Abstract
We describe direct measurements at a high temporal resolution of the changes experienced by the phase and amplitude of an ultra-short pulse upon propagation through an inhomogenously broadened semiconductor nanostructured optical gain medium. Using a cross frequency-resolved optical gating technique, we analyze 150 fs-wide pulses propagating along an InP based quantum dash optical amplifier in both the quasi-linear and saturated regimes. For very large electrical and optical excitations, a second, trailing peak is generated and enhanced by a unique two-photon-induced amplification process.
Highlights
The ultrafast dynamics of semiconductor nano structured (quantum dot (QD) and quantum dash (QDash)) optical gain media play crucial roles in determining their basic saturation and dephasing mechanisms
We describe direct measurements at a high temporal resolution of the changes experienced by the phase and amplitude of an ultra-short pulse upon propagation through an inhomogenously broadened semiconductor nanostructured optical gain medium
Using a cross frequency-resolved optical gating technique, we analyze 150 fs-wide pulses propagating along an InP based quantum dash optical amplifier in both the quasi-linear and saturated regimes
Summary
The ultrafast dynamics of semiconductor nano structured (quantum dot (QD) and quantum dash (QDash)) optical gain media play crucial roles in determining their basic saturation and dephasing mechanisms. The inhomogeneously broadened nature of these gain media requires that multi-wavelength pump-probe schemes be employed in order to obtain a detailed understanding of the cross saturation dynamics Such experiments were reported recently [4] for the quasi-linear and highly saturated regimes where the phenomenon of a nearly instantaneous gain response [5] was identified. These imprint a nonlinear signature on the perturbing (pump) pulse itself and cannot be observed in a pump-probe experiment Such ultrafast processes can be characterized using the techniques of frequency-resolved (or cross frequency-resolved) optical gating (FROG or XFROG) [6,7] which measure amplitude and phase changes experienced by a pulse upon propagation in a nonlinear medium with a temporal resolution which can be a fraction of the pulse width. For much larger input pulse energies and bias levels, the pulse shape is modified as a two-photon-induced instantaneous-gain response [5] initiates the buildup of a second peak
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