We demonstrate non-contact temperature measurement with one tenth of a kelvin precision at distances of several meters using omnidirectional laser emission from dye-doped cholesteric liquid crystal droplets freely floating in a fluid medium. Upon the excitation with a pulsed laser the liquid crystal droplet emits laser light due to 3D Bragg lasing in all directions. The spectral position of the lasing is highly dependent on temperature, which enables remote and contact-less temperature measurement with high precision. Both laser excitation and collection of light emitted by microlasers is performed through a wide telescope aperture optics at a distance of up to several meters. The optical excitation volume, where the droplets are excited and emitting the laser light is of the order of ten cubic millimeters. The measurement is performed with ten second accumulation time, when several droplets pass through the excitation volume due to their motion. The time of measurement could easily be shortened to less than a second by increasing the rate of the excitation laser. Since the method is based solely on measuring the spectral position of a single and strong laser line, it is quite insensitive to scattering, absorption and background signals, such as autofluorescence. This enables a wide use in science and industry, with a detection range exceeding tens of meters.

Droplets are ideally suited to support high‐Q‐factor whispering gallery modes (WGMs) due to their perfectly smooth surface. WGMs enable extremely precise measurements of the droplet properties such as size and shape. Herein, a simple, fast, and very precise technique to measure interfacial tension (IFT) between two immiscible liquids based on WGMs is demonstrated. A microdroplet is generated at the end of a glass microcapillary, submerged in a continuous liquid phase, and its size changes are monitored with nanometer precision via WGMs, while simultaneously applying finely tunable pressure through the microcapillary. IFT is determined from the size of the droplet and the pressure in the microcapillary at equilibrium. Droplets as small as 8 μm are used, thus requiring extremely small sample volume. The IFT measurements can be carried out also at nonequilibrium state when either the size of the droplet or the chemical composition of the continuous phase changes in time. Simultaneously, the WGMs enable very precise measurement of the refractive index of either the droplet or the continuous phase.

Lasers based on Fabry–Pérot or whispering gallery resonators generally require complex fabrication stages and sensitive alignment of cavity configurations. The structural defects on reflective surfaces result in scattering and induce optical losses that can be detrimental to laser performance. On the other hand, random lasers can be simply obtained by forming disordered gain media and scatterers, but they generally show omnidirectional emission with a low Q-factor. Here, we demonstrate directional random lasers with a high Q-factor emission (∼1.5 × 104) via self-assembled microstructural cracks that are spontaneously formed upon radial strain-release of colloidal nanoparticles from the wet to dry phase. The rough sidewalls of cracks facilitate light oscillation via diffuse reflection that forms a spatially localized feedback, and they also serve as the laser out-coupler. These self-assembled cracks exhibit random lasing at optical pump powers as low as tens of μJ/mm2. We demonstrate a wide variety of random lasers from nano- and biomaterials including silica nanoparticles, fluorescent proteins, and biopolymers. These findings pave the way toward self-assembled, configurable, and scalable random lasers for sensing, displays, and communication applications.

Droplets are ideally suited to support high Q-factor whispering gallery modes (WGMs) due to their perfectly smooth surface. WGMs enable extremely precise measurements of the droplet properties such as size and shape. In this article a simple, fast and very precise technique to measure interfacial tension (IFT) between two immiscible liquids based on WGMs is demonstrated. A microdroplet is generated at the end of a glass microcapillary, submerged in a continuous liquid phase, and its size is measured to a 1 nm precision via WGMs, while simultaneously applying finely tunable pressure through the microcapillary.IFT is determined from the size of the droplet and the pressure in the microcapillary at equilibrium. Droplets as small as 8 µm were used, thus requiring extremely small sample volume. The IFT measurements can be performed also at non-equilibrium state when either the size of the droplet or the chemical composition of the continuous phase changes in time. Simultaneously, the WGMs enable very precise measurement of the refractive index of either the droplet or the continuous phase. WGMs can also be detected through media with high scattering, absorption and autofluorescence, which makes our method adaptable to many applications.The IFT is a crucial quantity in the fundamental interfacial science, as well as extremely important for wide variety of applications ranging from biology, food, pharmaceutical, cosmetic to fossil fuel industries [1,2,3,4]. Due to the importance of the IFT, numerous tensiometric techniques have been developed to date. The IFT can be measured by probing the elastic

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