20Congreso Nacional 
Sociedad Mexicana de Ciencia de Superficies y Vacío A.C.

Quantum Cascade Lasers: Recent Advances and Applications

Claire Gmachl, Rüdeger Köhler, Alessandro Tredicucci, Federico Capasso, Albert L. Hutchinson, Deborah L. Sivco, James N. Baillargeon, and Alfred Y. Cho
Bell Laboratories, Lucent Technologies
600 Mountain Avenue, Murray Hill, NJ 07974

Recent advances in quantum cascade (QC) lasers include widely tunable single-mode distributed feedback (DFB) lasers with high optical power at ? ? 4.6 ?m, and single-mode DFB lasers at ? ? 16 ?m based on new surface plasmon waveguides with dual-metal gratings. Incorporation of a strong Bragg-grating into the waveguide of the QC-DFB laser leads to very large tuning ranges of approximately 100 and 150 nm for 5 ?m and 10 ?m wavelength lasers, respectively.
Single-mode and tunable QC-DFB lasers at various wavelengths from 5.2 to 8.6 ?m are presently used in collaborations with expert spectroscopists for various trace gas sensing. To achieve a narrow linewidth, the lasers are operated in continuous wave. The tuning of the single-mode output is accomplished by varying the current through the device and by Joule’s heating. C. Webster and coworkers at the Jet Propulsion Laboratory conducted measurements of the concentration of CH4 and N2O in Earth’s atmosphere from ground level to the stratosphere using a 7.95 ?m QC-laser on board a high-altitude air-plane. B. Paldus and coworkers at Informed Diagnostics Inc. have also demonstrated sub-ppbv sensitivity measurements using cavity ring down spectroscopy of ammonia (NH3). A. A. Kosterev et al. at Rice University, TX, reported on measurements of the concentration of 12CH4, its natural isotopes 13CH4 and 12CH3D, H2O, N2O, and C2H5OH diluted in standard air using a direct absorption technique around 7.95 ?m wavelength. R. Williams et al. at PNNL in collaboration with M. Taubman et al. at JILA, NIST, CO, measured the intrinsic linewidth of several of our QC-DFB lasers around 8 ?m wavelength as ~ 1 MHz. The laser could furthermore be electronically stabilized to a linewidth < 20 kHz.
Band-structure engineering of unipolar structures is a very powerful tool for the design and fabrication of devices with particular characteristics. We recently demonstrated a bi-directional QC-laser with emission wavelength dependent on bias-polarity, ?? ? 6.5 ?m and ?+ ? 6.35 ?m. This is a new concept for the generation of two wavelengths from a single laser device. In fact, a single device appears as being made of two different laser materials according to the two bias-polarities. The wavelengths are excited separated in time, which simplifies multiple-wavelength detection schemes, such as differential LIDAR (light detection and ranging).
This material is based upon work supported in part by DARPA/US Army Research Office under Contract No. DAAG55-98-C-0050. R. K. acknowledges support by Studienstiftung des Deutschen Volkes, Germany.

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