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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A polarização da onda eletromagnética 101<<strong>br</strong> />
1,0<<strong>br</strong> />
0,5<<strong>br</strong> />
0,0<<strong>br</strong> />
-0,5<<strong>br</strong> />
θB<<strong>br</strong> />
θC<<strong>br</strong> />
ângulo (graus)<<strong>br</strong> />
ρσ<<strong>br</strong> />
0 15 30 45 60<<strong>br</strong> />
ρπ<<strong>br</strong> />
75 90<<strong>br</strong> />
Fig. 5.16 - Coeficiente de reflexão interna.<<strong>br</strong> />
= E exp i<<strong>br</strong> />
r r<<strong>br</strong> />
k.<<strong>br</strong> />
r −ω<<strong>br</strong> />
t = E exp<<strong>br</strong> />
i k x + k y −ω<<strong>br</strong> />
t<<strong>br</strong> />
{ ( ) } ( )<<strong>br</strong> />
{ }<<strong>br</strong> />
E o<<strong>br</strong> />
o<<strong>br</strong> />
x y<<strong>br</strong> />
(5.31)<<strong>br</strong> />
onde na última passagem usamos o fato que ao onda se propaga no plano<<strong>br</strong> />
r<<strong>br</strong> />
xy ( r = xî<<strong>br</strong> />
+ yjˆ<<strong>br</strong> />
). Note que kx<<strong>br</strong> />
= k senθ e ky<<strong>br</strong> />
= k cosθ são as projeções de<<strong>br</strong> />
k no plano xy. O módulo de k é (ω/c) n<<strong>br</strong> />
r<<strong>br</strong> />
1. No meio com índice n2, o<<strong>br</strong> />
campo elétrico pode ser escrito de maneira similar:<<strong>br</strong> />
r r<<strong>br</strong> />
E " = E"<<strong>br</strong> />
exp { i ( k"<<strong>br</strong> />
. r ωt<<strong>br</strong> />
) } E"<<strong>br</strong> />
exp{<<strong>br</strong> />
i ( k"<<strong>br</strong> />
x k "<<strong>br</strong> />
0 − = 0<<strong>br</strong> />
x + yy<<strong>br</strong> />
−ω<<strong>br</strong> />
t)<<strong>br</strong> />
} (5.32)<<strong>br</strong> />
sendo as projeções de k ” dadas por k<<strong>br</strong> />
r<<strong>br</strong> />
x” = k” senθ” e ky” = k” cosθ”, e seu<<strong>br</strong> />
módulo por k”= (ω/c)n 2. Lem<strong>br</strong>ando que n = n 2/n1, pela lei de Snell temos<<strong>br</strong> />
senθ = n senθ” e consequentemente:<<strong>br</strong> />
2<<strong>br</strong> />
2 2<<strong>br</strong> />
2 2<<strong>br</strong> />
ncosθ<<strong>br</strong> />
" = n 1−<<strong>br</strong> />
sen θ"<<strong>br</strong> />
= n −sen<<strong>br</strong> />
θ = i sen θ−<<strong>br</strong> />
n (5.33)<<strong>br</strong> />
Desta forma, a parte espacial da fase da onda fica:<<strong>br</strong> />
2 2<<strong>br</strong> />
( senθ<<strong>br</strong> />
x + i sen θ − n y)<<strong>br</strong> />
" "<<strong>br</strong> />
k x + k y = k<<strong>br</strong> />
(5.34)<<strong>br</strong> />
x<<strong>br</strong> />
Como i 2 = -1, o campo é dado por:<<strong>br</strong> />
E<<strong>br</strong> />
"<<strong>br</strong> />
y<<strong>br</strong> />
{ i ( k senθ<<strong>br</strong> />
x −ω<<strong>br</strong> />
t)<<strong>br</strong> />
}<<strong>br</strong> />
"<<strong>br</strong> />
= E exp(<<strong>br</strong> />
−αy)<<strong>br</strong> />
exp<<strong>br</strong> />
(5.35)<<strong>br</strong> />
0<<strong>br</strong> />
2 2<<strong>br</strong> />
onde . Note que a luz se propaga paralelamente à<<strong>br</strong> />
α = k sen θ−<<strong>br</strong> />
n<<strong>br</strong> />
interface, na direção do eixo x. Por outro lado, ela penetra no meio menos<<strong>br</strong> />
S. C. Zilio <strong>Óptica</strong> <strong>Moderna</strong> – <strong>Fundamentos</strong> e Aplicações