Aluminum film thickness dependence of surface plasmon resonance (SPR) in the far- and deep-ultraviolet regions (170300 nm) was revealed using an attenuated total reflectance spectrometer. In the far-ultraviolet region (&lt
200 nm), films of thicknesses 23 and 9 nm showed strong SPR excitations in air and 1,1,1,3,3,3-hexafluoro-2-propanol, which were reproduced by simulations based on the Fresnel equations, respectively. Therefore, Al-SPR sensors are expected to work both in air and in liquids by controlling the film thickness.