered filed of sphere with 1 to 2 coatings
2004 M.Jonasz Fortran Compute parameters of single coated sphere
2003 L. Liu C Light scattering by a coated sphere
Codesforelectromagne&csca(eringbyalayeredsphere
Source:Wikipedia.org
Calculateop3calparameters
PHY4422 Lightsca*eringwithPar3cles 15
Par3clesizeRefrac3veindex,m(λ)
Forasinglesphericalpar3cle,theMietheorygivestheex3nc3on,sca*eringandabsorp3oncross‐sec3ons,thesca*eringamplitudesandphasematrix.
Mietheory
Sca*eringcrosssec3on,σsAbsorp3oncrosssec3on,σaEx3nc3oncrosssec3on,σe
(asafunc3onofapar3clesizeandwavelength)
Sca*eringcoefficient,σsAbsorp3oncoefficient,σaEx3nc3oncoefficient,σe
(asafunc3onofapar3clesizeandwavelength)
Mietheory
Miesca*ering�
PHY4422 Lightsca*eringwithPar3cles 16
Ex3nc3onefficiencyvssizeparameter(noabsorp3on):1)SmallinRayleighlimitQextx∝x4
2)LargestQextwhenpar3cleandwavelengthhavesimilarsize.3)Qext2ingeometriclimit(x∞).4)Oscilla3onsfrominterferenceoftransmi*edanddiffractedwaves.5)Periodinxofinterferenceoscilla3onsdependsontherefrac3veindex.Absorp3onreducesinterferenceoscilla3onsandkillsripplestructure.
SomehighlightsofMiesca(eringresults:�
ApplyMieSca*eringtoaerosolstudy�
PHY4422 Lightsca*eringwithPar3cles 17
UV/VisLight
FilterFilter
Detector
UV‐lamp
GC‐FID
SMPS
TempRH
Par3cles
2)UV/Visspectrometer
1)TeflonChamber
3)Nephelometer
1.Chamberexperimentpar3clesize,concentra3on2.UV/Visabsorp3oncoefficient,3.Nephelometerex3c3oncoefficient,3wavelength4.InputtheabovedataintoMiesca*eringcodeandfindouttherefrac3veindex(m)5.Comparethecomputed(m)tothemeasuredmmcanbemeasuredbytheelectronenergy‐lossspectroscopyusingTEMequippedwithaGatanTriDiemspectrometer(DuncanT.L.Alexander,etal.Science321,833,2008)
Applica3on
References
PHY4422 Lightsca*eringwithPar3cles 18
1. M. Kerker. The scattering of light and other electromagnetic radiation. Academic, New York. 1969. 2. H.C. van de Hulst. Light scattering by small particles. John Wiley & Sons, New York, 1957. 3. C.F. Bohren and D.R. Huffman. Absorption and scattering of light by small particles. John Wiley & Sons, New York, 1983. 4. http://plaza.ufl.edu/dwhahn/Diagnostic%20Tutorials.html 5.Willian C. Hinds. Aerosol Technology, John Wiley & Sons, New York, 1998. 6. John H. Seinfeld and Spyros N. Pandis. Atmospheric Chemistry and Physics. John Wiley & Sons, New York, 1997. 7. Benjamin Chu, Laser light scattering, Academic, New York, 1974.
Thankyou!
PHY4422 Lightsca*eringwithPar3cles 19
Whatcanthecodedo
PHY4422 Lightsca*eringwithPar3cles 20
Interac&veMieSca(eringCalculatorath*p://omlc.ogi.edu/calc/mie_calc.html