Fluorescence fiber probe for nanoscale thermometry

High-sensitivity temperature measurements require the reduction of the auto-fluorescence produced by an optical fiber probe. Additionally, a novel fluorescence fiber probe allowing decreasing the noise has been developed by fusion-splicing a photonic crystal fiber (PCF) and a traditional single-mode fiber. 

The operation of the novel fiber probe was already tested experimentally by evaluating the auto-fluorescence spectra of the photonic crystal fiber. Thus, the fluorescence fiber probe demonstrates a six- to ten-fold increase of S/N in the near-field fluorescence lifetime detection because of the reduction of auto-fluorescence.

It should be noted that the developed near-field optical fiber probe performed a successful measurement of the quantum dot lifetime at room temperature. Even though different types of micro- and nanoscale thermometry methods have been created and improved, and a thermocouple fiber probe tip in the contact-mode scanning thermal microscopy reaches a nanoscale spatial resolution but the heat transfer way between the fiber optic probe and the sample remains unverified.

Moreover, usually in contact-mode techniques, “there is a concern that nano-structured samples may suffer damage due to the friction between the sample and the fiber probe; also, the temperature change due to heat transfer during the operation can be significant.”

The operation of surface-modified fluorescence fiber probes is based on near-field light that excites probes locally, resulting in the measurement of the fluorescence lifetime, which includes data about the sample temperature. The fluorescence probes provide such advantages as long fluorescence lifetime and high quantum yield. 

The fluorescence lifetimes of dried QD layers were measured with optical fiber probe up to 100nm before, nevertheless, the auto-fluorescence produced by the near-field fiber probe is regarded as a critical noise factor when the QDs are modified as a monomolecular layer on the sample surface.

Nonetheless, the novel fluorescence fiber probe has low auto-fluorescence parameters because it is made in the result of fusion-splicing a photonic crystal fiber and a traditional single-mode fiber. The developed fiber probe provides highly sensitive fluorescence lifetime measurements.

Finally, the optical fiber probes allow increasing the sensitivity of the lifetime measurement. The thing is that an average splice loss of 1.43 dB and a minimum splice loss of 1.08 dB were achieved during the measurement by the fluorescence fiber probe. Also, the auto-fluorescence intensity of the fluorescence probe had been decreased to 15.2%.

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