Structure of the wake field in plasma channels

An equation is derived that describes the linear response of an underdense inhomogeneous plasma [ω0≫ωp (r), where ω0 and ωp (r) are the laser-carrier and plasma frequencies, respectively] during the propagation of a laser pulse along the axis of a plasma channel with a characteristic width R ch. For a wide channel, i.e., when R ch/λp0>1 (where λp0=2πc/ωp0 is the wavelength of the excited plasma wave and ωp0 is the plasma frequency at the channel axis), the structure of the wake field is studied analytically. It is shown that this structure changes with the distance from the trailing edge of the pulse. As a result, at a certain distance behind the pulse, the fraction of the plasma wave period in which the simultaneous focusing and acceleration of electrons are possible increases by a factor of 2. For a narrow channel (R ch/λp0