E1=a1*exp(-iwt)exp(-t/t1)(*first decay path*)
E1=a1*exp(-i(w+f)t)exp(-t/t2) (*second decay path*)
I=|(E1+E2)|^2 (*interference fringes is because of interference of two decay fields*)
I=a1^2*exp(-2t/t1)+a2^2*exp(-2t/t2)+a1a2*exp-(t/t1+t/t2)*2cos(ft)