Multispecies Heterodyne Phase Sensitive Dispersion Spectroscopy over 80 nm Using a MEMS-VCSEL

Abstract

Vertical cavity surface emitting lasers fabricated with movable microelectromechanical mirrors can offer continuous single-mode wavelength tuning up to 100 nm with high efficiency and in a very small package. Wide tunability makes these diode lasers ideally suited for multispecies and high-density gas analysis and the first demonstrations of direct absorption spectroscopy and wavelength modulation spectroscopy have already been published. The performance of these systems could nevertheless be enhanced by the use of the new molecular dispersion spectroscopic methods, as heterodyne phase sensitive dispersion spectroscopy. This technique bases its operation on the detection of the profile of the refractive index of the sample under analysis, in contrast to traditional architectures based on the measurement of optical absorption, and this provides noticeable advantages. First, the method is normalization-free, and therefore, the characteristic issue of the nonmonotonic intensity profile during wavelength tuni...