questions on point source phase

Hi all,

I am trying to simulate the interference of two point sources. I want them to be out-of-phase.
In Helmholtz equation model, the two sources are given as weak contribution.
One of them is test(u*exp(i*phase_basis)), where phase_basis is pi
the other is test(u*exp(i*phase_diff)), where phase_diff is sweeping from -pi/2 to pi/2

I wish to see the changing interference pattern as phase_diff sweeps.

Now, my questions are:
1: If I define the source expressions in a right way?
2: If I am right in the first question, then what the expression would be, in order to pick up the phase information at each point?

Thanks,
Ferris