I've heard of ptychography as an imaging technique a number of times in the past, and recently I found myself in need of a refresher on what it actually entails. Unfortunately, the Wikipedia page on the subject is extremely technical and laden with detail, but it does an extremely poor job at conveying the fundamentals of the technique, and naive web searches quickly go into paywalled research papers that won't be particularly readable for a general public.
So, in a nutshell: What is ptychography? That is:
- What is the conceptual core of the method?
- What are the core physical requirements on the light source used for illumination?
- To what extent does the method rely on algorithmic and computational reconstruction? Is it fully constrained, or do the algorithms require models of the sample to work? That is, does the measured experimental data contain complete information to uniquely specify the image?
- What is the method for? I.e., what advantages does it have with respect to competing methods?
I'm primarily interested in imaging using XUV and soft x-rays (i.e. the sort of things that might come out of a high-order harmonic source), and to make this answer as broadly useful as possible (or at least, in a manner commensurate to the specialized nature of the technique), I'd like answers to be accessible to undergraduates with a solid course in optics under their belt.