  The Bubble regime of electron acceleration in ultra-relativistic laser plasma
is considered. It has been shown that the bubble can produce ultra-short dense
bunches of electrons with quasi-monoenergetic energy spectra. The first
experiment in this regime done at LOA has confirmed the peaked electron
spectrum (J. Faure, et al., {\it submitted}, 2004). The generated electron
bunch may have density an order of magnitude higher than that of the background
plasma. The bubble is able to guide the laser pulse over many Rayleigh lengths,
thus no preformed plasma channel is needed for high-energy particle
acceleration in the bubble regime. In the present work we discuss a simple
analytical model for the bubble fields as well as the scaling laws.
