Pure amplitude and wavelength modulation spectroscopy for detection of N2O using a three-sections quantum cascade laser

Abstract

We report on a novel quantum cascade laser (QCL) capable of operating in pure amplitude or wavelength modulation configuration thereby allowing the acquisition of background-free gas absorption-line profiles using quartz-enhanced photoacoustic spectroscopy (QEPAS). The QCL is composed of three electrically independent sections: Gain, Phase (PS) and Master Oscillator (MO). The non-uniform pumping of these three QCL sections allows laser wavelength tuning with constant optical power and vice-versa. Pure QEPAS amplitude modulation operating conditions were obtained by modulating the PS current, while pure wavelength modulation was obtained by modulating the MO section and slowly scanning the PS current.