**5.1.1 The first charging stage (first pulse injection)**

The first stage is intended to achieve a charging reference state, which is attained once σ reaches the constant value of 1, i.e. the situation where for each electron entering one is emitted. This charging reference state is associated with the trapping of a maximum quantity of charges Qst (cf. Fig. 6). The embedded charges can be either indefinitely trapped or just localised for some time lapse (seconds, minutes, hours or more). If all the charges were trapped in a stable way, the foregoing reference state would stay unchanged when irradiation is turned off. In the case of partially localised charges, some fraction of Qst could manage to spread out from irradiated region, through conduction. To take into account this fact, a pause time long enough to appraise the degree of charge spreading is chosen for the pause stage.
