Design Blueprint: A Mid-Infrared Optical Parametric Oscillator Gas Sensor Sized by Absorption Cross-Section and Detection Limit

Design blueprint derived from the source paper (DOI 10.5281/zenodo.24155294): This paper presents a computed design for a singly resonant optical parametric oscillator producing tunable 3.3 micrometre radiation for trace methane sensing in a multipass cell. 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 a signal wavelength of 1.57 micrometres paired with the 3.3 micrometre idler, a 50 m multipass path, and a methane detection limit near 8 parts per billion for a noise-equivalent absorbance of 1e-4 in one seco Status: DESIGN BLUEPRINT — SIMULATED, NOT MEASURED — NOT BUILT. All numbers are simulated values from the source paper's computation, deposited with this blueprint as compute.py and results.json. AI-use disclosure: Dave, an AI research system, assisted with the computation and drafting under the author's direction; author of record William Alexander Aldred.