A Cavity-Enhanced Frequency-Comb Spectrometer Sized by Effective Path Length and Absorption Sensitivity

This paper presents a computed design for a cavity-enhanced direct frequency-comb spectrometer covering a broad near-infrared band in a single acquisition. The sizing follows from applying the relevant intensity, thermal, nonlinear and geometric bounds at a single stated operating point, with every number produced by a deposited computation. The headline result is an effective absorption path of 12 km from a 0.60 m physical cavity, a finesse near 62830, a minimum detectable absorption coefficient of 8.3e-08 per metre per spectral element, and about 40000 spectral elements recorded in parallel across a 10 THz span. The binding constraint is identified explicitly: comb-to-cavity locking across the full bandwidth, where mirror dispersion walks the cavity modes away from a uniform comb grid. The design is SIMULATED, NOT MEASURED: no hardware was built for this study, and all performance figures are predictions from stated assumptions, offered as a basis for a build decision and a measurement plan.