Here we perform a series of time-resolved experiments where a 100 fs pump pulse is tuned between 528 nm and 555 nm, across the second indirect gap of intrinsic silicon at ~540 nm which involves electrons in a higher-lying conduction band with minimum at the L point. The photo-injected carriers, after inter- and intra-band relaxations are complete, are subsequently probed with high-field single-cycle terahertz radiation. When the energy of the pump pulses exceeds the second indirect gap, the probed terahertz absorption decreases by a factor 2.7±0.2. We suggest that this dramatic change could be due to the different phonon populations obtained when the carriers undergo the L to X inter-band scattering, instead of just cooling within the X-valley.
@article{arxiv.1608.01759,
title = {Transient THz conductivity of silicon with optical pumping above and below the second indirect transition},
author = {Fabio Novelli and Jeffrey A Davis},
journal= {arXiv preprint arXiv:1608.01759},
year = {2017}
}