Picosecond Optical Absorption at 1.06 μm and 1.55 μm in Thin Germanium Samples at High Optically-Created Carrier Densities
Recently, the enhanced transmission of single, ultrashort optical pulses at 1.06 μm through germanium as a function of incident pulse energy has been measured . In addition, the temporal evolution of this enhanced transmission has been determined on a picosecond time scale using the excite and probe technique [1,2]. The latter measurements reveal that the probe transmission increases for 50–100 psec following excitation with an intense optical pulse. ELCI. et al.  have attributed this rise in the probe transmission to a cooling of the hot electron-hole plasma created by the excitation pulse. In sharp contrast to this interpretation, AUSTON et al.  have stated that they expect the energy relaxation time to be too short to account for the rise in the probe transmission. AUSTON et al. also suggest that enhanced free-hole  and Coulomb-assisted indirect absorption  effects can be significant at the high optically-created carrier densities encountered in the excitation-probe measurements at 1.06 μm. Indeed, they suggest that these processes could introduce a minimum in the absorption versus carrier density relationship. AUS-TON and MCAFEE  have proposed an alternative explanation for the temporal evolution of the probe transmission by combining the details of the way the absorption saturates as a function of carrier density with a monotonic decrease in carrier density with time due to Auger recombination . The rise in probe transmission with time can then be explained in the followina manner.
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- 7.S. McAfee and D.H. Auston, private communication, July 28, 1977.Google Scholar