Timescales and schematic representation of expected accumulation effects in Si. Strong single pulse will develop plasma in prefocal region that limits the intensity and energy deposition near the focus. With a THz-repetition-rate train of weaker pulses, one can accumulate carrier at the focus. With train duration exceeding electron-phonon coupling time but below diffusion times, we can expect local heating gradually increasing absorption during the train. At repetition rates down to GHz, thermal and electronic diffusions come into play that may limit energy localization.