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.
150<<strong>br</strong> />
γ<<strong>br</strong> />
12<<strong>br</strong> />
() τ<<strong>br</strong> />
e portanto,<<strong>br</strong> />
< E 0exp<<strong>br</strong> />
=<<strong>br</strong> />
12<<strong>br</strong> />
{ i[<<strong>br</strong> />
−ωt<<strong>br</strong> />
+ φ(<<strong>br</strong> />
t)<<strong>br</strong> />
] } E exp{<<strong>br</strong> />
− i[<<strong>br</strong> />
−ω(<<strong>br</strong> />
t + τ)<<strong>br</strong> />
+ φ(<<strong>br</strong> />
t + τ)<<strong>br</strong> />
] }<<strong>br</strong> />
0<<strong>br</strong> />
*<<strong>br</strong> />
1 1<<strong>br</strong> />
< E E<<strong>br</strong> />
> <<<strong>br</strong> />
2<<strong>br</strong> />
2 () τ = exp{ iωτ}<<strong>br</strong> />
E 0 exp{<<strong>br</strong> />
i[<<strong>br</strong> />
φ(<<strong>br</strong> />
t)<<strong>br</strong> />
− φ(<<strong>br</strong> />
t + τ)<<strong>br</strong> />
] } / E 0<<strong>br</strong> />
E<<strong>br</strong> />
2<<strong>br</strong> />
E<<strong>br</strong> />
* 2<<strong>br</strong> />
><<strong>br</strong> />
Coerência<<strong>br</strong> />
><<strong>br</strong> />
(7.11)<<strong>br</strong> />
γ (7.12)<<strong>br</strong> />
Escrevendo a média temporal de forma explícita obtemos:<<strong>br</strong> />
1 T<<strong>br</strong> />
γ12 () τ = exp{<<strong>br</strong> />
iωτ}<<strong>br</strong> />
lim exp{<<strong>br</strong> />
i[<<strong>br</strong> />
φ()<<strong>br</strong> />
t − φ(<<strong>br</strong> />
t + τ)<<strong>br</strong> />
}dt<<strong>br</strong> />
T T ∫<<strong>br</strong> />
] (7.13)<<strong>br</strong> />
→∞<<strong>br</strong> />
0<<strong>br</strong> />
Para resolver esta integral devemos considerar dois casos: τ0 > τ e<<strong>br</strong> />
τ0 < τ, que serão analisados a seguir.<<strong>br</strong> />
Caso a) τ 0 > τ<<strong>br</strong> />
A Fig. 7.3 mostra como Δφ(t) = φ(t) - φ(t +τ) varia com o tempo.<<strong>br</strong> />
Para n τ 0 < t < (n+1) τ 0 - τ temos Δ φ = 0 e para (n + 1) τ 0 - τ < t <<<strong>br</strong> />
(n+1) τ 0 , temos Δ φ = Δ n+1. Logo, realizando explicitamente a integral<<strong>br</strong> />
temos:<<strong>br</strong> />
∫<<strong>br</strong> />
0<<strong>br</strong> />
T<<strong>br</strong> />
exp<<strong>br</strong> />
∞<<strong>br</strong> />
2π<<strong>br</strong> />
[ i Δφ()<<strong>br</strong> />
t ]<<strong>br</strong> />
π<<strong>br</strong> />
0<<strong>br</strong> />
dt<<strong>br</strong> />
0<<strong>br</strong> />
Δφ(t) nτ0 t t+τ (n+1)τ0<<strong>br</strong> />
Δ1 Δ2<<strong>br</strong> />
Δ3<<strong>br</strong> />
τ0<<strong>br</strong> />
τ0 2τ0 3τ0<<strong>br</strong> />
τ0-τ 2τ0-τ 3τ0-τ<<strong>br</strong> />
Fig. 7.3 - Variação de Δφ com o tempo.<<strong>br</strong> />
∞ ( n+<<strong>br</strong> />
1)<<strong>br</strong> />
τ0<<strong>br</strong> />
−τ<<strong>br</strong> />
( n+<<strong>br</strong> />
1)<<strong>br</strong> />
τ0<<strong>br</strong> />
= ∑ { ∫ e xp(<<strong>br</strong> />
i0)<<strong>br</strong> />
dt + ∫ exp(<<strong>br</strong> />
i Δ n+<<strong>br</strong> />
1 ) dt }<<strong>br</strong> />
nτ<<strong>br</strong> />
( n+<<strong>br</strong> />
1)<<strong>br</strong> />
τ −τ<<strong>br</strong> />
n=<<strong>br</strong> />
0<<strong>br</strong> />
0<<strong>br</strong> />
∞<<strong>br</strong> />
[ ( n + 1)<<strong>br</strong> />
τ − τ − nτ<<strong>br</strong> />
] + exp[<<strong>br</strong> />
iΔ<<strong>br</strong> />
] [ ( n + 1)<<strong>br</strong> />
τ − ( n + 1)<<strong>br</strong> />
τ + τ]<<strong>br</strong> />
= ∑<<strong>br</strong> />
0<<strong>br</strong> />
0 ∑<<strong>br</strong> />
n=<<strong>br</strong> />
0<<strong>br</strong> />
∞<<strong>br</strong> />
n=<<strong>br</strong> />
0<<strong>br</strong> />
∞<<strong>br</strong> />
n+<<strong>br</strong> />
1<<strong>br</strong> />
( τ − τ)<<strong>br</strong> />
+ τ exp(<<strong>br</strong> />
i Δ ) = n(<<strong>br</strong> />
τ − τ)<<strong>br</strong> />
= ∑ 0 ∑<<strong>br</strong> />
n=<<strong>br</strong> />
0<<strong>br</strong> />
n=<<strong>br</strong> />
0<<strong>br</strong> />
n+<<strong>br</strong> />
1<<strong>br</strong> />
0<<strong>br</strong> />
0<<strong>br</strong> />
0<<strong>br</strong> />
t<<strong>br</strong> />
0<<strong>br</strong> />
(7.14)<<strong>br</strong> />
S. C. Zilio <strong>Óptica</strong> <strong>Moderna</strong> – <strong>Fundamentos</strong> e Aplicações