Thulium (Tm, Z=69) is among the scarcest of the commercially recovered lanthanides by basket share — approximately 0.07% of the global rare earth oxide basket — yielding an estimated world output of roughly 270 tonnes Tm2O3 in 2024e (derived from the USGS MCS 2025 aggregate of 390,000 t REO). Its commercial importance is disproportionate to its tonnage, concentrated in three specialized applications that exploit properties unique to the element: rare-earth-doped solid-state and fiber lasers in the 1.9–2.1 µm atmospheric window, specialty optical glass for fiber amplifiers and near-infrared optics, and the Tm-170 radioisotope used as a compact portable X-ray source in field radiography. Unlike the magnet REEs (Nd, Pr, Dy, Tb) that dominate rare earth demand growth from EVs and wind turbines, Thulium's demand profile is driven by specialized photonics and nondestructive testing markets rather than bulk clean-energy applications.

The Tm:YAG solid-state laser (2.01 µm) and Tm-doped fiber laser systems represent the fastest-growing application segment. The 2 µm wavelength aligns with strong water absorption, enabling precise soft-tissue incision with minimal thermal spread — making Tm lasers competitive with Ho:YAG in urological procedures, otolaryngology, and ophthalmology. Industrial Tm-fiber lasers (multi-watt to kilowatt class) serve polymer cutting, atmospheric LIDAR, and defense countermeasure applications. The Tm-170 radioisotope application is niche but unique: reactor-irradiated Tm-169 targets generate compact sources of ~52–59 keV X-rays for field inspection of welds and structural components where portable, battery-free radiography is required.

Supply is structurally dependent on China's ion adsorption clay sector, where HREE enrichment yields Tm content of 0.2–0.5% of total REO — roughly 3–7 times the global weighted basket average of ~0.07%. China controls approximately 90% of global REE separation and refining capacity. Thulium was not directly targeted by China's April 2025 export licensing controls on seven HREEs, but the regulatory infrastructure governing HREE concentrate exports from China creates indirect exposure for Tm supply chains. Both the US Critical Minerals List and EU Regulation 2024/1252 (Critical Raw Materials Act) designate rare earth elements — including heavy REEs such as Tm — as critical and strategic materials. The practical supply risk is less acute than for controlled HREEs like Tb and Dy, but Tm's extremely small production volume (~270 t/y) and concentration in Chinese HREE-enriched deposits means that even minor supply disruptions could materially affect the specialty laser and radioisotope markets it serves.