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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


Source:sciencedaily.com

• Aerosolcanabsorborsca*ersunlight,warmingeffectandcoolingeffect

• Theuncertaintyofaerosolmakesthetotales3matesolarge

• Aerosolisthekeytoclimatechange

Introduc3on

Interac3onbetweenlightandpar3cle


• Elas&csca(eringThewavelengthofthesca*eringisthesameasthatoftheincidentlight

• Inelas&csca(eringTheemi*edlighthasawavelengthdifferentfromthatoftheincidentlight

Reflec3onλ0

Incidentlightλ0

RamanλR

FluorescenceλF

Refrac3onλ0

Thermalemissionλj

Par3cle

Sca*eringλ0

Absorp3on

Fortheinterac3onofsolarradia3onwithatmosphericaerosols,elas3clightsca*eringistheprocessofinterest.

Introduc3on


Elas3cLightSca*ering

•  RayleighSca*ering– Spherical,small,non‐absorbing,.

•  MieSca*ering– Spherical,absorbing/non‐absorbing,nosizebound.

LordRayleigh GustavMieSource:Nobelprize.org

Introduc3on

LightSca*ering


•  Redirec3onofEMwavewhenencountersanobstacleornon‐homogeneity(Sca*eringAerosol).

•  ItisNOTasimplebounceofPhoton.Hahn,D.W.etal

Introduc3on

LightSca*ering


Threeparametersthatgovernthesca*ering:

1.Wavelengthλofincidentlight2.Sizeofthepar3cle,sizeparameter

3.thepar3cleop3calpropertyrela3vetothesurroundingmedium,refrac0veindex

CriteriaforRayleighRegimex<<1,or|m|x<<1

Introduc3on

RayleighTheory


Theory

 Assump&on:par3cleissmallcomparedtothewavelengthsothattheelectricfieldinsidethepar3cleduetoEMwaveisuniform.

Source:wikimedia

Auniformelectricfiledinsidethepar3cle

Hi

Ei

CoordinategeometryforRayleighandMiesca*ering,

Source:ipac.caltech.edu

 Rayleightheorydescribesthesca*eringofelectromagne3cradia3onbysmallsphericalpar3clesbasedonthedipolemoment �


RayleighTheory

p:dipolemomenta:par3cleradiusE0:incidentelectricfieldε:electricconstant

Source:MKerker

 Incidentoscilla3onelectricfiled:inducedoscilla3ondipolemoment

 Accelera3ngchargescanemitradiatetheoscilla3ondipoleswillradiateatthesamefrequencyastheappliedfieldinallthedirec3on

Bluesky

Theory

Bluesky&RedSunsets


• Day3meskylooksblueonaclearday• Theskylooksredatsunriseandsunset

Bluelightissca*eredmoreefficientlythanred

Why?

h*p://www.forbrf.lth.se/

Applica3on

Miesca*ering�


 Mietheorydescribesthesca*eringandabsorp3onofelectromagne3cradia3onbysphericalpar3clesthroughsolvingtheMaxwellequa3ons �

 KeyAssump*ons �

i)Par3cleisasphere;ii)Par3cleishomogeneous(thereforeitischaracterizedbyasinglerefrac&veindexm=n‐ikatagivenwavelength);�

Solu3onofMiesca*ering


Intensi3esofsca*eringradia3on Crosssec3ons

Fortunately,therearesomepeoplewhoenjoysolvingtheseequa3onsandsepngupcomputerprogramstocalculatetheresults.

 OverviewofMiesca(eringsolu&onforspheres:

•  BeginwithMaxwell’sequa3ons•  Deriveawaveequa3oninsphericalpolarcoordinates

•  Provideboundarycondi3onsatsurfaceofasphere

•  Solvethepar3aldifferen3alwaveequa3onfordependenceonr,θ, φ.

MieSca*eringCode


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


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�


Ex3nc3onefficiencyvssizeparameter(noabsorp3on):1)SmallinRayleighlimitQextx∝x4

2)LargestQextwhenpar3cleandwavelengthhavesimilarsize.3)Qext2ingeometriclimit(x∞).4)Oscilla3onsfrominterferenceoftransmi*edanddiffractedwaves.5)Periodinxofinterferenceoscilla3onsdependsontherefrac3veindex.Absorp3onreducesinterferenceoscilla3onsandkillsripplestructure.

SomehighlightsofMiesca(eringresults:�

ApplyMieSca*eringtoaerosolstudy�


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


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!


Whatcanthecodedo


Interac&veMieSca(eringCalculatorath*p://omlc.ogi.edu/calc/mie_calc.html

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