Dispersing upconversion nanocrystals in PMMA microfiber: a novel methodology for temperature sensing.

This paper reports the synthesis of a ß-NaYF4:Yb3+/Tm3+ phosphor by a thermal decomposition method and focuses on the fabrication of microfibers by the co-doping of nanocrystals with PMMA solution via a facile drawing method. The structural characteristics of the nanocrystals are studied by XRD and TEM techniques. Meanwhile, the optical properties of the microfibers are probed by wave guiding performance and upconversion spectroscopy. With the excitation of a 980 nm laser source, the microfiber presented blue upconversion emission of Tm3+ ions. The fluorescence intensity ratio (FIR) method is utilized for the non-thermally coupling transition (1D2 → 3F4 (452 nm) and 1G4 → 3H6 (476 nm)) levels to carry out the optical thermometry. The maximum sensitivity is recorded at 298 K and is 0.00157 K-1. The results suggest that the microfibers have potential applications in thermometry with high sensitivity.

Micro-gun based on laser pulse propulsion.

This paper proposes a novel "micro-gun" structure for laser pulse propulsion. The "micro-bullets" (glass microspheres) are irradiated by a laser pulse with a 10 ns duration in a dynamic process. Experimental parameters such as the microsphere diameter and the laser pulse energy are varied to investigate their influence on laser pulse propulsion. The energy field and spatial intensity distribution in the capillary tube were simulated using a three-dimensional finite-difference time-domain method. The experimental results demonstrate that the propulsion efficiency is dependent on the laser pulse energy and the microsphere size. The propulsion modes and sources of the propelling force were confirmed through direct observation and theoretical calculation. Waves also generated by light-pressure and thermal expansions assisted the propulsion.

Whispering gallery modes in a liquid-filled hollow glass microsphere.

We develop a hydrofluoric (HF) etching process to open a microhole on the hollow glass microsphere (HGM). The typical whispering gallery mode (WGM) resonance was observed by coupling the HGM with a tapered fiber. Dioctyl phthalate was filled into the HGM, and the resonance wavelength decreased at elevated temperatures. We analyzed the WGM resonance properties inside the liquid-filled HGM with a higher or lower refractive index in comparison to the HGM wall. Four different liquids were also injected into the HGM to investigate the influence of the thermo-optic coefficient on the temperature sensitivity. Size-dependent experiments further showed that HGMs with varying sizes have varying temperature sensitivity. The maximum temperature sensitivity observed was 334.3 pm/°C.

Humidity-insensitive temperature sensor based on a quartz capillary anti-resonant reflection optical waveguide.

A compact, humidity-insensitive, fiber optic temperature sensor based on a quartz capillary, antiresonant reflecting optical waveguide was proposed and experimentally demonstrated. The transmission spectral responses of the proposed sensor were experimentally investigated regarding temperature variation and environmental humidity. Resonant dips exhibited temperature sensitivity as large as 201 pm/°C from -30 to 45 °C in a humid environment. By coating a sufficiently thick gold film onto the sensor surface, the humidity cross-sensitivity issue was effectively resolved. This proposed sensor was anticipated to find potential applications in humid environments, and moreover, immunity to humidity-sensitivity ensures its applicability in marine environments.