Calculations of femtosecond differential optical transmission in germanium

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Abstract
Nonequilibrium electron and hole carrier dynamics are calculated for femtosecond photoexcitation in Ge using an ensemble Monte Carlo method. From the carrier distributions and k⋅p band-structure calculations, the time-dependent differential optical transmission that corresponds to pump-probe experiments is determined. It is found that electrons quickly scatter out of the optically coupled region and that the primary electron relaxation channel is from the Γ valley to the X valleys, then to the L valleys. Holes dominate the nonlinear absorption spectra in Ge. It is also found that light holes make a substantial contribution to the initial transient of the differential transmission, particularly for high-energy photoexcitation.