Ultrafast Mid-Infrared Dynamics in Quantum Cascade Lasers

This report summarizes the entire research period. In this program, we performed experiments using a femtosecond mid-infrared pump-probe system implemented for QCL samples operating at 4.6 and 5.3 μm. We employed femtosecond time-resolved pump-probe measurements to probe the nature of the transport through the laser structure via the dynamics of the gain. The gain recovery was determined by the time-dependent transport of electrons through the cascade heterostructure; as the laser approaches and exceeds threshold, the gain recovery shows a dramatic reduction due to the onset of quantum stimulated emission. Since the electron transport through each state in the cascade is determined by the state lifetime, the transport in a cascade laser is driven by the photon density in the cavity. The gain recovery is qualitatively different from that in conventional atomic, molecular and interband semiconductor lasers due to the superlattice transport in the cascade. We also studied the effects of pulse propagation in the laser, including group velocity dispersion and coherent pulse reshaping due to ultrafast Rabi flopping of the gain medium. (a) Papers published in peer-reviewed journals (N/A for none) Hyunyong Choi, Laurent Diehl, Zong-kwei Wu, Marcella Giovannini, Jerome Faist, Federico Capasso, and Theodore B. Norris “Time-Resolved Investigations of Electronic Transport Dynamics in Quantum Cascade Lasers Based on Diagonal Lasing Transition,” IEEE. J. Quant. Electron. 45, 307 (2009). Hyunyong Choi, Laurent Diehl, Marcella Giovannini, Jerome Faist, Federico Capasso, and Theodore B. Norris, “Femtosecond pump-probe studies of carrier transport and gain dynamics in quantum cascade lasers,” phys. stat. sol. (c) 5, 225 (2008). Hyunyong Choi, Laurent Diehl, Federico Capasso, David Bour, Scott Corzine, Jintian Zhu, Gloria H ̈ofler, and Theodore B. Norris, “Time-domain upconversion measurements of group-velocity dispersion in quantum cascade lasers,” Opt. Express 15, 15898 (2007). H. Choi, L. Diehl, Z-K. Wu, M. Giovannini, J. Faist, F. Capasso, T.B. Norris , “Gain Recovery Dynamics and Photon-Driven Transport in Quantum Cascade Lasers,” Phys. Rev. Lett. 100, 167401 (2008). H. Choi, T.B. Norris, T. Gresch, M. Giovanni, J. Faist, L. Diehl, and F. Capasso, “Femtosecond Dynamics of Resonant Tunneling and Superlattice Relaxation in Quantum Cascade Lasers,” Appl. Phys. Lett. 92, 122114 (2008). List of papers submitted or published that acknowledge ARO support during this reporting period. List the papers, including journal references, in the following categories: (b) Papers published in non-peer-reviewed journals or in conference proceedings (N/A for none) 5.00 Number of Papers published in peer-reviewed journals: Number of Papers published in non peer-reviewed journals: (c) Presentations 0.00 H. Choi, V.-M. Gkortsas, F. X. Kärtner, L. Diehl, C.-Y. Wang, F. Capasso, D. Bour, S. Corzine, J. Zhu, G. Hofler, and T. B. Norris, “Femtosecond resonant pulse propagation in quantum cascade lasers: evidence of coherent effects,” CLEO/QELS 2008, San Jose, CA, May 2008. H. Choi, T. B. Norris, L. Diehl, F. Capasso, D. Bour, S. Corzine, J. Zhu, and G. Hofler, “Time-domain measurements of group-velocity dispersion in quantum cascade lasers,” CLEO/QELS 2008, San Jose, CA, May 2008. T.B. Norris, “Dynamics of Photon-Assisted Transport in Quantum Cascade Lasers,” Fundamental Optical Processes in Semiconductors, Big Sky 2007. Hyunyong Choi, Laurent Diehl, Marcella Giovannini, Jérôme Fais, and Federico Capasso, Theodore B. Norris, “Dynamics of Photon-Driven Electron Transport in InGaAs/InAlAs Quantum Cascade Lasers”, 9th International Conference on Intersubband Transitions in Quantum Wells, Ambleside, United Kingdom, Sep 2007. Hyunyong Choi, Laurent Diehl, Marcella Giovannini, Jérôme Fais, and Federico Capasso, Theodore B. Norris, “Observation of Photon-Driven Electronic Transport in Quantum Cascade Lasers”, CLEO-PR, Seoul, Korea, Aug 2007. Hyunyong Choi, Laurent Diehl, Tobias Gresch, Marcella Giovannini, Jérôme Fais, and Federico Capasso, Theodore B. Norris, “Femtosecond Pump-Probe Studies of Carrier Transport and Gain Dynamics in Quantum Cascade Lasers”, 15th International Conference on Nonequilibrium Carrier Dynamics in Semiconductors (HCIS-15), Tokyo, Japan, Jul 2007. Hyunyong Choi, Zong-Kwei Wu, Theodore B. Norris, Tobias Gresch, Marcella Giovannini, Jérôme Fais, Laurent Diehl and Federico Capasso, “Time-Resolved Studies of Gain Dynamics in Quantum Cascade Laser,” American Institute of Physics Proceedings on the 28th International Conference on the Physics of Semiconductors, vol 893, 2007. Hyunyong Choi, Laurent Diehl, Marcella Giovannini, Jérôme Fais, and Federico Capasso, Theodore B. Norris, ``Photon-Driven Transport in Quantum Cascade Lasers'', paper CThO3 presented at CLEO/QELS, Baltimore, MD, May 2007. Hyunyong Choi, Zong-Kwei Wu, Theodore B. Norris, Tobias Gresch, Marcella Giovannini, Jérôme Fais, Laurent Diehl and Federico Capasso, “Time-Resolved Studies of Gain Dynamics in Quantum Cascade Laser,” ICPS-28, Vienna, Austria, Jun 2006. Hyunyong Choi, Zong-Kwei Wu, Theodore B. Norris, Tobias Gresch, Marcella Giovannini, Jérôme Fais, Laurent Diehl and Federico Capasso, "Ultrafast Gain Dynamics in a Quantum Cascade Laser,” paper JTuD98 presented at CLEO/QELS, Long Beach, CA, 2006. Number of Presentations: 10.00 Non Peer-Reviewed Conference Proceeding publications (other than abstracts): Number of Non Peer-Reviewed Conference Proceeding publications (other than abstracts): 0 Peer-Reviewed Conference Proceeding publications (other than abstracts): (d) Manuscripts Number of Peer-Reviewed Conference Proceeding publications (other than abstracts): 0 Number of Manuscripts: 0.00