Design Of A Mid-infrared External Cavity Quantum Cascade Laser

Quantum cascade lasers (QCLs) have been used in a wide variety of spectroscop-ic experiments and applications due to their high power, broad gain profiles and oper-ating at room temperature. In addition, QCLs in external cavity (EC) configuration, which provides a narrow line-width and a broad tuning range in the mid-infrared spectral range, are well suited for the high-resolution spectroscopic investigations of all kinds of gas phase molecules. Recently, combining EC-QCLs with supersonic molecular jets to investigate the weakly bound complexes has been reported.In this thesis, we developed an EC-QCL using the Littman-Metcalf configuration, which works in a pulsed mode and operates at-25?. The main advantage of the EC-QCL is the broadly tuning range over more than 300 cm-1, which provides the ability to study multiple gas samples, or to investigate molecules with broad absorp-tion features.Using an infrared spectral analyzer (721B-XIR, Bristol) and a SR850 lock-in am-plifier, we constructed an EC-QCL system to characterize our EC-QCL and the ex-perimental results are listed below:? We have demonstrated that the QCL chip shows a multi-mode emission around 1595cm-1, but a single-mode emission was achieved when the EC is applied.? The EC-QCL line-width of 0.45 and 0.14cm-1 (FWHM) are achieved near 1561.3cm-1 with a pulse width of 200 and 30ns, respectively.? The tuning range of the EC-QCL from 1340 to 1640cm-1 is realized by rotating the tuning mirror from-16° to-4°.? We have demonstrated that the EC-QCL is capable of detecting the absorption spectra of both simple and complex molecules at atmospheric pressure by meas-uring the absorption spectrum of water in the ambient air.