You may be interested in my latest publication on the subject, just out - here:
Basically, I explain new ways to generate high NA illumination (and new ways to measure the NA of illumination) using a piece of paper. So, I suppose you could say, I just published a paper about a piece of paper. Enjoy.
I’ll be making a series of videos to explain the topics covered in the paper on my YouTube channel so subscribe now not to miss them: