  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$\pm$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.
