Abstract
Optical forces provide an efficient way to sort particles and biological materials according to their optical properties. However, both enhanced optical forces and a large interaction volume are needed in order to optically sort a large number of nanoparticles. We investigate the use of a tapered glass capillary as an optofluidic platform for optical manipulation and optical sorting applications. Tapered capillaries with micrometre and sub-micrometre sizes are fabricated. After filling the tapered capillary with a colloidal solution of red fluorescent diamond particles, a green laser light is coupled into the capillary. The tapered capillary acts both as a microfluidic channel and as an optical waveguide, making it possible for the light to interact with the particles inside the sample solution. Using an incident laser power of few tens of milliwatts, we achieve optical transportation of the brightest particles inside the tapered part of the capillary. Particle velocities as high as few tens of micrometres per second are measured.
Highlights
Based on optical forces, optical sorting provides an efficient and contactless method to separate materials in liquid suspension according to their optical properties [18]
Efficient optical manipulation of a large number of nanoparticles remains a challenging task since it would require both an intense laser light to cover a large interaction volume, and near-field enhanced optical forces that drastically reduce the size of the interaction volume [4,9-15]
Larger multimode capillaries may still provide an optofluidic platform for studying light-matter interactions as long as a non-negligible part of the guided light propagates in the evanescent field near the glass-water interface
Summary
Based on optical forces, optical sorting provides an efficient and contactless method to separate materials in liquid suspension according to their optical properties [18]. Various properties of light such as its wavelength, its polarization, and its spatial distribution, can be used to tailor the optical forces being applied to different particles in solution. As light-matter interactions depend on the light properties and on the optical properties of materials, selective optical trapping or transportation can be achieved and used in order to optically sort nanoparticles with different optical properties. Such an optical sieve is highly needed for sorting a large variety of nanomaterials. In order to overcome this issue, we focus here on the fabrication and the use of tapered glass capillaries for optofluidic applications such as nanoparticle optical manipulation. We report on the optical transport of fluorescent diamond particles inside a tapered capillary
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