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  • 2000-2004  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 4509-4511 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An improvement of an all-optical modulation scheme that utilizes an intersubband transition is proposed and investigated in connection with intersubband carrier relaxation dynamics. N-doped GaAs/AlGaAs quantum wells are pumped by an ultrashort (∼120 fs) intersubband-resonant pulse and probed by an interband-resonant white-light continuum. Ultrafast modulation speed of ∼0.4 ps is demonstrated, which is faster than that of the previous scheme by as much as a factor of 10. It is found that a large part of the carriers, which are excited from the first conduction subband to the second conduction subband, transfer to unknown trapping states at a relaxation time that is comparable to that of the pump–pulse duration. The existence of the carrier relaxation path via L valley subbands is strongly suggested as the cause. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 19-21 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Modulation of interband-resonant light (∼800 nm) by intersubband-resonant light (5–7 μm) was investigated in n-doped AlGaAs/GaAs multiple quantum wells by a two-color femtosecond pump-probe technique. Modulation with a recovery time of ∼1 ps is observed in a plainer-type modulation device at room temperature. The modulation of interband absorption coefficient is ∼1000 cm−1 when the energy density of the intersubband light pulse is ∼4 fJ/μm2. The modulation efficiency indicates that 99% modulation can be achieved with a control pulse energy of ∼1 pJ when a conventional waveguide-type device structure is utilized. The mechanism which determines the modulation speed is discussed in terms of carrier relaxation process. It is shown that the modulation speed is mainly determined by the inter- and intrasubband relaxation times, where the latter is influenced by hot phonon effects. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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