After reading the article and skimming some of the innumberable references (the article is all references) it seems like the unobtanium part of using laser pondermotive force to accelerate blocks high density plasma from solid state is that the laser "contrast ratio" has to be very high. In the paper it cites many failed replication efforts to use this particular laser pondermotive force due to lack of "contrast ratio".

I have no idea what "contrast ratio" means, it isn't defined, and isn't in the references. Does anyone know what "contrast ratio" means in terms of high power pulsed lasers?

edit: To answer my own question, ref: https://cdn.intechweb.org/pdfs/24813.pdf

> the laser pulse contrast ratio (LPCR) is a crucial parameter to take into consideration. Considering the laser pulse intensity temporal profile, the LPCR is the ratio between its maximum (peak intensity) and any fixed delay before it. A low contrast ratio can greatly modify the dynamics of energy coupling between the laser pulse and the initial target by producing a pre-plasma that can change the interaction mechanism.

It seems to be how fast the laser turns on, the rate of change of intensity.