Óptica Moderna Fundamentos e aplicações - Fotonica.ifsc.usp.br ...
Óptica Moderna Fundamentos e aplicações - Fotonica.ifsc.usp.br ...
Óptica Moderna Fundamentos e aplicações - Fotonica.ifsc.usp.br ...
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Interferência 135<<strong>br</strong> />
ρ′ τE<<strong>br</strong> />
0 exp{<<strong>br</strong> />
i(<<strong>br</strong> />
k 2AB<<strong>br</strong> />
+ k 2BC<<strong>br</strong> />
− ωt)<<strong>br</strong> />
}<<strong>br</strong> />
2<<strong>br</strong> />
em C: Refletido: ( ρ ) τE 0exp{<<strong>br</strong> />
i(<<strong>br</strong> />
k 2AB<<strong>br</strong> />
+ k 2BC<<strong>br</strong> />
− ωt)<<strong>br</strong> />
}<<strong>br</strong> />
ρ′ ττ′<<strong>br</strong> />
exp{<<strong>br</strong> />
i(<<strong>br</strong> />
k AB + k BC − ωt)<<strong>br</strong> />
}<<strong>br</strong> />
por:<<strong>br</strong> />
Incidente: (6.31a)<<strong>br</strong> />
′ (6.31b)<<strong>br</strong> />
Transmitido: (6.31c)<<strong>br</strong> />
E0 2<<strong>br</strong> />
2<<strong>br</strong> />
A frente de onda é constituída pelos campos em C e C’, dados<<strong>br</strong> />
E<<strong>br</strong> />
C<<strong>br</strong> />
= ρ′ ττ′<<strong>br</strong> />
E 0 exp<<strong>br</strong> />
= ρ′ ττ′<<strong>br</strong> />
E exp<<strong>br</strong> />
0<<strong>br</strong> />
{ i [ k 2 ( AB + BC)<<strong>br</strong> />
− ωt<<strong>br</strong> />
] }<<strong>br</strong> />
{ i ( 2k<<strong>br</strong> />
2 AB−<<strong>br</strong> />
ωt<<strong>br</strong> />
) }<<strong>br</strong> />
{ i(<<strong>br</strong> />
k AC′<<strong>br</strong> />
− ωt)<<strong>br</strong> />
}<<strong>br</strong> />
(6.32a)<<strong>br</strong> />
E C′<<strong>br</strong> />
= ρE<<strong>br</strong> />
0 exp<<strong>br</strong> />
(6.32b)<<strong>br</strong> />
1<<strong>br</strong> />
onde AB = BC . Por outro lado, vemos que AB = d / cos θ'<<strong>br</strong> />
' e<<strong>br</strong> />
AC′<<strong>br</strong> />
= ACsen<<strong>br</strong> />
θ , implicando que A C′<<strong>br</strong> />
= 2d tgθ′<<strong>br</strong> />
′ senθ.<<strong>br</strong> />
Definimos:<<strong>br</strong> />
φ = AC′<<strong>br</strong> />
= 2dk<<strong>br</strong> />
tgθ''sen<<strong>br</strong> />
θ<<strong>br</strong> />
1<<strong>br</strong> />
φ<<strong>br</strong> />
2<<strong>br</strong> />
k1 1<<strong>br</strong> />
=<<strong>br</strong> />
2 2<<strong>br</strong> />
2<<strong>br</strong> />
k AB = 2dk<<strong>br</strong> />
/ cos θ''<<strong>br</strong> />
(6.33a)<<strong>br</strong> />
(6.33b)<<strong>br</strong> />
Podemos ainda obter através das equações de Fresnel que<<strong>br</strong> />
2<<strong>br</strong> />
ρ=− ρ′ e ττ′ = 1−ρ<<strong>br</strong> />
. Desta forma o campo elétrico total na frente de<<strong>br</strong> />
onda será:<<strong>br</strong> />
E<<strong>br</strong> />
total<<strong>br</strong> />
= E +<<strong>br</strong> />
0<<strong>br</strong> />
1<<strong>br</strong> />
E 2 = E [ e i 1 e i 2<<strong>br</strong> />
0 ρ φ + ρ′ ττ′<<strong>br</strong> />
φ ] exp{<<strong>br</strong> />
− iωt<<strong>br</strong> />
}<<strong>br</strong> />
[ i ( φ −ωt)<<strong>br</strong> />
] [ 1 − ( 1−<<strong>br</strong> />
ρ 2 ) exp{<<strong>br</strong> />
i(<<strong>br</strong> />
φ − ) } ]<<strong>br</strong> />
= ρE<<strong>br</strong> />
exp<<strong>br</strong> />
φ (6.34)<<strong>br</strong> />
de forma que a intensidade será proporcional a:<<strong>br</strong> />
1<<strong>br</strong> />
2 2<<strong>br</strong> />
{ 1+<<strong>br</strong> />
( 1−<<strong>br</strong> />
ρ ) [ ( 1−<<strong>br</strong> />
ρ ) − 2cos(<<strong>br</strong> />
φ − ) ] }<<strong>br</strong> />
2 *<<strong>br</strong> />
2 2<<strong>br</strong> />
E total E total.<<strong>br</strong> />
E total = ρ E0<<strong>br</strong> />
2 φ1<<strong>br</strong> />
= (6.35)<<strong>br</strong> />
Se tivermos trabalhando com vidros teremos ρ ~ 0,2 ⇒ ρ 2 = 0,04<<strong>br</strong> />
1− ρ2<<strong>br</strong> />
= 0,<<strong>br</strong> />
96<<strong>br</strong> />
⇒ ( ) ~ 1. Então:<<strong>br</strong> />
A diferença de fases é:<<strong>br</strong> />
[ 1 − cos ( φ − ) ]<<strong>br</strong> />
2 2 2<<strong>br</strong> />
E total 2ρ<<strong>br</strong> />
E 0<<strong>br</strong> />
2 φ1<<strong>br</strong> />
2<<strong>br</strong> />
= (6.36)<<strong>br</strong> />
S. C. Zilio <strong>Óptica</strong> <strong>Moderna</strong> – <strong>Fundamentos</strong> e Aplicações<<strong>br</strong> />
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