Conincidence1[\[Tau]_] :=
1 + Sin[4 \[CapitalTheta]]^2 /(2 P1)*
NIntegrate[(AJ[\[Lambda]s, \[Lambda]i]^2 +
AJ[\[Lambda]i, \[Lambda]s]^2) (Cos[((
2 \[Pi] c)/\[Lambda]s + (
2 \[Pi] c)/\[Lambda]i ) \[Tau]] +
Cos[((2 \[Pi] c)/\[Lambda]s - (
2 \[Pi] c)/\[Lambda]i ) \[Tau]]) +
AJ[\[Lambda]s, \[Lambda]i]^2 Cos[((2 \[Pi] c)/\[Lambda]s - (
2 \[Pi] c)/\[Lambda]i ) \[CapitalDelta]t]*
Cos[((2 \[Pi] c)/\[Lambda]s + (
2 \[Pi] c)/\[Lambda]i ) \[Tau]], {\[Lambda]s, \[Lambda]0 -
ls, \[Lambda]0 + ls}, {\[Lambda]i, \[Lambda]0 - li, \[Lambda]0 +
li}] - 1/P1*
NIntegrate[
F3[\[Lambda]s, \[Lambda]i, \[Tau]], {\[Lambda]s, \[Lambda]0 -
ls, \[Lambda]0 + ls}, {\[Lambda]i, \[Lambda]0 - li, \[Lambda]0 +
li}]
Plot[Conincidence1[\[Tau]], {\[Tau], -4*10^(-12) - \[CapitalDelta]t,
4*10^(-12) + \[CapitalDelta]t}, PlotRange -> All]