The space charge effect on residual energy of electrons in optical-field-ionized plasmas is studied in detail by a cloud-in-cell simulation. It is found that a moderate space charge field can restrain ponderomotive heating and cause a transfer of a part of the kinetic energy of electrons into potential energy so that the residual energy of electrons can be reduced effectively. The effects of inverse Bremsstrahlung heating, stimulated Raman scattering and radiation on electron temperature are also briefly discussed. Comparison is made between our results and experimental data.

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A simple model is proposed to describe the propagation of the electromagnetic (EM) wave in gradually ionized plasmas. Particle simulation with particle-in-cell code is performed to verify this model. The frequency spectrum of the EM wave is studied in detail, and a new way to broaden the frequency of the wave effectively is proposed. The reflection and transmission of the EM wave in such plasmas are also discussed.