Design Blueprint: A High-Finesse Fabry-Perot Cavity Displacement Sensor Sized by Shot Noise and Coating Thermal Noise

Design blueprint derived from the source paper (DOI 10.5281/zenodo.24155197): This paper presents a computed design for a 0.40 m Fabry-Perot cavity displacement sensor with dielectric supermirrors, intended for picometre-scale length sensing. 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 free spectral range of 375 MHz, a cavity linewidth of 1874 Hz at a finesse of 200,000, a shot-noise displacement floor near 7.7e-21 m per root hertz, a coating thermal noise floor of 2e-18 m per root hertz that dominates a 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.