Optical propulsion of microspheres along a channel waveguide produced by Cs+ ion-exchange in glass

Giant resonant light forces in microspherical photonics

“…After that, we present our experimental observations of propelling of polystyrene microspheres in the near-field vicinity of tapered microfibers immersed in water. For a certain small fraction of spheres with D<15-20 mm, we observed giant power normalized propelling velocities ,10 mm s 21 W 21 that exceed the previous measurements in various evanescent couplers [20][21][22][23][24][25] by more than an order of magnitude. These extraordinary high propelling efficiencies approach estimations made in a total absorption limit that indicates that a significant part of the total guided power is used for the creating light pressure.…”

“…The particles reach a terminal velocity (v) when the scattering force (F x ) is equal to the drag force, C56pmRv, where m is the dynamic viscosity. [20][21][22][23][24][25] Due to the focus of the present study on resonant light pressure effects, we modified the conventional experimental approach to propelling measurements by evanescent fields [20][21][22][23][24][25] in regard to the following factors: (i) range of sphere diameters was increased up to 3fDf20 mm (compared to previously studied D,10 mm range); (ii) instead of the average propelling velocities (v av 5,v. ), we measured maximal instantaneous propelling velocities (v max 5max(v)); and (iii) statistical distribution of v max was studied as a function of D.…”

“…The propelling velocity is expected to be almost linearly dependent on P 0 for spheres with D,10 mm. [20][21][22][23][24][25] In order to study the dependence of propelling as a function of D, we fixed the power at the taper waist for all measurements at relatively modest level of P 0 54362 mW. The laser emission linewidth was narrower than 0.1 nm and is smaller than the width of any WGM resonances studied in this work.…”

“…The propelling of dielectric microspheres was studied in liquid-immersed evanescent couplers based on dielectric waveguides, [20][21][22][23] tapered fibers 24 and prisms. 25 The light pressure in such structures and devices is determined by the conservation of the total momentum along the propagation direction.…”

“…The propelling velocity normalized by the incident power has been found to be below ,1 mm s 21 W 21 for dielectric microspheres with diameters (D) from 2 to 20 mm. [20][21][22][23][24][25] Propelling efficiencies can be increased for strongly absorbing particles. 26 However, in the later case, the dominant mechanism of propelling has been attributed to the photophoretic forces occurring due to non-uniform heating of the light-absorbing particle.…”