Laboratory-based Dual Frequency Comb Spectrometer for Atmospheric Chemistry Measurements

Abstract:

The dual frequency comb spectrometer is a new tool for performing atmospheric trace gas measurements. Laboratory studies for atmospheric kinetics experiments and cross section measurements often use Fourier Transform spectrometers; however, these are limited by instrument lineshape and resolution. We are developing a laboratory-based dual frequency comb spectrometer as a novel instrument for these measurements. This instrument will need to be able to cover a wide spectral region and be very high resolution in order to measure multiple molecules simultaneously, be tunable, have a flat baseline for measurements of broad-band absorbers, and have a negligible instrument line shape. Thus our instrument will push beyond the limits of previous laboratory instruments, especially in terms of resolution and instrument line shape. Our instrument will run from 1.3 to 2.1 μm and we hope to detect a number of VOCs and other trace gases, including CO₂, H₂O, CH₄, C₂H₆, C₃H₈, C₂H₄, C₃H₆, HCHO, and CH₃CHO. We will couple the system to 30-meter and 200-meter long-pass cells, enabling detection at atmospheric or near-atmospheric concentrations. The use of these cells will also enable us to perform kinetics measurements in situ. In this work, we will report on the performance, sensitivity, and construction of this new instrument and will show preliminary laboratory measurements of trace gases towards these applications.