Hi i have to write the split beam propagation program in matlab. My medium is 5*5*5 (in mm each). I have to consider the propagation in z direction. I have divided my spatial coordinates(bot x,y) in 64 parts and represented them as a 1x64 matrix. So, I have defined the gaussian beam in the form of a 64x64 matrix and plotted it.Till then it is fine. Now when it propagates, it will suffer diffraction as well as nonliearity(which in my case is 1D periodic refractive index structure). Now the diffraction is calculated in k space. so my question is..HOW WILL I CHOOSE THE FREQUENCY AXIS( Kx and Ky), given x, y matrix.. Again they should be 1x64 matrix each. But how will i decide there values?