Coarsely scannable comb-locked ECDL with fixed local oscillator for CRDS measurement of CO line strength

This study introduces a simplified method for scanning the optical frequency of an external cavity diode laser (ECDL) locked to an optical frequency comb (OFC) with a repetition rate of 250 MHz. Previous techniques have often been intricate, especially when dealing with a task of comb-mode hopping. In contrast, our method simplifies the mode-hoping method by tuning the piezoelectric transducer (PZT) at a rate of frep/2, while keeping the diode current locked to a fixed-frequency local oscillator (LO) at frep/4. This approach provides a reasonable sampling interval suitable for spectroscopic measurements of gas lines, typically spanning a few gigahertz. Our demonstration effectively improved the noise level of the ringdown traces in cavity ringdown spectroscopy (CRDS), even when using a passively stabilized optical cavity. Additionally, we report the line strength of the ¹²C¹⁶O R23 line, yielding results that closely align with previous research studies.