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 ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
<strong>Óptica</strong> de cristais<<strong>br</strong> />
de propagação sˆ . O sistema formado por esta equação tem três equações<<strong>br</strong> />
homogêneas, que só tem solução não trivial se o seu determinante for<<strong>br</strong> />
igual a zero, ou seja:<<strong>br</strong> />
n<<strong>br</strong> />
2<<strong>br</strong> />
xx<<strong>br</strong> />
+ n<<strong>br</strong> />
n<<strong>br</strong> />
2<<strong>br</strong> />
s<<strong>br</strong> />
2<<strong>br</strong> />
y<<strong>br</strong> />
2<<strong>br</strong> />
n s s<<strong>br</strong> />
z<<strong>br</strong> />
2 ( s −1)<<strong>br</strong> />
s<<strong>br</strong> />
x<<strong>br</strong> />
x<<strong>br</strong> />
x<<strong>br</strong> />
n<<strong>br</strong> />
2<<strong>br</strong> />
yy<<strong>br</strong> />
n<<strong>br</strong> />
s<<strong>br</strong> />
+ n<<strong>br</strong> />
s<<strong>br</strong> />
2<<strong>br</strong> />
x y<<strong>br</strong> />
2<<strong>br</strong> />
y<<strong>br</strong> />
2<<strong>br</strong> />
n s s<<strong>br</strong> />
2 ( s −1)<<strong>br</strong> />
z<<strong>br</strong> />
y<<strong>br</strong> />
+ n<<strong>br</strong> />
2 ( s −1)<<strong>br</strong> />
= 0<<strong>br</strong> />
S. C. Zilio <strong>Óptica</strong> <strong>Moderna</strong> – <strong>Fundamentos</strong> e Aplicações<<strong>br</strong> />
n<<strong>br</strong> />
2<<strong>br</strong> />
zz<<strong>br</strong> />
n<<strong>br</strong> />
n<<strong>br</strong> />
s<<strong>br</strong> />
s<<strong>br</strong> />
2<<strong>br</strong> />
x z<<strong>br</strong> />
2<<strong>br</strong> />
sys<<strong>br</strong> />
z<<strong>br</strong> />
2<<strong>br</strong> />
z<<strong>br</strong> />
275<<strong>br</strong> />
(14.22)<<strong>br</strong> />
Desse determinante resulta uma equação biquadrada, cujas raízes<<strong>br</strong> />
fornecem quatro valores para n. Só iremos considerar as raízes positivas,<<strong>br</strong> />
uma vez que n é positivo por definição. Se usarmos como sistema de<<strong>br</strong> />
2<<strong>br</strong> />
referência os eixos dielétricos principais, que diagonalizam o tensor n t , a<<strong>br</strong> />
equação biquadrada terá uma forma mais simples. Usando novamente a<<strong>br</strong> />
eq. (14.8), temos:<<strong>br</strong> />
4 2<<strong>br</strong> />
An + Bn + C = 0<<strong>br</strong> />
(14.23)<<strong>br</strong> />
onde:<<strong>br</strong> />
2 2 2 2 2 2<<strong>br</strong> />
A = n s + n s + n s<<strong>br</strong> />
(14.24a)<<strong>br</strong> />
x<<strong>br</strong> />
x<<strong>br</strong> />
2 2 2 2 2 2 2 2 2<<strong>br</strong> />
( 1−<<strong>br</strong> />
s ) n n + ( 1−<<strong>br</strong> />
s ) n n + ( 1 s ) n n<<strong>br</strong> />
x<<strong>br</strong> />
y<<strong>br</strong> />
z<<strong>br</strong> />
y<<strong>br</strong> />
y<<strong>br</strong> />
y<<strong>br</strong> />
B = − (14.24b)<<strong>br</strong> />
2<<strong>br</strong> />
x<<strong>br</strong> />
x<<strong>br</strong> />
2<<strong>br</strong> />
y<<strong>br</strong> />
z<<strong>br</strong> />
2<<strong>br</strong> />
z<<strong>br</strong> />
z<<strong>br</strong> />
z<<strong>br</strong> />
C = n n n<<strong>br</strong> />
(14.24c)<<strong>br</strong> />
Resolvendo a eq. (14.23) encontramos os dois valores possíveis para n.<<strong>br</strong> />
Para se obter as componentes do campo elétrico, referentes a cada valor<<strong>br</strong> />
de n, basta substitui-lo na eq. (14.21).<<strong>br</strong> />
z<<strong>br</strong> />
14.4 Superfície normal<<strong>br</strong> />
Usando as eqs. (14.14) e (14.19) podemos escrever a eq. (14.17)<<strong>br</strong> />
na seguinte forma:<<strong>br</strong> />
⎛ωµε<<strong>br</strong> />
⎜<<strong>br</strong> />
⎜<<strong>br</strong> />
⎜<<strong>br</strong> />
⎝<<strong>br</strong> />
x<<strong>br</strong> />
− k<<strong>br</strong> />
k<<strong>br</strong> />
k<<strong>br</strong> />
y<<strong>br</strong> />
z<<strong>br</strong> />
k<<strong>br</strong> />
k<<strong>br</strong> />
2<<strong>br</strong> />
y<<strong>br</strong> />
x<<strong>br</strong> />
x<<strong>br</strong> />
− k<<strong>br</strong> />
2<<strong>br</strong> />
z<<strong>br</strong> />
ωµε<<strong>br</strong> />
y<<strong>br</strong> />
k<<strong>br</strong> />
− k<<strong>br</strong> />
k<<strong>br</strong> />
x<<strong>br</strong> />
z<<strong>br</strong> />
k<<strong>br</strong> />
k<<strong>br</strong> />
y<<strong>br</strong> />
2<<strong>br</strong> />
x<<strong>br</strong> />
y<<strong>br</strong> />
− k<<strong>br</strong> />
2<<strong>br</strong> />
z<<strong>br</strong> />
ωµε<<strong>br</strong> />
z<<strong>br</strong> />
k<<strong>br</strong> />
k<<strong>br</strong> />
x<<strong>br</strong> />
y<<strong>br</strong> />
k<<strong>br</strong> />
k<<strong>br</strong> />
− k<<strong>br</strong> />
z<<strong>br</strong> />
z<<strong>br</strong> />
2<<strong>br</strong> />
x<<strong>br</strong> />
x<<strong>br</strong> />
− k<<strong>br</strong> />
y<<strong>br</strong> />
2<<strong>br</strong> />
y<<strong>br</strong> />
⎞⎛E<<strong>br</strong> />
x ⎞<<strong>br</strong> />
⎟⎜<<strong>br</strong> />
⎟<<strong>br</strong> />
⎟⎜<<strong>br</strong> />
E y ⎟ = 0<<strong>br</strong> />
⎟⎜<<strong>br</strong> />
E ⎟<<strong>br</strong> />
⎠⎝<<strong>br</strong> />
z ⎠<<strong>br</strong> />
(14.25)