[20p-E214-1~14] 4.3 Ultrafast Optics and Laser Processing

▲ [20p-E214-6] A mid-IR QCL referenced to a fiber-based frequency comb applied to cavity ring-down spectroscopy for trace detection of CO₂ isotopologues

〇(PC)Volker Thomas Sonnenschein¹, Ryohei Terabayashi¹, Hideki Tomita¹, Keisuke Saito¹, Masahito Yamanaka¹, Norihiko Nishizawa¹, Kenji Yoshida², Tetsuo Iguchi¹ (1.Nagoya Univ., 2.Sekisui Medical, Co., Ltd.)

Keywords:CRDS, frequency comb, beat-note

We perform abundance ratio measurements of CO₂ isotopologues using a cavity ring-down spectrometer operating in the mid-infrared with a main focus on the radioisotope ¹⁴C. To make the technique more competitive with alternative techniques such as accelerator mass specrometery (AMS) and liquid scintillation counting (LSC) the noise level and systematic factors need to be further improved. Due to contaminants and interfering absorption lines the spectral fitting can be difficult without a precise frequency axis. To improve upon the frequency uncertainty we use a fiber based frequency comb in conjucntion with a nonlinear crystal to generate an offset-free DFG comb in the mid-infrared. This comb is used to detect the optical beat-note of our quantum cascade laser (QCL) system. Frequency tracking and stabilization via feedback to the lasers injection current is applied via a labview routine. With the improved calibration an better repeatability of isotope ratio measurements was confirmed.