Efficient mixed-state ptychography via sparse S-matrix
Mixed-state ptychography
In Chen et al. 20211, the authors estimate a mixture of incoherent probe wavefunctions in ptychography. Their reference 212 gives the basics of the method, which is simple: using K many probe wavefunctions, simulate CBED patterns with each then sum the intensities (squared modulus) of the resulting CBED patterns across all K simulations, before comparing to the observed 4D-STEM data in order to do ePIE or gradient descent.
Efficient computation
Implementing #8 gives us a way to share computations between all K mixed probe states. We simply compute the basis CBEDs as in #8, by simulating pure plane waves. Then each probe state corresponds to a different collection of complex weights (the coefficients in that basis) which we can easily compute. This means only the combination step scales linearly in K, so we do not need to propagate any more beams through the multislice algorithm in order to do mixed-state ptychography.
Plan
Once #8 is implemented, we will implement mixed states in an example that uses the SparseProbeMultislice class to generate a basis, then performs ptychography using a collection of estimated probe coefficients.