Abstract

It has recently been shown that high-intensity femtosecond pulses that saturate the gain medium can undergo net absorption when propagating in semiconductor amplifiers.¹ The relevant behavior cannot be captured by a conventional gain saturation model of a semiconductor amplifier² but instead requires the resolution of full many-body dynamics such as bandgap renormalization, dynamic Coulomb screening, Pauli blocking, etc.³ In contrast to uniformly inverted atomic levels, the inverted semiconductor is characterized by an electron-hole plasma, which obeys Fermi-Dirac statistics, causing gain below and absorption above the quasi-chemical potential. Therefore, after strong pulse excitation, saturation of the gain of the leading part of the pulse leads to absorption of the trailing part by those noninverted states that have a finite spectral (absorptive) overlap with the pulse.

© 1994 IEEE