Swept dual-comb spectroscopy via common-mode cavity tuning and stabilization

We demonstrate gas spectroscopy of low-pressure acetylene using a single-cavity dual-comb Yb:CaF$_2$ laser operating at a 1-GHz repetition rate. To improve the spectral resolution under low-pressure conditions, we implement spectral interleaving, achieving an effective resolution of 50 MHz within a acquisition time of 0.8 s and a normalized signal-to-noise ratio (SNR) of 20~dB$\sqrt{Hz}$. The high repetition rate of the laser enables phase tracking and access to a broad aliasing-free optical bandwidth exceeding 4 THz. During interleaving measurements the spectroscopy comb is actively controlled while the second comb passively tracks the first. This ensures long-term stability of radio-frequency (RF) comb line positions and maintains a one-to-one correspondence between RF and optical comb line numbers following an initial calibration against a reference database. Spectral interleaving is realized by simultaneously sweeping the repetition rate of both combs via piezoelectric cavity length modulation. This system allows for dual-comb interleaving through control of a single degree of freedom, or frequency-stabilized interleaving with only two degrees of freedom. This provides an effective compromise between resolution, simplicity and acquisition speed, thereby advancing the practical implementation of single-cavity dual-comb spectroscopy.