This program calculates the phase of vortex light with specified angular momentum L.
In the program, the function is vortex_phase(L=1.0,Nx=501,Ny=501,lx=2.0,ly=2.0)
you need to specify the number of grid points (Nx,Ny),the length of the box (lx,ly) as well as the value of angular momentum L.
Nx,Ny should be odd numbers, default value is Nx=501,Ny=501.
(lx,ly) is set default as (2.0,2.0) with origin at (1,1), so the box spans from (-1,-1) to (1,1).
L is set default as equal to 1.