Photon acceleration in plasma wake wave

The photon acceleration effect in a laser wake field is investigated based on photon Hamiltonian dynamics. A test laser pulse is injected into a plasma wave at an incident angle θ_i, which could slow down the photon velocity along the propagating direction of the wake wave so as to increase the acceleration distance for the photons. The photon trapping condition is analyzed in detail, and the maximum frequency shift of the trapped photon is obtained. The acceleration gradient and dephasing length are emphatically studied. The compression of the test laser pulse is examined and used to interpret the acceleration process. The limit of finite transverse width of the wake wave on photon acceleration is also discussed