<p>Advances in optical technology have led to the commercialization and widespread use of broadband optical frequency combs for multiplexed measurements of trace-gas species. Increasingly available in the mid-infrared spectral region, these devices can be leveraged to interrogate the molecular fingerprint region where many fundamental rovibrational transitions occur. Here we present a cross-dispersed spectrometer employing a virtually imaged phased array etalon and ruled diffraction grating coupled with a difference frequency generation comb centered near 4.5 &#181;m. The spectrometer achieves sub-GHz spectral resolution with a 30 cm<sup>-1</sup> instantaneous bandwidth. Laboratory results for nitrous oxide isotopic abundance retrieval will be presented. Challenges relating to characterizing the instrument lineshape function, constructing a frequency axis traceable to the comb, and accurate spectral modelling will be addressed and progress towards incorporating a more compact laser frequency comb source into the system will be discussed.</p>
Modelocked Mid-Infrared Frequency Combs in a Silicon Microresonator