Fast molecular fingerprinting with a coherent, rapidly tunable dual-comb spectrometer near 3 μm.

Molecular spectroscopy in the mid-infrared spectral range is expected to present fingerprints of chemical species that provide a unique identification with adequate sensitivity. Dual-comb spectroscopy, a promising successor to conventional Fourier-transform spectroscopy, enables rapid molecular fingerprinting with high-resolution and high-precision. Here, we report gas-phase transmittance and dispersion spectra by employing a rapidly tunable dual-comb spectrometer based on electro-optic frequency combs near 3 μm.

Precision saturated absorption spectroscopy of H.

In our previous work on the Lamb-dips of the ν fundamental band transitions of H, the saturated absorption spectrum was obtained by third-derivative spectroscopy using frequency modulation with an optical parametric oscillator (OPO). However, frequency modulation also caused errors in the absolute frequency determination. To solve this problem, we built a tunable offset locking system to lock the pump frequency of the OPO to an iodine-stabilized Nd:YAG laser.

Absolute frequency measurement of molecular iodine hyperfine transitions at 647 nm.

We report absolute frequency measurements of molecular iodine P(46) 5-4 a, a, and a hyperfine transitions at 647 nm with a fiber-based frequency comb. The light source is based on a Littrow-type external-cavity diode laser. A frequency stability of 5×10 at a 200 s integration time is achieved when the light source is stabilized to the P(46) 5-4 a line.