A coherent dual fiber-comb spectrometer centered at 1.5 µm wavelengths is transferred to 3.4 µm by difference-frequency generation with a 1064 nm cw laser. It is shown that the residual linewidth between the comb teeth at 3.4 µm is resolution-limited to 200 mHz; such narrow linewidths can enable coherent dual-comb spectroscopy at high-precision and signal-to-noise ratio. We then discuss different interferometric configurations for coherent dual-comb spectroscopy. We find that a two branch interferometric setup is appropriate to measure both the magnitude and phase spectrum of purely Doppler broadened absorption lines. An initial measurement of methane lines in the nu3 band P-branch with a resolution of 114 MHz is demonstrated.
Proceedings Title: SPIE Optical Engineering + Applications:Interferometry XV: Techniques and Analysis
Conference Dates: August 1-5, 2010
Conference Location: San Diego, CA
Pub Type: Conferences
Frequency combs, Mid-IR, Molecular spectroscopy