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W. H. Knox, R. L. Fork, M. C. Downer,
D. A. B. Miller, D. S. Chemla, C. V. Shank, A. C. Gossard and W. Wiegmann,
"Femtosecond Dynamics of Resonantly Excited Excitons in Room Temperature GaAs Quantum
Wells," Phys. Rev. Lett. 54, 1306-1309 (1985). The authors
investigate the effect of excess excitonic populations created by resonant ultrashort
excitation on the optical-absorption properties of GaAs quantum wells. They find that
under these conditions at room temperature excitons produce more absorption bleaching than
equal densities of free-carrier pairs. This bleaching partly recovers as the excitons
ionize to give free carriers. Hence, they directly measure the thermal ionization time of
excitons at room temperature for the first time, and find that tau approximately 300 fs
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