Polarization and Interference

Water waves are used to explain the diffraction and interference of light passing through a slit. Keeping with the water wave analogy, water would be polarized light, yet only coherent light is required, not polarized light. Apparently it doesn't make a difference. Explanation, please? Thank you
- Bruce (age 63)
Cedar Hill, TX, USA

Nice question. To maintain the diffraction pattern you need to maintain interference between the light that goes through all of the slit. Thus it's necessary for the light across the slit to have the same polarization, but it doesn' matter which polarization. The polarization can change without destroying the interference so long as it changes the same way across slit. Also, to keep the same diffration pattern the relative phase of the light reaching all parts of the slit must stay constant. Keeping the same relative phases and the same polarization is what we mean by "coherent". 

Mike W.

(published on 04/13/2014)