TABLE OF CONTENTS Ultrafast gain dynamics of laser diode amplifiers have been widely studied due to some emerging ultrafast non-linear applications [ [1] [2] [3] [4] [5] [6]]. Ultra-short pulses can be generated either by using a Q-switching laser or external cavity mode locking technique [ [7] [8] [9] [10] [11]]. Amplification is often desirable for such pulses. Sub-picosecond pulse amplification in a laser diode amplifier is affected by many factors. With regard to the gain dynamics, it is determined by carrier density depletion, spectral hole burning, carrier heating effects and two-photon absorption. There are various sources which result in carrier heating. Firstly, injected carriers need excess energy to overcome the barrier at the junction, to reach the active layer, and the release of this energy results in injection heating. On the other hand, recombination heating which results from the stimulated recombination process depletes carriers with below average energy, and hence leaves the system with those carriers having energies higher than average. In the process of Auger recombination, the carrier is excited to a higher energy state via the recombination of another carrier, resulting in an increase in the carrier energy. In addition, free-carrier absorption refers to the absorption of the photons by phonons or by impurities which results in a higher temperature.
The cooling is mainly due to inelastic longitudinal optical (LO) phonon scattering. In the case of spectral hole burning, it has been shown in a detailed calculation that the spectral hole burning effect is very closely...
