A developed spectrometer based on optical-feedback cavity ring-down spectroscopy (OF-CRDS) has been demonstrated with a distributed feedback laser diode and a V-shaped glass ceramic cavity. The laser is coupled to the V-shaped cavity, which creates an absorption path length greater than 2.8 km, and resonance between the laser frequency and the cavity modes is realized by modulating the cavity length instead of tuning the laser wavelength to obtain a higher resolution. A noise-equivalent absorption coefficient of ∼2.6 × 10−8 cm−1Hz−1/2 (1σ) is determined with spectral resolution of ∼0.003 cm−1 and spectral range of 1.2 cm−1. As an application example, the absorption spectrum measurement of water vapor in the spectral range of 6590.3∼6591.5 cm−1 is demonstrated with this spectrometer.
Zhongqi Tan and Xingwu Long, "A Developed Optical-Feedback Cavity Ring-Down Spectrometer and Its Application," Appl. Spectrosc. 66, 492-495 (2012)