Lectures on Electromagnetism, Charged Particles, and Quantum Wells. Number two.

In the previous lecture we defined a function in space and time that looked like it would model the electromagnetic phenomenon of a propagating electric field. It looked something like f(a,b,c,x)f(j,k,l,y)cos(dx)cos(gy)cos(ht) where...

from https://en.wikipedia.org/wiki/Gaussian_function

Scary, but don't be scared. It's just a zero centered gausian on x times a zero centered gausian on y times a zero centered cosine on x times a zero centered cosine on y times a cosine on t, time for long. The cosine transform of this will be a gausian on x times a gausian on y both centered on the point defined by b on the frequency axis.