Excitation of wakefields in a plasma channel by a laser pulse

The excitation of wakefields by a triangular temporal profile laser pulse with an abrupt fall in a step density profile plasma channel is investigated analytically and an exact solution is obtained. The excitation is more efficient for t~tp, where t is the rise time of the pulse and tp is the plasma period, though it is still significant for t~20 tp. The wake potential in the former case is 1.7 times the ponderomotive potential, whereas it falls to 1.4 times the ponderomotive potential for the latter.