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Adhi Harmoko S
LCD
Nature wave of light
Polarization
Liquid Crystal Display (LCD)Liquid Crystals are unpolarized in the absence of an external voltage, and will easily transmit light. When an external voltage is applied, the crystal become polarized and no longer transmit; they appear dark
Ray Approximation in Geometric Optics
Wave frontWave front usually refer to simply as a wave
All the pointss along the wave forming the wave crest
Ray : A line drawn in the direction of motion, perpendicular to the wave front
Reflection
Specular Reflection Diffuse Reflection
Reflection and TransmissionThe law of reflection: the angle of reflection equals the angle of incidance
ri θθ =
Double Reflection
RefractionWhen any wave strikes a boundary
Some of energy is reflected
Some of energy is transmitted or absorbed
Different velocity
The index of refraction is defined
as the speed of light in vacuum
divided by the speed of light in
the medium.
constantsinsin
==i
r
i
r
vv
θθ
vc
n =
Snell's LawSnell's Law relates the indices of refraction n of the two media to the directions of propagation in terms of the angles to the normal.
2
1
sinsin
nn
i
r =θθ
Light Propagation Through a Slab
12
12 sinsin θθ
nn
=
21
23 sinsin θθ
nn
=
112
1
1
23 sinsinsin θθθ ==
nn
nn
h
2cosθh
x =
αsinxd =
21 θθα −=
( )212
sincos
θθθ
−=h
d
d
hx
θ2 α
θ1
Dispersion and Prisms
( )λnn =
angle of deviation
Measuring n Using a Prism
22Φ
=θ
22min
21δαθθ +
Φ=+=
21 sinsin θθ n=
⎟⎠⎞
⎜⎝⎛ Φ=⎟
⎠⎞
⎜⎝⎛ +Φ
2sin
2sin min n
δ
( )2sin2
sin min
Φ
⎟⎠⎞
⎜⎝⎛ +Φ
=
δ
n
Angle of Deviation
δ
α
θ1θ4 αθθδ −+= 41
Total Internal Reflection
°= 90sinsin 21 nn cθ
1
2sinnn
c =θ Only for n1 > n2
Critical Angle, θc
View From a Fish Eye
°=
===
8.48
752.033.11
sin1
2
c
c nn
θ
θ
For θ<θc: The fish sees above the water
For θ=θc : The fish sees the shoreline
For θ>θc : The fish sees the pond bottom
Polarization of Light WaveAn ordinary beam of light consists of a large number of waves emitted by the atoms of the light source.Each atom produces a wave having some particular orientation of the electric field vector E, corresponding to the direction of atomic vibration.The direction of polarization of each individual wave is defined to be the direction in which the electric field is vibrating.
PolarizationAn important and useful property of lightTransverse waves on a rope polarized
Place an obstacle containing slit in the path of the wave
A vertical polarized waves passes through
PolaroidObtaining plane polarized light from unpolarized light
Using crystal : tourmaline
Intensity of a plane polarized beam transmitted by polarizer
θ2cosoII =
Polarizer
Polarization EquationPada gelombang transversal, arah simpangan dapat ke segalaarah asal tegak lurus pada arah rambat .Karena gel EM merupakan gabungan gelombang transversal, maka arah arah simpangan medan listrik E dinyatakan sebagaiarah polarisasi gelombang EM.Secara umum komponen medan listrik E dapat dinyatakandalam bentuk sbb :
jtkzEitkzE
jEiEE
oyoyoxox
yx
ˆ)cos(ˆ)cos(
ˆˆ
αωαω +−++−=
+=
Type of polarization
Linier PolarizationBila αoy ‐ αox =0,πmaka proyeksi E terhadap bidang yang tegaklurus arah perambatan akan membentuk garis lurus
jtkzEitkzEE oyoxˆ)cos(ˆ)cos( ωω −+−=
Circular PolarizationBila αoy ‐ αox =±nπ/2, n=bil. ganjil maka proyeksi E terhadapbidang yang tegak lurus arah perambatan akan membentuklingkaran
jtkzEitkzEE oyoxˆ)sin(ˆ)cos( ωω −+−=
Fresnel's EquationsFresnel's equations describe the reflection and transmission of electromagnetic waves at an interfaceThat is, they give the reflection and transmission coefficients for waves parallel and perpendicular to the plane of incidence. For a dielectric medium where Snell's Law can be used to relate the incident and transmitted angles, Fresnel's Equations can be stated in terms of the angles of incidence and transmission.
Fresnel's EquationsThe reflection coefficients:
The transmission coefficients
Reflectance and transmittance
ti
i
i
t
nnn
E
ET
θθθcoscos
cos2
21
1
,
,
+==
⊥
⊥⊥
⊥⊥
⊥⊥
⊥
==
=⊥===
Tn
ntT
n
nt
RI
IrR
I
Ir
i
tII
i
tII
i
rII
IIi
IIrII
θθ
θθ
cos
cos
cos
cos
1
2
1
2
2
,
,2
,
,
1
1
=+=+
⊥⊥ tr
tr IIII
it
it
IIi
IIrII nn
nn
E
ER
θθθθ
coscos
coscos
21
21
,
,
+−
==ti
ti
i
r
nn
nn
E
ER
θθθθ
coscos
coscos
21
21
,
,
+−
==⊥
⊥⊥
it
t
IIi
IItII nn
n
E
ET
θθθcoscos
cos2
21
1
,
,
+==
Polarization by reflectionPhotograph of river
Allowing all light into camera lens
Using a polarizer
Fresnel's EquationsSudut Brewster terjadi saat RII=0 atau Er hanya terdiri dari E⊥
it
it
IIi
IIrII nn
nn
E
ER
θθθθ
coscos
coscos
21
21
,
,
+−
==ti
ti
i
r
nn
nn
E
ER
θθθθ
coscos
coscos
21
21
,
,
+−
==⊥
⊥⊥
22
1
sinsin
sinsin
θθ
θθ Pn == Pn θtan=
Derajat Polarisasi P
IP = intensitas cahaya yang terpolarisasi linierIa = intensitas cahaya alamiahGel terpolarisasi linier Imax=I dan Imin=0 maka P =1Gel terpolarisasi lingkaran Imax= Imin = Imaka P=0Gel terpolarisasi elips Imax < I < Imin
minmax
minmax
minminmax
minmax
2 IIII
IIIII
III
PaP
P
+−
=+−
−=
+=
Polarization by Double RefractionUnpolarized light incident on a calcite crystal splits into an ordinary (O) ray and an extraordinary (E) ray. These two rays are polarized in mutually perpendicular directions (drawing not to scale).
QuizTentukan persamaan gelombang EM terpolarisasi linear yang merambat pada arah y positif dengan simpangan membentuksudut 30o terhadap bidang YZ dan diketahui pada t=0 dan y=0 simpangan =0.Tentukan jenis polarisasi, arah rambat dan arah simpangandari persamaan dibawah ini :
Tentukan persamaan gelombang EM yang merambat padaarah z dengan amplitudo simpangan E0 polarisasi lingkaran
putar kanan, pada t=0 dan z=0 :E= E0 iPutar kiri, pada=t=0, z=0, E=E0 iPutar kanan pada t=0, z=0, E0x = ½ Eoy
jtkzitkzE ˆ)3
cos(8,0ˆ)3
cos(6,0πωπω +−++−=
QuizFungsi gelombang sebuah gelombang elektromagnetik sebagaiberikut :
Tentukan jenis polarisasi dan gambar sketsa gelombangnya!Suatu sinar datang (cahaya alamiah) datang dengan sudut 30 jatuh pada ke suatu media n = 1,5
Berapa persenkah bagian yang dipantulkanBerapa persenkah bagian yang diteruskanBila amplitudo gelombang awal E, carilah amplitudo gelombang refleksi dan transmisiBila sudut datang gelombang dirubah sehingga gelombang pantulnya terpolarisasi sempurna, carilah sudut datang gelombang sekarang
⎟⎠⎞
⎜⎝⎛ +++⎟
⎠⎞
⎜⎝⎛ ++−=
3cos 3
3cos ),(
πωπω tkyxEtkyzEtyE oo))