A physical unclonable function is a hardware fingerprint — a structure so complex that it cannot be duplicated, not even by the process that created it. The manufacturing randomness that makes each device unique is the security feature, not a defect to be minimized. The problem is fabrication speed: most PUFs require slow, expensive lithography.
A nanosecond pulsed laser scrawled across a surface exploits Rayleigh-Bénard instability to generate random plasmonic nanostructures in nanoseconds. The laser energy melts a thin metal film, and as it solidifies, natural hydrodynamic instabilities create stochastic nanoscale topography. Each scrawl produces morphology-dependent optical resonances — plasmonic fingerprints that depend on the exact nanostructure, which depends on the exact instability dynamics, which are chaotic and irreproducible.
The encoding capacity expands fivefold through multidimensional multiplexing: both the topography (surface height map) and the color (wavelength-dependent plasmonic response) carry independent bits. Approximately 28,000 bits per device, with bit uniformity at 0.500 and inter-device Hamming distance at 0.499 — the theoretical optimum for randomness.
What matters structurally is the inversion. In precision manufacturing, instability is the enemy — you suppress it to make uniform, reproducible structures. Here, instability is the product. The less controlled the solidification, the better the security. The same physics that makes thin-film manufacturing difficult (Rayleigh-Bénard convection introducing unwanted variation) makes authentication robust (each variation is a unique key). The manufacturing process is valued for its irreproducibility. The defect is the feature.
(arXiv:2603.18518)