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(a)Schematic energy diagram of the unit coupled double quantum well structure. There are four subbands (c1–c4) in the conduction band. Probe 1 and probe 2 are corresponding optical transitions in the pump-probe experiments on the waveguide sample and the wafer sample, respectively. (b) Upper panel: absorption spectra of the wafer sample measured with a 45° internal multiple reflection configuration (see inset) with which the intersubband transition is partially allowed. Lower panel: absorption spectra with in-plane polarization for the doped and undoped samples.
The temporal behavior of the photoinduced phase change (cross-phase modulation) in the waveguide sample. The positive sign corresponds to the delay of the phase. Both the pump and probe wavelengths were 1550 nm. The pump intensity was before the input facet of the waveguide.
(a) The probe photon energy dependence of the pump induced absorption change as a function of the probe delay time. The experimental configuration is shown schematically in the inset. (b) The spectra of for various probe delay times.
(a)Temporal behavior of the change in the number of conduction electrons and the electron temperature estimated from the spectra by relations (2) and (3), respectively. Schematic diagram of the electron (b) heating and (c) cooling processes. The shaded areas indicate electron occupation in the bands. LO and EE denote longitudinal-optical phonon scattering and electron-electron scattering, respectively.
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