# Why there is interference pattern?

1. Dec 30, 2008

### KFC

I am reading something about electromagnetic wave. There is a semi-infinite medium with refractive index n>1 on z>0 region. For z<0 region, it is medium with refractive index n=1. Two EM waves starting to propogate at the origin of xy plane with same wavenumber but different direction. Both of them are making angle $$\alpha (\alpha<\pi/2)$$ with positive z-axis on xz plane (one wave travel on -xz plane, the other on +xz plane). The material told there is an interference in x-direction? But I don't see how this happen. How to find the interference pattern?

BTW, could you recommend some book contains related concept?

Thanks.