Flying Particle Thermosensor in Hollow-Core Fiber Based on Fluorescence Lifetime Measurements

Thermosensitive fluorescence lifetime measurements enable accurate thermometry independent of intensity fluctuations along the optical path. Here, we report lifetime-based temperature measurements of a single europium-doped particle optically trapped in an air-filled hollow-core fiber. A frequency-domain fluorescence lifetime measurement setup was integrated into a dual-beam optical trap. The measured apparent lifetime shows a linear temperature dependence of -1.8 μs/K for excitation at 400 Hz. The results were repeatable over multiple cooling and heating cycles. In addition to temperature sensing, the influence of the high-power trapping laser on the measured apparent lifetime and fluorescence intensity was investigated. The observed laser-induced particle heating can be exploited to increase the fluorophore's sensitivity and operating range for low-temperature sensing. Fluorescence lifetime measurements of optically trapped particles inside a hollow-core fiber are promising for temperature sensing with micrometer spatial resolution over meter-scale distances.