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Terahertz Quantum Cascade Lasers Based on Resonant Phonon Scattering for Depopulation

Qing Hu, Benjamin S. Williams, Sushil Kumar, Hans Callebaut and John L. Reno
Philosophical Transactions: Mathematical, Physical and Engineering Sciences
Vol. 362, No. 1815, The Terahertz Gap: The Generation of Far-Infrared Radiation and its Applications (Feb. 15, 2004), pp. 233-249
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/4142447
Page Count: 17
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Terahertz Quantum Cascade Lasers Based on Resonant Phonon Scattering for Depopulation
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Abstract

We report our development of terahertz (THz) quantum cascade lasers (QCLs), in which the depopulation of the lower radiative level is achieved through resonant longitudinal optical (LO) phonon scattering. This depopulation mechanism, similar to that implemented in all the QCLs operating at mid-infrared frequencies, is robust at high temperatures and high injection levels. The unique feature of resonant LO-phonon scattering in our THz QCL structures allows a highly selective depopulation of the lower radiative level with a sub-picosecond lifetime, while maintaining a relatively long upper level lifetime (more than 5 ps) that is due to upper-to-ground-state scattering. The first QCL based on this mechanism achieved lasing at 3.4 THz (λ ≈ 87 µm) up to 87 K for pulsed operations, with peak power levels exceeding 10 mW at ca. 40 K. Using a novel double-sided metal waveguide for mode confinement, which yields a unity mode confinement factor and therefore a low total cavity loss at THz frequencies, we have also achieved lasing at wavelengths longer than 100 µm.

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