On acceleration of a relativistic particle by a radiation pulse

Concerning direct acceleration of charges by pulses of electromagnetic (laser) radiation with arbitrary shapes, we have found a relationship between the components of the mechanical momentum of a relativistic (but not ultrarelativistic) particle. In a wide range of conditions, the energy transferred by the radiation to a particle to be accelerated is determined by the electric area of the laser pulse, i.e., by the integral of the electric field strength over the pulse time. This indicates that it is promising to develop schemes for generation of quasi-unipolar radiation laser pulses, in which the strength of the dominant component of the electric field does not change its sign during the main pulse duration.