Mid-infrared upconversion spectroscopy based on a Yb:fiber frequency laser
Scott A. Diddams, Todd Johnson
We present a system for molecular spectroscopy using a mid-infrared broadband frequency comb source with near infrared detection. Difference frequency generation of a Yb:fiber frequency comb produced a mid-infrared (MIR) comb tunable from 2.7 − 4.7 υm (2100 − 3700 cm−1) with average power up to 40 mW. The MIR comb was upconverted to near-infrared wavelengths for broadband detection using a two-dimensional dispersion imaging technique. Absorption measurements were performed over bandwidths of 240 cm−1 with 0.048 cm−1 resolution, and absolute frequency scale accuracy was better than 0.005 cm−1. The minimum absorption sensitivity per spectral element was determined to be 4.4 x 10−7 cm−1 from measurements with low pressure CH4. The spectral range, resolution, and frequency accuracy of this system show promise for determination of trace concentrations in gas mixtures containing both narrow and broad overlapping spectral features, and we demonstrate this in measurements of air and solvent samples.
Applied Physics B
frequency comb, infrared, spectroscopy, molecular spectroscopy, trace gas