I was just wondering if anyone was aware of a good explanation or physical cause of single slit interference that doesn't involve the Huygens-Fresnel principle. To me, the principle is not very intuitive, light does not eminate from other light (as far as I know). I think I understand that the wave bends at the boundaries of a single slit, but I do not understand what the diffracted wave interferes with.
It works just like water waves ... or sound waves. They all have different physical processes, but they all obey the wave equation. The Huyghens' wavelets are a geometric "mechanism" for waves which explains the most common wave phenomena.
You say light does not emanate from other light, but that's a matter of interpretation. In the electromagnetic wave equation, a magnetic oscillation drives an electric oscillation which drives a magnetic oscillation. So, light at any point propagates to nearby points. Again, this is just an interpretation, since all we are sure about is the math, not the interpretation.
If you think of the word "interference" as applying to two or more ideal, point sources, this gives the simplest analysis of a wave situation in two dimensions (I.e. Young's slits). It's a special case of Diffraction and the Maths involves a straightforward Summation of finite elements (sources all over the Internet - to suit the individual reader). To get an idea of this subject, I think it is at least necessary to understand the Maths of two slit interference. Without the maths (geometry, at least) of the situation, I can't think of any way of understanding what's happening. The word Diffraction applies to a real case where you can have extended sized sources. In that situation, you can treat the source as an infinite set of point sources and this involves Integration. A single slit diffraction pattern can be calculated by integrating the effect of contributions from elements across the slit width. You either need to accept it or learn about the integration process. Whenever you see a real two slit pattern, what you are seeing is the result of two (broad) diffraction patterns, due to the individual slit widths, multiplied by the ideal (fine) interference pattern, due to the spaced sources. This is a very handy approach as it works perfectly in many cases and saves computation time and effort. (It's a Variable Separable problem)
You may prefer the Feynman approach. It take a bit of wrapping your head around though, see: http://vega.org.uk/video/subseries/8