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Homework Help: Fourier transform

  1. Jan 26, 2012 #1
    1. The problem statement, all variables and given/known data

    An atom raised at t=0 to an excited state with energy [itex] E_0= \hbar \omega_0 [itex] has the time dependence [itex] T(t)=\frac{1}{\sqrt \tau}e^{-t/ 2 \tau} [itex] for t>0 and T(t)=0 for t<0. Thus the probability of being in an excited state decays exponentially with time.

    [itex] T(t)^2= \ frac {1} {\tau} e^ {-t/ \tau} [itex]

    a.) Find the transform b(w) of T(t).

    ('w' is omega, frequency)

    b.) Plot |b(w)|^2 as a function of w.

    c.) show that b(w) traces a circle on the complex plane as w runs from well below w_0 to well above it.

    2. Relevant equations

    [tex] b(\omega)=\frac{1}{\sqrt{2 \pi}}\int{T(t)e^{i \omega t}} [/tex]

    The integral runs from -infinity to infinity.

    3. The attempt at a solution

    [tex] b(\omega)=-\frac{1}{\sqrt{2 \pi \tau}}\frac{1}{i(\omega - \omega _0)-\frac{1}{2 \tau}} [/tex]

    When I do plot for part b, I get exponential incerase. Does that sound right?

    But when I do part (c), I don't get a circle nor elipse.
     
  2. jcsd
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