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GaAs/Al0.15Ga0.85As terahertz quantum cascade lasers with double-phonon resonant depopulation operating up to 172 K R. W. Adams, K. Vijayraghavan, Q. J. Wang, J. Fan, F. Capasso, S. P. Khanna, A. G. Davies, E. H. Linfield, M. A. Belkin Applied Physics Letters 97, 13111 (2010)