# Interference of plane waves

1. Nov 29, 2014

### AwesomeTrains

1. The problem statement, all variables and given/known data
I have to show that the interference of plane waves: $f^{(\pm)}(\vec r,t)=\int \frac {d^3k}{(2\pi)^{3/2}}\int \frac {d\omega}{(2\pi)^{1/2}}e^{i(\vec k \cdot \vec r - \omega t)}\tilde f^{(\pm)}(\vec k, \omega)$

where the amplitudes are given as: $\tilde f^{(\pm)}(\vec k, \omega)=\frac {2\delta(\omega-\omega_0)}{k^2-(\omega\pm i\delta)^2/c^2}$
is a spherical wave of the form: $f^{(\pm)}(\vec r, t)=\frac{1}{r}e^{-i\omega_0(t\mp r/c)}$

2. Relevant equations
They recommend that I use the residue theorem.

3. The attempt at a solution
I thought about doing some sort of coordinate transformation.
What are the integration limits? They weren't given, do I have to figure those out?
Would it be useful to do a Fourier transform of the amplitudes?

Any tips to get me started are really appreciated. (I get confused when I look at the integral)

Alex

2. Nov 30, 2014

### AwesomeTrains

Thought about it. I guess I should do the integral over $d\omega$ first, but what is the meaning of this $\delta$ in $(ω±iδ)^2/c^2$ I know that it's the delta function when it has some argument but there it hasn't.