He has not stopped working, ever; with recent contributions to the detection of gravitational waves and the theory of quasicrystals.
Books or papers; let's say at the level of math heavy CS/undergrad math degree.
Here's an online demo for a C library that can do DWT and CWT. The code is a little rough but it's functional: http://rafat.github.io/#/sites/wavelib/front
Also, a really basic but easy to understand video series: https://www.youtube.com/watch?v=QX1-xGVFqmw
He has not stopped working, ever; with recent contributions to the detection of gravitational waves and the theory of quasicrystals.