Nonlinear Optics in Quantum Cascade Lasers

Quantum-well semiconductor structures provide a unique opportunity to manipulate the nonlinear optical response of a medium by tailoring the energies and strengths of electronic resonances. These structures with giant nonlinear susceptibilities can be incorporated into the quantum cascade laser active region. As a result, the laser radiation experiences nonlinear self-conversion into radiation at other frequencies via the interaction with the nonlinearity of the gain medium. We are working to incorporate the quantum-well structures with giant optical nonlinearities into QCLs for stimulated Raman scattering, second harmonic generation, or difference-frequency generation. The aim of this work is to extend the spectral range available to QCLs into near IR and THz.

Mikhail Belkin

Terahertz Quantum Cascade Lasers

Terahertz semiconducting lasers today exhibit low far field output power (~mW) due to a number of limitations, one of which involves waveguiding in edge-emitting metal-metal and semi-insulating structures. This project focuses on the design of high power THz QCLs at the waveguide level, particularly for surface emission. Surface emission would be advantageous to edge-emission in devices because the output laser profile would be less divergent and because device power would scale with waveguide surface area. A second order diffraction grating will be implemented for surface emission.

Mikhail Belkin and Jonathan Fan in collaboration with Edmund Linfield (University of Leeds, UK)

Coherent Instabilities and Self-pulsation in QCLs

In this project, the ultrafast dynamics of quantum cascade lasers is studied. Conventional QCLs have gain recovery time of only a few picoseconds, which is about an order of magnitude shorter than the cavity-round-trip time. This makes stable mode locking impossible, but leads to a rich variety of nonlinear and ultrafast phenomena. At present, our research focuses on the physics of coherent instabilities in state-of-the-art QCLs. Furthermore, we hope to design QCL structures that produce stable mode-locked pulses.

Christine Wang and Laurent Diehl in collaboration with A. Gordon, J. Jirauschek, and F. Kartner (MIT), A. Belyanin (Texas A&M), M. Giovannini and J. Faist (University of Neuchatel, Switzerland), D. Bour, S. Corzine, J. Zhu, and G. Hofler (Agilent Technologies), P. Grant and H. C. Liu (National Research Council, Ottawa, Canada), and T. Maier and H. Schneider (Frauenhofer Institut, Freiburg, Germany)