{"tool":"built-in image_gen","asset":"/img/pdh/00-cover.png","purpose":"Conceptual editorial cover; not a wiring diagram or measured data.","prompt":"Create a sophisticated editorial illustration for a Chinese university laser physics tutorial on Pound-Drever-Hall frequency stabilization. Wide landscape 1536x1024. A precision optical reference cavity with two mirrors and a luminous red laser beam on a dark navy optical laboratory background, restrained copper and cyan accents, subtle abstract sideband triplet and a smooth dispersive error curve as visual motifs in the background, elegant scientific magazine cover, crisp physically inspired optics, quiet negative space near top. This is conceptual art, not an experimental wiring diagram. No words, no lettering, no numbers, no logos, no watermark. Avoid excessive beams and avoid presenting invented circuit connections.","other_figures":"01 through 05 are deterministic original diagrams and scientific plots generated by figures-and-checks.py."}