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 ...
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
236<<strong>br</strong> />
Cavidades ópticas<<strong>br</strong> />
D A<<strong>br</strong> />
1<<strong>br</strong> />
⎛ +<<strong>br</strong> />
−<<strong>br</strong> />
⎞<<strong>br</strong> />
1 ( D − A)<<strong>br</strong> />
⎜ ⎟<<strong>br</strong> />
2 1 λ<<strong>br</strong> />
= ± i<<strong>br</strong> />
⎝ ⎠<<strong>br</strong> />
= − i<<strong>br</strong> />
(11.16)<<strong>br</strong> />
2<<strong>br</strong> />
q 2B<<strong>br</strong> />
B R πw<<strong>br</strong> />
n<<strong>br</strong> />
onde na última passagem usamos a eq. (11.3). Assim, dependendo do<<strong>br</strong> />
sinal de B, apenas + ou – deve ser considerado na raiz, de forma a<<strong>br</strong> />
obtermos:<<strong>br</strong> />
2B<<strong>br</strong> />
R = (11.17a)<<strong>br</strong> />
( D − A)<<strong>br</strong> />
w =<<strong>br</strong> />
⎛<<strong>br</strong> />
⎜<<strong>br</strong> />
⎝<<strong>br</strong> />
λ ⎞<<strong>br</strong> />
⎟<<strong>br</strong> />
πn<<strong>br</strong> />
⎠<<strong>br</strong> />
1/<<strong>br</strong> />
2<<strong>br</strong> />
S. C. Zilio <strong>Óptica</strong> <strong>Moderna</strong> – <strong>Fundamentos</strong> e Aplicações<<strong>br</strong> />
B<<strong>br</strong> />
2<<strong>br</strong> />
1/<<strong>br</strong> />
2<<strong>br</strong> />
2<<strong>br</strong> />
⎡ D A<<strong>br</strong> />
1<<strong>br</strong> />
⎛ + ⎤<<strong>br</strong> />
⎢ −<<strong>br</strong> />
⎞<<strong>br</strong> />
⎜ ⎟<<strong>br</strong> />
2<<strong>br</strong> />
⎥<<strong>br</strong> />
⎣ ⎝ ⎠ ⎦<<strong>br</strong> />
1/<<strong>br</strong> />
4<<strong>br</strong> />
(11.17b)<<strong>br</strong> />
A análise desta equação mostra que só teremos solução real<<strong>br</strong> />
quando:<<strong>br</strong> />
D + A<<strong>br</strong> />
≤ 1<<strong>br</strong> />
2<<strong>br</strong> />
(11.18)<<strong>br</strong> />
Esta é a condição de confinamento (estabilidade) para uma<<strong>br</strong> />
cavidade genérica. No caso particular em que temos uma cavidade com<<strong>br</strong> />
dois espelhos de raios R1 e R2, e usando que f i = Ri/2,<<strong>br</strong> />
encontramos a<<strong>br</strong> />
matriz do sistema como:<<strong>br</strong> />
⎛<<strong>br</strong> />
⎜<<strong>br</strong> />
M = ⎜<<strong>br</strong> />
⎜<<strong>br</strong> />
⎜<<strong>br</strong> />
⎝<<strong>br</strong> />
de onde tiramos que:<<strong>br</strong> />
( ) ( )<<strong>br</strong> />
( ) ⎟ ⎟⎟⎟<<strong>br</strong> />
2<<strong>br</strong> />
4l<<strong>br</strong> />
⎞<<strong>br</strong> />
1−<<strong>br</strong> />
2l<<strong>br</strong> />
2 / R1<<strong>br</strong> />
+ 1/<<strong>br</strong> />
R 2 +<<strong>br</strong> />
2l<<strong>br</strong> />
1−<<strong>br</strong> />
l / R 2<<strong>br</strong> />
R1R<<strong>br</strong> />
2<<strong>br</strong> />
⎛<<strong>br</strong> />
2l<<strong>br</strong> />
⎞<<strong>br</strong> />
− 2⎜1/<<strong>br</strong> />
R1<<strong>br</strong> />
+ 1/<<strong>br</strong> />
R 2 + ⎟ 1−<<strong>br</strong> />
2l<<strong>br</strong> />
/ R 2<<strong>br</strong> />
⎝<<strong>br</strong> />
R1R<<strong>br</strong> />
2 ⎠<<strong>br</strong> />
⎠<<strong>br</strong> />
(11.19)<<strong>br</strong> />
2<<strong>br</strong> />
D + A<<strong>br</strong> />
2l<<strong>br</strong> />
= 1−<<strong>br</strong> />
2l<<strong>br</strong> />
( 1/<<strong>br</strong> />
R1<<strong>br</strong> />
+ 1/<<strong>br</strong> />
R 2 ) + ≤ 1 (11.20)<<strong>br</strong> />
2<<strong>br</strong> />
R R<<strong>br</strong> />
Com um pouco de manipulação algé<strong>br</strong>ica chegamos à condição de<<strong>br</strong> />
confinamento para a cavidade esférica simétrica:<<strong>br</strong> />
1<<strong>br</strong> />
2