Robust, fast and sensitive near-infrared continuous-filtering Vernier spectrometer

We present a new design of a robust cavity-enhanced frequency comb-based spectrometer operating under the continuous-filtering Vernier principle. The spectrometer is based on a compact femtosecond Er-doped fiber laser, a medium finesse cavity, a diffraction grating, a custom-made moving aperture, and two photodetectors. The new design removes the requirement for high-bandwidth active stabilization present in the previous implementations of the technique, and allows scan rates up to 100 Hz. We demonstrate the spectrometer performance over a wide spectral range by detecting CO₂ around 1575 nm (1.7 THz bandwidth and 6 GHz resolution) and CH₄ around 1650 nm (2.7 THz bandwidth and 13 GHz resolution). We achieve absorption sensitivity of 5 × 10⁻⁹ cm⁻¹ Hz⁻¹/² at 1575 nm, and 1 × 10⁻⁷ cm⁻¹ Hz⁻¹/² cm⁻¹ at 1650 nm. We discuss the influence of the scanning speed above the adiabatic limit on the amplitude of the absorption signal.