Ultra-broadband high-resolution microdroplet spectrometers for the near infrared.

By stabilizing the evaporation dynamics of a microliter fluorocarbon droplet, we demonstrate a fast-scan optofluidic Fourier transform (FT) spectrometer on the tip of an optical fiber operating in the 1000-2000 nm window with a resolution of 3.5 cm-1 (i.e., <1 nm at 1560 nm). Compared with other FT near-infrared (NIR) small-scale spectrometers reported in the literature, the fluorocarbon droplet spectrometer shows the largest wavelength span and span/resolution ratio, allowing spectral analysis of broadband or narrowband radiation to be easily performed. Our results open the way for the practical application of droplet spectrometers as advanced optofluidic NIR analyzers with small size and low cost that are capable of operating in harsh environments, even in the absence of electrical power sources.

Light pressure in droplet micro-resonators excited by free-space scattering.

A droplet optical resonator is a unique environment to investigate light-matter interaction and optomechanics in liquids. Here, we report on light pressure effects derived from whispering gallery modes excited in a liquid-polymer droplet micro-resonator by free-space laser scattering. From the nonlinear resonance spectrum observed in the visible, we provide evidence of photon pressure exerted at the liquid-air boundary and quantify it with a coherent physical model. Our findings pave the way to studies on micro-rheology and nonlinear optofluidics, where droplets serve as miniature liquid laboratories.