In research field of high intensity laser, the ponderomotive force is the important concept. Most of us got the description from Kruer's book, in fact this phenomena was obtained at first time in 1957. From web site of Nature Physics looking back, it tells us:
In 1957, Boot and Harvie reported the observation of a force on charged particles in an inhomogeneous electric field, which originated from second-order terms of the equation for the Lorentz force on the particles. Almost immediately it was realized that this 'ponderomotive force' could be used to trap and control electrons. But the force is weak: only with the development of modern laser technology is the ponderomotive force being exploited in new particle-acceleration techniques and inertial confinement fusion.
Nature 180, 1187 (1957)