Laser field absorption in self-generated electron-positron pair plasma.

Recently, much attention has been attracted to the problem of limitations on the attainable intensity of high power lasers [A. M. Fedotov et al., Phys. Rev. Lett. 105, 080402 (2010)]. The laser energy can be absorbed by electron-positron pair plasma produced from a seed by a strong laser field via the development of the electromagnetic cascades. The numerical model for a self-consistent study of electron-positron pair plasma dynamics is developed. Strong absorption of the laser energy in self-generated overdense electron-positron pair plasma is demonstrated. It is shown that the absorption becomes important for a not extremely high laser intensity I ∼ 10(24) W/cm(2) achievable in the near future.

Multiple colliding electromagnetic pulses: a way to lower the threshold of e+ e- pair production from vacuum.

The scheme of a simultaneous multiple pulse focusing on one spot naturally arises from the structural features of projected new laser systems, such as the Extreme Light Infrastructure (ELI) and High Power laser Energy Research (HiPER). It is shown that the multiple pulse configuration is beneficial for observing e+ e- pair production from a vacuum under the action of sufficiently strong electromagnetic fields. The field of focused pulses is described using a realistic three-dimensional model based on an exact solution of the Maxwell equations. The e+ e- pair production threshold in terms of electromagnetic field energy can be substantially lowered if, instead of one or even two colliding pulses, multiple pulses are focused on one spot. The multiple pulse interaction geometry gives rise to subwavelength field features in the focal region. These features result in the production of extremely short e+ e- bunches.

Limitations on the attainable intensity of high power lasers.

It is shown that even a single e- e+ pair created by a superstrong laser field in vacuum would cause development of an avalanchelike QED cascade which rapidly depletes the incoming laser pulse. This confirms Bohr's old conjecture that the electric field of the critical QED strength E(S) = m2c3/eℏ could never be created.

Comment on "Quantum processes in the field of a two-frequency circularly polarized plane electromagnetic wave".

We show that there is a mistake in the results recently published by An Yu and H. Takahashi [Phys. Rev. E 57, 2276 (1998)] for the probabilities of a photon emission by an electron and a pair production by a photon in the field of a two-frequency plane electromagnetic wave. In this paper we present the corrected expression for the probability of a photon emission which contains terms missed by Yu and Takahashi. We argue also that the effect of presence of the waves with combination frequencies in the external field proposed by the authors of the paper [Phys. Rev. E 57, 2276 (1998)] has no physical basis.