Mid-infrared cavity ring-down spectroscopy using DFB quantum cascade laser with optical feedback for radiocarbon detection
Ryohei Terabayashi, Keisuke Saito, Volker Sonnenschein, Yuki Okuyama, T. Iguchi, Masahito Yamanaka, Norihiko Nishizawa, Kenji Yoshida, Shinichi Ninomiya, Hideki Tomita
Abstract
Abstract A linewidth reduction of a distributed feedback quantum cascade laser (DFB-QCL) based on optical feedback for a mid-infrared (MIR) cavity ring down spectroscopy (CRDS) 14 C spectrometer is presented. A cat-eye reflector as well as a path-length enhancement by a Herriott cell were employed for a compact optical setup. The laser linewidth was evaluated by monitoring the beat frequency between the DFB-QCL and a MIR optical frequency comb (OFC). The linewidth reduction by optical feedback was clearly observed although slow frequency drifts caused by environmental changes were still visible. A low-bandwidth beat-note lock to the OFC was conducted for long-term stabilization as well as for precise frequency scanning and thereby 14 C measurement by MIR CRDS with optical feedback was demonstrated successfully.