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A ponderomotive potential is an effective potential seen by a particle
in ac field on average over the fast oscillations. It is not a true
potential though, and hence can be used for particle manipulations more
advanced compared to those via static potentials. If the field scale is
small enough, the particle motion in a ponderomotive barrier is
essentially phase-dependent and resembles the dynamics of a quantum
object in a conservative field. Probabilistic transmission is possible
in this case [1, 2] and can produce attosecond electron bunches when a
uniform relativistic electron beam is scattered off an intense laser
wave in vacuum.
For particles exhibiting natural oscillations (e.g., Larmor rotation or
internal vibrations), nonadiabatic yet phase-independent ponderomotive
manipulations by resonant ac fields are also available [3-5]. An
approximate integral of particle motion is found for resonant nonlinear
interactions, and a new ponderomotive potential is introduced
accordingly [6]. Because of the irreversibility of the effective
potential, a resonant barrier can also produce a ratchet effect by
asymmetrically transmitting thermal particles in a preferential
direction [3, 4, 7]. Possible applications of this and related effects
comprise current drive [3, 4], selective separation, and cooling of
plasma species [6].**

[1] I. Y. Dodin and N. J. Fisch, Phys. Rev. Lett.

[2] I. Y. Dodin and N. J. Fisch, submitted to Phys. Rev. E.

[3] N. J. Fisch, J. M. Rax, and I. Y. Dodin, Phys. Rev. Lett.

[4] I. Y. Dodin, N. J. Fisch, and J. M. Rax, Phys. Plasmas

[5] I. Y. Dodin and N. J. Fisch, J. Plasma Phys.

[6] I. Y. Dodin and N. J. Fisch, Phys. Lett. A

[7] I. Y. Dodin and N. J. Fisch, Phys. Rev. E

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