Abstract
In this study, we report the effect of the excitation of non-exciton components caused by broadband pulses on quantum beat oscillation. Using a spectrally controlled pump pulse, a long-lived oscillation is clearly observed, and the pump-power dependence shows the suppression of the dephasing rate of the oscillation. Our results from incoherent carrier generation using a continuous wave laser demonstrate that the non-exciton components behaving as free carriers increase the oscillation dephasing rate.
Highlights
-1.0 -0.5 0.0 0.5 1.0 1.5 Time Delay uncontrolled spectrum has a single peak described approximately by a sech[2] function, the spectrally controlled pulse has several peaks
The dashed line indicates the dephasing rate by the uncontrolled pump pulse at 1 μJ/cm[2]
While the amplitude increases proportionally to the pump power, the dephasing rate is nearly constant in this pump power region, which is a key point in this study
Summary
The sample used in this study was a (GaAs)35/(AlAs)[35] multiple quantum well (MQW). The quantum beat was measured using a time-resolved reflection-type pump-probe technique. The laser source used was a mode-locked Ti:sapphire pulse laser, delivering an approximately 90 fs pulse with a repetition rate of 80 MHz. While the probe power was kept at 0.06 μJ/cm[2], the pump power was changed from 0.1 to 2 μJ/cm[2]. The pump beam was orthogonally polarized to the probe beam in order to eliminate its contribution. The pump beam was chopped at 2 kHz, and the intensity of the reflected probe beam was modulated. The probe intensity detected by the Si photodiode was amplified using a lock-in amplifier
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