We have developed a broadly tunable diode laser system by employing custom-designed asymmetric multiple-quantum-well (AMQW) InGaAsP lasers in an external cavity configuration. Feedback is provided by a diffractive optical element with high coupling efficiency and wavelength selectivity, allowing for single-mode tuning of the output wavelength by varying the external cavity length. This tunable laser system was used experimentally to perform absorption spectroscopy on weak CO<sub>2</sub> lines over a broad wavelength region in the near infrared. An experimental tuning range of 80 nm has been observed for a laser cavity length of 600 μm, which is double the tuning range found with conventional, uncoated quantum-well lasers. We achieved a detection sensitivity of 5 × 10<sup>−6</sup> at 95% confidence over the wavelength range of 1.54–1.62 μm by employing a second-harmonic detection technique. The theoretical predictions of a broad gain profile from an ambipolar rate equation model are found to correspond to the experimentally observed increased tunability of the uncoated AMQW lasers.
© 2001 Optical Society of America
Sean C. Woodworth, Daniel T. Cassidy, and Michael J. Hamp, "Sensitive Absorption Spectroscopy by Use of an Asymmetric Multiple-Quantum-Well Diode Laser in an External Cavity," Appl. Opt. 40, 6719-6724 (2001)