RESUMEN
We report on the broadening of the optical bandwidth of a distributed feedback quantum cascade laser (QCL) caused by the application of radio frequency (RF) noise to the injection current. The broadening is quantified both via Lamb-dip spectroscopy and the frequency noise power spectral density (PSD). The linewidth of the unperturbed QCL (emitting at â¼5.3 µm) determined by Lamb-dip spectroscopy is 680±170 kHz, and is in reasonable agreement with the linewidth of 460±40 kHz estimated by integrating the PSD measured under the same laser operating conditions. Measurements with both techniques reveal that by mixing the driving current with broadband RF noise the laser lineshape was reproducibly broadened up to ca 6 MHz with an increasing Gaussian contribution. The effects of linewidth broadening are then demonstrated in the two-color coherent transient spectra of nitric oxide.
RESUMEN
We report on the observation of saturation effects in Intracavity Faraday Modulation Spectroscopy (INFAMOS). A quantum cascade laser operating at â¼5.3 µm is used to probe the 2Π3/2 and 2Π1/2 R(3.5) transitions in the fundamental band of nitric oxide. With average intracavity intensities up to 450 W cm-2, the saturation of these molecular transitions is observed up to a total pressure of â¼240 Torr. The experimental data are interpreted by incorporating saturation into a model for the INFAMOS line shape in the homogeneously broadened limit.
RESUMEN
We present the intra-cavity Faraday modulation spectroscopy technique, whereby optical feedback cavity-enhanced spectroscopy is coupled with Faraday modulation spectroscopy to greatly enhance the interaction path length of a laser beam with a paramagnetic sample in a magnetic field. We describe a first prototype based upon a cw quantum cascade laser targeting a selection of fundamental rovibrational R-branch transitions of nitric oxide (1890 cm-1), consisting of a linear cavity (finesse F=6300) and a water-cooled solenoid. We demonstrate a minimum detectable Verdet constant of Vmin=4.7×10-14 rad cm-1 G-1 Hz-1/2 (at SNR = 1), corresponding to a single-pass rotation angle of 1.6×10-10 rad Hz-1/2 and a limit of detection of 0.21 ppbv Hz-1/2 NO.